INIS-mf—13336

europhysicsconference

12™ GENERAL CONFERENCEOF THE

CONDENSED MATTER DIVISIONOF THE E.P.S.

6-9 APRIL 1892

PRAHA

. I

Published by:

Series Editor:

European Physical Society

Prof. K. Bethge, Frankfurt/M.

Managing Editor: G. Thomas, Geneva

VOLUME

16 A

EdNors: B. VMd^i V. VofHocksndK.

EUROPEAN PHYSICAL SOCIETY

•• ' • " !

-••••-4.

EUROPEAN PHYSICAL SOCIETY

12th General Conferenceof the

Condensed Matter Division

Praha, Czechoslovakia6-9 April 1992

EUROPHYSICS CONFERENCE ABSTRACTSEuropean Physical Society ©1992 Reproduction Rights Reserved

This volume is published under the copyright of the European Physical Society. We wantto inform the authors that the transfer of the copyright to the EPS should not prevent anauthor to publish an article in a journal quoting the first publication or to use the sameabstract for another conference. The copyright is just to protect the EPS against usingthe same material in similar publications.

The Proceedings of this conference will be published by Physica Scripta.

Published by:Union of Czechoslovak Mathematicians and Physicists, Praha 1992

Printed by:Polygrafia, a.s., PrometheusPraha 8, Czechoslovakia

57-552-92

ISBN 80-7015-336-9

CONTENTS

Foreword VIISponsors VIIICommittees VIIIScientific Programme XProgramme of Oral Presentations XIIIList of Poster Presentations XXIIAbstracts of Oral Presentations 1Abstracts of Poster Presentations 51Author Index 317ESPRIT Actions

Conference Chairman:

Dr. V. Smi'dInstitute of Physics, Czechoslovak Academy of SciencesCukrovarnicka 10, 162 00 Praha 6, CzechoslovakiaPhone: +42-2-3120741 to 3120749 and +42-2-357714Telex: 122018 ATOM C, Fax: +42-2-3123184

Chairman of the Programme Committee:

Dr. B. VelickyInstitute of Physics, Czechoslovak Academy of SciencesNa Slovance 2, 180 40 Praha 8, CzechoslovakiaPhone: +42-2-8152153 or +42-2-840932Telex: 122018 ATOM C, Fax: +42-2-8584569

Conference Secretary:

Dr. J. KristofikInstitute of Physics, Czechoslovak Academy of SciencesCukrovarnicka 10, 162 00 Praha 6, CzechoslovakiaPhone: +42-2-3120741 to 3120749 and +42-2-357714Telex: 122018 ATOM C, Fax: +42-2-3123184

Foreword

This beginning Conference of the Condensed Matter Division of the European PhysicalSociety is the twelfth in the series started in Antwerp in 1980 and follows the Exetermeeting of the last year. It is organized by the Physical Section, Union of CzechoslovakMathematicians and Physicists, under the auspices of Vaclav Havel, President of CSFR,and the Presidium of the Czechoslovak Academy of Sciences.

The scientific sessions will cover the whole range of Condensed Matter Physics. Theywill include plenary invited lectures and parallel symposia with individual invited talksand orally presented contributions. Most contributions will be, however, displayed in theform of posters.

The only evening session on the first day of the Conference is devoted to the talkof the representative of the CEC, professor G. Metakides, on European Research andDevelopment policy for information technologies. A special plenary lecture will be givenby the Hewlett- Packard Prize winner on Wednesday morning. One of the Wednesdayafternoon sessions will be used for the Workshop on the ESPRIT Basic Research Projectsas a pendant to the Exhibition oa this subject.

This booklet contains the Abstracts of all the types of contributions, which reachedus before January 22, quite a time after the officially announced deadline of December31. The required camera-ready format of the abstracts makes it impossible for the editorsto take any responsibility for the technical and language quality of the contributions,that entirely rests with the authors. The only criterion was the length and legibility ofthe abstracts. In the exceptional cases when time permitted to retype the contributionsseverely disagreeing with the instructions, we tried to keep as close to the original aspossible and correct.

I We wish the editors of the next Conference in Regensburg to have fewer difficultiesj with the publication of the book of abstracts in spite of the fact that they are the 13th; in the series.

Editors

I

VII

PATRONAGE AND SPONSORS

The Conference is organized under the auspices ofthe President of CSFR Vaclav Havel and

the Presidium of the Czechoslovak Academy of Sciencesby the Physical Section of the Union of Czechoslovak Mathematicians and Physicists

(JCSMF) and the Institute of Physics, Czechoslovak Academy of Sciences.The organizers wish to further acknowledge support from:

ArtiaCommission of the European Communities (CEC)CKD PolovodiceCzech Technical UniversityFaculty of Mathematics and Physics, Charles UniversityHewlett PackardHlavka's FoundationNEC, Microelectronics Research LaboratoriesMinolta, CzechoslovakiaMotorola EuropePhysica ScriptaSiemensUNESCOUniel

INTERNATIONAL PROGRAMME COMMITTEE

E. ANTONCIK, AarhusM. BALKANSKI, ParisF. BASSANI, PisaG. BAUER, LinzJ. L. BEEBY, LeicesterG. BENEDEK, MilanY. BRUYNSERAEDE, LeuvenJ. T. DEVREESE, Antwerp(co-chairman)H. G. KILIAN, Ulm

R. KLEIN, KonstanzG. MARTINEZ, GrenobleE. I. RASHBA, ChernogolovkaH. SPRINGFORD, BristolV. SMID, PrahaM. TOSI, TriesteB. VELICKY, Praha(chairman)P. WACHTER, ZurichG. WINSTEL, Munich

VIII

INTERNATIONAL ADVISORY COMMITTEE

V. BEZAK, BratislavaR. BLINC, LjubljanaS. BRATOS, ParisM. S. BRODIN, KievM. CARDONA, StuttgartG. CHIAROTTI, RomeF. CYROT-LACKMANN, GrenobleW. DE JONGE, EindhovenV. DVORAK, PrahaN. A. ECONOMOU, ThessalonikiS. F. EDWARDS, CambridgeF. FLORES, MadridJ. FRIEDEL, OrsayR. GERBER, SalfordE. GOBEL, MarburgR. GRIGOROVICI, BucharestH. G. GRIMMEISS, LundV. HEINE, CambridgeL. HRIVNAK, BratislavaJ. C. INKSON, ExeterJ. JORTNER, Tel AvivG. M. KALVIUS, GarchingH. R. KIRCHMAYR, ViennaK. von KLITZING, Stuttgart

F. KOCH, GarchingN. KROO, BudapestS. KRUPICKA, PrahaM. KRUSIUS, HelsinkiA. LAGENDIJK, AmsterdamJ. P. LAHEURTE, NiceM. LANDOLT, ZurichA. R. MACKINTOSH, CopenhagenE.MAJERNIKOVA, BratislavaF. MEZEI, BerlinA. R. MIEDEMA, EindhovenK. A. MULLER, RuschlikonG. PARISI, RomeA. Ya. PARSHIN, MoscowR. M. PICK, ParisK. K. REBANE, TallinM. RODOT, MeudonU. ROSSLER, RegensburgM. SCHWOERER, BayreuthJ. B. SOUSA, PortoR. A. STRADLING, LondonM. SUFFCZYNSKI, WarsawH. SZYMCZAK, WarsawD. L. WEAIRE, Dublin

ORGANIZING COMMITTEE

M. CERNANSKYP. DEMOP. HUBIKJ. FOUSEKE. HULICIUSA. KALVOVAZ. KALVAJ. KACZERZ. KOZISEKI. KRAUSR. KUZELF. LAUDATM. NIKL

J. PANTOFLICEKJ. ROSAL. ROSKOVCOVAT. SIMECEKZ. SIMSAB. STEPANEKK. VAVRINAV. VORLICEKP. VOSTRYK. ZAVETAM. ZAVETOVAJ. ZEMAN

IX

SCIENTIFIC PROGRAMME

LECTURE HALLSOpening, plenary, evening and closing sessions will be held in Room A (Koncertni sal). All other oralsessions will be held three or four in parallel in Room A, Room B (Maly sal), Room C (Klub), andRoom D (Komorni sal).

ORAL PAPERS

The time allocated for contributed papers is 15 minutes, for invited papers the time is 30 minutes, forplenary invited papers it is 45 minutes. This includes the time for discussions. The timekeeping willbe very strict.

VISUAL AIDS

Use of overhead transparencies is recommended. Also standard 50x50 mm slides with frames notthicker than 2.5 mm can be used, and should be handed to the Chairman's assistant before the startof the session. The slides may be checked in the Slide room.Projection of a video or of a film should be made known to the organizers well in advance of thesession, if possible before the start of the Conference.

POSTERS

Poster sessions will take place in three areas, a, b, and c, adjacent respectively to the Lecture halls A,B, and C. The posters can be displayed for the whole day of the corresponding poster session. Theposter boards will be 150 cm wide and 120 cm high and will be marked with the code of paper.Pinsto attach the sheets will be provided.The authors are kindly asked to display their posters by noon on the day of the respective session, tobe stationed by their posters during the session, and to remove the posters immediately after the endof the session.

EXHIBITION

An exhibition of scientific instruments and books on physics will be arranged during the first threedays of the Conference in the Exhibition Area. Part of the exhibition will be devoted to the ESPRITProgramme of the CEC.

PAPER CODE

Oral papers:date, time of day/:/ room, paper number.EXAMPLE:7a2:D3Tuesday .second morning session/:/Room D, 3rd paper

Posters:date, P (oster)/:/poster area, paper numberEXAMPLE:8P:bl42Wednesday,Poster session/:/area b, paper&board number 142.

PROGRAMME TABLE

s

MO

6

TU

7

WE

8

TU

9

10

al

opening

A

PLENARY

(LANDER)

1L,

L 121

13i

a2

APLENARY

(HENSEL) (TIMOFEEV)

A New dev. in HTc supercond.

B Semicond. multilayers

C Cond.syst. with compl.str.

DA Surf, atomic microscopy

B Ph.sep. in cupr.sup. (Miller

C Dilute mag.semic. (Gaituka)

D

A Application of HTc supercond.

B Defects in semicon. (Grimmtiss)

C Submicron metall. struct.

D

A Important new developments

B Correl.efF. in quantum wells

C Phys. of complex fluids

D Magnetism

APLENARY

BEENAKKER)! H P p n z e (IBACH)1 ceremony

APLENARY

(WEAIRE) (LE COMBER)closing

143O 15 16

A

B

C

D

ABC

D

A

B

C

D

i 1 i i i i

i | i i I i

pm

Magnetic multilayers (Mathon)

Ab initio (Kunc)

El.tun. & IR spect. in HTc supercond.

Glass transition

Fullerenes

Adsorbates

Si based heterost. (Abstreiter)

Flux dynamics

Quant.wires & dots (Kotthaus)

Heavy fermions

Time resolv.spect. (Ryan)

ESPRIT workshop

POSTER

POSTER

POSTER

17~ 18

Monday April 620oo _ 21oo EVENING SESSION

ROOM A (METAKIDES)(Names in italics: session organizers)

PROGRAMME OF ORAL PRESENTATIONS

MONDAY APRIL 6

6al:A Plenary session9:00 OPENING OF THE CONFERENCE

9:30 1. MA GNETIC X-RA Y SCATTERINGG. H. Lander

6a2:A Applications of high temperature superconductors11:00 1. THIN FILM HIGH-Tc SQUID MAGNETOMETERS

C. Heiden

11:30 2. PROGRESS IN HIGH Tc MAGNETIC SENSORS AND THEIRAPPLICATIONSG. B. Donaldson, R.M. Bowman, A. Cochran, K.J. Kirk, J.C. Macfarlane, CM.Pegrum

12:00 3. THE PRESENT STATE OF Ag/Bi(222S) TAPESR. Flukiger, B. Hensel, A. Jeremie, A. Perin, J.-C. Grivel

6a2:B Defects in semiconductorsOrganizer: H. Grimmeiss

11:00 1. THE THEORY OF IMPURITY STATES IN SEMICONDUCTORSM. Lannoo

11:30 2. INTRA- AND INTERDEFECT ELECTRONIC CORRELATION OF DX-CENTERS IN III-VSEMICONDUCTORSW. Jantscb, G. Ostermayer, Z. Wilamowski

12:00 3. NEGATIVE-DONOR CENTRES AND RELATED PHENOMENA IN QUAN-TUM WELLSS. Huant, A. Mandray, B. Etienne

12:30 4. THEORY OF DEFECT METASTABILITY IN III- V COMPOUNDSJ. Dabrowski, M. Scheffler

6a2:C Submicron metallic structures11:00 1. QUANTUM AC-CONDUCTANCE OF WEAKLY DISORDERED MESO-

SCOPIC STRUCTURES ?J. Masek, B. Kramer -

11:30 2. SINGLE ELECTRON CHARGING AND ZERO-DIMENSIONAL STATES AIN LATERAL QUANTUM DOTS fA.T. Johnson 7

12:00 3. PERSISTENT CURRENTS AND DISSIPATION IN ISOLATED MESO- <SCOPIC RINGSH. Bouchiat, L.P. Levy, D. Mailly, G. Montambaux, B. Reulet

XIII

12:30 4. AHARONOV-BOHM EFFECT IN LOOPS DOPED WITH MAGNETICIMPURITIESC. Van Haesendonck, H. Vloeberghs, A.H. Verbruggen, S. Radelaar, Y. Bruyn-seraede

6pm:A Magnetic multilayersOrganizer: J. Mathon

14:30 1. EXCHANGE COUPLING IN MAGNETIC MULTILAYERSD. M. Edwards, J. Mathon, R.B. Muniz

15:00 2. EXCHANGE OF Ft LAYERS ACROSS INTERLAYERS WITH GOODMATCHP. Gruenberg

15:30 3. MAGNETIC PROPERTIES OF METALLIC MULTILAYERSW. J. M. De Jonge, P.J.H. Bloemen, H.A.M. De Gronckel

16:00 4. RELATIONSHIP BETWEEN STRUCTURE AND GIANT MAGNETORE-SISTANCEI. K. Schuller, D.M. Kelly, E.E. Fullerton, J. Guimpel, F. Belien, E. Osquiguil,Y. Bruynseraede

6pm:B Ab initio computationsOrganizer: K. Kunc

14:30 1. AB INITIO TOTAL ENERGY CALCULATIONS ON PARALLEL COMPU-TERSM. C. Payne, I. Stich, L.J. Clarke, R.D. King-Smith, J.S. Lin

15:00 2. PHONONS IN AlGaAs ALLOYS AND THE EFFECT OF DISORDER ONTHE VIBRATIONAL PROPERTIES OF GaAs/AlAs SUPERLATTICESS. Baroni, S. de Gironccli, P. Giannozzi, E. Molinari

15:30 3. DIELECTRIC RESPONSE AND QUASIPARTICLE ENERGIES IN NICKELF. Aryasetiawan, U. von Barth

16:00 4. SURFACE INDUCED ORDERING IN GALLIUM-INDIUM PHOSPHATE3. Froyen

6pm:C Electron tunneling and IR spectroscopy in high temperaturesuperconductors

14:30 1. ANISOTROPIC OPTICAL PROPERTIES OF UNTWINNED

B. Bucher, P. Wachter

15:00 2. LOCAL-PAIR APPROACH TO HIGH-Tc SUPERCONDUCTIVITY %L. J. De Jongh, S.I. Mukhin, D. Reefman f

15:30 3. ELLIPSOMETRICALLY DETERMINED FAR-INFRARED OPTICALCONSTANTS OF YBaCuO CERAMICS AND THIN FILMSK.L. Barth, F. Keihnann

XIV

6pm:D Glass transition14:30 1. GLASS TRANSITION SINGULARITIES: RECENT RESULTS

W, Goetze

15:00 2. SHORT-TIME DYNAMICS OF POLYMERS NEAR THE GLASS TRANSI-TION - INVESTIGATED BY INELASTIC NEUTRON SCATTERINGB Prick

15:30 3. THE GLASS TRANSITION OF HARD-SPHERE COLLOIDSP. N. Pusey, W. Van Megen

16:00 4. LIGHT SCATTERING STUDIES OF THE LIQUID-GLASS TRANSITIONRANGE IN A POLYMERIC LIQUIDL.M. Torell, D.L. Sidebottom

6ev:A Evening session20:00 EUROPEAN RESEARCH AND DEVELOPMENT POLICY FOR INFORMA-

TION TECHNOLOGIESG. Metakides

TUESDAY APRIL 7

7al:A Plenary session9:00 1. METALS IN THE LIQUID- VAPOUR CRITICAL REGION

F. Henael

I 9:45 2. MAGNETOOPTICS OF STRONGLY CORRELATED SD ELECTRONIC:j SYSTEMS! V. B. Timofeev

7a2:A Important new developments11:00 1. THE POSITIVE MUON AS A MAGNETIC RESONANCE PROBE OF

STRUCTURE AND DYNAMICSS. F. J. Cox

11:30 2. UNIVERSAL BEHAVIOUR OF THE ELECTRONIC TRANSPORTG. Dorda

12:00 3. VISIBLE LIGHT EMISSION FROM ELECTRO-OXIDIZED POROUSSILICONJ.C. Vial, S. Billat, A. Bsiesy, F. Gaspard, R. Herino, M. Ligeon, I. Mihalcescu,F. Muller, R. Romestain

12:30 4. THE ORIGIN OF VISIBLE LUMINESCENCE FROM "POROUS SI"H.D. Fuchs, M.S. Brandt, J. Weber, M. Stutzmann, M. Cardona

12:45 5. OPTICAL STUDIES ON SILICON 'QUANTUM WIRES'E.F. Steigmeier, B. Delley, H. Auderaet

Ii X V

7a2:B Correlation effects in quantum wells11:00 1. PARAEXCITONS AND SCREENING IN EXCITED QUANTUM WELLS

G. E. W. Bauer

11:30 2. MANY-BODY EFFECTS IN SD SEMICONDUCTORS STUDIED MA GNE-TOOPTICALLYM. Potemski

12:00 3. CORRELATED STATES OF DEGENERATE 2D ELECTRONS STUDIEDBY OPTICAL SPECTROSCOPYA.J. Turberfield, R.A. Ford, I.N. Harris, J.F. Ryan, C.T. Foxon, J.J. Harris

12:30 4. TWO-DIMENSIONAL ELECTRON CORRELATION IN HIGH MAGNETICFIELDS |H.L. Stormer '

7a2:C Physics of complex fluids11:00 1. A STATISTICAL MECHANICS APPROACH TO COLLOIDAL SUSPEN-

SIONSH. Loewen, J.P. Hansen

11:30 2. PHASES OF AMPHIPHILIC MONOLA YERS IN DIFFERENT ENVIRON-MENTSI.R. Peterson

12:00 3. SMALL-ANGLE NEUTRON SCATTERING OF AQUEOUS SOLUTIONSOF 2-BUTOXYETHANOL AND NON-IONIC SURFACTANTSG. D'Arrigo, R. Giordano, J. Teixeira

12:15 4. PHASE EQUILIBRIUM IN LIQUID BINARY MIXTURES OF NON-ADDITIVE HARD SPHERESG. Pastore, M. Rovere

12:30 5. KINETIC BEHAVIOUR OF A STRUCTURAL PHASE TRANSITION INLANGMUIR-BLODGETT MULTILA YERS STUDIED BY ENERGY DISPER-SIVE X-RAY REFLECTIVITYU. Pietsch, H.J. Merle, H. Metzger

7a2:D Magnetism11:00 1. ANISOTROPIC HYBRIDIZATION AND MAGNETISM IN ACTINIDE

INTERMETALLICS ,V. Sechovsky, L. Havela

11:30 2. MAGNETISM OF MONOCHALCOGENIDES AND -PNICTIDES OF THEACTINIDES 'iK. Mattenberger, O. Vogt if

12:00 3. MAGNETISM OF INTERFACES IN METALLIC MULTILA YERS XW. Zinn *

12:30 4. MAGNETOSTRICTION - 150 YEARS FROM THE DISCOVERYM.R.J. Gibbs

XVI

7pm:A Fullerenes14:30 1. FULLERENES AND FULLERITES: NEW FORMS OF CARBON

W. Kratschmer

15:00 2. ISOLATION, SPECTRGSCOPY AND REACTIONS OF FULLERENESR. Taylor

15:30 3. ELECTRON SPECTROSCOPY OF FULLERENES: SOME THEORETICALASPECTSA. A. Lucas, G. Gensterblum, J.J. Pireaux, P.A. Thiry, R. Caudano, J.P. Vi-gneron, Ph. Lam bin

16:00 4. A3Ceo COMPOUNDS; SUPERCONDUCTING AND NORMAL STATEPROPERTIESK. Holczer

7pm:B Adsorbates14:30 1. RE A CTIVE EVENTS IN MOLECULE-SURFA CE ENCOUNTERS

B. Kasemo

15:00 2. RECENT RESULTS IN THEORETICAL DESCRIPTION OFADSORPTIONB. Lundqvist

15:30 3. METALLIC ADSORBATES AS APPROXIMATIONS TO REDUCED DI-MENSIONALITY ELECTRON SYSTEMSC. Binns, C. Norris, M.G. Barthes-Li.brousse

| 16:00 4. CHEMISORPTION OF METALS OR ELECTRONEGATIVE ATOMS ON! GaAs1 J. Ortega, F.J. Garcia-Vidal, R. Perez, R. Rincon, F. Flores

i' 7pm:C Si based heterostructures

Organizer: G. Abstreiter14:30 1. OPTICAL PROPERTIES OF MESOSCOPIC Si-Ge STRUCTURES

M. Jaros15:00 2. MODULA TION DOPING IN THE Si/SiGe HETEROSYSTEM

F. Schaeffler

15:30 3. SILICON HETEROSTRUCTURES AND NANOSTRUCTUREST. P. Smith

16:00 4. VALENCE-BAND OFFSET AT Si/Gt INTERFACES: THE ROLE OF THESTRAIN :;L. Colombo '

I

XVII

7pm:D Flux dynamics14:30 1. VORTEX PINNING, FLUX CREEP AND ANISOTROPY IN YBCO AND

RELATED COMPOUNDSL. Fruchter, B. Janossy, LA. Campbell

15:00 2. FLUX CREEP, CRITICAL CURRENTS AND LOW CRITICAL FIELDS OF123 AND 2211 SINGLE CRYSTALSV. V. Moshchalkov

15:30 3. LINEAR AC RESPONSE OF HIGH-Tc SUPERCONDUCTORS AND THEIRREVERSIBILITY LINEE. H. Brandt

16:00 4. FLUX MOTION BY QUANTUM TUNNELINGA. C. Mota, G. Juri, P. Visani, A. Pollini, T. Teruzzi, K. Aupke, B. Hilti

WEDNESDAY APRIL 8

8al:A New developments in high temperature superconductors9:00 1. NEUTRON SCATTERING INVESTIGATION OF THE SPIN DYNAMICS

IN THE HIGH Tc SUPERCONDUCTING SYSTEM YBa2Cv306+x

J. Rossat-Mignod, L.P. Regnault, P. Bourges, C. Vettier, P. Burlet, J.Y. Henry

9:30 2. MAGNETIC EXCITATIONS IN THE HIGH-Tc SUPERCONDUCTINGSYSTEMSS.M. Hayden, G. Aeppli, P.C. Canfield, S.-W. Cheong, K.N. Clausen, Z. Fisk,M.F. Hundley, T.E. Mason, J.L. Martinez, H.A. Mook, D. Rytz

10:00 3. LAYER BY LAYER DEPOSITED OXIDE COMPOUNDS - INVESTIGA-TION OF ARTIFICIAL HTc SUPERLATTICES0 . Fischer, J.M. Triscone, L. Antognazza, O. Brunner, L. Mieville

8al:B Semiconductor multilayers9:00 1. QUANTUM CONFINEMENT IN II-VI HETEROSTRUCTURES: EXCI-

TONIC LASERS AT BLUE-GREEN WAVELENGTHSA. V. Nurmikko

9:30 2. METALORGANIC VAPOUR PHASE EPITAXY(MOVPE) OF III/V-SEMI-CONDUCTOR HETEROSTRUCTURES USING ALTERNATIVE PRECUR-SOR MOLECULES: NEW DEVELOPMENTSW. Stolz

10:00 3. INTERNALLY DETECTED ELECTRON PHOTOEXCITATION SPEC-TROSCOPY ON HETEROSTRUCTURES *C. Coluzza •

r.i8al:C Condensed systems with complex structure9:00 1. NEW PHYSICS IN STRUCTURAL PHASE TRANSITIONS IN SILICATE

FRAMEWORK MINERALSV. Heine

9:30 2. PERSISTENT SPECTRAL HOLES PROBING COMPLEX CRYSTALLINEDEFECT STRUCTURES AND AMORPHOUS SYSTEMSR. Bauer, T. Attenberger, I. Sildos, G. Jones, U. Bogner

XVIII

9:45 3. PROTON DYNAMICS IN A 2D - "SINGLE-CRYSTAL" OFBA CTERIORHODCPSINR.E. Lechner, N.A. Dencher, J. Fitter, G. Buldt

10:00 4. CONDUCTIVITY AND PHOTOCONDUCTIVITY OF CONDUCTINGPOLYMERSS. Roth, M. Kaiser, J. Reichenbach

8a2:A Plenary session11:00 1. MESOSCOPIC JOSEPHSON JUNCTIONS

C.W.J. Beenakker

11:45 HEWLETT-PACKARD 1992 EUROPEAN PRIZE AWARD CEREMONY

2. INTERATOMIC FORCES AND ATOMIC MOTION AT SURFACESH. Ibach

8pm:A Quantum wires and quantum dotsOrganizer: J. P. Kotthaus

14:30 1. OPTICAL PROPERTIES OF QUANTUM WIRES AND DOTSS. Beaumont

15:00 2. QUASI-ONE-DIMENSIONAL TRANSPORT IN SEMICONDUCTORMICROSTRUCTURESM. J. Kelly

15:30 3. LINEAR AND NONLINEAR OPTICAL PROPERTIED OF GaAs QUAN-TUM WIRES - CENTER-OF-MASS, EXCITONIC AND ELECTRON-HOLEPLASMA QUANTIZATIONH. Lage, D. Heitmann, R. Cingoiani

8pm:B Heavy fermions14:30 1. THE PHYSICS OF HEAVY FERMIONS WITH A HYBRIDIZATION GAP

F. Marabelli, P. Wachter

15:00 2. PERTURBATIONAL TREATMENT OF HEAVY FERMIONS IN HIGHDIMENSIONSG. Czycholl, H. Schweitzer

15:30 3. HOLE DYNAMICS IN QUANTUM ANTIFERROMAGNETS: CONSE-QUENCES FOR PHOTOEMISSION AND OPTICAL CONDUCTIVITYP. Horsch, W. Stephan

16:00 4. TRANSPORT MEASUREMENTS OF HEAVY FERMION SUPERCON-DUCTORSD. Jaccard, K. Behnia, J. Sierro, J. Flouquet

XIX

8pm:C Time resolved spectroscopyOrganizer: J.F. Ryan

14:30 1 NUMERICAL SIMULATION OF THE LASER-PULSE SPECTROSCOPYOF HOT CARRIERS IN SEMICONDUCTORSP. Kocevar

15:00 2. ULTRAFAST PROPERTIES OF QUANTUM WELLS AND SUPERLAT-TICES BY SUBP1COSECOND LUMINESCENCEB. Deveaud

8pm:D ESPRIT workshop

THURSDAY APRIL 9 )

9al:A Surface atomic microscopy9:00 1. RECENT PROGRESS IN SCANNING PROBE MICROSCOPY

H.-J. Guentherodt

9:30 2. SINGLE-ELECTRON TUNNELING UP TO ROOM TEMPERATURESCh. Schoenenberger, H. Van Houten

10:00 3. ROLE OF TIP ELECTRONIC STRUCTURE IN SCANNING TUNNELINGMICROSCOPYJ. Tersoff

9al:B Phase separation in cuprate superconductorsOrganizer: K. A. Mueller

9:00 1. MAGNETIC AND CHARGE TRANSFER COUPLINGS, ELECTRONICPHASE SEPARATION AND SUPERCONDUCTIVITYC. Di Castro

9:30 2. ELECTRONIC PHASE SEPARATION AND HIGH-TEMPERATURESUPERCONDUCTIVITYV. J. Emery

10:00 3. PERCOLATIVE PHASE SEPARATION AND HIGH-TcSUPERCONDUCTIVITYE. Sigmund, V. Hizhnyakov

9al:C Dilute magnetic semiconductors ,Organizer: R. R. Galazka

9:00 1. NOVEL MA GNETO-OPTIC AND SPECTROSCOPIC PHENOMENA IN II- •;VI SEMICONDUCTORS AND THEIR HETEROSTRUCTURES aA. K. Ramdas \]

9:30 2. HETEROSTRUCTURES OF DILUTE MAGNETIC IV-VI COMPOUNDS $H. Pascher '

10:00 3. EXCHANGE INTERACTION AND PHOTOMAGNETIZATION IN DI- ;

LUTE MAGNETIC SEMICONDUCTOR HETEROSTRUCTURES AND/ORSUPERLATTICESH. Krenn

XX

9a2:A Plenary session11:00 1. SOAP FROTH, MAGNETIC FROTH ...

D. Weaire

11:45 2. APPLICATION OF AMORPHOUS SILICON DEVICESP. G. LeComber

12:30 CLOSING OF THE CONFERENCE

XXI

LIST OF POSTER PRESENTATIONS

6P:a 1 STRUCTURAL AND MAGNETIC PROPERTIES OF FePt MULTILAYERSE. Devlin, V. Psicharis, A. Kostikas, A. Simopoulos, A. Jankowski, T. Tsakalakos

2 MAGNETOTHERMOELECTRIC POWER OF MAGNETIC MULTILAYERSL. Piraux, A. Fert, R. Loloee, P.A. Schroeder, P. Etienne

3 NEW TRENDS FOR THE MAGNETISM IN LOW-DIMENSIONAL TRANSITION-METAL STRUCTURESC. Demangeat, L.C. Balbas, J. Dorantes-Davila, K.H. Bennemann, H. Dreysse

4 ARE COBALT LAYERS DILATED IN MAGNETIC MULTILAYERS?N. Mliki, K. Abdelmoula, G. Nihoul, Ch. Marliere, D. Renard

5 BLUE ENHANCED MAGNETO-OPTIC Co/Pt MULTILAYERS WITH ZERO KERRELLIPTICITYR. Atkinson, I.W. Salter, A.H. El-Astal, J. Xu

6 CHARACTERIZATION OF QUADRILAYER MAGNETIC RECORDING MEDIA BYELLIPSOMETRY AND RBS EXPERIMENTR. Atkinson, J. Hrdina, L. Jastrabik, V. Perina, P. Siroky

7 ELASTIC CHARACTERIZATION OF Ta/Al PERIODIC SUPERLATTICES BYBRILLOUIN LIGHT SPECTROSCOPYG. Carlotti, D. Fioretto, L. Palmieri, G. Socino, L. Verdini, H. Xia, R.W. Peng, A. Hu,S.S. Jiang, X.K. Zhang, D Feng

11 MAGNETIC ANISOTROPY OF ULTRATHIN COBALT [0001] FILMS ON Au(l l l )P. Beauvillain, V. Grolier, R. Megy, S. Ould-Mahfoud, D. Renard, P. Veillet

12 THE OBSERVATION OF A DIMENSIONAL CROSSOVER IN ULTRATHIN Ni FILMSYi Li, K. Baberschke

13 VALENCY AND SITE DISTRIBUTION OF LEAD IN YlG:Pb THIN FILMA. Campos, H. Doetsch, H. Luetgemeier, P. Novak, S. Sure

14 MAGNETIC PROPERTIES OF AMORPHOUS Fe IN Y/Fe/Y THIN FILMSS. Dorrer, J. Landes, Ch. Sauer, U. Kobler, A. Fuss, W. Zinn

15 COUPLING BETWEEN FERROMAGNETIC FILMS ACROSS A NONMAGNETICLAYERJ. Barnas

16 DOMAIN STRUCTURE OF THIN SINGLE CRYSTAL PLATELETS OFB a F e 1 2 - X - Y C o X T i Y ° 1 9R. Gemperle, V. Kambersky, J. Simsova, L. Pust, L. Murtinova, P. Goernert, W. Schup-pel, R. Gerber

17 NUCLEAR SPIN-LATTICE RELAXATION IN FERROMAGNETIC AMORPHOUSALLOYS Fe80 5Co-j j B ; 6 4 AND Fe70Col0B20 I1. Kohout, J. Englich, M. Trhlik, H. Lutgemeier

18 THE PREISACH DIAGRAM AND WOHLFARTH's REMANENCE FORMULA iP. Hejda, E. Petrovsky, T. Zelinka, V. Kropacek *f

19 CALCULATION OF CRYSTAL FIELD PARAMETERS AND ELECTRIC FIELDGRADIENT IN RARE EARTH METALSJ. Kuriplach, P. Novak

XXII

6P:a20 MAGNETOMECHANICAL HYSTERESIS LOOP EVALUATION FROM MECHANI-

CAL BARKHAUSEN EFFECTB. Augustyniak

21 NO MORE TRANSCENDENTAL EQUATIONS IN HOMOGENEOUS MEAN-FIELDMODELS OF FERROMAGNETISMY. Millev, M. Fahnle

22 THE GAUSSIAN THEORY OF DIPOLAR FERRO- AND ANTIFERROMAGNETSY. Millev, K. Ried, M. Fahnle

23 ITINERANT ELECTRON THEORY OF SPIN WAVES IN HCP COBALTJ.M. Bass, J.A. Blackman, J.F. Cooke

24 CALCULATION OF ELECTRONIC AND MAGNETIC PROPERTIES OF METALLICA i Bj An LAYERED SYSTEMSW. Hergert, H. Dreysse, P. Rennert, C. Demangeat

25 INTERACTING FERROMAGNETIC PARTICLES: NUMERICAL SIMULATION OFTHE DYNAMICSJ. Planes, A. Fintl

26 MAGNETIC ABSORPTION AT l23 - EDGES IN HoP. Fischer, G. Schutz, G. Wiesinger

27 FAR INFRARED MAGNETOTRANSMISSION OF YbIGJ. Kolacek, Z. Simsa, R. Tesar

28 ENHANCEMENT OF MAGNETOOPTICAL EFFECTS IN Au/Co/Au ULTRATHINFILM SANDWICHESJ. Ferre, M. Nyvlt, G. Penissard, V. Prosser, D. Renard, G. S«igel, S. Visnovsky

33 EVIDENCE OF THE NEGATIVE-DIFFERENTIAL-RESISTANCE EFFECT INHIGH-TC OXIDES: PROSPECT OF THE NONJOSEPHSON SUPERCONDUCTIVEELECTRONICSR. Nicolsky, M.A. Luiz

34 LOSSFREE AND D1SSIPATIVE LATERAL MOTION OF A MAGNET LEVITATEDBY A HIGH TC SUPERCONDUCTORT.H. Johansen, H. Bratsberg, Z.J. Yang

35 SHEAR SOUND ATTENUATION IN LAYERED HIGH-Tc SUPERCONDUCTORSI.E. Boulyjenkov

36 EFFECT OF COMPLEX STRUCTURE OF HIGH TEMPERATURE SUPERCON-DUCTORS ON ITS DYNAMICAL CHARACTERISTICSA.M. Kosevich, E.S. Syrkin, S.B. Feodosyev, LA. Gospodarev

37 RENORMALIZATION OF PHONON FREQUENCIES BY ELECTRONIC CARRIERSIN LAYERED HIGH-TEMPERATURE SUPERCONDUCTORSG. Hastreiter, D. Strauch, J. Keller |

38 MODE-SOFTENING AND STRUCTURAL TRANSITIONS IN LAYERED OXIDE APEROVSK1TES fH. Blaschke, G. Meissner I

39 EXPRESSION FOR THE CRITICAL CURRENT DENSITY OF THE HIGH- *TEMPERATURE SUPERCONDUCTORS \Z. Rajilic, D.Lj. Mirjanic

XXIII

6P:a40 STUDIES OF STRUCTURAL CHANGES IN HIGH TEMPERATURE

SUPERCONDUCTORS BV ELECTRON ACOUSTIC MICROSCOPY ANDCATHODOLUMINESCENCEJ. Piqueras, P. Fernandez, F. Dominguez-Adame

41 ON FIELD-INDUCED GRANULAR BEHAVIOUR IN DEOXYGENATED AND/ORIRRADIATED HIGH TEMPERATURE SUPERCONDUCTORSS.A. Sergeenkov

42 COMPARISON OF THE U(J)-RELATION FOR DIFFERENTHTC-SUPERCONDUCTORSM. Reissner, W. Steiner

43 COMPLEX AC-IMPEDANCE OF HTSC-FILM AND EFFECT OF ULTRASOUNDA. Voronel, S. Feldberg, M. Levin, R. Pogreb, V. Sandomirski

44 SUPERCONDUCTING PROPERTIES OF WxSiy/Si MULTILAYERSI. Vavra, P. Lobotka, S. Benacka, R. Senderak

45 JOSEPHSON EFFECT IN MAGNETIC SUPERCONDUCTOR GdMogSegJ. Kuznik, K. Rogacki

46 ALTERNATIVES TO THE FROHLICH TRANSFORMATION INSUPERCONDUCTIVITYM. Wagner

47 A THEORY FOR THE EFFECT OF IMPURITIES ON THE RAMAN SPECTRA OFSUPERCONDUCTORST .P. Devereaux

48 READ-OUT SCHEMES FOR REDUCTION OF FLICKER NOISE IN DC SQUIDSS. Papez, P. Vrabcek

49 SCALING OF THE VOLUME PINNING FORCE AND THE INFLUENCE OF THER-MALLY ACTIVATED FLUX MOTION IN TYPE-II SUPERCONDUCTORSL. Niel

50 ANTIFERROMAGNETIC ORDER IN UPt3 UNDER PRESSURE: EVIDENCE FORA DIRECT COUPLING TO SUPERCONDUCTIVITYS.M. Hayden, L. Taillefer, C. Vettier, J. Flouquet

51 MAGNETIC PROPERTIES OF THE YBaCuO SUPERCONDUCTIVITY POWDERSM. Timko, I. Sargankova, A. Zentko, J. Kovac

52 YBaCu0/ZrO2/SAPPHIRE LASER DEPOSITIONS.V. Gaponov, E.B. Kluenkov, L.N. Mazo, M. Jelinek, L. Jastrabik, L. Soukup, V.Hnatowitz

53 THERMAL CONDUCTIVITY OF YBa 2 Cu 4 0 8

B.M. Andersson, B. Sundqvist

54 SUPERCONDUCTING FLUCTUATIONS OF TRANSPORT PROPERTIES IN Y-BaCuO THIN FILMSW. Lang, G. Heine, H. Jodlbauer, P. Schwab, X.Z. Wang, D. Baeuerle

55 MAGNETIC RELAXATION IN THE EPITAXIAL THIN YBaCuO THIN FILMS INBOTH CONSTANT AND CHANGING MAGNETIC FIELDL. Pust, M. Jirsa, V. Gregor

56 LOCAL Cu(2) MAGNETIC BEHAVIOUR IN Y0g7 1 7 0 Y b 0 03Ba2Cu,}Ox AS A

FUNCTION OF OXYGEN LEVELJ.A. Hodges, P. Bonville, P. Imbert, G. Jehanno

XXIV

6P:a

57 STUDIES OF Ca-Th SUBSTITUTION IN YBa 2 Cu 3 0 7 _ 4 BY RAMAN SCATTERINGAND CALCULATION OF THE ELECTRON-PHONON INTERACTIONL. Boerjesson, H.V. Phuong, T. Jarlborg, M. Anderason, O. Rapp

58 NORMAL STATE HALL ANGLE DETERMINATION IN OXYGEN DEFICIENTY B a 2 C u 3 0 x EPITAXIAL FILMSB. Wuyts, M. Maenhoudt, Z.X. Gao, S. Libbrecht, E. Osquiguil, Y. Bruynseraede

59 SAW ACOUSTOELECTRIC EFFECTS IN LAYER STRUCTURES WITH HTSC(1:2:3)-FILMSM. Levin, R. Fogreb, V. Sandomirski, A. Voronel, S. Feldberg

60 INTERACTION OF Pb WITH YBaCuO THIN FILM SURFACET.J. Sarapatka, P. Mikusik

61 THERMODYNAMIC PROPERTIES OF PHASES IN THE Y-Ba-Cu-0 SYSTEMJ. Sestak, C.K. Moiseev

65 ON-SITE REPULSION AND SPIN ORDERING OF ITINERANT ELECTRONSE.V. Kholopov

66 SPECIFIC HEAT OF MAGNETIC KONDO LATTICES UNDER HIGH PRESSUREA. Eichler, E. Hanke, T. Kitsch, J. Michal, S. Sullow

67 AGING EFFECT IN SPIN GLASSES REVISITEDP. Erhart, B. Senning, F. Waldner

68 THE GROUND STATE O^ FERMION TRIMERj S. Sunaric, T. Persi

«. 69 CYCLOTRON RESONANCE OF ELECTRONS IN THE W1GNER SOLID REGIME", M. Besson, CM. Engelhardt, E. Gornik, G. Weimann

• 70 GROUND STATE ENERGY OF MANY-BODY FERMI SYSTEM BY USING FEEN-V BERG PERTURBATION THEORY

S. Kilic, T. Persi

71 EXACT INFINITE RESULTS FOR THE HUBBARD MODEL ON A 4x4 CLUS-TER POINTING TOWARDS A FERROMAGNETIC FERMI LIQUID NEAR HALF-FILLINGG. Chiappe, E. Louis, F. Guinea, J.A. Verges

72 WARD IDENTITIES AND RESPONSE FUNCTIONS IN THE LUTTINGER LIQUIDC. Di Castro, W. Metzner

73 MOMENT EXPANSION OF THE TWO PARTICLE GREEN FUNCTION FOR THEHUBBARD HAMILTONIANM. Kotrla, V. Drchal

74 PERTURBATION THEORY FOR THE TWO-DIMENSIONAL HUBBARD MODEL: IABSENCE OF QUASIPARTICLE EXCITATIONSJ. Galan, J.A. Verges I

75 SELF-CONSISTENT THEORY OF THE ANDERSON LATTICE §;; J. Petru ,'•

76 ANYON STATES IN CRYSTALS WITH ROTATIONAL DEFECTS ]I1 V.A. Osipov \

77 PHASE DIAGRAM OF THE 2-D HUBBARD MODELi J. Beenen, D.M. Edwards

XXV

78 SINGLE PARTICLE AND OPTICAL GAPS NEAR THE METAL - INSULATORTRANSITIONR. Raimondi, C. Castellani, M. Grilli, Y. Bang, G. Kotliar, Z. Wang

79 MOMENTUM DEPENDENCE OF THE SELF-ENERGY FOR THE 2-D HUBBARDMODELC.J. Rhodes, R.L. Jacobs

80 ONE-PARTICLE SPECTRAL DENSITIES IN THE EXTENDED ONE-BAND HUB-BARD MODELSM.P. Lopez Sancho, J.M. Lopez Sancho, M.C. Refolio, J. Rubio

81 ANTI-FERROMAGNETIC MOMENTS AND ONE-ELECTRON SPECTRA OF THE2D-HUBBARD-PEIERLS MODEL IN THE SELF-INTERACTION CORRECTEDDENSITY FUNCTIONAL FORMALISMJ.A. Majewski

6P .b 101 AB INITIO CALCULATIONS OF YTTRIUM DISILICIDE AND INTERFACE WITHSILICONL. Magaud, J.P. Julien, F. Cyrot-Lackmann

102 STRAINING INTERMETALLICS FOR FUN AND PROFIT VIA TOTAL ENERGYCALCULATIONSM.J. Mehl, D.A. Papaconstantopoulos, B.M. Klein, L.L. Boyer

103 AB INITIO ELASTIC CONSTANT AND ELECTRONIC STRUCTURE OF A1PP. Rodriguez-Hernandez, A. Munoz

104 NEW DEVELOPEMENTS IN BAND-STRUCTURE METHODSH. Bross, G.M. Fehrenbach

105 A METHOD FOR FREE ENERGY CALCULATION AT THE SECOND ORDERPHASE TRANSITION BELOW CRITICAL TEMPERATUREI.R. Yukhnovskii, M.P. Kozlovskii, I.V. Pylyuk

106 ULTRASOFT PSEUDOPOTENTIAL FOR FLUORINEF. Meloni, K. Laasonen, A. Pasquarello, A. Satta

107 FIRST PRINCIPLES CALCULATIONS OF THE STRUCTURAL PROPERTIES OFORDERED INTERMETALLIC ALLOYSM.J. Mehl, D.A. Papaconstantopoulos, B.M. Klein

108 'AB-INITIO'-CALCULATIONS OF PHONONS IN SiCK. Karch, 0 . Schutt, P. Pavone, W. Windl

109 AB-INITIO CALCULATION OF PHONON EIGENVECTORS,GRUNEISEN PARAMETERS, AND THERMAL EXPANSION COEFFICIENTS OFSEMICONDUCTORSP. Pavone, S. Baroni

110 TOWARDS A NEW CLASS OF MODELS FOR LATTICE DYNAMICAL CALCULA-TIONS IN SEMICONDUCTORSL. Colombo, P. Giannozzi

111 SYMMETRIZED SELF-CONSISTENT WEIGHTED DENSITY APPROXIMATIONFOR EXCHANGE-CORRELATION FUNCTIONAL OF THE ELECTRON GASE. Chacon, J.E. Alvarellos

112 AN EFFICIENT METHOD FOR CALCULATING QUAS1PARTICLE ENERGIES INSEMICONDUCTORSR. Del Sole, F. Bechstedt, G. Cappellini, L. Reining

XXVI

6P:b113 FIRST PRINCIPLES STUDY OF THE STACKING EFFECT ON THE ELECTRONIC

PROPERTIES OF GRAPHITE(S)J.-C. Charlier, X. Gonze, J.-P. Michenaud

114 ELECTRONIC STRUCTURE OF ALKALINE EARTH OXIDESE.J. Whitehead, D.M. Bird

115 FERROMAGNETIC SPINELS: A FIRST-PRINCIPLES STUDYA. Continenza, T.M. De Paacale, F. Meloni, M. Serra

116 SELF-CONSISTENTLY DETERMINED PROPERTIES OF SOLIDS WITHOUTBAND-STRUCTURE CALCULATIONSP. Cortona

117 SURFACE STRESS THEOREM-GENERALIZED SURFACE VIRIAL THEOREMFOR THE JELLIUM MODEL OF HALFSPACE METALSJ. Grafenstein, R. Kaschner, P. Ziesche

118 CRYSTAL BINDING ENERGIES FROM ATOMIC CLUSTER CALCULATIONSY. Jinlong, W. Kelin, F. Casula, G. Mula

119 CALCULATION OF WANNIER FUNCTIONS FOR d-s BAND OF Cu BY MODIFIEDVARIATIONAL METHODP. Modrak

121 UNIVERSAL BEHAVIOR IN ELECTRONIC PROPERTIES OF STABLE ICOSAHE-DRAL PHASES WITH TRANSITION ELEMENTS?F. Cyrot-Lackmann, C. Berger, T. Klein, P. Lanco, D. Mayou, G. Trambly

• 122 ABSORPTION SPECTRA OF RARE EARTH DOPED SM OPTICAL FIBERS'•. M. Pospisilova, M. Schneiderova

I 123 CLUSTER MATTER: INHOMOGENEOUS MATERIALS BASED UPON CLUSTERSI U. Kreibig

| 124 SYMMETRY OF A QUASICRYSTALI C. Ripamonti

I 125 A THEORETICAL SIMULATION OF DAMAGE IN COMPOSITE MATERIALS: A| CHAOTIC MODELI F. Meloni, A. Varone, F. Ginesu

' 126 TIME LAG IN HOMOGENEOUS NUCLEATION: AN ANALYTICAL APPROACHP. Demo, Z. Kozisek

127 METASTABLE STATES AND SP1NODALS IN THE BEG MODELV.H. Boyko

128 CRITICAL BEHAVIOR IN THE EXTENDED BEG MODELC. Buzano, A. Pelizzola

129 ON THE PHASE TRANSITIONS THEORY IN BINARY SYSTEMSO. Patsagan

130 EPR IN IRRADIATED POLYACETYLENEI O. Hola

I 131 ELECTRICAL CONDUCTIVITY AND ESR LINEWIDTH OF DIFFERENT< POLYACETYLENE

A. Bartl, J. Froehner, R. Zuiok, S. Roth

1 132 KIRCHHOFF'S THEOREM IN LATTICE MODELS OF POLYMERSI E.I. Kornilov, V.B. Priezzhev

i

XXVII

6P:b133 DIELECTRIC AND MECHANICAL BEHAVIOUR OF POLYURETHANE

NETWORKSJ. Nedbal, M. llavsky, J. Faehnrich

134 ELECTRICAL PROPERTIES OF POLYMER COMPOSITESA. Lundin

135 PHOTOEXCITATION DYNAMICS IN CONJUGATED POLYMER CRYSTALSI. Zozulenko

136 PRESSURE DEPENDENCE OF ELECTRICAL CONDUCTIVITY OF THE CON-DUCTING POLYMERSP. Fedorko, V. Skakalova, S. Kosina, V. Laurinc

137 RELAXATION OF CONDUCTIVITY OF POLYPYRROLE UNDER PRESSURE )V. Skakalova, P. Fedorko, J. Annus, M. Omastova, S. Baluch, D. Walton

138 NEW POLYMERIC COMPOSITESR. Kuzel, J. Kubat, I. Krivka, J. Prokes, P. Nozar

139 DIELECTRIC PROPERTIES OF POLYMERIC COMPOSITESJ. Kubat, J. Prokes, R. Kuzel, I. Krivka, O. Stefan

140 CORRELATION EFFECTS AND STRUCTURE OF CRYSTALLINE LIQUIDS (BLUEPHASES)E. Demikhov

141 FERROELECTRICITY IN LIQUID CRYSTALS INFLUENCED BY THE SUB-STANCE CHIRALITYM. Glogarova, Ch. Destrade, J P. Marcerou, J.J. Bonvent, H.T. Nguyen

142 POLAR LIQUID CRYSTALS IN THE NON-UNIAX1AL MOLECULES MODELK. Szumilin, J.J. Milczarek

143 ON THE OPTICAL NOISE IN PLANAR NEMATIC LIQUID CRYSTALS NEAR THEFREEDERICKSZ TRANSITIONP. Allia, P. Galatola, C. Oldano, P. Taverna-Valabrega, L. Trossi

144 ON THE SWITCHING FROM THREE DIMENSIONAL TO ONE DIMENSIONALBEHAVIOUR IN A MODEL LIQUID CRYSTALC. Chiccoli, P. Pasini, F. Semeria, C. Zannoni

145 THERMOCHROMIC VO2 SPECIMENS MORPHOLOGY RELATED TO VARIOUSELABORATION TECHNIQUES AND W CONCENTRATIONJ.C. Rakotoniaina, R. Mokrani-Tamellin, J.R. Gavarri, W. Chodkiewicz, G. Vacquier, C.Cesari

146 THE ATOMIC AND ELECTRONIC STRUCTURE OF SELF-TRAPPED HOLES INCORUNDUM (a-AI2Oj) CRYSTALS ;E.A. Kotomin, I.A. Tale, P.W.M. Jacobs \

147 SOME PROPERTIES OF RuO2 THICK FILM RESISTORS DOWN TO 50 mK $I. Batko, K. Flachbart, M. Somora, D. Vanicky, K. Winzer !

148 DEUTERATION EFFECT ON COUPLED MODES IN A Rb i _ x NH 4 x H 2 PO 4 D1PO- JLAR GLASS %F. Moussa, E. Courtens '•

149 THE PRESSURE DEPENDENCE OF PHASE SHIFT OF PHOTOACOUSTIC SIG-NAL IN RUBY AS NEW METHOD FOR PRESSURE MEASUREMENTB.R. Jovanic, Lj.D. Zekovic, B. Radenkovic

XXVIII

6P:b150 SOLID ON SOLID CELLULAR AUTOMATA: GROWTH OF Ta-OXIDE PARTICLES

IN THE NONSTATIONARY THERMAL FIELDS. Lugomer, M. Kerenovic, M. Stipancic

151 NEW METHOD FOR MEASURING PRESSURE IN ALEXANDRITE(BeAl2O4:Cr3+)Lj.D. Zekovic, B.R. Jovanic, B. Radenkovic, V.V. Urosevic

152 VIBRATIONAL DYNAMICS IN AMORPHOUS SILICA BY LIGHT SCATTERINGMEASUREMENTSP. Benassi, A. Fontana, L.M. Gratton, M. Montagna, O. Pilla, G. Viliani

153 TRANSPORT PROPERTIES IN Nb-DOPED BARIUM TITANATE CERAMICS ANDSINGLE CRYSTALS:A COMPARISONC. Gillot, J.-P. Michenaud

154 EELS STUDY OF SINGLE-CRYSTALLINE NIO(IOO)A. Gorschluter, C. Henig

155 OPTICAL PROPERTIES AND EPR CENTERS IN CUBIC STABILIZED ZIRCONIAC.B. Azzoni, A. Paleari

156 THE ORIENTATION OF YIG PARTICLES IN A VISCOUS MEDIUM BY MEAN-S OF THE MAGNETIC IMPULSES FORMING THE CONFIGURATION OF THEDIRECTIONS < 111 >J. Kolovrat

j 157 STUDY OF THE PHASE TRANSITION OF DOPED KTaO3 BY OPTICAL; fj TECHNIQUES

, J G.P. Banfi, P. Calvi, P. Camagni, E. Giulotto, G. Samoggia

I 158 OPTICAL ACTIVITY OF FERROELECTRIC TGS CRYSTALSI O.S. Kushnir, Y.I. Shopa, O.G. Vlokh

1 159 OPTICAL REFLECTANCE DATA OF NiO AND Li:NiO SINGLE CRYSTALS IN THEI RANGE 4 TO 30 eV'• F. Parmigiani, A. Revcolevschi, L. Sangaletti, M. Scagliotti, N. Zema

'i 160 OPTICAL REFLECTANCE AND XPS SPECTRA OF YTTRIUM STABILIZED| ZIRCONIAIt P- Camagni, F. Parmigiani, G. Samoggia, L. Sangaletti, M. Scagliotti, N. Zema

I 161 VUV REFLECTIVITY ON SiO2

| C. Bosio, W. Czaja

162 STUDY OF THE OPTICAL ABSORPTION EDGE OF YTTRIUM-STABILIZEDZIRCONIAP. Camagni, P. Galinetto, G. Samoggia, N. Zema

( 163 ADVANCES IN EMISSION KINETICS ANALYSIS OF HEAVY ns 2 IONS IN ALKALI *i'; HALIDE CRYSTALS| M. Nikl, J. Hlinka, K. Polak, E. Mihokova, P. Fabeni, G.P. Pazzi, L. Salvini , || 164 RED LUMINESCENCE OF STRUCTURAL DEFECTS IN Hg2CI2 CRYSTALS ;•?I 1. Bryknar, A. Konakova, P. Jirousek \

\ 165 PHOTOEMISSION SPECTROMICROSCOPY INVESTIGATION OF SnOx-BASED %\ GAS SENSORS '• D. Rosenfeld, P. Almeras, C. Coluzza, F. Gozzo, R. Sanjines, G. Margaritondo

I 169 ELECTRIC BIREFRINGENCE MEASUREMENTS OF AQUEOUS FD-VIRUS- '| SOLUTIONS 2\ H. Kramer, R. Weber

XXIX

170 MONTE CARLO SIMULATIONS OF CLOSED DNA MOLECULESM. Botta, G. Chirico, G. Baldini

171 MICROSCOPIC BASIS FOR SUPERIONIC CHARGE TRANSPORT MODEL IN BI-OLOGICAL MEMBRANE CHANNELSA.S. Rakitin

172 EVIDENCE OF HEMOGLOBIN DISSOCIATION FROM LIGHT SCATTERINGL. Lunelli, N. Romani, G. Baldini

173 BROWN1AN DYNAMICS OF CLOSED DNA MOLECULESG. Chirico, J. Langowski

174 RHEOLOGICAL PROPERTIES OF SUSPENSIONS OF INTERACTING RODLIKEFD-VIRUS PARTICLESCh. Graf, R. Weber

6P:c 201 LUMINESCENCE FROM SILICON DOPED WITH Cu AND Fe AND EXTENSIVEDEFECT DECORATIONM.C. Carmo, M. Lima

202 SPATIAL SENSITIVITY REVERSAL IN A MODIFIED DLTSI. Thurzo, V. Nadazdy

203 IMAGING OF DEFECTS IN GaAs:In BY SCANNING ELECTRON ACOUSTICMICROSCOPYB. Mendez, J. Piqueras

204 META-STABLE DEFECTS IN SILICON' N.A. Sulimov

205 NATURE OF POINT DEFECTS IN Bi2_xInxTe3 CRYSTALSJ. Horak, Z. Stary

206 INVESTIGATION BY THERMOLUM1NESCENT EXPERIMENTS OF POINT DE-FECTS IN ALUMINO-SILICATE LATTICESP. Brovetto, A. Delunai, V. Maria, M. Salis, G. Spano

207 THE EFFECT OF ELECTRON IRRADIATION DOSE ON THE PROFILE OF THEINTRODUCED DEFECTS IN GaAs VPE LAYERSCD. Kourkoutas, B. Kovacs, P.C. Euthymiou, B. Szentpali, K. Somogyi, PC. Banbury,G.E. Zardas

208 ELECTRICAL PROPERTIES OF ION IMPLANTATION INDUCED DEFECTS INSILICONP. Hazdra, V. Haslar, M. Kejhar

209 INTERACTION OF IMPURITIES IN CUPROUS OXIDER. Kuzel, F.L. Weichman

210 DEEP LEVELS IN SILICON AFTER NEUTRON IRRADIATIONJ. Mudron, P. Sutta, L. Macko, D. Pogany, P. Macko, P. Ballo

211 APPLICATION OF A NEW METHOD TO MEASURE DEFECTS INSEMICONDUCTORSL. Doua

212 ENERGY TRANSFER BETWEEN Ni 2 + AND CV+ CENTRES IN ZnSP. Thurian, R. Heitz, T. Jentxaeh, A. Hoffmann, I. Brewer

213 INVESTIGATION OF DEEP LEVELS IN SILICONJ. Prokea, O. Stefan

XXX

6P:c214 JAHN-TELLER EFFECT ON THE EL2 CENTER UNDER UNIAXIAL STRESS

L. Martinelli, G.P. Parravicini

215 PARAELECTRIC RESONANCE OF PHOTO-EXCITED Sn RELATED DX CENTER-S IN Al j tGai . x AT LOW TEMPERATURESK. Zdansky, A.R. Peaker

216 THE CONSEQUENCES OF THE FREE-CARRIER ENTROPY FOR TIGHTLYBOUND DEFECT STATES IN SEMICONDUCTORSD.H. Cobden, L. Martin-Moreno, M.J. Uren

217 VANADIUM LEVEL AND PHOTOCONDUCTIVITY IN n-InP UNDER PRESSUREA.K. Saxena

218 PECULARITIES OF THERMOSTIMULATED CURRENTS IN SEMIINSULATINGGaAs AND InP:FeE. Klier, F.L. Weichman

219 LOW TEMPERATURE DX CENTER IONIZATION BY FORWARD BIASING Al-GaAs SCHOTTKY BARRIERSR. Mosca, E. Gombia, C. Ghezzi, P. Frigeri, A. Boeacchi, S. Franchi

220 EVIDENCE FOR THE ROLE OF SPATIAL DISTRIBUTION OF CHARGED IM-PURITIES ON THE ELECTRON MOBILITY IN A l x G a j ^ A s CONTAINING DX-CENTRESPX. Coz, C. Ghezzi, A. Parisini

221 TEMPERATURE DEPENDENCE OF THE PHOTOQUENCHING OF EL2 LEVELIN SEMIINSULATING GaAs

. M. Chafai, A. Alvarez, J. Jimenez, J. Pascual

I 222 DEEP Zr- AND Hf- RELATED LEVELS IN InP| H. Scheffler, N. Baber, T. Wolf, A. Knecht, D. Bimberg, J. Winterfeld, H. Schumann

| 223 EPR STUDY OF TRIPLET Ni 2 + CENTRES IN NaCI SINGLE CRYSTALS? A.G. Badaljan, J. Rosa

I 224 ELECTRON SPIN RESONANCE SPECTROSCOPY OF SILVER DOPED SILICON\ N.T. Son, V.E. Kustov, T. Gregorkiewicz, C.A.J. Ammerlaan

; 225 STUDY OF Si RELATED DEFECT IN GaAs BY LVM SPECTROSCOPYM. Zavetova, J. Pastrnak, J. Oswald

226 EFFECTS OF ISOTOPIC DISORDER ON THE VIBRATIONAL PROPERTIES OFGe: A COMPARISON OF 7 0Ge, 7 4Ge, 7 6Ge, AND NATURAL GeH.D. Fuchs, C.H. Grein, R.I. Devlen, J. Kuhl, M. Cardona

227 DOPING DEPENDENCE OF THE RECOMBINATION KINETICS OF CdS:InCh. Fricke, R. Heitz, A. Hoffmann, I. Brooer

228 NONTUNNELING CHARACTER OF THE TRANSPORT PROCESS IN HIGH-TCSUPERCONDUCTORSR. Nicobky

229 ELECTRON-PHONON INTERACTION IN HIGH TEMPERATURE SUPERCON-DUCTORS: TUNNELING AND OTHER EXPERIMENTSM.A. Belogolovskii, V.M. Svistunov

230 ELECTRON-PHONON COUPLING IN THE TUNNELING CHARACTERISTICS OFi SUPERCONDUCTING Ba j_ x K x BiO 3 AND B i 2 S r 2 C a j C u 2 0 8 + x

; P. Sunuely, S.I. Vedeneev, A.G.M. Juueo, P. Wyderit

I XXXI

231 MEASUREMENT OF VORTEX DISSIPATION IN SINGLECRYSTALLINE

L. Legrand, I. Roeenman, Ch. Simon, G. Collin

235 COMPUTER SIMULATION OF GLASS TRANSITIONR. Boscolo, L. Roy Jacobs

236 THE GLASS TRANSITION: A SUPERLATTICE OF CLUSTERS FORMATIONV. Bouda

237 THE A4 GLASS TRANSITION SINGULARITYS. Flach, W. Gotze, L. Sjogren

238 THE INFLUENCE OF ACTIVATED HOPPING ON ^RELAXATIONA. Latz, M. Fuchs, S. Hildebtandt

239 MULTIPARAMETER TREATMENT OF GLASS TRANSITION KINETICS 'J. Faehnrich, M. Slama

240 HALIDE-CHALCOGENIDE GLASSES Te3IxSe4

J. Brydl, Z. Cimpl, F. Kosek

241 EXAFS STUDY OF LOCAL ORDER IN xBi 2 0 3 . yGe0 2 GLASSESG. Antonioli, P.P. Lottici, I. Manzini, G. Gnappi, A. Montenero

242 GLASS COMPOSITES - HETEROGENEOUS SYSTEMSI. Krivka, O. Stefan, R. Kuzel, J. Kubat, D. Rafaja

243 LINEAR AND NONLINEAR ACOUSTIC PROPERTIES OF RARE EARTH PHOS-PHATE GLASSESH.B. Senin, Q. Wang, R.C.J. Draper, G.A. Saunders, P.J. Ford, M. Cankurtaran

244 RAMAN CHARACTERIZATION OF GEL-DERIVED TITANIA GLASSP.P. Lottici, D. Bersani, M. Braghini, A. Montenero

7P:a 1 A POSSIBLE NEW HIGHLY STABLE FULLERITE CLUSTER: Li ]2Cg0J. KohanofT, W. Andreoni, M. Parrinello

2 A NOTE ON C60 UNDER HIGH PRESSUREV. Celebonovic

3 MULTIPOLE POLARIZATION WAVES AND VAN DER WAALS COHESION OF C60FULLERITEPh. Lambin, A.A. Lucas, J.-P. Vigneron

4 ESR AND MAGNETIC STUDIES OF Rb AND K DOPED C 6 0

P. Byszewski, J. Stankowski, M. Baran, R. Jablonski, Z. Trybula, W. Kempinski

5 FIELD-INDUCED MAGNETIC PHASE TRANSITIONS AND ELECTRICAL RESIS-TIVITY IN SOME RARE-EARTH INTERMETALLICS ].N.V. Baranov, P.E. Markin, E.V. Sinitsyn I

6 CRYSTALLOGRAPHIC AND PHYSICAL PROPERTIES OF Ce(Ge, S i ) 2 _ x SOLID <SOLUTIONS '•'N. Boutarek, R. Madar, B. Lambert-Andron, S. Auffret, J. Pierre \

7 INTERNAL MAGNETOSTRICTION ABOVE THE VERWEY TRANSITION IN S- iTO1CHIOMETRIC MAGNETITE hG. Galeczki

8 A TRANSPORT STUDY OF THE afpha-PHASE TRANSFORMATION IN FE-CR-SNALLOYSM.M. Amado, J.B. Souia, B.F.O. Costa, N. Ayres de Campos, £M. Dubiel

XXXII

7P:a

9 ELECTRON TRANSPORT AND DILATOMETRIC STUDY OF CRYSTALLIZATIONIN Fe - BASED AMORPHOUS ALLOYSK. Pekala, M. Pekala, V. Ocelik, P. Jaskiewicz, R. Rataj, T. Kulik

10 RESISTIVITY SATURATION UNDER HIGH PRESSURE: fee LaB. Sundqvist

11 TRANSPORT PROPERTIES OF (Nd2_xSrx) NiO4 + , COMPOUNDS. METAL-INSULATOR AND ANTIFERROMAGNETIC TRANSITIONSJ.M. Moreira, J.A. Mendes, J.B. Sousa, M.P.S. Kumar, S.B. Palmer

12 EFFECT OF CONDUCTION ELECTRONS ON THE PARAMAGNETIC SUSCEPTI-BILITY OF RARE EARTH INTERMETALLICSS. Zajac, F. Pesek

13 RESISTIVITY MEASUREMENTS OF Nd 2FeMB BASED SINTERED MAGNETSM.A. Sa, J.M. Machado da Silva, J.B. Oliveira

14 A SOLVABLE MODEL OF MOSSBAUER SCATTERINGB.S. Pavlov, A.A. Pokrovskiy

15 EFFECT OF ROLLING AND HEAT TREATMENT ON THE IRREVERSIBLE MAG-NETIZATION IN NICKEL-CHROMIUM WIREAH. Wafik

16 MAGNETOMETER FOR DETERMINATION OF THE M VALUES ANDORIENTATIONSA.N. Bazhan

17 REMANENT MAGNETISATION AND REMAGNETISATION MEASUREMENTSON DISPERSION OF FINE HAEMATITE PARTICLESE. Petrovsky, P. Hejda, T. Zelinka, J. Subrt

18 SIZE EFFECT AND TEMPERATURE DEPENDENCE OF A LOW-ENERGY ELEC-TRONIC TRANSITION IN BISMUTHV. De Renzi, M.G. Betti, C. Mariani

19 PARAMAGNETIC SUSCEPTIBILITY AND MAGNETIC PHASE DIAGRAM OFTMCU2

P. Svoboda, M. Divis, A.V. Andreev, N.V. Baranov, H. Maletta

20 STRUCTURAL PROPERTIES AND ESR OF THE (Gd-R)Cu2Sn2 COMPOUNDSK. Kaczmarska, A. Slebarski, A. Starczewska

21 THE MAGNETISATION OF TERBIUM IN GOLD SINGLE CRYSTALSD.St.P. Bunbury, C. Carboni, R.G. Graham, M.A.H. McCausland

22 ENHANCED NUCLEAR MAGNETISM IN HOLMIUM ORTHOALUMINATE: AN N-MR STUDYS.M. Warner, D.St.P. Bunbury, C. Carboni, R.G. Graham, M.A.H. McCausland

23 BEHAVIOUR OF UNiAl IN HIGH MAGNETIC FIELDSL. Havela, H. Nakotte, E. Brueck, F.R. De Boer, V. Sechovsky, H.P. Van Der Meulen,A.A. Menovsky

24 MAGNETIZATION PROCESSES IN STRESS-ANNEALED METALLIC GLASSK. Zaveta, O.V. Nielsen, K. Jurek

25 THE COERCIVE PROPERTIES OF CONSTRICTED MAGNETIC DOMAIN WALLSI. Tomas, G. Vertesy, L. Pust

XXXIII

7P:a26 ELECTRONIC STRUCTURE PROPERTIES OF Zn-OXIDE SPINELS FROM 67Zn

MOSSBAUER SPECTROSCOPYW. Potzel, G.M. Kalvius, W. Schiessl, H. Karzel, M. Steiner, I. Halevy, j . Gal, W.Schaefer, G. Will

27 MOSSBAUER SPECTROSCOPY ON LASER IRRADIATED AMORPHOUS SYSTEMD. Sorescu, M. Sorescu, A. Hening, I.N. Mihailescu, D. Barb

28 5 7 FE MOSSBAUER STUDY OF THE INFLUENCE OF SN ON THE FORMATIONOF THE SIGMA PHASE IN FE-CR ALLOYSB.F.O. Costa, S.M. Dubiel

29 TRENDS IN THE MAGNETIC ORDERING TEMPERATURES OF URANIUM- >TRANSITION METAL-SILICON (GERMANIUM) 1-2-2 COMPOUNDS JT. Endstra, G.J. Nieuwenhuys, J.A. Mydosh

30 STUDY OF THE MAGNETIC PHASE DIAGRAM OF MnSi CLOSE TO THE CRIT-ICAL TEMPERATUREC. Gregory, N. Bernhoeft, B. Lebech, P. Harris, J.S. Pedersen, K. Mortensen

31 TEMPERATURE-DEPENDENT QUASIPARTICLE PHOTOEMISSION IN NI ANDFE*J. Braun, G. Borstel, W. Nolting

32 THERMAL EXPANSION ANOMALIES AT SPIN REORIENTATION IN Tra2Co7

A.V. Andreev, S.M. Zadvorkin, E.N. Tarasov

33 CURIE TEMPERATURE OF TWO-COMPONENT AMORPHOUS FERROMAGNETI.F. Margolytch

34 THERMODYNAMICS OF QUANTUM EASY-PLANE FERROMAGNETIC CHAINSA. Cuccoli, V. Tognetti, P. Verrucchi, R. Vaia

35 THERMAL STABILITY OF Dy AND Tb DOPED Nd-Fe-B MAGNETSS. Szymura, Yu. M. Rabinovich, V.V. Sergeev, H. Bala, L.V. Potapova

36 MAGNETOCALORIC EFFECT IN NANOCRYSTALLINE MATERIALZ. Kalva

37 MAGNETIC FLUCTUATIONS IN THE VICINITY OF FIRST-ORDER PHASETRANSITION IN A Mn(10%Ge) ALLOYJ.J. Milczarek, E. Jaworska, K. Mikke

41 THERMODYNAMICS OF WHITE PHOSPHORUS IN BENZOIC SOLUTIONS AS AFUNCTION OF CONCENTRATION AND TEMPERATUREH. Craubner

42 QUASICONSERVED VARIABLES AND LIGHT SCATTERING IN VISCOELASTICLIQUIDSV.I. Motorin, P. Bezot, C. Hesse-Bezot 3

43 EXPERIMENTAL STUDY OF SOME MESOMORPHIC SAMPLES OF FATTY ACID-S AND MIXTURES -M. Dumitru, M. Honciuc, G.A. Dumitru

44 TEMPERATURE AND CONCENTRATION DEPENDENCE OF ORIENTATIONALCORRELATIONS OF NITRATE IONS IN Cu(NO3)2 AQUEOUS SOLUTIONSM.P. Fontana, B. Rosi-Schwartz, N. Micali

45 SANS ANALYSIS OF SOME GUANOSINE DERIVATES IN VERY DILUTEDSOLUTIONSF. Carsughi, M. Ceretti, P. Mariani, G.P. Spada

XXXIV

7P:a

46 INFLUENCE OF THE MAGNETIC FIELD ON THE STRUCTURE OF LIQUIDTWO-COMPONENT MAGNETI.O. Vakarchuk, I.F. Margolytch

47 THREE-BODY DISTRIBUTION FUNCTION IN LIQUIDSA. Di Cicco, A. Filipponi

48 STUDY OF THE ELECTRIC CONDUCTIVITY OF MOLTEN SALTSM. Rodova, K. Nitsch, P. Demo, Z. Kozisek

49 ALKALI METAL LIQUIDS: TOWARDS A LAW OF CORRESPONDING STATESU. Balucani, A. Torcini, R. Vallauri

50 CONFORMATIONS OF ETHOXYLATED SURFACTANTS IN AQUEOUSSOLUTIONST.O. Hushcha, G.S. Pop

51 APPLICATION OF THE COLLECTIVE VARIABLES METHOD IN DESCRIBINGOF THE LIQUID-GAS PHASE TRANSITIONI.R. Yukhnovskii, I.M. Idzyk, V.O. KolomieU

52 LIQUID-LIQUID TRANSITIONS: THEORY AND EXPERIMENTV.V. Brazhkin

53 (P-T) PHASE DIAGRAM OF SOLID AND LIQUID Te UNDER PRESSURE UP TOlOGPaV.V. Brazhkin, R.N. Voloehin, S.V. Popova, A.G. Umnov

54 THE INFLUENCE OF THE NONMETAL-METAL TRANSITION IN SELENIUMMELT ON THE SOLIDIFICATION PROCESSV.V. Brazhkin, R.N. Voloehin, S.V. Popova

55 a-RELAXATION STRETCHING IN SUPERCOOLED LIQUIDSM. Fuchs, A. Latz

56 FREE-ENERGY DENSITY FUNCTIONAL FOR THE MELTING OF SIMPLELIQUIDSL. Mederos, G. Navascues, P. Tarazona, E. Chacon

57 INSTABILITIES IN FLUID MIXTURESX.S. Chen, F. Forstmann

58 DIELECTRIC RELAXATION OF AQUEOUS SOLUTIONS OF MONOALCOHOLSD. Fioretto, A. Marini, G. Onori, L. Palmieri, A. Santucci, G. Socino, L. Verdini

59 COTTON-MOUTON AND KERR EFFECTS IN BINARY DILUTED SYSTEMS OFQ-PICOLINE IN BENZENE AND P-XYLENEM. Kaczmarek, Z. Wozniak

60 MAGNETOOPTICAL FARADAY EFFECT IN BINARY SOLUTIONS OF DIPOLARLIQUID DISSOLVED IN BENZENE AND p-XYLENEM. Surma

61 P-T PHASE DIAGRAM OF 1,3-CYCLOHEXANEDIONEM. Szafraiuki, P. Czarnecki, A. Katnuiak, S. Habrylo

63 TEM STUDY OF £5 GRAIN BOUNDARIES IN COPPERZ. Vicherkova

64 MOSSBAUER PHASE ANALYSIS OF THE NANOCRYSTALLINE ALLOYST. Zemcik

XXXV

7P:a

65 DETERMINATION OF ELECTROMECHANICAL NONLINEARITIES INCRYSTALSK.C. Hruska

66 THE DISLOCATION MOBILITY UNDER MAGNETIC FIELDS IN NON-MAGNETICCRYSTALSV.I. Alshits, E.V. Darinskaya, E.A. Petrzhik

67 X-RAY POWDER DIFFRACTION ANALYSIS OF PbMo<yS8 BETWEEN 25 K AND295 KM. Francois, K. Yvon, D. Cattani, M. Decroux, R. Chevrel, M. Sergent, S. Boudjada, T.Wroblewski

68 ON THE POSSIBILITY OF THE COEXISTENCE OF SUPERIONIC AND FERRO-ELECTRIC SUBSYSTEMS IN CRYSTALA.S. Rakitin

69 EFFECT OF LAYER FLEXURAL RIGIDITY UPON DYNAMIC CHARACTERIS-TICS OF LAYERED CRYSTALS WITH COMPLEX LATTICEE.S. Syrkin, S.B. Feodosyev, O.Ya. Shamfarova

70 POLARIZATION BY NONUNIFORM DISTORTION (PND)V.V. Gafyichuk, I.A. Lubashevskii

71 DIELECTRIC DISPERSION IN THE COMMENSURATE PHASE OF Rb2ZnCl4

V. Novotna, H. Kabelka, J. Fousek, M. Havrankova, H. Warhanek

72 SOME STUDIES GRAIN-BOUNDARY MICROSTRUCTURES OF HOT-PRESSEDBN-AIN-SiO2 ELECTROCERAMICSYa.l. Bulbik, N.V. Vasilenko, A.G. Kozlov

73 NEW ASPECTS IN DIAMOND SYNTHESISE. Pavel, Gh. Baluta, D. Barb, V. Sandu, M. Popescu

74 STRUCTURE OF POTASSIUM SALT OF HEXAMERIC MALONDIALDEHYDEA. Lopez-Castro, M.J. Dianez, M.D. Estrada, S. Perez-Garrido

75 QUANTITATIVE STRUCTURAL ANALYSIS OF SUPERLATTICES FROM X-RAYPROFILE REFINEMENTY. Brujrnseraede, H. Vanderstraeten, K. Temst, E.E. Fullerton, I.K. Schuller

76 HETEROGENEOUS MICROSTRUCTURE OF TITANIUM NITRIDE FILMS STUD-IED BY X-RAY DIFFRACTIONR.,Jr. Kuzel, R. Cerny, V. Valvoda, M. Blomberg, M. Merisalo

77 USE OF THE X-RAY PENETRATION POWER FOR STRESS ANALYSISI. Kraus, N. Ganev

78 THE X-RAY DIFFRACTION IN REAL PERIODICAL SUPERLATTICESV. Holy, L. Kubena

79 DOUBLE-CRYSTAL NEUTRON SMALL-ANGLE SCATTERING CAMERA WITHPOSITION SENSITIVE DETECTOR (PSD)J. Saroun, B. Alefeld, P. Lukas, P. Mikula, V. Wagner

80 STUDY OF He-BUBBLE GROWTH IN MANET STEEL BY SMALL-ANGLE NEU-TRON SCATTERINGG. Albertini, F. Carsughi, R. Coppola, W. Kesternich, G. Mercurio, F. Rustichelli, D.Schwhan, H. Ullmaier

81 RESIDUAL STRAIN IN A FUSION REACTOR FIRST WALL COMPONENT SUB-JECTED TO THERMAL FATIGUEG. Albertini, G. Andre, R. Matera, P. Miele, M. Merola, M. Perrin, F. Rustichelli

XXXVI

82 STRUCTURAL AND TRANSPORT PROPERTIES OF ReSi j 75

B. Lambert-Andron, M. Kuhn, U. Gottlieb, R. Madar

83 INFLUENCE OF MELT STATE ON PROPERTIES OF RAPIDLY QUENCHEDMETALLIC MATERIALSO. Schneeweiss, N. Pizurova, T. Zak

84 HELIUM IN METALSH. UUmaier

85 ON STRUCTURAL PHASE TRANSITIONS IN C20?42V. Dvorak, J. Holakovsky

86 WATER VAPOUR INDUCED TRANSFORMATION OF Cs2CdBr4

P, Vanek, J. Horvath, M. Havrankova

87 NOSE-HOOVER MOLECULAR DYNAMICS STUDY ON SELF-DIFFUSION ALONGTHE DISSOCIATED [112] EDGE DISLOCATION OF GOLDJ. von Boehm, R.M. Nisminen

88 INFLUENCE OF ELECTRIC, MAGNETIC FIELDS AND IRRADIATION ON THEPROPERTIES OF INCOMMENSURATE STRUCTURESI.I. Polovinko, S.A. Sveleba, V.S. Zhmurko, V.B. Kapustianik

89 NON-STOECHIOMETRY AND PHASE TRANSITION IN SPUTTERED NbTex

THIN FILMSY. Mathey, M. Kanem, D. Pailharey, G. Richard, S. Fayeulle

90 ON THE NUCLEATION PROCESS IN THE MARTENS1TIC TRANSFORMATIONOF A Cu-Zn-Al SINGLE CRYSTALY. Amazit, A. Zarembowitch

7P:b 101 ON THE WIDTH OF IMPURITY BANDS IN DOPED SEMICONDUCTORSJ. Monecke, W. Cordts, 3. Kortus

102 STUDY OF THE OUTPUT PROPERTIES OF NONDEGENERATE PARAMETRICAMPLIFIERS WITH LINEAR LOSSES BY MEANS OF SYMMETRICALLY OR-DERED TWO-MODE OPERATORSP. Garcia-Femandez

103 OPTICAL RESPONSE OF INTERFACES WITH ARBITRARY DETERMINISTICROUGHNESSS. Wang, P. Halevi

104 THE DYNAMIC CROSSOVER IN THE •4-MODEL(d=l)-AN EXAMPLE FOR ANA2-SCENARIO OF MODE COUPLING THEORY?S. Flach, J. Siewert

105 BOSE CONDENSATION FOR THE Wu-AUSTIN HAMILTONIAN WITHOUTPUMPINGH. Bolterauer, L. Ludwig {

106 THE FUNCTIONAL FORMULATION OF THE STATISTICAL MECHANICS )L.F. Blszhievsky, G.B. Gill, S.S. Semak <

107 FLUCTUATIONS IN LEVY FLIGHT GAS tH.C. Fogedby, T.Bohr, H.J.Jenien |

108 THE LONGITUDINAL RELAXATION FUNCTION OF THE ID ISING MODEL IN 'TRANSVERSE FIELDR.R. LeviUku, S.I. Sorokov

\ XXXVII

7P:b109 THE INVESTIGATION OF CLUSTER EXPANSION'S CONVERGENCE FOR THE

ISING MODELR.R. Levitskii, S.I. Sorokov, O.R. Baran

110 ON THE KINETICS OF THE SYSTEM OF PARTICLES WITH THE ELECTRO-MAGNETIC INTERACTIONL.F. Blazhievsky, G.B. Gill

111 PSEUDOHAMILTONIANS FOR QUANTUM MONTECARLOA. Benin, A. Lastri, V. Fiorentini, A. Continenza, G.B. Bachelet

112 CHARGE FLUCTUATIONS IN DOPED MOTT INSULATORM. Cyrot

113 LIGHT SCATTERING NEAR PHASE TRANSITIONS IN BCCD. A PERTURBATIVEAPPROACHH. Poulet, R.M. Pick

114 TWO-FLUID RELATIVISTIC MODEL FOR SUPERCONDUCTORSI.E. Boulyjenkov

115 TUNNELING TIME MEASUREMENTS BY MICROWAVE MODELP. Fabeni, D. Mugnai, G.P. Pazzi, A. Ranfagni

116 THERMODYNAMICS AND CORRELATION FUNCTIONS OF THE QUANTUM TO-DA LATTICEA. Cuccoli, M. Spicci, V. Tognetii, R. Vaia

117 BROWNIAN MOTION IN PERIODIC SYSTEMSR. Ferrando, R. Spadacini, G.E. Tommei

118 FREE RELAXATION INDUCED BY COLORED NOISE: ANALYTICAL NON PER-TURBATIVE RESULTS FOR MULTILEVEL SYSTEMSL. Andreozzi, C. Donati, M. Giordano, D. Leporini

119 DEVELOPMENT OF BASINS OF DUFFINGS OSCILLATORR.K. Raty

120 RENORMALIZATION GROUP APPROACH AT GENERAL DIMENSIONS. THREELOOP APPROXIMATION.Yu. Holovatch

121 OPTICAL PROPERTIES OF SOLIDS AND SPATIALLY NON-LOCAL POTENTIALSE. Piparo, R. Girlanda

122 MONTE CARLO CALCULATION OF THE GREEN'S FUNCTION OF HETEROGE-NOUS MATERIALSJ.P. Bouchaud, P.G. Zerah

123 X-RAY DIFFRACTION SPECTRA OF DETERMINISTIC NON-PERIODIC STRUC-TURES: DYNAMICAL VS KINEMATICAL THEORYG.C. La Rocca, L. Tapfer, R. Cingolani, K. Pfoog

124 CORREL - A PROGRAM FOR REPRESENTATION CORRELATIONS OF GROUP-SUBGROUP RELATED SPACE GROUPSN. Djourelov, M. Aroyo

125 SPECTRAL SHAPE OF QUANTUM CHAINSA. Cuccoli, A.A. Maradudin, A.R. McGurn, V. Tognetti, R. Vaia

126 MAPPING OF CRYSTAL GROWTH ONTO THE 6-VERTEX MODEL: GROWTHMODE AND SURFACE ROUGHNESSM. Kotrla, A.C. Levi

XXXVIII

127 DISORDERED PEIERLS CHAINSJ. Mertsching

128 ELECTRONIC STATES OF ALMOST PERIODIC DISCRETE SCHRODINGEREQUATIONSR. Farchioni, G. Grosso, G.P. Parravicini

129 SQUEEZING TRANSFORMATION FOR POLAR1TONSZ. Hradil, A. Quattropani, P. Schwendimann

130 ELECTRONIC PROPERTIES OF KINKS AT THE ORDER-DISORDER-LIKEPEIERLS INSTABILITYE.V. Kholopov

131 RENORMALIZATION OF LAUGHLIN'S INCOMPRESSIBLE QUANTUM LIQUIDU. Brockstieger, G. Meissner

7P:c 201 THE PHYSICS OF SiGe HETEROJUNCTION BIPOLAR TRANSISTORS. A MONTECARLO STUDY OF THE QUEST FOR ENHANCED SPEEDD.T. Hughes, R.A. Abram, R.W. Kelsall

202 DIPOLE EFFECTS AT SEMICONDUCTOR INTERFACES. TOWARDS A BAND-OFFSET ENGINEERINGA. Mujica, P. Rodriguez-Hernandez, A. Munoz

203 STRONG CHANGES OF THE ABSORPTION AND REFRACTIVE INDEX IN N-I-P-I-HETERO-STRUCTURES BY BANDFILLINGS. Malzer, P. Kiesel, M. Kneissl, G.H. Doehler, K.H. Gulden, S. Smith, X.X. Wu, J.Whinnery

204 NARROW-BANDGAP TYPE II MISALIGNED HETEROJUNCTIONS BASED ONInGaAsSb SOLID SOLUTIONSM.P. Mikhailova, A.N. Baranov, V.V. Shentnev

205 INVESTIGATION OF BAND OFFSET TRANSITIVITY IN GaInA»-InP, GalnAa-AHnAs AND AHnAs-InP HETEROSTRUCTURESE. Lugagne-Delpon, P. Voisin, M. Voos, J.P. Andre

206 POTENTIAL FLUCTUATIONS AND BROADENING OF THE DENSITY OF S-TATES IN DOPING SUPERLATTICESM. Renn, C. Metzner, G. Doehler

207 EVOLUTION OF ANNIHILATION OF ANTIPHASE BOUNDARIESS.I. Molina, G. Aragon, R. Garcia

208 SELF-LIMITING MONOLAYER EPITAXY OF Il-VI HETEROSTRUCTURESW. Faschinger, P. Juza, H. Sitter

209 STUDY BY XTEM OF AlGaAs/GaAs MQW ON NON-PLANAR SUBSTRATESG. Aragon, S.I. Molina, P.S. Dominguez, M.J. De Castro, R. Garcia

210 VELOCITY DISTRIBUTION FUNCTION AND ELECTRON FREE PATH IN PERI-ODICALLY MODULATED AlGaAs/GaAs HETEROSTRUCTURESC. Wirner, E. Gornik, C. Kiener, G. Zandler, P. Vogl, G. Bohm, G. Weimann

211 INFLUENCE OF Cd AND Hg INTERDIFFUSION ON THE DISLOCATION FORMA-TION IN ISOVPE HgCdTe/CdTe EPILAYERSC. Frigeri, R. Gleichmann, G. Attolini, C. Peloii, C.A. Galeazzi

212 DISORDER EFFECTS ON OPTICAL PHONONS IN GaAlAs FROM RAMAN SCAT-TERING IN BULK AND SUPERLATT1CE ALLOYSB. Jusserand, L.G. Quagliano, F. Mollot

XXXIX

7P:c213 IMPACT IONISATION IN THE AlAaAs LAYER OF AaAs/ALUAs

HETEROJUNCTIONSP.J. Van Hall, E.A.E. Zwaal

214 CONFINEMENT OF OPTICAL GaAs PHONONS BY THIN AlGaAs BARRIERSC. Molteni, L. Colombo, L. Miglio, M. Bernasconi

215 LATTICE PLANE TILTING IN InP/GaAs HETEROSYSTEMS: HINTS TO THE INI-TIAL GROWTH MECHANISMF. Riesz, K. Lischka, K. Rakennus, T. Hakkarainen, A. Pesek

216 MAGNETO-TRANSPORT PROPERTIES OF AlGaAs/GaAs HETEROSTRUC-TURES IN PULSED FIELDS UP TO 50 TESLAI. Deckers, G. Pitsi, F. Herlach

217 INTERFACE ELECTRON STATES IN STRAINED SEMICONDUCTORHETEROJUNCTIONV.G. Kantser, N.M. Malkova

218 EXCITONIC TRANSITIONS IN (In, Ga) As-GaAs HETEROSTRUCTURES UNDERIN-PLANE UNIAXIAL STRESSJ.A. Brum, P. Hiergeist, G. Abstreiter, J.P. Reithmaier, H. Riechert

219 SUBBANDS IN INVERSION LAYERS FOR Eg*p~> 0B. Freytag, U. Roessler, O. Pankratov

220 SPATIO-TEMPORAL VOLTAGE OSCILLATIONS OF VERTICAL TRANSPORT INSEMICONDUCTOR HETEROSTRUCTURESA. Wacker, E. Schoell

221 VALIDITY OF THE EFFECTIVE MASS APPROACH FOR GaAs/AlGaAsHETEROSTRUCTURESJ.P. Cuypers, W. Van Haeringen

222 MAGNETOTRANSPORT IN DILUTE i-LAYERS, ANGLE-TUNED METAL-INSULATOR TRANSITIONX.M. Feng, J.J. Mares, F. Koch

223 NONLINEAR (PHOTO-) CONDUCTIVITY EXPERIMENTS ON SINGLE PERIODPbTe NiPisM. Pippan, J. Oswald, B. Tranta

224 TUNING HETEROJUNCTION BAND OFFSETS USING METAL AND SEMICON-DUCTOR INTRALAYERSR. Perez, F. Fiores, A. Mujica, A. Munoz

225 INTERFACE RELATED LUMINISCENCE FROM n-n HETEROJUNCTIONS OFTHE II TYPE IN GaSb/GalnAsSbE. Hulicius, J. Oswald, J. Pangrac, T. Simecek, A.N. Titkov, O.M. Gusev ?

226 DYNAMICAL ENERGY TRANSFER AT THE INTERFACE OF ZnSe/GaAs ]EPILAYERS *N. Presser, Ch. Fricke, G. Kudlek, R. Heitz, A. Hoffmann, J. Gutowski, I. Broser ,}

227 RADIATIVE EXCITONIC RECOMBINATIONS IN STRAINED ZnSe EPILAYERS |G. Kudlek, Ch. Fricke, N. Presser, R. Heitz, A. Hoffmann, J. Gutowski }

228 PREPARATION AND PROPERTIES OF CdS/CdTe HETEROJUNCTIONSJ. Touskova, D. Kindl, J. Kovanda, J. Tousek

229 RELATION BETWEEN HOMOGENEOUS LINEWIDTH AND RADIATIVE LIFE-TIME OF EXCITONS IN QUANTUM WELLSJ. Kuhl, R. Eccleston, B.F. Feuerbacher, W.W. Ruehle, K. Ploog

XL

230 ALLOY DISORDER SCATTERING IN FINITE QUANTUM WELLSB. Podor

231 A SELFCONSISTENT CALCULATION OF THE INTRINSIC BISTABIL1TY IN DOU-BLE BARRIERS HETEROSTRUCTURESP.L. Pernas, F. Flora, E.V. Anda

232 THE FORMATION OF A QUANTUM WELL IN MBE GROWN Si delta-DOPED GaAsLAYERS STUDIED BY PHOTOCURRENT SPECTROSCOPYF. Karel, J. Oswald, J. Pastrnak, O. Petricek, A. Salokatve

233 EXCITONIC TRANSITIONS IN GaA>-GaAlAs SUPERLATTICES UNDER A LOWELECTRIC FIELDJ. Depeyrot, P. Tronc, E. Umdenstock, J.F. Palmier, B. Etienne

234 TUNNELING ESCAPE RATE OF ELECTRONS FROM QUANTUM WELL INDOUBLE-BARRIER HETEROSTRUCTURES BY THE STABILIZATION METHODJ.A. Porto, J. Sanchez-Dehesa, L. Cury, A. Nogaret, J.C. Portal

235 COHERENT TUNNELING IN QUANTUM WELLS UNDER MAGNETIC FIELDSP. Aceituno, A. Hernandez-Cabrera, H. Cruz

236 SELF-CONSISTENT CALCULATIONS OF COHERENT TUNNELING OSCILLA-TIONS IN ASYMMETRIC DOUBLE QUANTUM WELLSA. Hernandez-Cabrera, P. Aceituno, H. Cruz

237 SUPERLATTICE MIN1BANDS UNDER APPLIED MAGNETIC FIELDSH. Cruz, F. Piazza, L. Pavesi

238 SPIN FLIP RAMAN SCATTERING IN GaAs/AlGaAs MULTIPLE QUANTUMWELLSV.F. Sapega, M. Cardona, K. Ploog, E.L. Ivchenko, D.N. Mirlin

239 LOW TEMPERATURE ABSORPTION SPECTRA OF GaAs/AlGaA«SUPERLATTICESV. Capozzi, J.L. Staehli, D. Martin, V. Augelli, P. Favia, T. Ligonxo, G.F. Lortuso

240 MAGNETOOPTICS OF NARROW GaAs/AlGaAs QUANTUM WELLS GROWN ONVICINAL SUBSTRATESJ. Sanchez-Dehesa, F. Meseguer, N. Mestres, C. Departs, G. Neu, J. Maasies

241 RAMAN SCATTERING SPECTROSCOPY OF NON-EQUILIBRIUM OPTICALPHONONS IN GaAs QUANTUM WELLSD.Y. Oberli, G. Bohm, G. Weimaan

242 OPTICAL INVESTIGATION OF THE THERMAL STABILITY OF GalnAj/InGaAsPQUANTUM WELLSR.W. Glew, H. Peyre, J. Camassel, F. Alsina, J. Pascual

243 OPTICAL INVESTIGATION OF THE COMPOSITIONAL GRADIENT ACROSSTHE INTERFACES IN MBE GalnAs/InP SUPERLATTICESE. Massone, J. Camassel, J. Pages, J. Pascual, J. Jimenez

8P:a 1 RAMAN SCATTERING ON HIGH DENSITY 2D ELECTRON GASES )B. Jimerand, H. Peric, D.R. Richards, B. Etienne \

2 EXCITONS AT FERMI LEVEL IN DENSE TWO-DIMENSIONAL ELECTRON- 'HOLE MAGNETOPLASMA |L.V. Butov, V.D. Kulakovskii, A. Forchel, D. Gruetimacher '

XLI

8P:a3 THEORY OF MACROSCOPIC LOCAL SINGLE-PARTICLE CHARGE STATES

AND LARGE-RADIUS LOCAL EXCITONS IN QUASI-ZERO-DIMENSIONALSTRUCTURESS.I. Pokutnyi,

4 PERTURBATIONAL ANALYSIS OF THE PLASMON DECAY IN A TWO-DIMENSIONAL ELECTRON GASM.E. Bachlechner,

5 MICROWAVE PHOTOCONDUCTIVITY OF A TWO DIMENSIONAL ELECTRONGAS AT LOW FILLING FACTORSR. Meisels, F. Kucbar, J.J. Harris, C.T. Foxon

6 CURRENT NOISE IN TUNNEL JUNCTIONS WITH MESOSCOPIC METALPARTICLESM.A. Belogolovskii, L.G. Levin

7 OPTICAL ABSORPTION OF QUASI-ONE DIMENSIONAL SEMICONDUCTORSTRUCTURESS. Glutsch, F. Bechstedt

8 SUPERCONDUCTING RESERVOIRS CONNECTED BY A QUANTUM WIREL. Hedin, B. Velicky '

9 AUGER-IONIZATION IN QUANTUM SEMICONDUCTOR STRUCTURES ANDATOMIC CLUSTERSV.A. Kbarchenko

10 THE INFLUENCE OF COULOMBIC INTERACTIONS ON THE ELECTRONICSTRUCTURE IN I D SYSTEMSW. Haeusler, K. Jauregui, B. Kramer

11 LINEAR- AND NONLINEAR- OPTICAL MANIFESTATIONS OF QUANTUM CON-FINEMENT IN COPPER CHLORIDE NANOCRYSTALSS.V. Gaponenko, I.N. Germanenko, V.P. Gribkovskii, L.G. Zimin, V.Yu. Lebed, I.E.Malinovskii

12 BALLISTIC TRANSPORT THROUGH A II-SHAPED ELECTRON WAVEGUIDEA. Onipko, I. Zozulenko

13 ELECTRON TRANSPORT ALONG A DISORDERED CHAIN IN PRESENCE OFDISSIPATIONK. Maschke, M. Schreiber

14 NEW NONLOCAL QUANTUM EFFECTS IN HIGH-MAGNETIC-FIELD fCONDUCTANCEA.K. Geim, P.C. Main, L. Eaves, P. Beton, P. Streda ••;

1 5 DIMENSIONAL RESONANCES OF QUANTUM WIRES IN ALAS/GAAS HETERO- iJUNCTIONS WITH NON-HARMONIC CONFINEMENT %H. Drexler, W. Hansen, J.P. Kotthaus, M. Holland, S.P. Beaumont £

16 EFFECT OF DISORDER ON THE CONDUCTANCE QUANTIZATION IN QUASI- r$ONE-DIMENSIONAL WIRE j !J. Wrobel, F. Kuchar, K. Ismail, K.Y. Lee, H. Nickel, W. Schlapp 'Jt

17 SYMMETRY BREAKING EFFECTS OF ELECTRONS IN QUANTUM DOTSF. Bolton, U. Roessler

18 MOMENTUM CONSERVATION IN 1D-2D TUNNELING PROCESSES ,W. Demmerle, J. Smoliner, E. Gornik, G. Bohm, G. Weimann ]

XLII

8P:a19 PIEZOELECTRIC EFFECTS IN QUANTUM WIRES AND DOTS GENERATED BY

PATTERNS OF INHOMOGENEOUS STRAINJ.M. Woriock

20 OPTICAL PROPERTIES OF QUANTUM NETWORKSH. Koerner, G. Mahler

21 LATERAL TUNNELLING AND MAGNETO-TRANSPORT IN A QUANTUMTRENCH IN-PLANE DIODEA.J. Peck, S.J. Bending, K. von Klitzing, K. Ploog

22 COLLECTIVE EXCITATIONS IN QUASI-ONE-DIMENSIONAL QUANTUM WELLWIRES.DEPOLARIZATON EFFECTS AND PLASMON-PHONON COUPLINGL. Wendler, R. Haupt

23 SINGLE-ELECTRON TUNNELING AND COULOMB CHARGING EFFECTS INASYMMETRIC DOUBLE BARRIER RESONANT TUNNELING DIODESM. Tewordt, L. Martin-Moreno, J.T. Nicholls, V.J. Law, M.J. Kelly, M. Pepper, D.A.Ritchie, J.E.F. Frost, G.A.C. Jones

24 PHONON DRAG HALL VOLTAGE IN QUANTUM HALL EFFECT DEVICESF. Dietzel, W. Dieteche, R. Noetzel, K. Ploog

25 FQHE IN THE DISK GEOMETRY. EXACT DIAGONALIZATION FOR FEW ELEC-TRONS WITH VARYING INTERACTIONSM. Kasner, W. Apel

26 TEMPERATURE DEPENDENT SCALING AND CURRENT DEPENDENT NON-OHMIC BEHAVIOUR BETWEEN INTEGER QUANTUM HALL PLATEAUXG. Nachtwei, C. Breitlow, A. Jaeger, P. Svoboda, P. Streda, L. Bliek, F.-J. Ahlen

27 TRANSITIONS BETWEEN SPIN-SPLIT EDGE CHANNELS IN THE QUANTUMHALL EFFECT REGIMEA.V. KhaeUkii

28 INVESTIGATION OF LOCALIZED STATES IN THE REGIME OF QUANTUM HAL-L EFFECT USING THE ACOUSTOELECTRIC EFFECTA. Esslinger, A. Wixforth, R.W. Winkler, S. Maims, J.P. Kotthaus, W. Nickel, G.Weimann

33 T l 2 B a 2 C u 0 e + x : FROM NORMAL STATE TO SUPERCONDUCTIVITYJ.L. Jorda, T.K. Jondo, M.T. Cohen-Adad, C. Opagiste, A. Khoder, M. Couach, F.Sibieude

34 NEUTRON DIFFRACTION STUDY OF SrxBafj.^Nb^Og CRYSTALSA.M. Balagurov, F. Prokert, D. Sangaa, B.N. Savenko

35 THE ANTIFERROMAGNETICS STATE INVESTIGATION OF L a 2 C u 0 4 + y SINGLECRYSTALS WITH DIFFERENT OXYGEN CONCENTRATIONSAN. Bazhan, V.N. Bevz

36 SUPERCONDUCTIVITY IN DOUBLE-DOPED Laj+ xCayBa2 .x_j,Cu3O7+ 4 s.

SYSTEM >1F.C. Matacotta, P. Staitny, C.U. Serge, T. Mertejj jl

37 ON THE VALENCE OF PRASEODYMIUM IN PrBa2Cu^O7_x 4V. Nekvasil, E. Holland-Moritx, H.-D. Joetarndt, U. Walter, G. Hilseher \

38 LIGHT SCATTERING FROM R2BaMO5 OXYDES WITH R = LANTHANIDE ANDM = Co, Ni AND CuA. De Andre*, S. Taboada, J.L. Martinez, A. Salinas, R. Saei-Puche

XLIII

8P:a39 FIELD-DEPENDENT THERMAL CONDUCTIVITY IN Bi 2 Sr 2 CaCu 2 0g + , : EVI-

DENCE FOR ANOMALOUS FLUX LINES?A.J. Smite, J.M Van Ruitenbeek, PH. Kes, M.J.V. Menken, A.A. Menovsky, L.J. DeJongh

40 OBSERVATION OF VORTEX PINNING BY TWINNING PLANES IN TILTED MAG-NETIC FIELDS IN YBaCuO SINGLE CRYSTALSI.V. Grigorieva, L.A. Gurevitch, L.A. Vinnikov

41 INFLUENCE OF PREPARATION CONDITIONS ON QUALITY OF YBaCuO ANDBiSrCaCuO SINGLE CRYSTALSM. Mehbod, P. Diko, Y. Min, R. Deltour

42 LOW-TEMPERATURE CRYSTALLIZATION OF HIGH TC Y-Ba-Cu-O THIN FILMSBY RESISTIVE EVAPORATIONJ. Aioulay,

43 YBaCuO THIN FILM LASER DEPOSITION ON POLYCRYSTALL1NE AND CRYS-TALLINE SUBSTRATESM. Jelinek, M. Bejdova, Z. Janu, V. Olian, V. Valvoda

44 A SYSTEMATIC STUDY OF THE IN-PLANE EPITAXY OF C-AXIS ORIENTEDYBCO THIN FILMS DEPOSITED ON SrTiOj SINGLE CRYSTALSH.-U. Habermeier, B. Leibold, R. Wegerer, H. Dittrich

45 TEMPERATURE AND MAGNETIC FIELD DEPENDENCE OF CRITICAL CUR-RENTS IN YBaCuO THIN FILMS PREPARED BY LASER METHODSC. Coutal, M.G. Medicis, 1. Aboudihab, A. Azema, P. Gaucherel, A. Gilabert, J.C.Rouitan, P. Sibillot

46 GROWTH OF YBa 2 Cu 3 O 7 FILMS ON SEMICONDUCTING Cu 2O SINGLE CRYS-TALS AND ON OXIDIZED COPPERA. Ginsbach, G. Adrian, W. Wilkens, R. Schneider, G. Schuli, G. Grueniagcr, G. Grabe

47 CONTROLLED PREPARATION OF OXYGEN DEFICIENT Y B a 2 C u 3 0 x FILMSM. Maenhoudt, B. WuyU, S. Libbrecht, Z.X. Gao, E. Osquigtul, Y. Bruynaeraede

48 MAGNETIC INVESTIGATION OF PINNING AND DISSIPATIVE EFFECTS INBi(Pb)-Sr-Cu-O SUPERCONDUCTORD. Fiorani, A.M. Te»U

49 ELASTIC AND INELASTIC NEUTRON DIFFRACTION ON ANTIFERROMAG-NETIC Bi2Cu04M. Ain, G. Dbalenne, J.P. Ambroue, P. Molina, G. Parette, A. Menelle, A. Revcolevgchi

50 HIGH Tc BISMUTH CUPRATES 2223 DOPED WITH Cr Mn AND FeA. Grozav, V. Kantier, L. Konopko, N. Leporda, M. Onu, G. Panaitov, G. Volodina

51 PHASE COMPOSITION STUDY OF Bi-Pb-Sr-Ca-CuO SUPERCONDUCTORSH. Sichova, K. Jirmanova, S. Bernik

52 THE EFFECT OF REACTION CONDITIONS ON THE Bij 0 P b o *Sr 2 _ x Pr x Cu0( j + 4

SYSTEMP. Staitny, N. Leyarovska, F.C. Matacotta, C.U. Serge, S. Bemik

53 REVERSIBLE 109-113 K AND 85-80 K SHIFTS OF TC'S IN Bi-Sr-Ca-Cu-0SUPERCONDUCTORSP. Bohacek, J. Pracharova

54 ELECTRICAL RESISTIVITY AND MAGNETIC SUSCEPTIBILITY ROUNDINGSABOVE THE SUPERCONDUCTING TRANSITION AND PAIRING STATE INBij 5Pbo5Sr2Ca2Cu3OyC. Torron, O. Cabew, J.A. Veira, J. Maia, F. Vidal

XLIV

8P:a55 POINT CONTACT SPECTROSCOPY ON j

B. Susla, S.C. Meepagala, E.L. Wolf

56 TEMPERATURE DEPENDENT PHASE SEPARATION IN THE EMERY MODELJ. Cartensen, K. Dichtel

59 THE SURFACE OPTICAL RESPONSE OF CLEAN AND OXIDIZED Si(100)SURFACESC.M.J. Wijere

60 SURFACE STATES ON SILICON: COMPARISON OF PSEUDO-PERIODIC ANDEMBEDDED SURFACE LAYER RESULTSD.I. Easterbrook, P.M. Lee, J.E. Inglesfield

61 SURFACE ELECTRONIC STRUCTURE AND UPS SPECTRA FOR Cu/PdSYSTEMSF. Maca, J. Koukal

62 UNOCCUPIED ELECTRONIC STATES OF RECONSTRUCTED InP(lOO)- ANDGaAs(100)-SURFACESS. Riese, E. Milas, H. Merz

63 SURFACE PLASMON COUPLING IN LAYERED METALLIC GRATINGSO.M. Sreseli, L.V. Belyakov, D.N. Goryachev, B.L. Rumyantsev, I.D. Yaroehetskii

64 ANOMALOUS VARIATION OF THE M4 5VV AUGER PROFILE OF Pd WITH SUR-FACE COVERAGE ON Ti SUBSTRATEZ. BastI, P. Mikusik

65 INFLUENCE OF SURFACE SCREENING ON THE PEAK HEIGHT IN PHOTOE-MISSION SPECTRAD. Samuelsen, W. Schattke

66 SCANNING TUNNELING MICROSCOPY AND SPECTROSCOPY AT Ge(l l l )SURFACESP. Molinas-Mata, J. Zegenhagen, M. Cardona

67 MODIFICATION OF H-PASSIVATED SILICON SURFACES STUDIED BY SCAN-NING TUNNELLING MICROSCOPY AND SPECTROSCOPYF. Perez-Murano, N. Barniol, X. Aymerich

68 THEORY OF TUNNELLING CURRENTS INDUCED BY LASER RADIATION INSTMA. Levy Yeyati, F. Flores

69 THEORY OF SCANNING TUNNELING MICROSCOPYTh. Laloyaux, I. Derycke, J.P. Vigneron, Ph. Lambin, A.A. Lucas

70 EDGE MELTING IN LOW-COVERAGE NEON MONOLAYERSD.B. Pengra, J.G. Dash

71 COMPRESSION PHASES IN COPPER/OXYGEN COADSORPTION LAYERS ON ARU(OOl) SURFACEM. Schmidt, H. Wolter, K. Wandelt "

72 THEORETICAL INVESTIGATIONS OF THE ELECTRONIC STRUCTURE OF \ALKALI/SEMICONDUCTOR SURFACESB. Wenzien, A. Chasw, W. Hergert, P. Rennert

73 V-W PHASE DIAGRAMME OF ALKALI-COVERED SEMICONDUCTORSURFACESM.C. Refolio, J.M. Lopez Sancho, J. Rubio, M.P. Lopex Sancho

XLV

74 ELECTRONIC STRUCTURE AND PROPERTIES OF LIGHT-ATOMS ADSORBEDON GRAPHITEA. Rakotomahevitra, C. Demangeat, J.C. Parlebas, G. Moraitis, E. Razafindrakoto

75 OSCILLATIONS IN A REACTION ON A HETEROGENEOUS SURFACEM.L. Bascon, A. Cordoba

76 ADSORPTION ON A SQUARE LATTICE: KINETIC EQUATIONS ANDSIMULATIONM.C. Lemos, A. Cordoba

77 MONTE CARLO SIMULATION OF A SURFACE REACTION MODEL WITH LO-CAL INTERACTIONJ.J. Luque, F. Jimenez-Morales, M.C. Lemos

78 X-RAY PHOTOELECTRON DIFFRACTION STUDY OF CO AND NO ADSORBEDONNi(Ul )L.S. Caputi, R.G. Agostino, A. Amoddeo, A. Rotella, A. Santaniello, E. Colavita

79 CHEMISORPTION OF SIMPLE ATOMS ON Al: FROM THE MONOLAYER TOTHE LOW COVERAGE LIMITF.J. Garcia-Vidal

8P:b 101 Z n , . x M n x T e EPILAYERS GROWN BY HOT WALL EPITAXY ON (001) GaAsE. Abramof, A. Pesek, P. Juza, H. Sitter, T. Fromherz, W. Jantsch

102 PECULIARITIES OF THE GAPLESS STATE IN CuFeTegA.A. Vaipolin, S.A. Kijaev, L.V. Kradinova, A.M. Polubotko, V.V. Popov, V.D.Prochukhan, Yu.V. Rud, V.E. Skoriukin

103 VALENCE BAND OF C d j ^ F e x S e IN Fe ENHANCED RESONANTPHOTOEMISSIONB.A. Orlowski, J. Fraxedas, R. Denecke, B.J. Kowalski, L. Ley

104 MECHANISMS OF s-p-d-f EXCHANGE INTERACTIONS IN Mn AND Eu BASEDIV-VI DILUTED MAGNETIC SEMICONDUCTORST. Dietl, G. Bauer

105 DMS WITH 4 F-STATE IONS - A THEORETICAL FORECASTJ. Blinovski, P. Kacman

106 INTERACTION BETWEEN BAND ELECTRONS AND TRANSITION-METAL IONSIN Il-VI SEMICONDUCTORSA.K. Bhattacharjee, F. Hamdani, D. Coquilllat, J.P. Lascaray

107 PHOTOCONDUCTIVITY IN Cdl-xCoxSe ALLOYSJ. Stankiewicz

108 RESONANT SPIN-FLIP RAMAN SCATTERING IN CdTe-CdMnTe QUANTUMWELLSP. Peyla, A. Wasiela, D'Aubigne Y. Merle, D.E. Ashenford, B. Lunn

109 ROLE OF ANION VACANCIES IN SOME TRANSITION METAL PNICTIDESJ. Pape, H. Kohnke, J.-W. Schuenemann, K. Baerner, I.V. Medvedeva

110 CALCULATION OF THE INCOMMENSURATE MAGNETIC STRUCTURE OF CuOM. Ain, A. Menelle, B. Wanklyn, G. Parette

111 MAGNETIC PROPERTIES OF U(Fe,Ti)2

M. Zeleny, F. Zounova

XLVI

8P:b112 SURFACE AND BULK ELECTRONIC STRUCTURE OF ORDERED MTi AND MjTi

(M=Ni, Pd, Pt) ALLOYSP. Mikusik, S. Pick

113 NON-COLLINEAR MAGNETIC MOMENTS IN THE GROUND AND EXCITED S-TATES OF TRANSITION METALSJ. Kubler, L.M. Sandratskii, M. Uhl

114 ORDERING EFFECTS, MAGNETISM AND INVAR PROPERTIES IN FexCRj.*E.G. Moroni, T. Jarlborg

115 STRUCTURAL AND MAGNETIC PROPERTIES OF Er 2 Ni I 7 _ x AI x INTERMETAL-LIC COMPOUNDSI. Pop, M. Dihoiu, M. Andrecut, I. Burda, V. Crisan, A. Vernes

116 ON THE Y^Fej 7 ELECTRONIC STRUCTUREV. Crisan, I. Pop, A. Vernes, V. Popescu, D. Kapusi, L. Dulca, M. Andrecut, I. Burda

117 NONEQUILIBRIUM STEADY STATES IN MAGNETIC SYSTEMSJ. Marro, A.I. Lopez-L&comba, J.J. Alonso

118 TRANSITION FROM IN-PLANE ANTIFERROMAGNETISM TO LAYERED ANTI-FERROMAGNETISM IN VANADIUM ISLANDS ON Ag(OOl)A. Mokrani, S. Bouarab, H. Nait-Laziz, C. Demangeat, H. Dreysae

119 PARAMAGNETIC PROPERTIES OF THE Gd(Alj_xMex)2 COMPOUNDSG. Cbelkowska, A. Cbelkowski

5 120 THE SPIN REORIENTATION TRANSITION IN FERROMAGNETIC Gd METAL! PROBED BY pSRI O. Hartmann, R. Waeppling, E. Karlsson, G.M. Kalvius, L. Asch, A. Kratier, J.F.•.•_ Litterst

t 121 MAGNETIC PHASE DIAGRAM OF UNiGat V. Sechovsky, L. Havela, L. Jirman, M. Divis, P. Burlet, H. Maletta, E. Brack, F.R. De! Boer

I 122 PRESSURE EFFECT ON THE MAGNETIC AND ELECTRICAL PROPERTIES OFTHE NEW INVAR SYSTEM La (Fe, Co, Al) i3

, l.V. Medvedeva, A.A. Ganin, V.A. Sidorov

123 SURFACE MAGNETIC PHASE TRANSITIONS WITH MODIFIED SURFACE-BULKCOUPLINGM. Vendruscolo, A. Fasolino, M. Rovere

124 PRESSURE EFFEC-T ON SPIN REORIENTATION BEHAVIOUR OF ( E r ; _ x R x ) 2 F e j 4 B (R=Y, Gd)COMPOUNDSZ. Arnold, J. Kamarad, M.R. Ibarra, P.A. Algarabel

.125 THE HYPERFINE INTERACTION OF TERBIUM IN TERBIUM HYDROXIDED.St.P. Bunbury, C. Carboni, R.G. Graham, M.A.H. McCausland, S.M. Warner

126 ON THE MAGNETIC STRUCTURE OF UPdSnH. Nakotte, F.R. De Boer, R.A. Robinson, S. Johnson, A.C. Larson, J.W. Lynn, L.Havela, V. Sechovsky

127 CRYSTAL AND MAGNETIC STRUCTURES OF UPtGe AND UPdSn COMPOUNDSM. Kolenda, A. Szytula, R. Troc, V.H. Tran, M. Bonnet, J. Rostat-Mignot

128 WALL MAGNETIZATION REVERSAL OF COBALT FOIL INVESTIGATED BYTEMA. Gemperle, R. Gemperle, P. Novotny

XLVII

8P:b129 NON-COLLINEAR SPIN STRUCTURES IN Fe-Zr AMORPHOUS ALLOYS

P. Kossacki, T. Stobiecki, H. Szymczak

130 INTRINSIC PROPERTIES AND COERCIVITY OF INTERSTITIAL MAGNETSL. Schultz, M. Katter, C. Kuhrt, K. Schnitzke, J. Wecker

131 THE EFFECT OF Nd PURITY ON THE MAGNETIC PROPERTIES OF SINTEREDNd-Fe-B MAGNETSYu.M. Rabinovich, V.V. Sergeev, S. Szymura, H. Bala

136 SILICON NITRIDE FILMS PREPARED BY ION BEAM ENHANCEDEVAPORATIONJ. Zemek, M. Zavetova, S. Kamba, K. Kokesova, P. Zich, F. Cerny

137 DEPTH DEPENDENT LATTICE PARAMETER CHANGE IN SI AFTER HIGHDOSE AS+ IMPLANTATION AND LONG TIME ANNEALINGH. Metzger, S. Rugel, J. Peisl, I. Robinson, U. Pietsch

138 EPITAXIAL GROWTH AND CHARACTERIZATION OF TERNARY AND QUATER-NARY Hl-V SEMICONDUCTORSA. Camera, G. Attolini, C. Frigeri, C. Pelosi, D. Ajo, M. L. Favaro

139 CHARACTERIZATION OF SI-GaAs CRYSTALS BY PICTSP. Hlinomaz, V. Smid, J. Kristofik

140 INFLUENCE OF As PRESSURE DURING GaAs CRYSTAL GROWTH ONCOMPENSATIONH. Boudriot, W. Siegel, E. Buhrig, K. Deus

141 REGISTRATION ENVIRONMENT ON THE BASIS OF CHALKOGENIDE ARSENICJ. Bircak, D. Semak, J. Janic

142 INVESTIGATION OF Ti AND TiN DIFFUSION BARRIER LAYERS BY VOLATILECOMPONENT LOSS SPECTROSCOPYJ. Karanyi, L. Liptak

143 CONTACTLESS MEASUREMENT OF THE ELECTRON TUNNELING PROBABIL-ITY IN NATIVE OXIDES OF SILICONF. Riesz, J. Mizsei, I. Zolomy

144 RAMAN SPECTROSCOPY FOR ELECTRICAL CHARACTERIZATION OF IM-PLANTED GaAs LAYERSK. Kokesova, I. Gregora, V. Vorlicek

145 OXYGEN PRECIPITATES IN SILICON: STOICHIOMETRY STUDY BY INFRAREDSPECTROSCOPYA. Borghesi, G. Guizzetti, A. Piaggi, A. Sassella, A. Stella, B. Pivac

146 AUGER OXYGEN KLL LINE SHAPES IN SUBOXIDES OF SILICON: PATTERNRECOGNITION ANALYSISJ. Zemek, T. Vystrcil

147 A NEW WAY TO THE GROWTH OF OPTOELECTRONIC SUBSTRATESJ. Venkrbec, Z. Cecil, V. Rosicka, J. Kohout, J. Sedlacek, Z. Kodejs, P. Pacak

148 INVESTIGATIONS ON OHMIC CONTACTS TO N-TYPE GaAsM.R. Leyes, H.A. Coenen, P.A.M. Nouwens, J.H. Wolter

XLVIII

8P:b149 FIELD INDUCED CHANGES OF THE DIELECTRIC FUNCTION AND OPTICAL

BISTABILITY IN InGaA»P/InP p-i-n AND n-i-p-i STRUCTURESP. Kiesel, A. Hoefler, M. Kneissl, B. Knupfer, N. Linder, S. Quassowgki, P. Riel, G.H.Doehler, E. Veuhoff

150 ELECTRON MAGNETOTRANSPORT IN SILICON FET-STRUCTURESA.I. Vainer

151 ABSOLUTE NEGATIVE RESISTANCE OF SUBMICRON MIS-STRUCTURESA.I. Vakser

152 DEFECTS AT THE WAFER BONDED UNIPOLAR SILICON - SILICON JUNCTIONS. Bengtsson, G.I. Anderason, M.O. Anderason, O. Engstroem

153 EARLY STAGES OF THE SCHOTTKY BARRIER FORMATION FOR Al DEPOSIT-ED ON GaAs(llO)R. Rincon, J. Ortega, R. Perez, F.J. Garcia-Vidal, F. Flores, C. Coluzza, F. Gozzo, Y.Hwu, G. Margaritondo

154 ON THE TEMPERATURE DEPENDENCE OF SCHOTTKY BARRIER HEIGHTZs.J. Horvath,

155 A CONTROL OF AN INTERFACE POLAR1TION DISPERSION RELATIONIN SEMICONDUCTOR BARRIER STRUCTURES: INTERFACE POLARITONOPTOELECTRONICSN. Savostyanova, V. Sandomirski

156 NONLINEAR CONDUCTIVITY OF THE HETEROCONTACT BASED ON PrNis

AND CeNi5

Y.G. Naidyuk, M. Reiffers, A.G.M. Jansen, I.K. Yanson, P. Wyder, D. Gignoux, D.Schmitt

157 HEAT WAVES IN SUBMICRON SEMICONDUCTOR STRUCTURESJ. Marciak-Kozlowska

158 INELASTIC ELECTRONIC SCATTERING OF LIGHT IN SEMICONDUCTORMICROSTRUCTURESB.H. Bairamov, V.V. Toporov, G. Irmer, J. Monecke

159 NEUTRON-TRANSMUTATION-DOPED InSe INVESTIGATED BY POSITRON AN-NIHILATION SPECTROSCOPYR. Pareja, R.M. De la Cruz, B. Mari, A. Segura, V. Munoz

160 GaSb SINGLE CRYSTALS WITH A LOW DISLOCATION DENSITYV. Sestakova, B. Stepanek

161 SINGLE CRYSTALS OF GaN AND A1N. PHYSICAL PROPERTIES UNDER PRES-SURE UP TO 0.5 MbarP. Perlin, A. Polian, H. Teisseyre, 1. Gorczyca, N.E. Christensen, T. Suski

162 ON THE ORIGIN OF STACKING FAULTS IN SPHALERITE TYPESEMICONDUCTORC.A. Galeazzi, C. Pelosi

164 PULSED EXCIMER LASER SYNTHESIS OF TUNGSTEN SILICIDESS. Luby, E. Majkova, E. D'Anna, G. Leggieri, A. Luches, M. Martino

165 A PRIMARY ION BEAM SOURCE AND DIRECT ION BEAM DEPOSITION OFFILMS ON POLY AND SINGLE CRYSTALLINE SUBSTRATESH.R. Khan, O. Loebich, Cb.J. Raub

IL

166 EXPERIMENTAL ANALYSIS OF THE NOISE OF STATISTICAL ESTIMATORSUSED IN CORRELATION SPECTROSCOPYG.F. Lorusso, V. Capozzi, A. Minafra

167 SUBMILLIMETRE SPECTROSCOPY - PROMISING TECHNIQUE OF THE SOLIDSTATE PHYSICSG.V. Kozlov, A.M. Prokhorov, A.A. Volkov, S. Kamba, J. Petzelt

168 DISORDERED INDUCED LIGHT SCATTERING IN SOLIDS:THEORY ANDAPPLICATIONSP. Benassi, V. Maizacurati, M. Montagna, O. Pilla, G. Ruocco, G. Signorelli

169 A CALORIMETRIC PARTICLE DETECTOR WITH HIGH ENERGY RESOLUTIONM. Buhler, E. Umlauf

170 TRAPPING EFFECTS IN EXCITON MOTION IN THE FRAMEWORK OF CTRWP. Herman, I. Barvik

171 OBSERVING FREE RELAXATION INDUCED BY COLORED NOISE VIA NON-LINEAR MAGNETIC RESONANCE SPECTROSCOPIESL. Andreozzi, C. Donati, M. Giordano, D. Leporini

8P:c 201 THEORY OF ONE- AND TWO-STEP PULSED PHOTOBURNING OF SPECTRALHOLESI. Rebane

202 THEORETICAL STUDY OF THE VERY FAST ELECTRON DYNAMICS IN DISOR-DERED SOLIDSA. Kalvova, B. Velicky

203 THE SILICON DIODE STRUCTURE FOR PICOSECOND RESOLUTION PHOTOHCOUNTINGB. Sopko, I. Macha, I. Prochazka, K. Hamal

204 MONTE-CARLO SIMULATION OF ULTRAFAST ELECTRON RELAXATION IN AgPJ. Van Hall, R.H.M. Groeneveld

205 TIME RESOLVED EXCITON TRANSFER IN BIASED ASYMMETRIC DOUBLEQUANTUM WELLS - THEORYR. Ferreira, Ph. Rousaignol, P. Rolland, C. Delalande

206 TIME RESOLVED EXCITON TRANSFER IN BIASED ASYMMETRIC DOUBLEQUANTUM WELLS - EXPERIMENTSPh. Roussignol, R. Ferreira, P. Rolland, C. Delalande, A. Vinattieri, L. Carraresi, M.Colocci, N. Roy, B. Sermage, J.-F. Palmier, B. Etienne

207 NON-RADIATIVE RELAXATION OF JAHN-TELLER SYSTEMS IN CRYSTALS BYTHE PULSE MODELM. Dominoni, N. Terzi

208 ULTRAFAST ELECTRON DYNAMICS AT THE Ge(l l l ) 2x1 SURFACEM. Baeumler, R. Haight

209 PHOTODARKEN1NG EFFECT IN SEMICONDUCTOR-DOPED GLASS STUDIEDBY PICOSECOND SPECTROSCOPYP. Maly, F. Trojanek, A. Svoboda

210 ULTRAFAST PROCESSES IN SEMICONDUCTORS: MONTE CARLO SIMULA-TION INCLUDING COHERENT PHENOMENAT. Kuhn, F. Rossi

211 TIME RESOLVED PHOSPHORESCENCE EMISSION IN THIANTHREN CRYSTALSA. Arena, A.M. Mezzasalma, G. Saitta

8P:c212 THE ENERGY OF EXCITON EXCITATION THAT ACCOUNTS KINEMATIC IN-

TERACTION EXACTLYO.V. Deizhko, R.R. Levitskii, A.Ph. Moina

213 OPTICAL PROPERTIES OF As2S3 THIN LAYERSZ. Cimpl

214 ANOMALOUS POSTLUMINISCENCE IN MIXED CRYSTALS AND NEAR-SURFACE LAYER OF SEMICONDUCTORSB.V. Novikov, SR. Grigoriev

215 OPTICAL NONLINEARITIES OF ZnCdTeI. Pelant, D. Oblmann, B. Hoenerlage, R. Levy

216 EXCITONS IN STRAINED ZnTe:TWO-PHONON ABSORPTION AND THEORYM. Schlierkamp, F. Kubacki, M. Steckermeier, U. Roessler

217 PLASMON BANDS AND FANO-RESONANCES IN SEMICONDUCTORSK. Sturm, W. Schulke

218 PHOTOCONDUCTIVITY DECAY IN CulnSe2

M. Igalson

219 DETERMINATION OF PERSISTENT PHOTOCONDUCTIVITY WITHIN SEMI-CONDUCTOR EPITAXIAL LAYERS BY PHOTOCONDUCTIVE GAINE.A. Anagnostakis

220 SPECTRAL BEHAVIOR OF THREE-PHOTON ABSORPTION COEFFICIENT INII-VI COMPOUNDS: ZnO CdS and ZnSeI.M. Catalano, M. Lepore, R. Tommasi

221 TWO-PHONON RESONANT RAMAN SCATTERING IN SEMICONDUCTORSWITH EQUAL EFFECTIVE MASSES OF ELECTRONS AND HOLES IN MAGNET-IC FIELDV.I. Belitsky, M. C&rdona

222 DOUBLE PEAK SPECTRA IN SPONTANEOUS EDGE ELECTROLUMINISCENCEJ. Zavadil, K. Zdansky

223 INVESTIGATION OF BISTABLE OPTOELECTRONIC STRUCTURES ON THIN II-VI FILMSL.N. Zalyubinskaya

224 RAMAN SCATTERING IN DIAMOND AND GRAPHITE-LIKE FILMS AT HIGHPRESSURESA.F. Goncharov, V.D. Andreyev

225 INDIRECT ENERGY GAP DEPENDENCE ON Al CONCENTRATION INAlxGaj.jAs ALLOYSM. Guzzi, E. Grilli, S. Oggioni, J.L. Staehli, C. Bosio, L. Pavesi

226 PHOTOCURRBNT SPECTROSCOPY OF AMORPHOUS MIS-STRUCTURESR. Schwarz, M. Reiasner, M. Miosga, T. Fischer

227 PHOTOACOUSTIC CHARACTERIZATION OF CHALCOGENIDEGLASSES:THERMAL DIFFUSIVITY OF GexTej _x

J.C. De Lima, N. Cells, L.C.M. Miranda

228 SOLID STATE AMORPHIZATION OF 11IV SEMICONDUCTORS FROM HIGHPRESSURE PHASESV.V. Brazhkin, S.V. Demiihev, A.G. Lyapin, N.E. Sluchanko

LI

8P:c229 OPTICAL MODULATION SPECTROSCOPY OF AMORPHOUS SILICON CARBON

ALLOYSW. Grevendonk, H. Herremans

2S0 THE SCLC TECHNIQUE AND AMORPHOUS SEMICONDUCTORSV. Cech

231 SUBMICRON METALLIC INCLUSIONS IN AN AMORPHOUS GALLIUMANTIMONIDES.V. Demishev, Yu.V. Koeichkin, A.G. Lyapin, N.E. Sluchanko, M.S. Shatambeyan

232 RELATIONS BETWEEN DEFECTS AND HYDROGEN INCORPORATION IN a-Si:HAS STUDIED BY COMBINED PHOTOCONDUCTIVITY AND PHOTOTHERMALDEFLECTION SPECTROSCOPYP. Sladek, Y. Bouizem, M.L. Theye, P. Roca

233 HIGH PRESSURE STRUCTURAL PHASE TRANSITION AND ELECTRONICPROPERTIES OF HIV NITRIDESA. Munoz, K. Kunc

234 ON THE ROLE OF ELECTRON TUNNELLING IN RECOMBINATION KINETICSIN INSULATING CRYSTALS WITH RADIATION DEFECTSE. Kotomin

235 THEORETICAL AND EXPERIMENTAL DEVELOPMENTS IN THE DETERMI-NATION OF THE MINORITY CARRIER PROPERTIES IN LOW MOBILITYSEMICONDUCTORSI. Balberg

236 TWO-STAGE RELAXATION OF HOT ELECTRON-PHONON SYSTEM WITH DIS-PERSIONLESS LO-PHONONS IN POLAR SEMICONDUCTORSK. Krai, B. Hejda

237 ELECTRON SCATTERING BY LOCALIZED OPTICAL MODES IN IONICSEMICONDUCTORSF.G. Bass, V.A. Pogrebnyak

238 BLOCK BOUNDARIES CONDUCTIVITY IN MOSAIC CRYSTALSV.A. Pogrebnyak, D.D. Khalameida, V.M. Yakovenko

239 A LOW TEMPERATURE HALL EFFECT AND PHOTOLUMINESCENCE STUDYOF GaSb MONOCRYSTALSF. Meinardi, L. Tarricone

240 APPLICATION OF THE DYNAMICAL TRANSPORT THEORY TO IONIZED IM-PURITY SCATTERING !N SEMICONDUCTORSB. Podor, G. Gombos, J.L. Farvacque, R. Meintrup, P. Magyar

241 IMPACT IONIZAT1ON IN SEMICONDUCTOR TRANSPORTW. Quade, E. Scholl

242 NUMBER AND MOBILITY FLUCTUATIONS:CLASSIFICATION OFNON-EQUILIBRIUM NOISE IN SEMICONDUCTORSL. Varani, T. Kuhn, L. Reggiani

243 CARRIER PHONON DRAG EFFECT IN CdTeS. Vackova

244 RECOMBINATION OF THE MINORITY CARRIERS ON DISLOCATIONS IN III-VSEMICONDUCTORSA.A. Ptaschenko, N.V. Moroz, J.W. Melkonyan

LII

ABSTRACTS

6al:Al

MAGNETIC X-RAY SCATTERING

G.H. LanderCommission of the European Communities, Joint Research Centre, Institute forTransuranium Elements, Postfach 2340, D-7500 Karlsruhe

The theoretical basis for observing the (weak) interaction between a photonbeam and ordered spin and orbital magnetic moments was formulated morethan 30 years ago. Despite the pioneering experiments by de Bergevin andBrunei (CNRS, Grenoble) in the 1970's, the technique remained a curiosity un-til the availability of synchrotron sources. With their high brightness, beam po-larisation, and tunability over a large energy range, new topics in magnetism,in most cases complementary to those studied with neutrons, are being investi-gated.

Significant effects have also been found when the energy is tuned to absorp-tion edges. In some cases very large enhancements of the normally small mag-netic signal are found- In scattering at the M edge energies in 5f systems, for ex-ample, the magnetic scattering can become comparable to the charge scatter-ing. This again opens up new possibilities for magnetic investigations at x-raysynchrotrons.

Collaborators: W.G. Stirling, C. Tang & S. Langridge (U. of Keele) and D.GibbS (Brookhaven Nat. Lab, NY)

6a2:AlTHIN FILM HIGH-TC SQUID MAGNETOMETERS

C. HEIDENInstitut fiir Schicht- und IonentechnikForschungszentrum Julich, GmbH, D-5170 Julich

Progress in the preparation of epitaxial high-Tc perovskitefilms on suitable substrates, their patterning intomicrostructures, and recent progress in Josephson junction ;technology using grainboundary engineering resulted in SQUID -. ''magnetometers with attractive noise performance for operation \at liquid nitrogen temperature. DC- as well as RF-SQUIDs usingJosephson junctions made on artificial step edges in the jsubstrate^surface exhibit a rather low 1/f excess noise. Values >below 10~4 >O/Hz

l/Z for the spectral flux noise at frequencies K

down to a fraction of 1 Hz, and of the order of 10~3 J/Hz for sthe spectral energy resolution in the white noise region havebeen observed At 77 K. Using flux focussing this leads tomagnetometers with field sensitivity below 1 pT/Hz1'2 that aresufficiently sensisitive for the detection of several humanbiomagnetic signals.

6a2:A2PROGRESS IN HIGH Tc MAGNETIC SENSORS AND THEIR APPLICATIONS

G.B. DCNALDSOJ, R.M. BOHMRN, A. COCHRAN, K.J. KIRK, J.C. MCEARWNE*and C.H. PB3RIWDepartment of Physics and Applied Physics, University of Strathclyde,Glasgow G4 ONG, Scotland.division of Applied Physics, CSIRO, Llndfield, 2070, Australia.

Vfe report recent progress in our own group and world-wide on the de-velopment of SQUID and other high 1^ magnetic sensors, and on some of theearly applications which are appearing or can be foreseen. Three technol-ogies for reproducible Josephson junctions will be discussed - the stepedge, the biepitaxial and the sandwich type edge junction. Vfe will discussthe performance of SQUIDs based on each of these and in particular presentdetails on our own YBCO step-edge devices based on steps and grooves whichare Ar ion-milled in MgO substrates. An account will also be given of ana magnetic gradiometer based en the use of "fluxgate" properties of bulksintered YBCO.

A review of applications prospects for these detectors will be givenin the light of the available noise performance which for high Tc DC SQUIDs,at less than 1 x 10~4 cr*2"1'2 is t**1 better than for commercial low TcRF SQUIDs. Etophasis will be placed on non-destructive evaluation of mate-rials such as steel and on clinical bionagnetism.

6a2:A3

THE PRESENT STATE OF Ag/Bi(2223) TAPES

R. FLUKIGER, B. HENSEL, A. JEREMIE, A. PERIN and J.-C. GRIVELDipt. Phys. Mat. Condensed, 1211 Geneve 4, Switzerland

The fabrication of Ag/Bi(2223) tapes by using the Powder in Tube process,comprising several press and annealing steps is described. It has been found thathigh Jc values can only be obtained on tapes with a high density, a high degree oftexturing and a very fine distribution of additional phases. However, the kineticsof the formation process leading from the Bi(2212) phase after calcination to theBi(2223) phase after reaction has not been completely elucidated. Atcntativedescription of the formation process will briefly be discussed. The variation of j c

at 4.2 and 77 K as a function of the applied field is presented for variousmonofilamentary tapes with values of j c exceeding 2 • 10 A/cnfi at 77K,0T. Theanisotropy of j c at 77 K for a series of tapes is analyzed as a function of theapplied magnetic field.

6a2:Bl

THE THEORY OF IMPURITY STATES IN SEMICONDUCTORS,Mkhfl f m x m , Laboratoire de Physique des Solides (CNRS), InstitutSupeneur d'eectronique du Nord, 41, boulevard Vauban, 59046 LilleCedex, FRANCE

The basic theoretical methods for treating defects and, in particular,impurities in semiconductors are first reviewed. They split into twogroups : the techniques appropriate to deep states (local density,empirical tight binding) or to shallow states (effective massapproximation). A discussion is given of how to handle the mostdifficult intermediate cases (corresponding to the shallow-deepinstability) and of the possible coexistence of these two types of states.

The second part describes applications of these general arguments tospecific cases. This begins with the well documented case of transitionmetal impurities followed by recent results obtained for rare earthimpurities. A fairly detailed analyzis is performed in the case of EL2showing that this center must be a complex involving the antisite. Thecase of the DX donor in Gai-xAlxAs compounds is also reviewed, withthe arguments in favor of the two competing models.

6a2:B2INTRA- AND INTERDEFECT ELECTRONIC CORRELATION OF

DX • CENTERS IN IH-V SEMICONDUCTORS

W. JANTSCH«, G. OSTERMAYER" and Z. WELAMOWSKI*

aInstitut fiir Experimentalphysik, Johaitnes-Kepler-Universititt, A-4045 Linz-Auhof, Austria*>Institute of Physics, Polish Academy of Sciences, P-02-668 Warsaw, Poland

We review experimental evidence for the negative intra-defect Hubbard correlation energyU of DX centers. In other words, we show from investigations of photoconductivity and theemission kinetics of free carriers that the ground state of donors in Ali^GaxAs and in otherIII-V compounds binds two electrons. Thus it is negatively charged in agreement with thetheoretical prediction by Chadi and Chang1.

As a consequence, all donors in these materials are always charged and thus produce astrongly fluctuating Coulomb potential, which manifests itself in the capture kinetics ofphoto-excited carriers and the apparent thermal activation energy of bound carriers.Additional interesting effects arise from the freedom in the spatial distribution of the doublyoccupied donors among the random matrix of donors. In order to minimize the total Coulombenergy, short range dipoles are prefentially formed which tend to increase the mobility inthermal equilibrium. Experiments and models are presented.

ID. J. Chadi and K. J. Chang, Phys. Rev. Lett 61,873 (1988) and PRB 39,10063 (1989)

6a2:B3

NEGATIVE-DONOR CENTRES AND RELATED PHENOMENA IN QUANTUM WELLS

S. HUANT"), A. MANDRAY") and B. ETIENNE'"

(1): SNCI/CNRS, BP 166, 38042 Grenoble Cedex 9, France(2): L2M/CNRS, BP 107, 92225 Bagneux Cedex, France

D" centres - neutral donors that trap a second electron - form readily Insuitably doped Multiple-quantum wells due to electron transfer fromremote donors In the barriers to donor sites In the wells1. Ourmagnetooptical spectroscopy of selectively doped GaAs-(Ga,Al)As quantumwells aiming at the study of confined D" centres and at D~ doping ofquantum wells 1s reviewed. Our work opens various physical phenomenarelated to negative-donor centres In semiconductors to be studied. As anexample, we will discuss the still controversial problem of the DX centrecharge state In (Ga,Al)As alloys and show how it can be optically probedIn D~ doped quantum wells.

1. S. Huant, S.P. Najda, and B. Etienne, Phys. Rev. Lett. 65 (1990) 1486.

6a2:B4

THEORY OF DEFECT METASTABILITY IN III-V COMPOUNDS

JAREK DABROWSKI* and MATTHIAS SCHEFFLER

Fritz-Haber-Institut der UPC, Faradayweg "4-6, 2000 Berlin 33, Germany

Up to recently the observation of a defect metastability was considered toreflect a rearrangement of a defect complex. A substltutional point defectwas believed to be structurally stable. We summarize our recent theoreticalstudies which show that these assumptions are incorrect and that point-defect instability is an intrinsic property of sp-bonded semiconductors.

The most prominent examples of metastable defects in III-V compounds arethe EL2 and DX centers. The EL2 defect is the dominant, native deep donorin undoped GaAs crystals and shows an optically Inducible metastability.The name "DX center" refers to another technologically Important andintensively studied deep defect which is an alternative state of shallow spdonors in AlGaAs alloys. We summarize theoretical indications thatstructural instabilities of these centers are due to tha same basicmechanism caused by different possibilities of sp hybridization. We arguewhy effects of this intrinsic metastability may be observable for somecenters but not for others. As examples, we discuss in details behavior ofthree defects in GaAs: the As antisite (a model for EL2), the Si Impurity(a model for DX), and the Sb donor (a stable center).

+ perm, addr.: Instytut Flzyki PAH, Al. LotnlkOw 32, 02-668 Warsaw, Poland

4

6a2:Cl

QUANTUM AC-CONDUCTANCE OF WEAKLY DISORDERED MESOSCOPIC

STRUCTURES

J. MASEK" and B. KRAMER'

"Institute of Physics, Czechoslovak Academy of Sciences, Na Slovance 2, 18040 Praha 8,

Czechoslovakia; *PTB Braunschweig, Box 3345, 3300 Braunschweig, Germany

We use a tight binding Hamiltonian to calculate frequency dependent conductance G(w)

of quasi-one-dimensional disordered mesoscopic conductors at zero temperature. We de-

scribe a transition from ballistic to metallic transport regime when the disorder increaaes

and unique features due to quantum coherence of electron states disappear. The transi-

tion is compared with an onset of the universal fluctuations in the dc-case.

We also go beyond the usual scattering approach to the conductance calculations and

use the linear response theory to study how the conductance in a "sample" is affected by

disorder in "leads".

6a2:C2SINGLE ELECTRON CHAROINO AND ZERO-DIMENSIONAL STATES IN LATERALQUANTUM DOTS

ALAN T.JOHNSON, JR.

Department of Applied Physics, Delft University of Technology, P.O. Box 5046,2600 OADelft. The Netherlands

I will present results from transport experiments on sab-micron lateral quantum don.

defined by gates In the two-dimensional electron gas of OaAs/AlGaAs heterostructures, and \

coupled to large area leads by tunable quantum point contacts. Both the tingle-electron chargtag '

energy and the energy level splitting can be larger man k&T at the dilution refrigerator bate i

temperature. Important results include: (1) observation of the onset of charging when the tingle- 1

channel trantnuwilon of die point contacts is one, resulting in a magnetic field dependent critical

resistance for the existence of charging effects, (2) demonstration of a quantized current, locked

to an external RF source, in the Quantum Dot Turnstile, and (3) observation of dramatic effects

associated with the phase-coherent motion of electrons within the dot

6a2:C3

PERSISTENT CURRENTS AND DISSIPATION IN ISOLATEDMESOSCOPIC RINGS

II. Bouchiat*. L.P. Levy*, D. M«illy**G. Montambaux* and B. Reulet*

+ Laboratoire de Physique des Solktes.Batiment 510,91405 Orsay.* SNCI38042 Grenoble Cedex.** LMM, 196 Avenue Raverra, 92220 Bagneux

The existence of a persistent current in a metallic (non superconducting) loop pierced by a •magnetic flux was predicted few years ago, as a consequence of the phase coherence of theelectronic wave functions along the ring at low enough temperature. The experimental evidence ofthere currents has been shown by measuring the magnetic moment of an assembly ofdisconnected copper rings and more recently of a single gold ring.

These experiments as well as related theoretical issues will be reviewed. We willparticularly discuss the problem of the ensemble average of these persistent currents whose signin a particular ring depends on the number of electrons and realisation of the disorder.

A next step in the understanding of transport in phase coherent samples is the study of themagnetic response of a ring to a time varying flux which induces an electric field along the ring.

We show that the dissipative current which coexists with the persistent non dissipativeone is expected to be essentially different from the Ohmic response of the same ring connected toa voltage source and we describe an experiment addressing this issue.

6a2:C4

AHARONOV-BOHM EFFECT IN LOOPS DOPED WITH MAGNETIC IMPURITIES •

C. VAN HAESENDONCK « , H. VLOEBERGHS <»>, A.H. VERBRUGGEN <2>, S. RADE-LAAR <2\ Y. BRUYNSERAEDE «C> Laboratorium voor Vaste Stof-Fysika en Magnetisme, Katholicke Universiteit Leuvtn,Celeatijnenlaan 200 D, B-SOOt Leuven, Belgium*2) Delft Institute of Microelectronics and Submicron Technology, Delft University of Tech-nology, P.O. Box 5046, 2600 GA Delft, The Netherlands

We have prepared submicrometer Au loops with an electron phase coherence length com-parable to the loop circumference. In these mesoscopic structures the electron interferencegives rise to pronounced oscillations "of the magnetoconductance. The oscillations with .flux period h/e can be scrambled by "annealing" the Au loops at T — 20 K. By averagingthe magnetoconductance traces, which are obtained after different annealing cycles, wecan reconstruct the h/2e oscillations caused by the coherent backscattering around the £loop. We have also studied the exponential damping of the A/e and h/2e oscillations,which occurs when the loops are doped with magnetic Fe impurities. For higher Fe con-centrations (~ 1 at.%) the time dependence of the magnetoconductance directly reflectsthe spin-glass freezing of the Fe impurities.

• Work supported by the Belgian National Fund for Scientific Research (N.F.W.O.) andby the Dutch 'Stichting voor Fundamenteel Ondenoek der Materie' (F.O.M.)

6

6pm:AlEXCHANGE COUPLING IN MAGNETIC MULTILAYERS

D.M. EDWARDS*, J. MATHONt and R.B. MUNIZ*•Department of Mathematics, Imperial College, London SW7 2BZ.tDepartment of Mathematics, City University, London EC1V OHB.

Our Initial work1 on the exchange coupling between two transition metalferromagnets, separated by a non-magnetic transition metal spacer, wasbased on some simplifying assumptions. We now report calculations for aCr spacer, using rea l i s t i c d bands. In which the osc i l la t ions of exchangecoupling as a function of spacer thickness have a long- and short-periodcomponent as observed. The amplitude and phase of the osc i l la t ions donot agree with experiment but It Is shown how both defects may beremedied by relaxing our original condition of zero penetration of dholes Into the majority spin band of the ferromagnet.

1. J. Phys,: Condens. Matter 3 (1991) 4941

6pm :A2

EXCHANGE OF Fe LAYERS ACROSS INTERLAYERS WITH GOOD MATCH

P. GRUNBERGForschungBientriim Jfilich, IFF, Postfach 1913, W-5170 Jfllich, Germany

isiI The exchange interaction of Fe across intedayers X, X = Cr, An, Ag, and Al has beenI investigated by means of M(H) corves and lightscattering from spinwaves. For these\ investigations Fe/X/Fe structures were grown with as good epitaxy and crystallinity as| possible, which is documented bj in ain RWF.F.n investigations. For the coupling across] Cr and An we find oscillations as a function of the interiayer thickness with a long and a

short period. For Al interlayers only long periods can be clearly resolved and for Ag nooscillations are observable. Apart from the oscillations between ferro- and antifenomag-netic type coupling we find also contributions of 90° type coupling which arein the case of Al and An and weak in the case of Cr. The results will be discussed in thelight of current theories.

6pm:A3MAGNETIC PROPERTIES OF METALLIC MULTILAYERS

W.J.M. DE JONGE, P.J.H. BLOEMEN AND H.A.M. DE GRONCKEL,Department of Physics, Eindhoven University of Technology,5600 MB Eindhoven, The Netherlands andPhilips Research Laboratories, P.O. Box 80000, 5600 JA Eindhoven, The Netherlands

Recent results of investigations on the magnetic behavior of layered metallic structureswill be reviewed. We will emphasize on the magnetic anisotropy (i.e. perpendicularmagnetized structures) and studies on the interface topology with nuclear magneticresonance.

6pm :A4RELATIONSHIP BETWEEN STRUCTURE AND GIANT MAGNETORESISTANCE

IVAN K. SCHULLER. D. M. KELLY. E. E. FULLERTON, J. GUIMPELPhysics Department, University of Califomia-San Diego. La Jolla. CA. 92093-0319. USAF. BEL1EN, E. OSQUKJUIL, Y. BRUYNSERAEDELabotatorium voor Vaste Stof-Fysika en Magnctisme, Katholieke Univcrsitcit Leuvcn, B-3001 Leuven,Belgium

V* have performed extensive structural, magnetolransport and magnetic measurements on sputtered andMBE grown Fe/Cr superlattices. High resolution X-ray diffraction studies were combined with a novelstructural refinement technique to determine structural parameters of the supcrlatticcs includingcrystallographic orientations, roughness, interdiffusion and local atomic arrangements. Transportmeasurements in photoliihographicatly prepared samples allowed an independent investigation of theresistivity and the magnetoresisiance as a function of structural parameters. Sensitive magnetization studiesusing SQUID maghetometry was used to study the magnetic ordering and its dependence on thestructure.The giant magnetoresistance is found to be strongly affected by interfacial roughness,crystallographic orientation and mosaic spread in antifcrromagnctically coupled samples.

Supported by the US Department of Energy (at UCSD) and the Belgian Concerted Action andInteruniversily Attraction Poles Programs (at KUL).

8

6pm:BlAB INITIO TOTAL ENERGY CALCULATIONS ON

PARALLEL COMPUTERS

M.C. PAYNE1,1. STICH1, L.J. CLARKE2, R.D. KING-SMITH1 and J-S. UN 1

1. Cavendish Laboratory, Madingley Road, Cambridge, UK.2. Edinburgh Parallel Computer Centre, Mayfield Road, Edinburgh, UK.

A set of total energy pseudopotential codes has been implemented on a parallelcomputer which allows calculations to be performed for systems containingmany hundreds of atoms in the unit cell. Using these codes we have calculatedthe total energies and relaxed structures of the 3x3, SxS and 7x7 Takayanagireconstructions of the (111) surface of silicon. We find that the 7x7 structureminimises the surface energy and observe structural trends across the series thatcan be correlated with the degree of charge transfer between the dangling bondson the adatoms and restatoms.

6pm:B2

Phonons in AlGaAs Alloys and the Effect of Disorder onthe Vibrational Properties of GaAs/AlAs Super-lattices

Stefano Baroni*Stefano de Gironcoli,2 Paolo Giannoni,* and Elisa Molinari.4

lSc*oU Internaxionmk Superiors di StudS Avanxati, Triette, IUly2Sc%oU Normmle Superior*, Pum, Ittly

3Itutit*t Romand de Recherche Nwmhique en Phvtique it* MaUruau, Laumnne, Switzerland*Cotuiglio fiazionale delle Ricerche, ItHtuto 'O.M. Corbino', Rom*, Italy

We report on recent theoretical investigation* of the vibrations! properties of AlGaAs alloysand (disordered) superlattices. The effects of disorder are described using large supcrcdls andthe interatomic force constants are calculated from first principles using Detmty FunctionalPerturbation Theory. In agreement with recent experimental evidence, we find that well dennedGaAs-like and AlAi-like phonon dispersions exist in the bulk alloy. Our results for the bulkalloy are then used to get insight into the Raman spectra of GaAs/AlAs thin superlattices. Wefind that some features of these spectra cannot be explained without taking into account somedisorder occurring at the interlaces. As an important byproduct, we show that some of theALAs-like LO modes are extremely sensitive to disorder and that they are therefore suitable fora rather precise characterisation of the samples.

6pm:B3

DIELECTRIC RESPONSE AND QUASIPARTICLE ENERGIES IN NICKEL.

F. ARYASET1AWAN1 and U. von BARTH2

'Max-Planck-lnsMut lllr Feaftorperforschunfl, Stuttgart, Germany.'Lund Universffy, Lund, Sweden..

The purpose of this paper to to Investigate the utfflty of traditional many-body perturbationtheory In highly correlated d-eteotron systems taWng ftiH account of the underlying one-parfcie structure. Starting from a zeroth oider Greens function based on a seff-oontfetenttooal-densrty oatoutetfon, we have here computed the dtelectrlc matrix of ferromagneticniokel within the RPA, thus demonstarOng the feasibility of many-body oateulatfons in real-(sOc systems. From our results we obtain the optical absorption, the optical conductivityand the eteotron-energy-toss spectra. A deviation from experiment in our optical absorp-tion spectrum Is easily traoed oaok to our toeeJ-densfty starting point Using insteadquasipartlcte energies In the zeroth order Greens (unction results in much better agree-ment wfth experiment The particle-hole Interaction as wen as the local-field effects areretotfvefy unimportant especially at lower energies and small momentum transfers. Fromthe dialectic matrix we also obtain the GW approximation for the electronic self-energyand from there, the quasiparticle bandsttuoture which compares weO with experiment Inparticular we obtain the desired bandnarrowtng but we obtain no satellte 6 eV below theFermi energy demonstrating the need lor a theory beyond the GW approximation.

6pm:B4

SURFACE INDUCED ORDERING IN GALLIUM-INDIUM PHOSPHATE

SVERREFROYENNational Renewable Energy Laboratory, Golden, CO 80401, USA

Although bulk IH-V semiconductor alloys exhibit phase separation, vapor-phase epitaxialgrowth of Gao.5Ino.5P on GaAs (001) shows spontaneous ordering into a <111> orientedmonolayer superlattice. This <111> ordering is believed to be induced at the surface duringgrowth. We have performed total-energy first-principles pseudopotential calculations for thesurface layers of cation- and anion-terminated (001) surfaces of Gao.5IHa.3P on GaAs sub-strates and valence-force-field model calculations for deeper layers. These calculations showthat the relative stability of the various Ga/In arrangements, is a strong function of the layerdepth below the surface. At the cation-terminated surface a Ga/In atomic arrangement cone-sponding to the observed bulk ordering is preferred over other arrangements by 90 meV persurface atom. This preference is intimately tied to electronically driven surface-reconstructions. For Ga/In layers below a cation-terminated surface the energy differences areall small (<30 meV per atom). Under a P-terminated, dimerized surface, however, elasticrelaxations create a stability enhancement of the observed arrangement in the third monolayerbelow the surface. Finally, thermodynamic calculations based on a configuration*] Hamilto-nian whose interaction energies are fit to the total energy calculations show that the observedordering can be explained as a thennodynamically stable phase at growth temperatures ofeither the surface or the first few subsurface layers depending on the atomic mobilities.

10

6pm:Cl

ANISOTROPIC OPTICAL PROPERTIES OF UNTWINNED Y2Ba4Cue+o0M+n

B. Bucher and P. Wachter

Laboratorivm fur Festkorperphysik, ETH Zurich8093 - Zurich, Switzerland

We will present the polarized-reflectivity spectra of Y2Ba4Cu6+nOi4+n (n = 1, 2) aboveand below the superconducting transition temperature Tc. These substances are nottwinned because of thermally stable double CuO chains insteade of single chains as inYBagCuaOy. The light was polarized along the two plane directions a and b with thechains running along the b direction.

We have detected a strong contribution of the chain to the optical conductivity, <Tj(w),and thus an anisotropy of the two plane directions of about 1:3. A flat plateau in thereflectance below 60 meV has been attributed to phonon interactions. The infra-redscattering rate of the charge carriers in the plane, l/ra(u/), is linear from 0.05 up to0.8 eV. In the superconducting state, plasma edges have developed below 25 meV whichwe assume to be caused rather by the density of superconducting carriers than by a gap.Good fits of the reflectivity are obtained by a two-fluid model pointing to a real spacepairing (bipolarons) with subsequent Bose condensation.

6pm:C2

L.J. DE JONGH, S.I. MUKHIN*. D. REEFMANKamerlingh Onnes Laboratory, Leiden University, P.O. Box 9506,2300 RA Leiden - The Netherlands* On leave of absence fron Moscow Inst. of Steel & Alloys.

A najor issue in high-Tc superconductivity is whether the carriers obeyFeral statistics above Tc (i.e. T a Tc) or whether bosons are formed in anappreciable range above Tc already, so that the superconductivity is due toa type of Bose-condensation at Tc of pre-existing, local pairs of carriers.In particular the observed very short coherence lengths are in favor of alocal-pair approach. For this reason we have started a program to predictthe physical properties of the high-T0 naterials on basis of the local-pairapproach. We have calculated the tunneling characteristics of a junctionforaed by a normal netal and a local-pair superconductor, in particularwhen including a very thin nonsuperconducting surface layer on the latter.In addition we have calculated the temperature dependences of the (order-ing) specific heats in the mean-field/random-phase approximation, using themapping of the local-pair model onto the anlsotropic Helsenberg pseudo-spinmodel (for 3-D and for quasi 2-D lattices). Recently, we have complementedthis work by Monte-Carlo calculations to be presented at the conference.Furthermore, we shall present preliminary results on the behavior predictedfor the MNR Knight-shift and relaxation time in the cuprates, followingfrom the model of hopping spin-less holes in an antlferromagnetlc back-ground.

11

6pm :C3

ELLDPSOMETRICALLY DETERMINED FAR-INFRARED OPTICALCONSTANTS OF YBaCuO CERAMICS AND THIN FILMS

Karl-Ludwig Barth and Fritz KeilmannMax-Planck-Institut fur Festkorperforschung7000 Stuttgart 80, Germany

The radiation of an optically pumped far-infrared laser is used to operate a ro-tating analyzer ellipsometer. This instrument determines the complex dielectricfunction at fixed frequencies between 10 and 150 cm'1. A cryostat allowsmeasurements even at large angles of incidence in the temperature range from10-330 K.We applied the instrument to Fe-doped YBaCuO ceramics, pure YBaCuO ce-ramics and thin YBaCuO films on SrTiO3. In all cases we clearly see the effectof the phase transition at Tc. The Fe-doped samples show a gap energy thatvaries with the Fe concentration. In the case of the undoped ceramic we see astrong temperature-dependent structure in the dielectric function between 120and 190 K. Measurements on thin films resulted in a hysteresis-like behavior ofthe dielectric function below T_.

6pm:Dl

GLASS TRANSITION SINGULARITIES: RECENT RESULTS

W. GOTZEPhysik-Department, Technische Univeraital Miinchen, D-8046 Garching, FRGand Max-Planck-Institut fur Physik und Astrophysik, D-8000 Munchen, FRG

The mode coupling theory for supercooled liquid dynamics predicts bifur-cation singularities of the cuspoid type, connected with slow stretchedrelaxation phenomena similar to what is known from the spectroecopy ofglass forming systems. There appears a special dynamical window, theB-relaxation regime, where rather specific predictions can be made for thespectra and their temperature dependence. The results of the theory willbt: sketched for the three simplest scenarios and compared with someexperimental findings.

12

6pm:D2

SHORT-TIME DYNAMICS OF POLYMERS NEAR THE GLASS TRANSITION -INVESTIGATED BY INELASTIC NEUTRON SCATTERING.

B. FRICKInstitut Laue-Langevin, B.P. 156, 38042 Grenoble Cedex9, France

Using inelastic neutron scattering we probe the dynamics of different polymers on atime scale of 108 -10*14 seconds and on a very local spatial scale {<, 10 A) in thetemperature range between T = 2K and T => Tg + 150K. However, approaching theglass transition temperature Tg the relaxation times of quantities connected withtransport are known to diverge strongly. Nevertheless, we observe essentialchanges of the local dynamics near Tg on a short time scale: the observeddynamical processes separate into a slow process, present above T ~ Tg + 30K,and a fast process, which is found down to Tg at least. We present experimentalresults for several polymers and compare the data of polybutadiene to the modecoupling theory, the temperature, Q-, and frequency dependence of the dynamicstructure factor, being reminiscent of some theoretical predictions.

I 6pm:D3I THE GLASS TRANSmON OF HARD-SPHERE COLLOIDS

P.N. PUSEY' and W. VAN MEGEN?1 Physics Department, Edinburgh University, Mayfleld Road. Edinburgh,EH9 3JZ, UK 2 Department of Applied Physics, Royal MelbourneInstitute of Technology, Melbourne, Victoria 3000, Australia

Arguably a suspension in a liquid of spherical colloidal particles ofnearly equal size constitutes the simplest system to show a dynamicglass transition. With increasing concentration, such a suspensionforms dense fluid-like, crystalline and glassy (amorphous solid) Mates.The crystalline phases can be "melted" into metastable fluid states,which take minutes or hours to recrystallize, simply by shaking thesamples. By dynamic light scattering we have studied paniclediffusion in the metastable fluid and glassy states of suspensions ofcolloidal particles whose interaction Is close to that of hard spheres.The measured intermediate scattering functions show the classic glasstransition scenario of a- and ^-relaxations; they are In reasonableagreement with the predictions of mode-coupling theories of the hard-sphere atomic glass transition.

I 13

6pm: 04

UGHT SCATTERING STUDIES OF THE LIQUID-GLASS TRANSITION RANGE IN A POLYMERICLIQUID

LM. TORELL AND D.L SIDEBOTTOM.Department of Physics, Chalmers University ,S-412 96 Gothenburg, Sweden.

At present much attention is focussed on the liquid-glass transition which to some extent Isdue to recent progress of the mode coupling theories (MCT). Some of the specific MCTpredictions have recently been verified in real glasses, however, since the relaxationdynamics for glass formation spans the enormous time range of some 13 decades, a majorproblem of the tests is the iimeted ikne range normaiiy avaiiabie in experiments, in ihisstudy we present observations of the structural relaxation in glassforming poly(propyleneoxide) (PPO) obtained over the wide time range of 8 decades by using recently developedphoton correlation spectroscopy techniques, m addition of the primary (a) relaxation whichshows stretched exponential behavior, we observe two relaxation processes not witnessedbefore. They are assigned to a and p processes and exhibit similar power law decays. Wedemonstrate that with such a broad time window available, several of the relevantparameters used in MCT can be obtained directly from the experimental relaxation function.This allows for a severe test of the theory.

6ev:AlEUROPEAN RESEARCH AND DEVELOPMENT POLICY

FOR INFORMATION TECHNOLOGIES

G. METAKIDES

Directorate - General, Commission of the European Conmunities

Brussels, Belgium

14

-l--t —-I-—

7al:AlMETALS IN THE LIQUID-VAPOUR CRITICAL REGION

F.HENSRL

Fachbereich Fhysikalische Cheaie und Zentrua fur Katerialvissanschaften

der Philipps-Universitkt, D-3550 Marburg

Fluid netals are typical examples of materials whose electronic structures

depend strongly on the theraodynaaic state of the systea- The aost

striking manifestation of this state dependence is the metal-nonmetal

transition which occurs when the dense liquid evaporates to the dilute

vapour or when the fluid is expanded by heating to its liquid-vapour

critical point.

Experimental results for fluid metals in the critical region show that the

very existence of this transition noticeably influences the electronic,

thermodynaaic and kinetic features of the liquid-vapour phase transition

of fluid aetals.

7al:A2MAGNETOOPTICS OF STRONGLY CORRELATED 2D ELECTRONIC SYSTEMS

V.B.TIMOFEEV

Institute of Solid State Physics, USSR Academy of Sciences,142432, Chernogolovka, Moscow district, USSR

The behaviour of strongly correlated 2D electron system inAlGaAs/GaAs heterostructures subjected in transverse magneticfield in ultra quantum limit has been analyzed with the use ofluminescence spectra. In fractional QHE regime singularitiesin spectral position of luminescence line have downward cuspsat fractional filling factors. The strength of these cusps aredirectly related to corresponding Coulomb gaps in fractionalQHE. The values of these gaps and their dependence on magneticfield and disorder have been measured. In Wigner solid regimean additional line has been observed in the luminescencespectra. Intrinsic nature of this line has been proved and itsproperties are associated with formation of the pinned Wignersolid. The phase diagram of liquid-Wigner solid is discussed.

15

7a2:Al

THE POSITIVE MUON AS A MAGNETIC RESONANCE PROBEOF STRUCTURE AND DYNAMICS

S.F.J. CoxISIS Pulsed Muon Facility, Rutherford Appleton Lab, Chilton, Oxfordshire, UK.

Implanted in matter,- the positive muon provides an accurate microscopic magnetome-ter. Its resonance or precession frequencies measure internal magnetic or hyperfine fields;its relaxation functions characterise the distribution of these fields {e.g. in superconductorvortex systems) or their fluctuations {e.g. near magnetic phase transitions). These signalsare displayed with huge sensitivity via the asymmetry in the muon radioactive decay.

This remarkable spectroscopic probe has the additional feature that it mimics pro-ton behaviour. It can pick up an electron to form muonium, the light pseudo isotopeof hydrogen. Studies of muons in place of protons, or of muonium substituted for hy-drogen, have solved problems or upset established views in several areas of solid stateand chemical physics. In semiconductors, muonium serves to model hydrogen defect cen-tres, with unexpected results for electronic structure. From metals to insulators, strikingdemonstrations are obtained of the quantum mobility of light interstitial defects. Sig-nificant isotope effects are found in the one-electron properties (notably hyperfine andquadrupole interactions) of muonium substituted molecules. Muonium labelling of largemolecules looks particularly promising, in studi . ranging from soliton motion in polymersto reorientation dynamics in plastic phases.

7a2:A2UNIVERSAL BEHAVIOUR OF THE ELECTRONIC TRANSPORT

GERHARD DORDASiemens AG, Corporate Research and Development, Muncben, Germany

The characteristic aspects of the universal bebaviour of tbe electronic transpon in two dimensional systemsand thin films will be discussed. Tbe quantum character of the conductance with tbe reference eVh isobserved not only in tbe quantum Hall effect and on high quality samples with a 1-dimensional point contact,but also within thin amorphous Si layers. Tbe magnetoresistance of MOSFETs at low temperatures and highmagnetic fields becomes independent of the size of tbe specimen. Tbe resistance of small size trapezoidalMOSFETs snows anomalous behaviour. Tbe abnormally large one-electron trapping influence on tberesistance of sub-ji MOSFETs can also be seen with regard to these data. Furthermore tbe recently observedincrease of the conductance with tbe increasing sample length will be commented.All these unexpected findings can be interpreted by means of a general quantum transpon model /1A It isbased on a generalization of tbe Bohr quantum condition, resulting in tbe fundamental reference lengthae * 7.25 nm. This fundamental length yields the critical electron density 3x10" m1, which limits tbeelectric current. This critical density results in tbe quantum carrier density effect, supported by very newexperimental data.Further consequences of the quantum transport model will be demonstrated, in particular I) the formulationof tbe electromagnetic quantities in quantized manner; 2) tbe formulation of the square of tbe electroniccharge by e^oth as the only physically allowed relation; 3) tbe formulation of a new system of units basedon e^ah; 4) tbe simple description of 1/f noise on the basis of this new unit system.

IV G. Dorda, Superlattices and Microstructures 7,103 (1990)

16

7a2:A3VISIBLE LIGHT EMISSION FROM ELECTRO-OXIDIZED POROUS SILICON.

J.C. Vial, S. Biltat, A. Bsiesy, F. Gaspard, R. Herlno, M. Ugeon, I. MihalcescB, F. Muller,R. RomesUinLaboratoire de Spectromitrie Physique, Universit6 Joseph Fourier de Grenoble, B.P. 87 -38402St Martin d'Heres -France

Since the recent discovery of visible light emission from porous silicon a lot of work hasbeen done to better control the numerous parameters of porous silicon formation and furtherprocessing in order to optimize the structure to give a high quantum efficiency forluminescence. The main requirements are: a high porosity in order to produce sufficientconfinement energy to bring the optical transitions into the visible region and an enhancementof the quantum efficiency of luminescence which can originate either in an increase of theradiative recombination rate or in a reduction of the non-radiative processes by passivation ofsurfaces surrounding the confined zone. Quantum efficiencies as high as 3 % is measured atroom temperature. Decay times are surprisingly long. For confinement giving rise to emissionpeaking at 700 nm for example, a 70 (is decay time at room temperature increases by twoorders of magnitude when the temperature is lowered to 4K. Non-radiative recombinationrates show an interesting dependence on confinement energy: it increases more than oneorder of magnitude from the blue wing to the red wing of the luminescence spectrum. Itsexponential dependence with confinement energy allows us to conclude that the likelymechanism for the non radiative contribution is an escape of carriers from the confined zoneby tunneling through barriers which we believe consist of SiOa. Although it has beensuggested that confinement breaks the indirect gap selection rule, the long radiative lifetimewe measured do not favor this hypothesis.

I

I 7a2:A4| THE ORIGIN OF VISIBLE LUMINESCENCE FROM "POROUS SP

H.D. FUCHS, M.S. BRANDT, J. WEBER, M. STUTZMANN, and M. CARDONAMax-Planck-Institut fur Festkorperforschung, Heisenbergstr. 1, 7000 Stuttgart, Ger-many.

Porous Si, obtained by electrochemical etching of silicon wafers, exhibits strong visi-ble photoluminescence at room temperature. This luminescence has previously beenexplained by confinement of the carriers in quantum wires in the porous layers. Wehave studied the photoluminescence of anodically oxidized Si by cw and pulsed-laserexcitation. Raman and infrared transmission measurements provide evidence that theobserved visible luminescence is not an intrinsic property of crystalline Si in the material,but rather originates from the presence of Siloxene (SieOaHe) and its derivates which areformed in porous Si during the etch process.

I'v

7a2:A5

OPTICAL STUDIES ON SILICON 'QUANTUM WIRES'

E.F.Stelgmeler, B.Delley, and H.AudersetPaul Scherrer Institute. Badenerstr.569. CH-8048 Zurich

Samples of porous silicon 1 have been prepared and studied by Raman scat-tering, by spectral photolumlnescence (PL), and by photolumlnescence to-pography. We observe a PL maximum at about 1.7 eV, shifting to higher en-ergies for the finest samples, where also the highest PL Is found. Ramanscattering gives evidence for an effective direct bandgap In these materialsdue to zone folding, which represents a plausible reason for the high PL.The appearance of a PL at an energy exceeding the bulk bandgap has beenstudied theoretically by means of density functional calculations for a modelof spherical silicon quantum dots of up to 1000 atoms, surface saturatedwith hydrogen. The fundamental gap Is found to extrapolate for large clus-ters to the bulk gap. The calculated radiative transition matrix elements fortransitions to the valence band edge, however, leads to a maximum intensityat an energy substantially higher than the gap. with weak Intensities fornear gap transitions. This may represent a plausible explanation for the ob-served 1.7 eV transitions.

1. L.T.Canham. Appl.Phys Lett.57,1046 (1990); V.Lehmann and U.GOsele,Appl.Phys.Lett.58,856 (1991).

7a2:Bl

PARAEXCITONS AND SCREENING IN EXCITED QUANTUM WELLS

GERRIT E.W. BAUERPhilips Research Laboratories, 5600 JA Eindhoven, The Netherlands

The theory of the magnctoptical properties of highly excited quantum wells is reviewedwith emphasis on recent experimental work by a collaboration lead by theChernogolovka group. Realistic numerical calculations strongly support the interpre- •*tation of the experimental magnetoluminescencc spectra in terms of bound electron- '\hole pairs, which may be called paraexcitons to emphasize the lack of phase-coherence ^at the experimental plasma temperatures of =?40- 50K. Important screening effects :jbeyond the Hartree-Fock approximation exist even at magnetic fields of =; 107". At 1lower densities evidence for dynamical screening of the electron-hole interaction is •• .,found. i |

1. Butov L.V., Kulakovskii V.D., Bauer G.E.W., Forchcl A. and Griitzmacher D., ;to be published.

18

7a2:B2MANY-BODY EFFECTS IN 2D SEMICONDUCTORS STUDIED MAGNITOOPTICALLY

MPOTEMSK.IGrenoble High Magnetic Field LaboratoryMax Planck Institut fur Festkorperfonchung and Centre National de la Recherche ScientifiqueBP 166 Grenoble Cedex 9, 38042 Grenoble, France

Due to Coulomb interaction between charged particles the optical response of semiconductorsis modified in the presence of free carriers which can be either optically excited or of extrin-sic origin. Both systems have been studied with interband magnetooptics under well definedconditions achieved by working with thin layers and applying high magnetic fields. Theenergy structure of high density electron-hole gas and the prcncused Auger-type processes(leading to observation of energy up conversion in case of modulation-doped structures) arediscussed.

7a2:B3CORRELATED STATES OF DEGENERATE 2D ELECTRONS STUDIED BY

OPTICAL SPECTROSCOPY

AJ. Turbcrficld. R.A. Ford, I.N. Harris and I.F. RyanDepartment of Physics, Clarendon Laboratory, University of Oxford. Oxford OX1 3PU

C.T. Foxon, Physics Department, The University, Nottingham NG7 2RD

J J. Harris, Semiconductor Materials I.R.C Imperial College, London SW7 2BZ

Correlated states of degenerate 2D electrons induced by high magnetic fields,including the incompressible liquid states responsible for the fractional quantumHall effect and the electron solid, have been investigated using photoluminescencespectroscopy. This technique measures properties of the ground and excited stateswhich are not readily accessible to transport measurements. Photoluminescenceintensities reveal effects of electron correlation that are strongly dependent on thenature of the electronic ground state. Hierarchies of FQHE states are clearlyidentified. The polarisation of the luminescence has been measured, and the role of \spin will be discussed. The interaction between the 2D electron system and the jjphotoexcited hole, whether free or localised, in of fundamental importance in |determining the photoluminescence spectrum; we will present recent measurements Jwhich reveal distinct Fermi edge singularities at zero and finite, magnetic field. I

19

7a2:B4

TWO-DIMENSIONAL ELECTRON-CORRELATION IN HIGH MAGNETIC FIELDS

H. L. STORMERAT&T Bell Laboratories, Murray Hill, N.J. 07974 U.S.A.

Two-dimensional electron systems exposed to low temperatures and high magnetic fieldsexhibit a rich spectrum of novel electronic phases. The highly correlated liquids underlyingthe fractional quantum Hall effect dominate this region of phase space. Beyond the primitiveLaughlin liquids, experiments have unraveled a multitude of higher order fractions whoseorigin and mutual relationship remains uncertain. The existence of the electron spin has ledto the appearance of yet other electron liquids with novel properties. At the highest fieldsand lowest electron densities much circumstantial evidence points to the formation of a two-dimensional electron solid. This talk will review the recent developments in this field.

7a2:ClA STATISTICAL MECHANICS APPROACH TO COLLOIDAL SUSPENSIONS

Hartmut LOWEN, Sektion" Physik der Universitat Munchen, Theresienstr. 37.D-8000 MUnchen 2. Germany

Jean-Pierre HANSEN, Laboratoire de Physique, Ecole Normale Superieure deLyon, 46 allee d'ltalie, 69364 Lyon cedex 07, France

Despite the large differences in mass, length and time scales, suspensionsof spherical colloidal particles in a solvent share many features of simple,atomic liquids, including structure, phase behaviour and even the transitionto a glassy state at high concentrations. The analogies, but also the diffe-rences, will be illustrated by a few recent applications of the StatisticalMechanics formalism of simple liquids to sterically or charge-stabilized,concentrated colloidal suspensions. Examples include non-linear screening ofcharged colloids by counterions and sedimentation equilibrium.

20

7a2:C2

PHASES OF AMnflPHDLIC MONOLAYERS IN DIFFERENT ENVIRONMENTS

I.R.Petersonlast. f. phys. Chemie, Johannes Gutenberg-Universit&tJakob Welder-Weg 11, D6S00 Mainz FRG

Amphlphiles are organic molecules which spontaneously form two-dimensionalphases, particularly at pre-existing interfaces. This is the physical basis for cellmembranes and detergents, and is very important in colloidal systems. Recentlyavailable techniques have provided proof that monolayers of many amphiphilesdisplay a rich variety of phases1. Many of these phases display behaviourcharacteristic for low-dimensional (I.e. highly anlsotroplc) systems, and some arehexatic1'2. It has been found that the particular phase adopted by a monolayerdepends on its environment3-4. It is possible to talk about a bulk pressure withinthe monolayer, which is influenced by the interactions at the monolayer interfacesand which controls the molecular tilt.

1. R.M.Kenn et al., /. Phys. Chem. 95 (1991) 20922. A.M.Bibo, C.M.Knobler and I.R-Peterson, J. Phys. Chem. 95 (1991) SS913. R.Steitz, E.E.Mitchell and I.R.Peterson, Thin Solid Films 205 (1991) 1244. M.Engel et al., Ber. Bun.-Ges. Phys. Chem. 95 (1991) 1514

7a2:C3SMALL-ANGLE NEUTRON SCATTERING OF AQUEOUS SOLUTIONS OP2-BUTOXYETHANOL AND NON-IONIC SURFACTANTS

G. D'Arrigo*, R. Giordano* and J. Teixeira+

* University of Rome, Italy+ Lab.Leon Brillouin (CNRS/CEA) Saclay, France

Mixtures of water and 2-butoxyethanol (C4E1)show importantconcentration fluctuations. Above a narrow concentration-range there is evidence of micelle-like structures, which sizedepend on temperature and concentration.

When a non-ionic surfactant (CgE3> is added in differentamounts, the micelles are stabilized. Small angle neutronscattering experiments allowed the determination of thestructural characteristics of these aqueous solutions.

The main findings are that the stability of the micellaraggregates increase with the addition of C$E$ and with thereduction of temperature (down to 4°C). Beyond roomtemperature,pure concentration fluctuations can be identifiedwith correlation lengths increasing with the amount of CE

•"': 2 1

7a2:C4

PHASE EQUILIBRIUM IN LIQUID BINARY MIXTURESOF NON-ADDITIVE HARD SPHERES

G. PASTORE and M. ROVEREDipartimento di Fisica Teorica, Strada Costiera 11,1-34100 Trieste

The mixtures of hard spheres with positive non-additivity of the diameters <r,i.e. era = (<r« +<Tjj)/2 + A, A > 0, undergo phase separation at high density.Notwithstanding the simplicity of the interaction, they appear the naturalreference systems for studying liquid-liquid phase separation in realistic mix-tures. In spite of the interest, there has been very few simulation work onthese systems. We performed Monte Carlo simulation with the Gibbs en-semble technique, which allows a direct study of the coexisting phases. Westudied the trends in the phase behaviour of the system as function of thecontrolling parameters: concentration, density, non-additivity and asymme-try {(Ttt/tTu). Detailed analysis of the simulation data and the comparisonwith integral equation results are presented.

7a2:C5

KINETIC BEHAVIOUR OF A STRUCTURAL PHASE TRANSITION INLANGMUIR- BLODGETT MULTILAYERS STUDIED BY

ENERGY DISPERSIVE X-RAY REFLECTIVITY

U.P1ETSCH *, H.-J.MERLE+ and H.METZGER #

* FB Physik der Universitat Potsdam, D-O-1571 Potsdam, Germany+ Institut fur physikaLChemie der Universitat Mainz, D-W-6500 Mainz, Germany* Sektion Physik der Universitat Munchen, D-W-8000 Munchen 22, Germany

Using the Langmuir-Blodgett (LB) technique various multilayers of fatty acids containingCd-salts were prepared and heated up to about T = Tm- AT (Tm - melting point of LB-film)'. The scattering spectrum was recorded in several time intervals using an energy dis-persive x-ray set up. For AT = 1..5°C we observed an intensity reduction of the Bragg peakswhich correspond to the LB multilayer periodicity after about 45 min of elapsed time. In ad-dition new peaks appear. After about 2-3 hours the initial phase disappeared completely. Themeasured layer spacing of the new phase is larger than the monolayer thickness of a singleLB-film. We suggest the new phase to be interpreted as a two dimensional array of cylindri-cal structure elements as known from bulk material2. The detected phase transition can bethermally activated and is obviously kinetically restrained at lower temperatures.1. Merle H.J., Lvov Y.M. and Peterson I.R., Macromol.Chemie, Macromol.Symp. 46

(1991)2712. Spegt P.A. and Skonlious, Acta Cryst.16 (1963) 301

22

7a2:Dl

ANISOTROPIC HYBRIDIZATION AND MAGNETISM IN ACTINIDE INTERMETALLICS

V. SECHOVSK?, L. HAVELADepartment of Metal Physics, Charles University, Ke Karlovu 5,CS-121 16 Prague 2, Czechoslovakia

Magnetism based on 5 / electronic states in light actinide intermetallicsis closely connected with the underlying electronic structure of thevalence band. Different ground states reflect the varying hybridization ofthe 5 / states with electronic states of ligands. Some general tendenciesare revealed when inspecting behaviour of e.g. a large group of L'TX com-pounds, where filling of the d states of the transition metal T affectsthe 5f-d hybridization in a transparent way. Different types of magneticordering and the huge anisotropy of magnetic and other electronic prop-erties point to a hybridization-mediated anisotropic exchange mechanismbeing responsible for magnetic ordering. Despite the band character ofmagnetism, considerable orbital moments, created due to the strong spin-orbit interaction, form the major portion of uranium magnetic moments.These findings provide a convenient framework for the critical assessmentand systematization of a bulk of experimental results observed in thecourse of investigations of numerous inter metal lie compounds, which wetake as the main objective of this review contribution.

7a2:D2

MAGNETISM OF MONOCHALCOGENIDES AND -PNICTIDES OF THE ACTINIDES

K.Mattenberger and O.VogtLab. fur Festkorperphysik, ETHZ, CH-8093 Zurich, Switzerland

The monopnictides of both the lanthanides and the actinides(Ln, An)-N,P,As,Sb,Bi), as well as the monochalcogenides (Ln,An)-s,Se,Te) form with very few exceptions isostructuralseries of the NaCl type. The magnetic properties of the Lncompounds can be described by localised moments of the 4felectrons of the corresponding trivalent ions under theinfluence of the crystalline electric field and exchange

' forces with both isotropic and anisotropic contributions. Incontrast to the 4f electrons the 5f electrons are lesslocalised. Therefore, in the actinides hybridization effects

; have to be taken into account. Reshaping of the 5fn ions byhybridization always depresses their magnetic moments.Anisotropic exchange fields give rise to a further depression

: of the moments in the ordered state. U and Np compounds all; order either ferro-, ferri- or antiferromagnetically, as do

the pnictides of Pu. The moments in the Pu monochalcogenidesI are completely depressed. Am compounds have no local momentI (J-0 ion). Due to the increasing localization of the 5f shellI in the heavier actinides the behavior of the Cm and Cf| compounds is similar to their Ln analogues.

23

7a2:D3

MAGNETISM OF INTERFACES IN METALLIC MULTILAYERS

W. ZINN

Forschungssentrum Julich, IFF, Postfach 1913, W-5170 Julich, Germany

The interface properties in ferromagnetic multilayers are crucial for the understanding of

their oscillating interlayer exchange interactions and attributed giant magnetoresistance

effects observed in various Fe/M— and Co/M-multilayers / l / .

Recent studies by 57Pe-conversion electron mussuauer spectroscopy (CEMS) OH ultra-

thin Fe films and Fe/M interfaces in Fe/Cr-, Fe /Y- and Fe/Gd-multilayers using 57Fe

monolayers to probe the modifications of the Fe—Fe—interlayer exchange couplings and

the spin density oscillations at different distances of the Fe/M interfaces will be reviewed

1. See e.g. Grflnberg, P., Demokritov, S., Fuss, A., Vohl, M., and Wolf, J.A., J. Appl.

Phys. 69(1991) 4789 and the reviews in the Magnetic Multilayer Symposium at this

conference.

2. Landes, J., Saner, Ch., Dorrer, S. and Zinn, W., J. Magn. Mag. Mat. 1992 (in press).

7a2:D4

MAGNETOSTRICTION -150 YEARS FROM THE DISCOVERY

M.R.J.GIBBSSchool of Physics, University of Bath, Bath, BA2 7AY.

This paper will review the progress that has been made with magnctostrictive materials sincethe discovery of the Joule effect in 1842. Consideration will be given to hard magnetic materialssuch as Terfenol* (Tb-Dy-Fe), and soft magnetic materials such as metallic glasses. An insightwill also be given into the potential of magnetic multilayer structures in producing usefulmagnetostrictive responses. The discussion will centre round the factors which go towardsmaking materials with magnetostrictive responses which are useful in device applications, andwill highlight methods of materials design which can be employed. Present limitations will beoutlined, and features discussed which require further study.

24

7pm:AlFULLERENES AND FULLERITES: NEW FORMS OF CARBON

W. KRATSCHMERMax-Planck-Institut fur Kernphysik, P.O.Box 103980,

6900 Heidelberg, FRG

Fullerenes are large, round carbon molecules exhibiting closed

cage structures. The most prominent member of the family of

fullerenes is the soccer-ball shaped C „ molecule. DuringbO

laboratory experiments carried out to understand the

composition of interstellar dust, a simple method of fullerene

synthesis was discovered. This allowed the production of

fullerites, i.e. new forms of solid carbon consisting entirely

of fullerene molecules (predominantly C and c7 0) • The

present worldwide research on C -fullerite and related

substances- indicates that the future importace of fullerenes

in chemistry and material science may be substantial.

i

7pm:A2ISOLATION, SPECTROSCOPY, AND CHEMICAL REACTIONS OF FULLERENES

j ROGER TAYLOR: School of Chemistry and Molecular Sciences, University of Sussex,I Brighton, BN1 9QJ, Sussex, UK.

The chromatographic work that led to the isolation of the firstpure samples of C60 and C70 will be described, together with themost recent work on the HPLC separation of higher fullerenes.Structural features which account for the wide difference instability of different fullerenes will be identified.

An account will be given of some of the spectroscopic work bythe Sussex group on C60 and C?o, including C NMR, UV, IR, Raman,inelastic neutron scattering, and neutron diffraction spectra.This work provided both the definitive proof of the cage structureof the fullerenes, and also precise details of the crystal packingof Buckminsterfullerene.

Some general principles guiding the type and magnitude ofchemical reactions of C60, and the probable sites involved, willbe considered. In particular, our results taken along with those

: of others indicate the emergence of a reactivity pattern whereby: either 2, 3, 4, 6 or 12 of the high-order bonds of C60 appear to; be commonly involved in chemical reactions. Some reasons for this, will be suggested. It is hoped to report preliminary results on•' the chemical reactions of C70.

25

7pm: A3

ELECTRON SPECTROSCOPY OF FULLERENESSOME THEORETICAL ASPECTS

A. A. Lucas, G. Gensterblum, J.J. Pireaux, P.A. Thiry, R. Caudano, J.P.Vigneron and Ph. Lambin.Facultes Universitaires Notre-Dame de la Paix, 61 rue de Bruxelles, B-5000Namur, Belgium.

The paper will start with a short review of the elementary vibrational andelectronic excitations of CSO and other fuJletencs observed by severalspectroscopic techniques. The results obtained for C60 by High ResolutionElectron Energy Loss Spectroscopy will be particularly discussed in the light ofthe dielectric theory of EELS. The talk will then concentrate on theinterpretation of collective properties in terms of shell models of a one-or two-components plasma. The possibility of new observations of the collective modesby XPS core line spectroscopy of an andohedral atom in a fullerene cage will bediscussed.

7pm:A4A C COMPOUNDS; SUPERCONDUCTING AND NORMAL STATE PROPERTIES3 60

KAROLY HOLCZERU.P.S., Laboratoire de Physique des Solides, 91405 Orsay, Franceand Department of Physics, UCLA, Los Angeles, CA 9002*, USA

A short introduction of the solid C60 is followed by thediscussion of the solid state chemistry and structure of thesuperconducting homolog A3C60 series. The critical temperature,Tc of these materials decreases strongly under pressure implyingthat the chemical nature of the donor is of secondary importancein determining Tc, the primary parameter being the

i inter - molecular distance (bandwidth). Parameters of thesuperconducting state (coherence length and penetration depth)

i* evaluated from critical field, muon spin rotation and C NMR: measurements are consistent with an s-wave singlet pairing, and I

BCS - like description seems to describe their temperatureI. dependence reasonably. The normal state magnetic properties, 'iV susceptibility (as seen by ESR) and nuclear relaxation Ti, if •••

discussed in terms of conventional band theory, indicate slight %(5-8) mass enhancement of the electrons in a narrow band - a f

, simple consequence of the unusual low electron density in this jmaterials. At present several observations are in qualitative /•

C disagreement with this simplistic analyzes. )

26

7pm:Bl

Reactive events in molecule surface encounters

B. KASRNO

Chalmers tMiiversity of Technology

S-'»1296 G6tr>borg, Sweden

Molecule-surface encounters can result In elastic, inelastic and reactiveevents. Typical examples of the latter are molecule dissociation, stickingand catalytic reactions. With molecular beam scattering techniques onecan explore the nature of these events, the potential energy hypersurfaceson which they occur and so on. Examples of elementary studies concernactivation barriers for sticking and reactions, translational energydependence of the studied events. In .1 morp complex dom.iln the surfacecoverage dependance of the overall kinetics is studied.

In this talk these subjects are reviewed and given front reactive events onPt (H2 + 1 /2 O2 - • H2O, OH, CO + X-Pt(111) X = CO, O7, NO) and fromsurface chemJluminescence in the Cl?gM/Kmctal system.

7pm:B2

RECENT RESULTS IN THEORETICAL DESCRIPTIONS OF

ADSORPTION

B. LUNDQVIST

Chalmers University of Technology, Institute of Theoretical Physics,

Goteborg, Sweden

>Results are discussed and put into a perspective. \

I

27

7pm:B3

METALLIC ADSORB ATES AS APPROXIMATIONS TO REDUCEDDIMENSIONALITY ELECTRON SYSTEMS

C. Binns C. Norris and M-G. Barthes-Labrousse1

Department of Physics and Astronomy, University of Leicester, Leicester LEI 7RH, UK1 CNRS, Centre d"Etudes de Chimie Metallurgique, 94400 Vitry-sur-Seine, FRANCE

This paper presents some results of measurements using photoelectron spectroscopy ofmetallic layers grown as monolayers, bilayers, sandwich structures, ultra-small particlesand quasi-one-dimensional chains. Particular attention is paid to two aspects of novelelectronic behaviour, that is, the magnetic properties of 3d transition metals grown in someof the above structures and the stability of charge density waves in quasi-one-dimensionalchains of heavy polyvalent metals grown on single-crystal noble metal substrates.

7pm:B4

CHEMISORPTION OF METALS OR ELECTRONEGATIVE ATOMS ON GaAs

J. Ortega, F.J. Garcia-Vidal, R. Perez, R. Rincon and F. FloresDepartamento de Fi'sica de la Materia Condensada C-XII. Facultad de Ciencias. UniversidadAutonoma. E-28049 Madrid. Spain.

An ab-initio LCAO method is used to calculate the electronic properties of metals ( Li, Na,K and Al ) and electronegative atoms ( Cl and 0 ) chemisorbed on GaAs(llO). Results for amonolayer, half a monolayer and the isolated atom are presented. The adsorption geometry,the corresponding chemisorption energy, the local density of states and the transfer of chargeare obtained for each case. An important conclusion is that alkali atoms are initially bonded tothe Ga-atoms at the semiconductor surface, while 0 is bonded to the As-atoms. The Schottkybarrier formation is also discussed.

28

7pm:ClOPTICAL PROPERTIES OF MESOSCOPIC Si-Ge STRUCTURES

H.JarosPhysics Department, The University, Newcastle upon Tyne, U.K.

Si-Ge heterostructures are new materials in which the effects ofstrain and differences in the atomic potentials of Si and Ge maybe tailored so that they combine to produce a system with a quasi-direct band gap [1]. Strong optical properties can be engineeredto cover the technologically interesting ranges of wavelengths,i.e. 1-2 and 10-15 micrometers [2]. However, practical applicationsrest on the designer's ability to understand and control therecombination process in question. In particular, a number of newphenomena have recently come to light which point to the importancein this process of interface quality and defect and alloyformation, i.e. the effects that reflect the finite character ofthe system and that have so far been ignored in the literature.

[1] H.Jaros, Semiconductors and Semimetals 32, 175 (1990)[2] R.J.Turton and M.Jaros, Appl. Phys. Lett. 56, 767 (1990)

7pm:C2

MODULATION DOPING IN THE Si/SiGe HETEROSYSTEM

F. SCHAFFLERDaimler-Benz Research Center, Wilhelm-Runge-Str.ll, D-7900 Ulm, Germany

Proper exploitation of the strain-dependent band alignment in the lattice mismatchedSi/SiGe heterosystem allows the realization of enhanced electron and hole mobilities bymeans of modulation doping (MOD). Since a finite conduction band offset is only achieved,if the Si channel is put under tensile in-plane strain, a partly or completely strain-relaxedSiGe buffer layer is required as a virtual substrate for n-type structures. In the presentcontribution an overview of modulation doped Si/SiGe heterostructures grown by molecularbeam epitaxy is given, with special emphasis being put on n-type modulation dopedquantum well (MODQW) structures. Main aspects are the growth and characterization ofthe strain-adjusting SiGe buffer layer, the mechanisms of strain relaxation by the nucleationof misfit dislocations, and the recent break-through achieved by introducing a Ge grading *into these buffers. Electrical and optical characterizations of high quality samples with low- 'temperature electron mobilities of up to 170000 c m W s are reviewed. These includemeasurements in the quantum Hall regime and intersubband absorption measurements in the ifar infrared frequency range. Recent experimental data of modulation doped field-effecttransistors (MODFETs) with enhanced transconductance values are presented todemonstrate the device relevance of Si/SiGe MODQW structures.

29

7pm:C3SILICON HETEROSTRUCTURES AND NMJOSTRUCTURES

T.P. SMITHIBM T.J. Watson Res. Center, P.O.B. 218, Yorktown Heights, NY 10598, USA.

Hie last decade has witnessed tremendous progress in nanostructure fab-rication and mesoscopic physics. At the sane time, major breakthroughs haveoccurred in growth and fabrication of silicon-based heterostructures. Wewill highlight some of the developments that have enabled this progress. Wewill give an overview of the state of the art in silicon epitaxy and thenovel materials that have emerged as a result. We will then address appli-cations of these materials. We will discuss recent work on SiGe MOS de-vices, resonant tunneling diodes, and infrared detectors as well as novelSiC heterostructures. Finally we will present results on silicon-basednanostructures. We have begun to fabricate nanometer-scale structures usingSiGe and related Si alloys. Ihe ability to exploit the extraordinary prop-erties of Si and SiO2 should yield intriguing new mesoscopic physics.

This work was done in collaboration with U. Gennser, V. Kesan,A. Zaslavsky, K. Eberl, S.S. Iyer, D. Syph s, D. Kern, K. Chang, Y.H.Lee,D. Grutzmacher,and T. Sedgwick. It was supported in part by the UnitedStates Office of Naval Research.

7pm:C4

VALENCE-BAND OFFSET AT Si/Ge INTERFACES: THE ROLE OF THESTRAIN

L. Colombo

Dipartimento di Fisica, Universita di Milano, via Celoria 16,1-20133 Milano, Italy

In the framework of a linear-response theory, we present a study of the valence band-

oiTset problem (VBO) at Si/Ge interfaces: we explicitly take into account the role of

the strain which is induced by the lattice mismatch between the two semiconductors. ••;

We find out that the VBO is a bulk property, depending only upon the macroscopic >:

strain present in the two materials far from the interface. In particular, it turns out to be ,".

independent of any interface feature: abruptness, interface strain or buckling. Moreover, ^

the strain variations affect only weakly the VBO, while simple band-structure effects i

are responsible for a rather large strain-induced tunability of the offset between the |

topmost valence states.

30

7pm:Dl

VORTEX PINNING. FLUX CREEP AND ANISOTROPY IN YBCO AND RE-LATED COMPOUNDS

L.FRUOHTER. B.JANOSSY AND I.A.CAMPBELLPhysique des Solides. Universite Paris Sud. 91405 Orsay, France

We report on the anisotropy of the critical current in bulk single crystal YBCO. Thefully oxidized undoped material behaves essentially as a 3D anisotropie material whileoxygen deficient samples show an increased 2D character. In this case we observethe disappearance of the angular resolved contribution of the twin planes to pinningand an extended scaling of the iritical current with the transverse component of themagnetic field. Doping with Fe dramatically aiters the anisotropy of the material.The dynamics of depinning i» also found to be anisotropic.

7pm:D2

FLUX CREEP, CRITICAL CURRENTS AND LOW CRITICAL FIELDS OF 123 AND2211 S1NCLE CRYSTALS

V.V.MOSHCHALKOVLaboratorium voor Vaste Stof-Fysika en Magnctisme, Katholieke Universiteit Leuven,Celestijnenlaan 200 D, B-3001 Leiiven, Belgium andLaboratory of High Tc Superconductivity, Moscow State University, Moscow GSP-119S99,USSR-Temperature dependences of the lower critical field Hcj(T) are studied in YBaaCuaOxsingle crystals, as a function of the oxygen content X. The modified Bean model, takinginto account the reversible contibution from the Abrikosov vortex lattice, has been usedto derive the relation dM ~ |JJ«- JLi)2 befweej) the magnetization deviation dAJ from theM vs Ho linearity and the applied field Ho, wich makes it possible to determine the lowercritical field values by the extrapolation dM l " •-• 0. For Ha |j c, HC,(T) demonstrates analmost linear T behaviour, without a usual low temperature saturation, whereas for Ha ||ab, Hci(T) exhibits an ordinary behaviour. The anisotropy of the lower critical fields andcritical currents j , . increases a.s the oxygen content X decreases and the coupling betweenthe CuOj planes becomes weaker. In BiiSraCaCujOg single crystals an abrupt growthof the pinning potential, found from the flux creep measurements, has been observedat T = 18K.indicating the onset of the collective pinning at high temperatures. Thecritical current is strongly enhanced after the irradiation with the relativistic Ar+ ions. ',The analysis of the flux creep, field and temperature dependences of j c in the as grown j{and irradiated 2212 single crystals has revealed the existence of the two different pinning '?regimes: (I) low temperature intrinsic and (2) high temperature collective pinning by sextrinsic, delects, which are still efficient even in the case when their size is considerably 1larger than the coherence length. *

This work is supported by the High Temperature Superconductivity Impuls and Concerted i)Action Programs, financed by the Belgian Slate.

31

7pm:D3

LINEAR AC RESPONSE OF HIGH-2b SUPERCONDUCTORS A N DTHE IRREVERSIBILITY LINE

E. H. BRANDTMax-Planck Institut fur Metallforschung, Institut fur Physik, 7000 Stuttgart 80

The response of a type-II superconductor containing pinned flux lines to an alternatingmagnetic field Bac is typically non-linear since the current-voltage curve and the irrever-sible magnetization curve are highly nonlinear. The ac-response becomes linear if Bac isvery small (elastic pinning), or the frequency is high (rf or microwaves), or if in high-Tc

superconductors (HTSC) the dc-field B and temperature T arc sufficiently high such thatlinear flux creep (thermally assisted flux flow, TAFF) occurs. General expressions for thecomplex ac-penetratiou depth, surface impedance, and ac-resistivity of HTSC are derivedwhich account for elastic pinning, viscous drag (usual flux flow), and linear creep of fluxlines, and for the correct boundary conditions (image flux-lines) for B at arbitrary anglewith respect to a planar surface. Application to vibrating HTSC is discussed.Numerous experiments define an irreversibility line or depinuing line as the locus in theB, T-plane where the HTSC passes from nonlinear via linear creep to flux flow with com-plete depinning, or as a curve along which the ac-resistivity or flux diffusivity equals aconstant which depends on specimen she, frequency, and sensitivity of the experiment.

7pm:D4

FLUX MOTION BY QUANTUM TUNNELING

A.C. Mota*, G. Juri*. P. Visani*. A. Pollini*. T. Teruzzi*, K. Aupke*, and B. Hilti+

* Laboratorium fur Festkorperphysik, ETH Honggerberg, CH-8093 Zurich, SwitzerlandCiba-Geigy AG, CH-4002 Basel, Switzerland+

At low temperatures, large, temperature independent magnetic relaxation effects are found inthe high-temperature superconducting ceramics and also in the organic superconductors givingevidence that, at these temperatures, vortex motion involves mainly a form of macroscopicquantum tunneling. At higher temperatures, the tunneling is thermally assisted. The measuredtunneling rates at T = 6 mK and low magnetic induction are in excellent agreement with theT -> 0 values given for single vortex tunneling by the quantum collective creep theory ofBlatter, Geshkenbein, and Vinokur. The effects of anisotropy and layering in the tunnelingrates of single crystals are in very good agreement with the aforementioned theory.

32

8al:Al

NEUTRON SCATTERING INVESTIGATION OF THE SPIN DYNAMICS IN THE HIGHTc SUPERCONDUCTING SYSTEM YBa2Cu3O6fx

J. ROSSAT-MIGNODU, L.P. REGNAULTl, P. BOURGES2, C. VETTIER3,P. BURLETl, J.Y. HENRY1

tCentre d*Etudes Nucleates de Grenoble, DRFMC/SPSMS/MDN, 8SX, 38041 GrenobleCedex, France2Labotatoire Leon Brillouin, CE-Saclay, 91191 Gif-sur-Yvette Cedex, FranceEuropean Synchrotron Research Facility, BP 220,38043 Grenoble Cedex, France

We shall report on inelastic neutron scattering experiments carried out on single crystals of theYBa2Cu3O6+x system, both in the weakly and the heavily doped metallic states which exhibit asuperconducting ground state below Tc = 40 K and Tc = 60 K or 90 K, respectively. Thehole doping suppresses the AF-order but dynamical AF-correlations remain in the metallic statewhich, surprisingly, involves only in-plane spin components. An energy gap has been found inthe spin excitation spectrum for any superconducting samples, however it becomes weakerclose to the I-M transition. A quite unusual T-dependence of the spin excitation spectra wasfound, but at room temperature they exhibit the same energy scale (To = 30 me V).

8al:A2

MAGNETIC EXCITATIONS IN THE HIGH-TC SUPERCONDUCTING SYSTEMS

S. M. Havdenl. G. Aeppli2, R c . Canfield3, S.-W. Cheong2, K. N. Clausen4, Z. Fisk3,M. F. Hundley3, T. E. Mason4, J. L. Martinez*, H. A. Mook6 and D. Rytz']H. H. Wills Physics Laboratory, University of Bristol, Bristol, UK.2AT&T Bells Laboratories, Murray Hill, NJ 07974, USA.3Los Alamos National Laboratory, Los Alamos, MN 87545, USA.4Ris0 National Laboratory, Roslrilde DK-4000, Denmark.5Institute Laue-Langevin, 38042 Grenoble, France.6Oak Ridge National Laboratory, Oak Ridge TN 37831, USA.7Sandoz Optoelectronics, Bau 88, CH-4002, Basel, Switzerland.

Recent neutron scattering measurements of the spectrum Km(^,0)))|2 for the spin fluctuations in

La2-x(Ba,Sr)xCuO4 are reviewed. In particular, I will discuss the strongly temperature-

dependent magnetic relaxation rate observed in Lai.95Bao.osCu04 which is reminiscent of a

'marginal Fermi liquid'. Also, the dynamics of the more heavily-doped cuprates

Lai.925Sro.o7sCu04 and Lai.86Srn.i4CuO4 in which the modulation vectors of the

incommensurate magnetic fluctuations have recently been determined.

33

8al:A3

LAYER BY LAYER DEPOSITED OXIDE COMPOUNDS-INVESTIGATION OFARTIFICIAL HTC SUPERLATHCES.

0 . FISCHER, J.-M. TRISCONE, L. ANTOGNAZZA, O. BRUNNFR andL. MIEVILLED€partement de Physique de la Matiere Condensed, University de GeneveQuai E. Ansermet 24,1211 Geneve 4, Switzerland.

The high temperature superconductors have all a layered structure with C11O2 planes as

the common feature. This quasi two dimensional structure reflect itself in the physicalproperties of these materials which in some respects differ considerably from theconventional superconductors. The fact that these compounds can be thonght of asstacks of metal or metal oxide planes suggested that it would be possible to growsuperlattices of them and thus modify artificially the stacking in order to change theproperties in a controlled manner. Using thin film deposition techniques such structureshave been grown and it has been found that it is possible to control the thickness of theindividual layers down to one unit cell. In particular YBa2Cii3O7/PrBa2C»3O7(YBCO/PrBCO) superlattices have been used to study how (he superconductingproperties change when going from ultrathin YBCO films, containing only a doubleG1O2 plane, to bulk, 3D anisotropic, YBCO.

8al:Bl

QUANTUM CONFINEMENT IN H-VIHETEROSTRUCTURES: EXCITONIC LASERSAT BLUE-GREEN WAVELENGTHS

ARTO V. NURMIKKOBrown University, Providence RI 02912, USAMajor recent developments in wide bandgap II-VI heterostructures have culminated in thedemonstration of the blue-green diode laser [1], [2]. These devices are based on pn-heterojunctions where the (Zn,Cd)Se/ZnSe quantum well (QW) and, most recently, the(Zn,Cd)Se/Zn(S,Se) QW [3] form the optical gain medium. The (Zn,Cd)Se/ZnSe QWdisplays strong excitonic effects beyond room temperature in absorption [4]. The quasi-2Dexciton gas is surprisingly stable against the normally very efficient dissociation by opticalphonon absorption (Frohlich interaction) as the confinement induced increase in the ;;binding energy now leads to the situation Ex > huu,. The role of excitons in also providing •*?gain in optically pumped quantum well lasers have been established up to room .«temperature [5]. The gain mechanism, based on the concept of partial phase-space filling, 5appears to remain a useful factor also in the new diode lasers as well as blue LEDs which .1have been fabricated in different geometries. -•"I

[1] M. Haase et al, Appl. Phys. Letters 59, 1272 (1991) ;

[2] H. Jeon et al, Appl. Phys. Letters 59, 3619 (1991)[3] H. Jeon et al, Appl. Phys. Letters (in press)[4] N. Pelekanos et al, Phys. Rev. B (in press)[5] J. Ding et al, MSS-V, Nara, Japan (1991) and Phys. Rev. B (in press)

34

8al:B2

METALORGANIC VAPOUR PHASE EPITAXY (MOVPE) OFIH/V-SEMICONDUCTOR HETEROSTRUCTURES USING

ALTERNATIVE PRECURSOR MOLECULES: NEW DEVELOPMENTS

W. STOLZWiss. Zentrum fur Materialwissenschaften (WZMW) und Fachbereich Physik, Philipps-Universitat, D-3550 Marburg, Fed. Rep. Germany

The standardly used source molecules in the metalorganic vapour phase epitaxy(MOVPE) of IH/V-semiconductor heterostructures (trialkyl-III-compounds and V-hydrides) have severe drawbacks. The trialkyl-III-compounds are pyrophoric and the V-hydrides are highly toxic substances. These properties lead to problems of the MOVPEprocess with respect to safety concerns as well as crystal purity (incorporation of O andC especially for Al-containing epitaxial layers). In this work, we describe newdevelopments of the interdisciplinary research for alternative precursor molecules. Theprinciple ways for changing the molecular structure of alternative III- as well as V-compounds are discussed in order to overcome the above mentioned problems.MOVPE growth experiments are reported for heterostructures in the GaAs/(AIGa)Asmaterial system. The applicability of the alternative precursors is established by studyingthe structural, electrical and optical properties of GaAs, (AlGa)As bulk layers as well asof single und multi quantum well heterostructures by high-resolution X-ray diffraction,temperature-dependent Hall as well as photoluminescence investigations.

35

2

8al:B3

INTERNALLY DETECTED ELECTRON PHOTOEXCITATION SPECTROSCOPY onHETEROSTRUCTURES

C. ColuzzaIPA-Departement de Physique, PHB-Ecublens, 1015 Lausanne, Switzerland

We applied an extension of the Internal Photoemission (IPE) to the direct observation ofdeep levels and band discontinuities at different semiconductor heterostructure interfaces. Itsperformance and capabilities are superior to those of established techniques: the energyresolution is excellent and it can be applied to "real" devices interfaces under bias. The methodconsists in analyzing the Internally Detected Photoexcitation (IDEPS), not limited to the regionof internal photoemission threshold, but over an extended energy range. The technique wassuccessfully tested for Schottky barriers (Pd/n-GaAs, Ni-Au-Ge/n-GaAs, or Pd/a-Si:H) and forheterojunctions (a-Ge/n-GaAs, or a-Ge/n-GaAs). We found, for Pd/n-GaAs Schottkyheterostructure, a barrier height of 0.78 eV, regardless of the measurement configuration. Acontribution at 1.09 eV, probably due to Pd induced interfacial states, was measured. Westudied also how a bombardment by hydrogen ions of this Schottky barrier modifies thescenario of the interfacial states. In the case of Ni-Au-Ge/n-GaAs Schottky heterostructure westudied the barrier height and the density of interfacial states versus surface treatments andtemperature post-annealing, demonstrating that the ohmic contact formation is not stronglyrelated to the presence of interfacial localized states. The presence of these defect states seemsnot to be correlated with The barrier height ($5) in our Pd/n-GaAs and bands discontinuities in

our a-Ge/n-GaAs heterostructures was fixed by the presence of a state near 0.78 eV from theGaAs conduction band. For the heterojunctions measured we obtained bands discontinuityvalues in good agreements with previously reported data. Finally, in the Pd/a-Si:H Schottkybarrier, we demonstrated the contribution of Resonant Tunneling through localized states of theconduction band.

36

8al:ClNEW PHYSICS IN STRUCTURAL PHASE TRANSITIONS IN SILICATE

FRAMEWORK MINERALS

Volker HeineCavendish Laboratory, Madingley Road, Cambridge CB3 OHE, UK

Quartz, feldspars and other silicates in rocks have many structural phase transitions, bothdisplacive and atomic ordering. Their structures are built up of rather rigid tetrahedral andoctahedral units, joined into a framework by shared oxygen atoms at the comers.

Rigid Unit Modes (RUM's) are special phonons where the tetrahedra/ octahedra rotate andmove while remaining rigid. RUM's give soft mode phase transitions, directional short rangecorrelations, negative Gruneisen constant etc.

Ordering is often driven by atomic size or atomic motion which can result in long range strainfields. These influence profoundly the course of the ordering process, the rate of ordering andany metastable texture.

8al:C2PERSISTENT SPECTRAL HOLES PROBING COMPLEX CRYSTALLINE DEFECT STRUCTURESAND AMORPHOUS SYSTEMS

R. BAUER, T. ATTENBERGER. I. SILDOS*. G. JONES" AND U. BOGNER

Institute of Physics III, University of Regensburg, 8400 Regensburg, Germany;'Institute of Physics, Estonian Academy of Sciences, Tartu, Estonia;"Department of Physics, University of Canterbury, Christchurch, New Zealand.

With the technique of pe.sistent spectral hole-burning in the electronic transitions of impurities westudied low-temperature dynamics, electric-field effects and pressure effects in complex crystallinedefect structures and amorphous systems. We used organic systems like periyene molecules inShpol'skii matrices' and anorganic systems, in particular SrFa:Pr":D and neutron-irradiatedsapphire2'3. Concerning strongly disordered systems we investigated perytene embedded indifferent amorphous matrices such as polymers and the amorphous regions of Langmuir-Blodgettfilms. The system peryten/n-heptane turned out to be an ideal model system providing informationabout the physical nature of the asymmetric double-well potentials (ADWP) which are characteristicfor all disordered systems. The results of thermally induced hole refilling are explained by the photo-physical model4 based on matrix-shift variations by phonon-induced crossing of the barriers of theADWP. In addition we demonstrate that perylene/n-heptane is also an ideal model system for theelucidation of the electric-ffekMnduced level shifts1 and its physical origin.

1. Attenberger T. et al., Chem. Phys. Lett 180 (1991) 207.2. Aizengendfer M. et al., Chem. Phys. Lett. 183 (1991) 245.3. Attenberger T. et al., Radiation Effects and Defects in Solids 119 (1991) 325.4. Bogner U., Phys. Rev. Lett. 37 (1976) 909; Bogner U. et al.. Phys. Rev. B24 (1981) 2846.

37

8al:C3PROTON DYNAMICS IN A 2D - "SINGLE-CRYSTAL" OF BACTERIORHODOPSIN

R.E.LECHNER*, N.A.DENCHER*, J.FITTER+ and G.BULDT+

*Hahn-Meitner-Institut, Glienicker Strasse 100, D-1000 Berlin39Freie Universitat, FB Physik, Arnimallee 14, D-1000 Berlin 33

The protein bacteriorhodopsin (BR) is used by Halobacteriumhalobium for the conversion of sun-light to create an electro-chemical proton gradient as an internal energy source ("protonpump"). Trimers of BR form well-ordered two-dimensional hexago-nal lattices in the natural purple membrane (PM). Stacks of thelatter are thus excellent candidates for investigations, whichaim at elucidating relations between protein structure, dynamicsand function . In quasielastic incoherent neutron scatteringexperiments on PM-multilayer stacks under dark conditions wehave obtained results on the proton mobility as a function ofspecimen orientation, temperature and hydration. Our analysisby comparison with model calculations concerns the proton mo-tion parallel and perpendicular to the membrane plane. Parallelto the latter we observe fast diffusion of protons as a func-tion of the number of hydration layers between PM-layers. Light-activated proton transport across BR is expected mainly in theperpendicular direction. In the near future we will study thisin BR under illumination. The present results are of fundamen-tal interest in the fields of ionic transport properties, struc-tural hydration and hydrogen bonding.l.Koch M.H.J., Dencher N.A., et al., EMBO J. 10(1991)521-526.

8al:C4CONDUCTIVITY AND PHOTOCONDUCTIVITY OF CONDUCTING POLYMERS

S. Roth, M. Kaiser, J. Reichenbach

Max-Planck-Institut fur Festkorperforschung, Heisenbergstr. 1, D-7000 Stuttgart 80, FRG

A review will be presented of the present state of the art of conducting polymers. Special atten-

tion will be given to the high electrical conductivity of highly ordered doped polyacetylene, on *•<

the attempts to reproduce a-values above lOr S/cm, and on results of an effort to correlate the .?

electrical conductivity with other physical parameters (European BRITE/EURAM Project -i

HICOPOL). |

i

38

8a2:AlMESOSCOPIC JOSEPHSON JUNCTION

C. W. J. BEENAKKER

Instituut-Lorentz, University of Leiden,P.O. Box 9506, 2300 RA Leiden, The Netherlands

Nanostructures combining semiconducting and superconducting elements form a new classof systems in which to search for mesoscopic phenomena. The correspondencies betweentransport of normal electrons and transport of Bogoliubov quasipartides serves as a use-ful guide in the search. In this lecture we will present three mesoscopic phenomena inJosephson junctions, and the analogies with their counterparts in the normal state:

1. Discretization of the critical current of a superconducting quantum point contact.

2. Resonant Josephson current through a superconducting quantum dot.

3. Universal critical-current fluctuations in disordered Josephson junctions.

Each of the three phenomena provides a measurement of the supercurrent unit eAo/h,which plays the role of the conductance quantum e2/h in the normal state (Ao beingthe superconducting energy gap). Observation of these effects remains an experimentalchallenge.

The research reported was done in a collaboration with H. van Houten.

8a2:A2

INTERATOMIC FORCES AND ATOMIC MOTION AT SURFACES

H. I BACHForschungszentrum Jiilich, IGV, D-5170 Jiiiich, Germany

The development of surface sensitive vibration spectroscopies enabled thefingerprinting of chemical bonds and hence the analysis of chemical reac-tions and surface intermediate species under well controlled conditions.More recently, techniques of He and e~-scattering were developed to inves-tigate the dispersion of surface phonons on clean and adsorbate coveredsurfaces. Particular interest is in phonon anomalies arising from electron-ic and structural instabilities of surfaces and surface stress. Adsorbateinduced surface stress was identified as the driving force for some surfacereconstructions. Quite generally vibrational modes at surfaces are more an-harmonic than bulk modes. For adsorbed H-atoms aspects of quantum motionmust be considered in the interpretation of the spectra. Nonperiodic atomicmotion will also be discussed, as it is involved in diffusion, oscillatoricsurface reactions and equilibrium fluctuations of surface structures. Aparticular example are the rapid fluctuations of the position of monoatomicsteps on the surfaces caused by kink creation anJ annihilation and the wan-dering of kinks due to the ID-evaporation of adatoros from kinks.

39

8pm:Al

OPTICAL PROPERTIES OF QUANTUM WIRES AND DOTS

S. BEAUMONT

Dept. of E&EE Eng., Glasgow University, U.K.

8pm:A2

QUASI-ONE-DIMENSIONAL TRANSPORT INSEMICONDUCTOR MICROSTRUCTURES

MJ Kelly,Cavendish Laboratory, Madingley Road, Cambridge CB3 OHE, UK.

andGEC-Marconi Led, Hirst Research Centre, East Lane, Wembley, HA9 7PP, UK.

I describe some of the physics peculiar to electron transport in quasi-one-dimensionalsystems in semiconductors, with particular reference to three systems in which it has beeninvestigated: ultra-fine free-standing wires of doped GaAs, the split-gatehigh-electron-mobility-transistor (with and without a back-gate to vary the carrierconcentration), and vertical quantum pillars fabricated from multiple-barrierheterostructure material. They are all electron waveguide structures, characterised by<.0.1ian feature sizes in two of the three spatial dimensions, and they all exhibit phenomenaquite different from those seen in macroscopic semiconductor structures, I try to identifythe subset of this physics that may be exploitable, and comment on the more generalrelevance of this new physics to devices.

Collaborators: A Potts, R J Brown, A Hamilton, M Tewordt.

40

8pm:A3

LINEAR AND NONLINEAR OPTICAL PROPERTIES OF GaAs QUANTUM WIRES -CENTER-OF-MASS, EXCITONIC AND ELECTRON-HOLE PLASMA QUANTIZATION

H. LAGE \ D. HEITMANN 1, R. CINGOLANI 2

1 Max-Planck-Institut fur Festkorperforschung, W-7000 Stuttgart 80, Germany.2 Dipart. di Science dei Materiali, Universita di Lecce, Via per Arnesano, 73100 Lecce, Italy

We have studied wide quantum well wire structures with various spectroscopic tools.The effects originating from lateral quantization are found to be strongly dependentboth on the states under investigation and on the optically excited carrier density.While conventional photoluminescence excitation spectroscopy reveals the quantizationof the excitonic center-of-mass motion, two-photon absorption spectra indicate thathigher excitonic states are completely quantized by the lateral confinement. The energypositions of the observed transitions are then found to be in good agreement with 1D-subband calculations. Additionally, transitions between one-dimensional subbands canbe found under high excitation conditions. The singularity of the ID-density of statesis reflected by distinct peaks in time resolved luminescence spectra of a dense electron-hole plasma, which is optically excited by high-power laser pulses.

8pm:BlTHE PHYSICS OF HEAVY FERMIONS WITH A HYBRIDIZATION GAP

*F.MARABELLI, tRWACHTER* Dipartimento di Fisica A.Volta, Universita degli Studi di Pavia, 27100 Pavia, Italyf Laboratorium fur Festkorperphysik, ETH Zurich, 8093 Zurich, Switzerland

Optical measurements in the far infrared performed at low temperature on heavyfermion compounds have given surprizing results and important information aboutthe electronic structure, complementary to the one obtained by the other techniques(e.g. specific heat, magnetization). •

The existence of a narrow gap a few meV below (above) the Fermi level has been 'observed as a common features of heavy fermions, together with the evidence of a ;

_ coherent hybridization of / - and conduction- electrons. \I

The implications of the hybridization gap on other physical properties such as the |temperature dependence of the resistivity, the specific heat and susceptibility will be !discussed. ';

Low plasma frequencies, due to heavy effective masses, have been measured. The effect ,of alloying has also been studied and discussed.

41

8pm: B2

PERTURBATIONAL TREATMENT OF HEAVY FERMIONS IN HIGH DIMENSIONS

G.CZYCHOLL, H.SCHWEITZERInstltot fitr Theoretische Physik, Unlversitat Bremen, D-2800 Bremen 33, Germany

Heavy fermion systems are described by the periodic Anderson model, which isstudied within the selfconsistent second order U-perturbatlon treatment. Thisapproach, within which explicit calculations are possible In the limit of a largespatial dimension d for correlated lattice electrons, properly fulfills the Luttingersum rules. In the limit d-»<» the selfenergy is k-independent, i.e. the localapproximation becomes correct; consistently, for transport quantities the vertexcorrections vanish. We have calculated the temperature dependence of actual,measurable physical quantities like the specific heat, the static magneticsusceptibility, the resistivity and the thennopower and found that an excellentqualitaive reproduction of the typical experimental results is possible by simplyusing the d=<» result for d=3. We also shortly discuss extensions of our approachgoing beyond the U2-treatment by means of partial resummatlons and Includingl/d-correctk>ns. Finally we discuss possible simplifications, which arise in thelimit d->oo in perturbation treatments around the opposite atomic limit, i.e. in ahybridization (V—) perturbation treatment (lattice version of the "non-crossingapproximation", etc.).

8pm :B3HOLE DYNAMICS IN QUANTUM ANTIFERROMAGNETS: CONSEQUENCES FOR PHOTOEMIS-SION AND OPTICAL CONDUCTIVITY.

PETER HORSCH+ and WALTER STEPHAN*+Max-Planck-Institut fur Festkorperforschung, 7000 Stuttgart 80, Germany,•King's College London, Strand, London WC2R 2LS, U.K.

Recent analytical and numerical results for the single-particle spectral function and optical conducti-vity of the two-dimensional Hubbard and t-J models are reviewed. A single hole may be described asspinless (slave) fermion coupled to spin waves, i.e. forming an antiferromagnetic spin-polaron. Its spec-tral function can be calculated with selfconsistent Green's function techniques in good agreement withexact diagonalization. The moderate doping case is more difficult, since the spin-correlations are stronglyinfluenced due to the presence of the carriers. Already for two holes in systems of 16 to 20 sites (> 10%doping) a large electronic Fermi surface, compatible with Luttinger's theorem, is observed1. From thesingle hole problem one would expect instead a Fermi surface consisting of hole pockets centered around(±x/2, ±jr/2). The full-single particle Green's function is examined and is shown to exhibit quasiparticle-like behavior, with a dispersion consistent with the noninteracting limit, yet a band width scaling withJ (for 3 < t)\ The optical conductivity of the Hubbard and t-J models is shown to have many featuresin common with recent experiments on copper- oxide superconductors. Finally the importance of 3-siteterms for optical and transport properties is discussed. Such terms arise in the derivation of the t-J modelfrom the Hubbard model in the strong coupling limit but are usually neglected.1. Stephan W. and Horsch P., Phys. Rev. Lett. 66, 2258 (1991).

42

8pm:B4

TRANSPORT MEASUREMENTS OF HEAVY FERMIONSUPERCONDUCTORS

D. JACCARD, K BEHNIA, J. SIERRODepanement de Physique de la Matiere Condense*,24, quai Ernest-Ansermet, 1211 Geneve 4, Switzerland

and

J. FLOUQUETDepartement de la Recherche Fondamentale de la Matiere Condensed,CENG, BP 85X, 38041 Grenoble ttdex, France

Thermal conductivity and pressure resistivity experiments on UPt^ URu2 Si2

single crystals have been realized in order to precise the nature of the orderparameters and the link between the properties of normal (Nedl temperature,Fermi liquid parameters) and superconducting phases. Furthermore, the heavyfermion compound CeCu2Ge2 was found to undergo a superconducting

< transition at very high pressure. At 100 kbar, Tc s 0.64 K and H<.(o) = 2 T.

4

I 8pm:Cl| NUMERICAL SIMULATION OF THE LASER-PULSE SPECTROSCOPY• OF HOT CARRIERS IN SEMICONDUCTORS

' P.KOCEVAR

Inst.f.Theor.Physik, Univ.Graz, Universitatsplatz 5, A-8010 Graz

We present a theoretical study of the internal thermalization and the energy relax-

ation of highly photoexcited electrons and holes in bulk intrinsic and doped GaAs and

InP for a wide range of excitation and doping densities. The theoretical approach con- •

sists of an Ensemble-Monte-Carlo analysis of time-resolved spectral luminescence and |

I pump-and-probe absorption measurements which were recently performed with time |

I resolutions of 50 fs and 5 ps. A detailed comparison between theory and spectroscopic J

i: data for different experimental scenarios provides the input for a critical discussion of t\

i our present understanding of the hot-carrier dynamics in polar semiconductors and of -;

the quasiclassical transport model underlying conventional Monte-Cark> techniques. -;

43

8pm:C2

ULTKAKAST PROPERTIES OF QUANTUM WELLS ANDSUPERLATTICES BY SUBPICOSECOND LUMINESCENCE

Benoft DeveaudCentre National d'Etudes des Telecommunications

22301 LANNION FRANCE

Superlattices and quantum wells have been studied by subpicosecondluminescence. Using the technique of upconversion, we are able to obtainluminescence spectra with a resolution as good as 120 fs. In this talk, we willconcentrate on two main aspects:

-Carrier capture in quantum wells. The observed times are alwaysshorter than 2 ps. They are well explained by theoretical estimates of thequantum mechanical capture processes including the effect of impurityscattering.

-Radiative recombination of 2D free excitons differ in a fundamentalway from the recombination of 3D excitons. Under resonant excitation at lowtemperature, we have observed lifetimes as short as 24 ps. Such times are dueto the changes in the polariton picture brough by the breakdown of thetranslationnal symmetry of the crystal.

44

I

9al:Al

RECENT PROGRESS IN SCANNING PROBE MICROSCOPY

H.-J. GUNTHERODTInstltut fur Physik der Universitat Basel, CH-4056 Basel/Switzerland

The Scanning Tunneling Microscope (STM), created in 1931 by Binnig and Rohrer,opened a new area in the study of surfaces and interfaces. The restriction of thismethod to conducting materials has been overcome with the 1986 development ofthe Scanning Force Microscope (SFM or Atomic Force Microscope, AFM) by Binnig,Quate and Gerber. Today a variety of Scanning Probe Microscopes (SPM) areavailable where the probe-sample interaction is provided by tunneling current,force, optical, acustical and microwave fields. Yet the best known of these micros-copes remain the STM and SFM, achieving atomic and molecular resolution on awide variety of materials. Examples will be given of the different operation modes,Including imaging, spectroscopy, measuring and processing (material modificationand manipulation). Emphasis will be placed on a recently developed Friction ForceMicroscope (FFM) that allows the simultaneous study of topography and friction.

9al:A2

SINGLE-ELECTRON T U N N E L I N G UP TO ROOMT E M P E R A T U R E S

Ch. Schonenberger and H. van HoutenPhilips Research, P.O. Box 80.000, NL-5600 JA eindhoven, The Netherlands.

The electrical transport in ultrasmall double tunneling-junctions has been investigatedusing scanning tunneling microscopy (STM). The two junctions in series are formedby the STM tip positioned over a small metal particle <50A and a thin insulatingspacer between the particle and the conducting substrate. Single-electron effects havebeen seen, for the first time, at temperatures as large as 300K. A region of lowconductance around zero bias is found in the current-voltage characteristics. This is theCoulomb gap arising due to the large single-electron charging energy of the metalparticles (=; 0.2 eV). Moreover, the Coulomb staircase could also be observed at roomtemperatures. Additionally, the measurement of the zero-bias conductance as afunction of tip-sample distance shows oscillations which are caused by a change of the'fractional' charge on the metal particle proportional to the electric field in thetip-particle region due to a non-zero contact potential.

45

9al:A3

ROLE OF TIP ELECTRONIC STRUCTURE IN SCANNING TUNNELINGMICROSCOPY

J. TERSOFFIBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598, USA

With advances in the precision of scanning tunneling microscopy (STM), it has becomenecessary to carefully examine the role of the tip. While effects of tip shape are easilyunderstood, the role of tip electronic structure in STM images is more subtle. For aparabolic free-electron-like tip, the STM image is insensitive to the electronic structureof the tip (1), except in peculiar cases such as graphite (2). In graphite and other mate-rials where the sample electronic structure plays a special role in the image, the imagemay be quite sensitive to the tip electronic structure, but only at high spatial resolution.

1. J. Tersoff, Phys. Rev. B 41, 1235 (1990).2. J. Tersoff and N. D. Lang, Phys. Rev. Lett. 65, 1132 (1990).

9al:Bl

MAGNETIC AND CHARGE TRANSFER COUPLINGS, ELECTRONIC PHASE SEPARATION ANDSUPERCONDUCTIVITY

C. DI CASTRODipaDimento di Rsica, Universita di Roma "La Sapienza", P.le A.Moro 2,1-OO185 Roma

Phase separation is a generic feature of most of the models with snort range interactions proposed for high Tcsuperconductivity. If the effective attractive interaction leading lo phase separation manifests itself in the particle-particle channel also, it may mm out to be responsible for the pairing instability leading to superconductivity. Therecent observation of phase separation in some high Tc materials gives some confidence that this phenomenon isan intrinsic one and not a spurious feature to be avoided by roe introduction of long range forces.I will review the results in various models with particular emphasis firstly1 on the case of prevailing magneticinteraction, which should be valid at not too high doping regime and secondly2 on a model with dominating chargetransfer excitation mechanism, which should apply in the intermediaie and high doping regime.In die first case the spins of the mobile p-holes due to doping interact via a magnetic coupling with the spins ofthe amiferromagnetically correlated substrate formed by the preexisting d-holes. Competition between kinetic andmagnetic energy terms produces phase separation into a hole rich phase and a magnetically correlated phase. Pairformation stabilizes the system against phase separation.In the second case the undoped system is schematized by a charge transfer insulator, where the introduction of anearest neighbour coulombic repulsion between p and d-holes, leads upon doping to the relevance of low energycharge transfer excitations up lo a charge transfer instability. Phase separation preludes to it and is produced by thecompetition between the kinetic energy and the nearest neighbour repulsion. Superconductivity instability occursnear the phase separation region, thus enforcing in this case also a possible connection.

1. Cancrini N., Caprara S., Casiellani C . Di Castro C , Grilli M., Raimondi R.. Europhys.Lett. 14, S97 (1991).2. Grim M., Raimondi R., Casiellani C, Di Castro C . KoUiar G.. Phys.Rev.Lett. 67,253 (1991).

46

9al:B2ELECTRONIC PHASE SEPARATION AND HIGH-TEMPERATURE SU-PERCONDUCTIVITY

V. J. EMERYBrookhaven National Laboratory, Department of Physics, Upton, NY 11073

Doped holes in an antiferromagnetic insulator tend to phase separate intohole-rich and hole-poor regions, in order to minimize the total lero-point ki-netic energy. However bulk phase separation is prevented by the long-rangeCoulomb interaction between the holdes. As a consequence of this com-petition, the low-energy charge fluctuations of the system consist of small,phase-separated droplets. It is shown that such a picture is consistent withmany of the properties of high-temperature superconductors and that thescattering of charge carriers from the droplets can account for the anomalousnormal state properties and provide a mechanism for pairing.

This work was supported by the DOE under Contract No. DE-AC02-70CH00016.

9al:B3PERCOLAHVE PHASE SEPARATION AND HIGH-T 0 SUPERCONDUCTIVITY

E. SIGMUND and V. HIZHNYAKQVImt. f. Theor. Physik, Univ. Stuttgart, Pfaffenwaldring 57, D-7 Stuttgart 80

The undoped parent compound* of the superconducting cuprate perov-ikites are iniulating and antiferromagnetically (AF) ordered. Whendoping, already in the regime of imall hole concentration! AF order ifdestroyed and at higher doping the systems become conducting and belowTc superconducting. This behaviour can be explained by the existenceof small ferromagnetic clusters (magnetic polarons), which are formedby holes introduced into the CuO2 planes and which have low mobility.The process of cluster formation is favoured since the loss of exchangeenergy due to magnetic disordered is exceeded by the gain due tolowering of the kinetic energy . At higher hole concentrations and dueto cluster diffusion a phase separation is formed by establishing largefractal or percolative clusters, which are metallic and inside which theholes move freely. Superconductivity is achieved by attraction betweenthese holes caused by distortive type hole-lattice interaction. Withinthis percolation picture the experimentally obtained results for phaseseparation and magnetic and conductive phase diagrams can be under-stood very naturally .

47

9al:ClNOVEL MAGNETO-OPTIC AND SPECTROSCOPIC PHENOMENA IN II-VI SEMI-CONDUCTORS AND THEIR HETEROSTRUCTURES

A. K. RAMDASDepartment of Physics, Purdue University, West Lafayette, IN 47907 U.S.A.

The tetrahedrally coordinated II-VI semiconductors represent an important class of semi-conductors. An impressive range of band gaps; the dramatic increase in their ionicity incomparison to that of the III-V's; the diluted magnetic semiconductors (DMS) resultingfrom the incorporation of the magnetic ions belonging to the transition metal group; suc-cessful MBE growth of II-VI/II-VI as well as II-VI/III-V heterostructures - all of thesehave led to the discovery of numerous novel phenomena. The talk will focus on strains inII-VI pseudomorphjc films on III-V substrates explored with piezo- and photo-modulatedreflectivity and pressure tuning of the strain with a diamond anvil cell; Faraday and Voigteffect in bulk DMS's which illustrate all aspects of their characteristic magnetic behavior;photoluminescence and Raman spectroscopy of II-VI/II-VI quantum well structures inwhich magnetic interactions are controlled by the dimensional effects; the novel natureof the ground and excited states of Fe2+ and Co2+ in DMS as observed in Raman andFourier Transform Spectroscopy.

9al:C2HETEROSTRUCTURES OF DILUTE MAGNETIC VI-VI COMPOUNDS

H. PASCHER

Physikalisches Institut, Universitat, W-8580 Bayreuth, Germany

Quantum well (QW) structures composed of a diamagnetic narrow gap IV-VI semicon-ductor (PbTe, PbSe) and a dilute magnetic compound (PoMnTe, PbMnSe, PbEuTe) areinvestigated by various magnetooptical methods as coherent anti-Stokes Ramanscattering (CARS), interbandabsorption and photoluminescence. The CARS expert-ments yield precise values of the spin splittings of valence and conduction bandsas a function of magnetic field and temperature. By interband transmission energygaps and effective masses are determined. Luminescence efficiencies give hints onthe types of the super-lattices. jThe data are analyzed in the framework of an envelope function approach takinginto account the exchange interaction between free charge carriers and the magne-tic moments of the paramagnetic ions in a molecular field approximation . A com-parison of the spin splittings of the bands in the QW's with those observed inhomogeneous materials yields informations on the probabilities to find the mobilecarriers in the diamagnetic and the semimagnetic layers, respectively. Theseinformations allow the determination of the type of the superlattice and of thebandoffsets at the interfaces.

1. M.Kriechbaum, Springer Series in Solid-state Sciences 67, 120 (1986)ed. G.Bauer, F.Kuchar, H.Heinrich

2. H.Pascher, P.Rothlein, G.Bauer, M.von Ortenberg Phys. Rev. B40, 10469 (1989)

48

9al:C3

EXCHANGE INTERACTION AND PHOTOMAGNETIZATION IN DILUTE MAGNETICSEMICONDUCTOR HETEROSTRUCTURES AND/OR SUPERLATTICES

H. KRENNInstitut fur Halbleiterphysik, Johannes Kepler Universitat Linz, A-4040 Linz-Auhof, Austria

The Heisenberg exchange interaction between mobile carriers and the localized magnetic ions opens new aspectsfor modelling low-dimensional magnetic systems in context with electronic confinement effects: Whereas inwide-gap II-VI DMs structures the intra-ion transitions (of e.g. Mn 2 +) compete with interband transitions (thelatter predominate in superlattices with respect to bulk), in narrow gap DMS-structures some energy levels ofmagnetic ions (e.g. fe^+) resonate with energy bands. The manganese ions can be polarized by optical pumpingwith circularly polarized light either within the Mn-syslem itself or via exchange interaction with spin-polarizedcarriers. The magnetization of optically-oriented Mn-ions was detected by a superconducting quantuminterferometer (SQUID) for the first situation in bulk ZnS:Mn, for the second readily in modulated hetero- orsuperfattice structures fi'fce CdTe/Cdi . x Mn x re . Ctfi-xMnxre/Ctfi yMnyTe, ZnTe/C<ii-xMnxSe andPbi-xMnxTe/PbTe. in wide-gap modulated semiconductor structures time-resolved studies of the formation ofmagnetic polarons were performed, whereas in narrow-gap systems only CW measurements are available. Thefundamentals of optically induced magnetization depend critically on the exchange parameters which bythemselves reflect Essential properties of the crystal system and band-structure. In narrow gap systems likePb].xMnxTe/PbTe a quite unique model system is available to investigate the exhange interaction in a rocksalt-stmcture and in a majiy-valley electronic bandstructure. Also envelope-function calculations differ considerably inII-VI and IV-VI semiconductor structures. Therefore, the dependence of photomagnetization and of spin-relaxationof optically pumped carriers on the dimensionality and on the penetration of wavefunctions into DMS barriers isis also distinct in these systems. The different behaviour is critically reviewed in context of earlier and newstudies of optically induced magnetization.

9a2:AlSOAP FROTH, MAGNETIC FROTH . . .

D. WEAIREPhysics nept, Trinity College, Dublin, Ireland.

Many naturally occurring disordered structures divide space (in two orthree dimensions) into cells, whose surface energy plays a key role in de-termining structure, its evolution and its response to stress. Importantexamples include metallurgical grain structure and the common soap froth,whose two-dimensional realisation provides a particularly simple system.Nevertheless this prototypical case has required a decade or more of con-tributions fron theory and experiment to firmly establish some essentialproperties. The scaling behaviour of coarsening (due to gas diffusion) isnow clear. Another system which is superficially similar is that of the 2dmagnetic froth, which shows analogous coarsening when the applied magneticfield is increased, but also significant differences, as yet only partiallyexplained or simulated.

49

9a2:A2

APPLICATION OF AMORPHOUS SILICON DEVICES

P.G. LeCOMBERUniversity of Dundee, Dundee DD1 4HN, Scotland, U.K.

Thin films of amorphous silicon (a-Si:H) and its alloys are currently used

in a range of devices which include photovoltaic cells, photoreceptors,

page-width image sensors and thin-film transistors for active-matrix

liquid-crystal displays. In the latter alone it is estimated that some

$4 billion will be invested over the next three to four years in putting

these into large volume production.

This presentation will review the present applications of a-Si:H and

briefly describe a number of others which have been proposed for this

material. The physical principles underlying the a-Si:H devices in these

applications will be presented. The advantages and disadvantages of

a-Si:H, compared with its competitors, and the material and technological

issues of current importance, will be discussed.

50

6P:alSTRUCTURAL AND MAGNETIC PROPERTIES OF FePt MULTILAYERS

E. DEVLIN, V. PSICHARIS, A. KOSTIKAS, A. SIMOPOULOS,A. JANKOWSKI1 and T. TSAKALAKOS2

Institute of Materials Science, NCSR "Demokritos"GR-153 10 Ag. Paraskevi, Greece

1Lawrence Livermore National Lab., Livermore, California 945502Department of Mechanics and Materials Science, Rutgers Univer-sity, Piscataway, New Jersey 08855-0909, U.S.A.

A series of Fe/Pt multilayers (ML) have been synthesized usingmagnetron sputter deposition. The individual thicknesses of thecomponent layers as given from a quartz crystal monitor wereFe(3A)/Pt(9A, 19A, 39A) and Fe(9A)/Pt(9A). Low angle x-ray dif-fraction data have been fitted to all reflective orders and arein excellent agreement with the crystal monitor results. Satel-lite structure has been observed around Bragg peaks correspondingto the composite Fe-Pt peaks. Conversion electron Mossbauer(CEMS) data on the Fe(9A)/PT(9A) show that the magnetic moment isoriented parallel to the plane of the sample. The Fe(3A)/Pt(9A)spectra indicate a rotation out of the plane.

6P:a2

MAGNETOTHERMOELECTRIC POWER OF MAGNETIC MULTILAYERS

L. Piraux,Unit6 de Physico-Chimie et de Physique des Materiaux, Universite* Catholique deLouvain, place Croix du Sud 1, B-1348 Louvain-la-Neuve, BelgiumA. Fert, Laboratoire de Physique des Solides, University Paris-Sud, 91405 Orsay, FranceR. Loloee and P.A. Schroeder, Physics Department, Michigan State University, EastLansing, MI 48824, USAP. Etienne, Laboratoire Central de Recherche Thomson-CSF, 91404 Orsay, Ranee

Measurements of the thermoelectric power of Fc/Cr, Co/Cu and Fe/Cu multilayers have beencarried out in the temperature range 4K<T<150K and under magnetic field perpendicular to thelayers. All specimens were found to exhibit marqued magnetothermopower effects inaccordance with their giant negative magnetoresistance. At low temperature, themagnetothermoelectric power is positive while the results obtained below 6K on Fe/Crmultilayers agree with a modified expression of the Gorter-Nordheim relation, suggesting adominant diffusion thermoelectric power. In the high temperature range, the sign of themagnetothermoelectric becomes negative for the Co/Cu and the Fe/Cu multilayers while for theFe/Cr system it is positive above 120K. These high temperature results are analysed in terms ofelectron-magnon scattering in the two current conduction model. It is found that the sign of themagnetothcrmoelectric power should depend on whether the ratio of the impurity resistivities inthe two spin directions is greater or less than unity.

. | 51« . • ! •

-if

6P:a3

NEW TRENDS FOR THE MAGNETISM IN LOW-DIMENSIONALTRANSITION-METAL STRUCTURES

C. OEMANGEAT, IPCMS, UMR46. Universite Louis Pasteur,4 rue Blaise Pascal, 67070 Strasbourg, FranceL. C. BALBAS, Depto de Fisica Teorica, Universidad de Valladolid,47011 Valladolid, SpainJ. DORANTES-DAVILA, Instituto de Fisica Teorica, UASLP, Alvaro Obregon,78000 San Luis Potosi, SLP, MexicoK. H. BENNEMANN Institut fur Theoretische Physik, Freie Universitat Berlin.Arnimallee 14, 1000 Berlin 33, GermanyH. DREYSSE, Laboratoire de Physique des Solides, BP 239,54506 Vandoeuvre-les-Nancy, France

The magnetism of low-dimensional systems as clusters or slabs has gained a great

interest. For transition-metals, the direct-space tight-bindir.g method within the

Hubbard-Hamiltonian provides an unified way to describe the electronic structure

of these systems. We present and discuss recent results concerning V, Fe, Co,

Rh and Pd. From these results, general rules emerge and will be discussed in

details.

6P:a4

ARE COBALT LAYERS DILATED IN MAGNETIC MULTILAYERS?

N.Mliki+*. K. Abdelmoula+* and G.Nihoul * Ch. Mariiere°and D. Renard0

*GMET,University of Toulon.BP 132.F-83957 La Garde Cedex+INRST, Bordj Cedria, BP95, 2050 Hammam Lif, Tunisia." I.O., University of Orsay, 91405 Orsay Cedex, France.

Magnetic multilayers, where cobalt alternates with a non magnetic material (gold in ourcase), are often studied as there are numerous applications for them. The misfit between bulkgold and bulk cobalt is large ( 14% ) and when the cobalt layer is ultrathin, some adaptation isbound to arise, which will have a strong influence on the magnetic properties of the multilayer.

We have observed some metallic bilayers ( cobalt thickness of 0.8nm ). We report herethe results yielded by electron diffraction patterns obtained from frontviews and crossviews.

Frontviews diffractions confirm that the gold substrate has a [ 111 ] texture with cobaltlayers oriented with theirc axis parallel to the gold [111] axis. Microdiffractions, where thediffracting specimen area is less than lOOnm large, have been done to measure the parameter ofthe cobalt layer as compared with gold. These diffraction patterns show that the misfit is nowonly 10% + 1%: there is a dilatation of 4% for cobalt in the basal plane.

Crossviews microdiffractions give the misfit in the direction perpendicular to the layers:this is measured as 7% + 1%, which means cobalt is more dilated in this direction. This 7%dilatation, in the growth direction, is confirmed by X-Rays diffraction experiments done onmultilayers with the same cobalt layers thickness ( 0.8nm). Other measurements done on 2nmcobalt layers show no dilatation. Neither do multilayers with 0.8nm thick cobalt layers but withcopper used as the other metal (the misfit between cobalt and copper is negligible).

Hence, cobalt layers are dilated if thin enough and sandwiched between a suitablematerial. This might explain some of the magnetic properties of the observed multilayers.

6P:a5

BLUE ENHANCED MAGNETO-OPTIC Co/Pt MULTILAYERS WITH ZEROKERR ELLIPTICITY

R Atkinson, I W Salter, A H El-Astal, J XuDepartment of Pure and Applied PhysicsThe Queen's University of BelfastBELFAST, BT7 INN, UX

An eUipsometric study has been made of the fundamental optical and magneto—opticalconstants of a number Co/Pt multilayer films in the spectral region 300 — 900 nm. Theresults of these measurements have been used to assess the performance of the material,for magneto—optic recording, in terms of a figure of merit which is related entirely tothese material constants. The figure of merit indicates the ultimate performance of thematerial, when differential techniques are used to sense stored information by thedetection of the normal incidence Kerr effect, after the magnetic medium has beenincluded in a correctly designed quadrilayer structure.

Results clearly show that the best performance is to be obtained at wavelengths below300 nm. Quadrilayer designs for enhancing the detection of the magneto-optic Kerreffect will be presented which maximise the Kerr rotation for a particular systemreflectance and simultaneously reduce the parasitic Kerr ellipticity to zero.

6P:a6

CHARACTERIZATION OF QUADRILAYER MAGNETIC RECORDING MEDIA BYELLIPSOMETRY AND RBS EXPERIMENT

R. Atkinsona, J. Hrdinab, L. Jastrabikb, V. Pefinac, P. Sirokyb

aThe Queen's University of Belfast, Belfast BT7 INN NorthernIreland, U.K.

Institute of Physics, Czechoslovak Academy of Sciences,Na Slovance 2, 180 40 Praha 8, Czechoslovakia

'Nuclear Physics Institute,25068 fiez, Czechoslovakia

cNuclear Physics Institute, Czechoslovak Academy of Sciences

Optical response of ZnS/TbFeCo/ZnS/Al magneto-optical recording ithin film medium, optimalized in the sense of maximum m.-o. •]

.figure of merit , was studied by angle (50-82.5 deg) and spec- ;!tral (350-700 nm) dependent ellipsometry. Due to the complexi- 1-ty of the system, RBS data on chemical composition of indivi- Idual films were taken as supported piece of information. Non- Iequivalence of upper and lower ZnS film was proved by RBS and |taken into account in the analysis of ellipsometrical data. .;

1.Atkinson R. et al., Magneto-optic Quadrilayers showing ZeroKerr Ellipticity - to be published.

53

6P:a7ELASTIC CHARACTERIZATION OF Ta/AI PERIODIC SUPERLATTTCES

BY BRILLOUIN LIGHT SPECTROSCOPY

G.Carlotti, D.Fioretto, L.Palmicri, G.Socino and L.VcrdiniDipartimento di Fisica, Universita1 di Perugia

1-06100 Perugia, Italia

H.Xia, R.W.Peng, A.Hu, S.SJiang, X.K.Zhang and D.FengNational Laboratory of Solid State Microstructures, Nanjing University

Nanjing 210008, P. R. China

Brillouin scattering from surface acoustic phonons has been used to study the elasticproperties of periodic Ta/AI metallic superlaltices. This kind of artificially cteated structure isinteresting for its structural and elastic properties since the lattice parameters of theconstituents are highly matched, while their atomic numbers are very different. This makessuch a structure very suitable for application in the soft x-ray and neutron optics. Brillouinspectra were obtained in the backscattering geometry by means of a tandem 3+3 pass FabryPerot interferometer, on three different Ta/AI specimens 0.5 /Jtm thick, deposited by dcsputtering cm glass substrates. Taking measurements at different incidence angles, in the range30 -r 76°, enabled us to detect up to five guided acoustic modes (Rayleigh and Sezawa modes)and measure their phase velocity. The elastic constants were obtained from a a fittingprocedure to the dispersion curves calculated within the elastic continuum approximation. Acomparison of the values obtained in this way with those expected on the basis of the'effective modulus model' showed an anomalous increase of the shear effective constant CAAof about 20%. **

6P:allMAGNETIC; ANISOTROPY OF ULTRAFHIN COBALT [0001] FILMS ON A u ( H t ) .

P.BeanvilTain, V.Grol ier ' , R.Megy, S.Ould-Mahfoud, D.Renard'*, p .ve i i ie t .

IEF, LPS* , IOTA'*; laboratoires associes au CNRS, Umversite Paris-Sua,

SUQb Orsar, France.

Th$ or ig in of large perpendicular magnetic am^otropy in u l -

t ra th in Co f i lms is not completely elucidated. For instance, the

respective contr ibutions of magnetocrystal1ine interface aniso-

tropy eind magnetoelastic amsotropy inauced by arnsotropic

strains is not determined. The sp in-orb i t coupling in the non-

magnetic, metal may also contribute to the arnsotropy. in order to

investigate these points we nave measured, by magnetometry and i)

magneto^optic measurements, the hysteresis loops of Au/Co/X i;

sandwiches (X=Au,Ag,Cu,Pt,Pd ) with Co thicknesses varying from 2 ,f

to 30MI.. we could then experimentally determined the magnetic •":

an i so t ropy versus Co th i ck r i ess . As the an i so t ropy o f Co f i l m s ae- -

p&r>iis strongly on 9/owtb c o n d i t i o n s we s t a r t e d w i t h the same Au

sut)trat«s and v a r i e d on ly the m e t a l l i c coverage X.

54

6P:al2THE OBSERVATION OF A DIMENSIONAL CROSSOVER IN ULTRATfflN Ni

FILMS

Yi Li and K. Baberschke

lnstitut fur Expehmentalphysik, FU Berlin, Arnimallee 14, D-1000 Berlin 33, FRG

Recently it has been shown that magnetic resonance is monolayer sensitive and that the

increase of spin fluctuations at the ferromagnetic phase transition/1/ can well be

detected. These advances are used to study the magnetic properties of N i ( l l l ) films of 2

to 20 layers and their transition from a 3 to 2 dimensional behavior. Ni(ll l)/W(110) is

one of the most ideal cases: (i) it is known that diffusion is negligible for T < 600 K, and

(ii) bulk Ni has a relatively low Tc. From the divergence of the FMR linewidth at Tc~

the critical exponent 0 is determined. At a thickness of d = 6 ± 1 layers fi changes

suddenly from a 3D value to 1/8, the 2D-Ising value. At the same thickness Tc(d)

deviates from a finite size scaling law.

/ I / Yi Li, M. Farle, and K. Baberschke, Phys. Rev. ML 9596 (1990)

6P:al3VALENCY AND SITE DISTRIBUTION OF LEAD IN YIG:Pb THIN FILM

1 2 1 3 2A.Campos , H.Dotsch , H.Lutgemeier , P.Novak , S.SureInstitut fiir Festk6rperforschung. KFA jaiich, Jiilich, FRG

2Fachbereich Physik, Universitat Osnabrtlck, Osnabrilck, FRG

Institute of Physics, Prague, Czechoslovakia

57We have measured NMR of Fe nuclei in (YFePb) O thin garnet

8 12film with [111] orientation. The content of Pb determined by

the electron microprobe analysis is 0.1 pfu. The measurements

were made at zero external field and liquid helium temperature

using the spin echo method. The NMR spectrum exhibits a satel-

lite structure with several resolved satellites. By comparing

this structure with the spectra of YIG:Pb and YIG:In systems

studied by us earlier, we have identified the satellites caused2+ 4+

by Pb ions on dodecahedral sites and Pb ions on octahedral

sites. From the intensity of satellites the concentrations of

these ions were determined.

55

I

6P:aHMAGNETIC PROPERTIES OF AMORPHOUS Fe IN Y/Fe/Y THIN FILMS

S. DORRER, J. LANDES, CH. SAUER, U. KOBLER, A. FUSS, AND W. ZINN

Institut far Festkorperfbrschung, Forschungszentrum Julich, D-5170 Julich, Gennany

Recently it was observed that Fe grows on a Gd film in an amorphous structure up to a

critical thickness of 2.3 nm [1] . Y/Fe film systems reveal the same growth properties.

We have studied layered structures of (Y/d nra 57—Fe/Y) with varying Fe thickness of

d = 1.0 — 3.0 nm by means of 57—Fe CEMS and magnetization measurements. By re-

placing Gd by nonmagnetic Y the magnetic properties of the amorphous Fe (a—Fe)

interlayer could be determined. The results are: (i) strongly disturbed ferromagnetic

rather than spin glass behavior; (ii) a broad hyperfine field distribution, probably due to

a local scattering of the magnetic moments; (iii) reduced average magnetic moment of

H — (1.2 ± 0.2)/ig; (iv) reduced Curie temperature T c = (80 ± 3) K; (v) coercive fields of

s 1.6 • 10*A/m (200 Oe), i.e. no soft magnetic properties; (vi) qualitative agreement

with theoretical results by Krauss and Krey [2].

[1] J. Landes, Ch. Saner, B. Kabius, W. Zinn, Phys. Rev. B44 (1991) 8342.

[2] U. Krauss and U. Krey, J. Magn. Magn. Mat. 98 (1991) LI.

6P:al5COUPLING BETWEEN FERROMAGNETIC FILMS ACROSS A NONMAGNETIC LAYER

J. BARNASInstitute of Physics, Technical University, Piotrowo 3,60-965 Poznan, Poland

Coupling between two transition-metal ferromagnetic filmsthrough a simple-metal layer via conduction electrons has beenanalysed theoretically. Two different contributions have been Jconsidered. The first one results from the quantum-size effect. \The corresponding coupling parameter oscillates with the spacer ;|thickness. It oscillates also with the thickness of the ifmagnetic films. This kind of contribution to the coupling $between ferromagnetic films can be important for small sublayer j«thicknesses or when one of the conduction subbands in the %ferromagnetic metal is empty. In both cases the quasi-two- }dimensional behaviour of the conduction electrons is •'responsible for the coupling between the films. The secondcontribution to the coupling originates in the s-dhybridization. It consists of two parts - one is of RKKY-typeand the other one is of superexchange nature.

56

6P:al6DOMAIN STRUCTURE OF THIN SINGLE CRYSTAL PLATELETS OF B a F ei2- x-y

C oxT i °19

R.GEMPERLE, V.KAHBERSKY, J. SIRSOVA, L.PUST, L.MORTINOVA,Institute of Physics, Cukrovarnicka 10, 162 00 Prague 6, CzechoslovakiaP. GORNERT.H.SCHUPPELPhysikalisch-Technisches Institut, D-6900 Jena, GermanyR. GERBERDepartment of Pure and Applied Physics, University of Salford MS 4WT, OK

The domain structure in bexaferrite platelets was studied for various cobaltconcentrations, 0 i x i 0.7, using the colloid-SEN method, with the view ofpossible applications of thin films of such materials in high densitymagnetic recording. The magnitudes of uniaxial anisotropy constants, K, andK2, and the saturation magnetization, M s were measured using the VSM andtorque methods. Typical surface undulation,of Bloch walls was observed in thicker;platelets (Fig.1). The domain period de-!icreases with decreasing crystal thicknessand also with increasing cobalt concentra-tion. The critical sample thickness oftransition from undulated to simple stripestructure (Fig.2) was measured and,compared with the theoretical estimates.

6P:al7NUCLEAR SPIN-LATTICE RELAXATION IN FERROMAGNETIC AMORPHOUSALLOYS F e 8 ( K 5 C o 3 > 1 B 1 6 > 4 AND P e 7 0 C o 1 0 B 2 ( ) .

J.KOHOUTa, J.ENGLICHa, M.TRHLfKa and H.Li i tgemeier baDepartnent of Low Tenperature Physics, Charles University,

V Holesoviakach 2, 180 00 Prague 8, CzechoslovakiaDKFA Jiilich, W-5170 Julich, Germany

The nuclear spin-lattice relaxation of 1 1B and 59Co inamorphous alloys Fe-Co-B have been studied by NMR at 4.2Kusing various pulse techniques. The dependence on composi-tion, external magnetic field up to 1.2 T and frequency wasmeasured. In analyses of tine decays an influence of thequadrupole interaction was taken into account. Our resultsare compared to the previous ones that were obtained for thesame sample using low-temperature nuclear orientationtechnique1.^rhlik M. et al: J.Phys.F.:Met.Phys.18(1988)2283

57

6P:al8THE PREISACH DIAGRAM AND WOHLFARTH's REMANENCE FORMULA

PAVEL HEJDA, EDUARD PETROVSK^, TOMAS ZELINKA, VLADIMfR KROPACEKGeophysical Institute, Czechoslovak Academy of Sciences, Bocnf n, 141 31 Praha 4,Czechoslovakia

The Preisach diagram, representing a statistical approach to modelling magnetic expression ofdomain structure, proved to fit satisfactorily experimentally acquired hysteresis loops of weakmagnetic samples. Despite the increasing interest in the latest years, links between thePreisach parameters and physical characteristics of magnetic material are not clear yet. On theother hand, a remanence technique based on the Wohlfarth's relation have been recentlyestablished with a view to examine internal magnetic interactions. In this study, experimentalcomparison of the two approaches is given and possible links are discussed.

6P:al9CALCULATION OF CRYSTAL FIELD PARAMETERS AMD ELECTRIC FIELDGRADIENT IN RARE EARTH METALS

J.Kuriplach and P.Novak*Faculty of Mathematics and Physics, Charles University,V Holesovidkach 2, 180 00 PRAHA 8, CzechoslovakiaInstitute of Physics, Cukrovarnicka 10, 162 00 PRAHA 6,

Czechoslovakia

Electronic structure of hep rare earth metals is calculatedusing the spin-polarized version of the full potential LAPWmethod [1]. To investigate hybridization effects 4f-electronsare treated either as semi-core or core electrons. Crystalfield parameters are obtained from the nonspherical part of thepotential [2] and the influence of exchange-correlation part ofthe potential is discussed. The electric field gradient at \nucleus site is determined by the method [3] in which the -Coulomb potential is expanded into spherical harmonics and the Isecond order terms give directly the field gradient. "•[1] P.Blaha,K.Schwartz,P.Sorantin: Comp.Phys.Comm.59(1990)399 •;[2] P.Novak,J.Kuriplach: Calculation of Crystal Field ifParameters in Rare Earth Metals, ICM Edinburgh 1991, |,to be published <([3] P.Blaha, K.Schwartz,P.Herzig: Phys.Rev.Lett.54(1985)1192 ?

58

6P:a20

MAGNETOMECHANICAL HYSTERESIS LOOP EVALUATION FROMMECHANICAL BARKHAUSEN EFFECT

BOLESLAW AUGUSTYNIAKInstitute of Physics, Technical University of Gdaiiskul. Majakowskiego 11/12, 80-952 Gdaiisk, Poland.

Magnetomechanical Barkhausen Effect (MBE) is due to the irreversible motion of thenon-1800 domain walls when ferromagnetic sample is stressed. This change ofmagnetization is accompanied by a voltage pulse in pickup coil surrounding thesample. It is proposed a new method of magnetomechanical hysteresis loop researchby means of the MBE intensity measurement in function of applied stress. The meanvalue of the MBE voltage pulses time integral was treated as the MBE intensity level.The soft magnetic alloy CoPt ( wire, 4>=l mm ) was used because of high value ofits magnetostriction constant. The MBE intensity reversals U(?) were measured as thefunction of the torsional strain y applied using torque machine. Strain y was variedwith the constant time rate d^/dt = 10-10"3 s"1 for various strain amplitudes yo ( from1-10"* up to 10-10"4 ). These reversals show evolution of the magnetomechanicalhysteresis in function of the maximal strain y0. It was found that the U(-y) function asmeasured during the first increase of strain ( 0 < 7 < 7 0 ) reveals maximum at 7 =3-10"4. This first part of the MBE intensity reversal is used for direct calculation ofthe internal stress level o-.

6P:a21

N O MORE T R A N S C E N D E N T A L EQUATIONS IN H O M O G E N E O U S MEAN-FIELD MODELS O FFERROMAGNETISM

Y M1UJE.V m o M f A H M - EMPI fur MeUlIforscftung, Instilut fur Physik, Heisenbergstr. 1, 7 0 0 0 Stuttgart 80 , Fed. Rep. Germany

In > recent p iper 1 exact solutions for the magnetization within the effective (mean-field) approach to(ferro)nugnetic systems were reported for the particular case* o f spin-1/2 and spin-1 localized magneticmoments. W e generalise theae results in several respects:

(i) we reduce the transcendental equation for the detennination o f the magnetization to the problem o fsolving an explicit polynomial equation of degree 2S (where S i s the spin o f the localized magneticmoments) for the temperature as a function of magnetization;

(ii) w e describe various possibilities to achieve this reduction and s ingle out the physically t o o * tractable •variant; 1

(iii) w e explicate that the solution o f the obtained polynomial equation i s equivalent to finding the inverse o f .the Brillouin function. W e then find the inverted Brillouin function for S » 1/2, 1, and 3 /2 - ,

( IT) the above-mentioned reduction and the consequent inversion o f the Brillouin function are then applied to jjg ive a general framework for finding the magnetization in the considerably more complicated case with /structural disorder with or without an external mignetic field within the homogeneous mean-fieldapproximation. This approach has the advantage of a l lowing for explicit calculations with variousphysically plausible random-exchange probability distributions.

It i s not clear yet whether the approach is effective in inhomogeneoua mean-field treatments. Iii generality,however, should not b e underestimated.

1. Whitaker M . A . B . . A m . J. Phys. 57 (1989) 45 .

59

6P:a22THE GAUSSIAN THEORY OF DIPOLAR FERRO- AND ANTIFERROMAGNETS

Y MILLEV, K RIED, and M FAHNLEMPI fiir Metallforschung, Institut fur Physik, Heisenbergstr. 1, 7000 Stuttgart 80, Fed. Rep. Germany

In an attempt to trace as precisely as possible the influence of the quadratic cubic aniaotropy stemming fromdipolar interactions which are important near a phase transition point 111, we derive the exact expressions forthe longitudinal and transversal susceptibilities within the Gaussian approximation for the fluctuating fieldcomponents. When the calculations are carried out without simplifying assumptions, it turns out that thereexist two poles of the susceptibility indicating two possible competing phase transitions even within theGaussian approximation. One of mem is the usual phase transition corresponding to the suppressed influenceof the dipolar interactions; the other one corresponds to a shifted phase transition. Its critical temperature islower than that of the first one for ferromagnetic and higher for antiferromagnetic exchange. This latterfinding is consistent with the renormalization-group prediction about the stability of antifenomagnetic criticalbehaviour governed by a Gaussian fixed point 111. Although the qutrtic terms in the order parameterfluctuations are neglected in me present calculation, it has the advantage of taking explicit account of the lower(cubic) symmetry dipolar contributions, whereas previous analyses either assume the smallneat of thesecontributions III, or neglect them in the hope that they are irrelevant 12,31. On the other hand, the mostserious attempt to account for this cubic-symmetry interaction was done by neglecting all the other relevantparts of the dipolar interaction and, besides, it also ends up, for {insurmountable technical difficulties, with thelimit of small cubic perturbations only 141.

1. Aharony A. and Fisher M.E., Phys. Rev. B8 (1973) 3323.2. Aharony A., Phys. Rev. B8 (1973) 3349.3. Frey E. and Schwabl F., Phys. Rev. B43 (1991) 833.4. Bruce A.D., J. Phys. C7 (1974) 2089.

6P:a23ITINERANT ELECTRON THEORY OF SPIN WAVES IN HCP COBALT

J.M.BASS*, J.A.BLACKMAN* AND J.F.COOKE*

* Dept. of Physics, University of Reading, Reading RG6 2AF, UK.

+ Solid State Div., Oak Ridge National Laboratory", Oak Ridge, TN 37831, USA.

Calculations of the frequency and wavevector dependent magnetic susceptibility

for the cubic transition metals, using mulliband itinerant electron theory, .-

have predicted a rich structure which, at least qualitatively, has

been confirmed subsequently by experiment. These calculations have now been *

extended to hep cobalt with its two atoms per unit cell, and include both the Jl

most general screened coulomb matrix elements consistent with symmetry and \ <

also the form factors. This is a vital development for making quantitative *

comparisons with experiment. •

* * Managed by Martin Marietta Energy Systems, Inc. for the Division ofMaterials Sciences, U.S. Department of Energy under contractDE-AC05-84OR21400.

60

6P:a24

CALCULATION OF ELECTRONIC AND MAGNETIC PROPERTIES OFMETALLIC AiBtAn LAYERED SYSTEMS

W. HERGERTr,H. DREYSSE t, P. RENNERT1, and C. DEMANGEAT+i Department of Physics, Martin-Luther-University,PF,O-4G10 Halle, Germany ; +IPCMS, Universite Louis-Pasteur, 4, rue Blaise Pascal, 67070 Strasbourg, France ;fLaboratoire de Physique des Solides, BP239, 54506 Vandoevre-les Nancy, France

The electronic and magnetic properties of metallic overlayers on a metallic substrate arecalculated using tight-binding t-space and f-space recursion techniques. A tight-bindigHubbard Hamiltonian in the unrestricted Hartree-Fock approximation is used for the cal-culations. The full spd basis set is included in the calculations. The dependence of themagnetism on the relaxation of the overlayer plane and on the exchange integral is studiedin a selfconsistent way.The results of the calculations are discussed in comparison with experimental results andother calculations.The Rh/Ag interface is investigated in detail. The contraction of the Rh-Ag distance af-fects strongly the magnetic properties. The influence of an Ag monolayer on the Rh/Ag-system is also discussed.

6P:a25

INTERACTING FERROMAGNETIC PARTICLES : NUMERICAL SIMULATION OF THEDYNAMICS.

J. Planes and A. FinelONERA (OM), B P 72, F-92322 Chatillon c<5dex, France.

Numerical simulations have been performed to determine the high-frequency susceptibility of afinite cluster of 1000 identical interacting ferromagnetic spheres with uniaxial anisotropy. Easyaxes have been randomly chosen and dipolar interactions exactly computed. For the equilibriumstate it is shown that, in a cross-over region where interactions and anisotropy are of the sameorder of magnitude, the distribution of local fields experienced by particles is broadened up to arelative width AB/<B> equal to 0,5 without positional disorder and 0.8 with disorder (voids in Ithe cluster). The eigenmodes of the assembly are subsequently computed considering the linea- irised Landau-Lifshitz equation of motion and the susceptibility for a small alternative driving ifield determined. Essential features are those already given for the static study. A comparison jjwill be made with similar studies concerning elongated particles1. Some preliminary experi- |mental results on 4 0 nm diameter Fe and Co particles which are supposed to fulfilled the as- |sumptions of the model will be presented. 1

1 Dean B, Chantrell RW, Hart A and Parker DA, to appear in J. Magn. Magn. Mat (1992)

6 1

6P:a26

MAGNETIC ABSORPTION AT L y - EDGES IN Ho

P. FISCHER, G. SCHOTZ, G. WIESINGER+)

Physik Department, Technische Universitat MUnchen, D-8046 Garching+) Institut fiir Experimentalphysik, Technische Universitat, A-1040 Wien

Using circularly polarized synchrotron radiation magnetic x - r a y absorp-tion has been studied at the Ho - L y - edges in Ho metal, the ferrimag-netic insulator Ho3FejO12 and the binary intermetallic compounds Ho2Co17and Ho6Fe23. At the L3 - edges die magnetic signal was found to be almostindependent of the chemical environment. Furthermore, it could be shownthat its amplitude is directly correlated with the orientation of the 4fcore. In contrast to this, at the Lj - edges the magnetic absorption issignificantly different in the systems under investigation. It is ex-pected, that the variation observed for the magnetic I4 - absorption iscorrelated with the spin and orbital polarization of delocalized emptyd - states at the Fermi level as veil as with the magnetic anisotropy ofthe material.

1. Fischer, P., Schtttz, G., Wiesinger, G., Sol. State Comm.76 (1990) 777.

6P:a27FAR INFRARED MAGNETOTRANSMISSION OF YbIG

J.Kolacek, Z.Simsa, R.TesafInstitute of Physics CSAS, Cukrovarnicka 10, Prague 6,Czechoslovakia

Using FIR laser as a source of 13.5cm*1 radiation, themagnetotransmission of a monocrystalline ytterbium irongarnet with magnetic fields up to 8T along the 11103direction was measured in the temperature range 4.2 - 50K.The measurements confirmed the possibility of indicatingthe magnetic phase transitions by this method. Observed )hysteresis sugests the existence of a first ordertransition in contrary to the theoretical predictions for Jthis orientation*. Early experimental observation of '%clif erential susceptibility in pulsed magnetic fields1 i;i1 evealil alsn the first order transition. >

1. J.Ums: phys.stat .sol(b) S4,<1977), 4572. J.I..F*rr,n, G.Fillion, G.Hug, P.Morin : Proc. of the

ICM-73, Moakva(1973)

62

6P:a28

ENHANCEMENT OF MAGNETOOPTICAL EFFECTS IN Au/Co/AuULTRATHIN FILM SANDWICHES

J. Ferré1, M. Nyvlt2, G. Pénissard1, V. Prosser2, D.Renard3, G. Sczigel4,and S. Visnovsky2

'Laboratoire de Physique des Solides, Bât. 510; ^Institut d'Optique Théorique etAppliquée, Bât. 503; 4 Institut d'Electronique Fondamentale, Bât. 220; UniversitéParis-Sud, 91405 Orsay, France.

2Institut of Physics of the Charles University, Praha, Czechoslovakia.

Giant room temperature specific Faraday and Kerr rotations (~1have been measured in ultra-thin cobalt films with perpendicular magneticanisotropy, sandwiched between gold layers. Such a property is promizing forfuture applications to magnetooptical (MO) memories.We demonstrate that the enhancement of MO effects in such simple structuresis mainly related to multiple reflections at the interfaces, favoured at Au-plasma edge frequency. The dispersion of light transmission (Faraday rotationand ellipticity) or reflection (polar Kerr rotation and ellipticity) MO effects andtheir dependence upon Co and Au film thicknesses are satisfactorily

i interpreted from electromagnetic theory developped within the Yeh formalism.

j 6P:a33: EVIDENCE OF THE NEGATIVE-DIFFERENTIAL-RESISTANCE EFFECT IN HIGH-T OXIDES:I PROSPECT OF THE NONJOSEPHSON SUPERCONDUCTIVE ELECTRONICS °

: Roberto Nicolsky and Adir M. LulzInstituto de Fisica, Universidade Federal do Rio de JaneiroC.P. 68528, Fax: + 55 21 280-7693, Rio de Janeiro 21945, Brazil

A recent theory1 which explains the nonlinear current-voltage curves (CVC)of metallic (nontunneling) Josephson junctions, also called weak-links,predicts a novel effect: the negative-differential-resistance (NDR), whichhas been experimentally verified very recently in conventional Materials.The high temperature superconductors exhibit the NDR effect explicitly ina number of CVC In the low-voltage range, as well as other CVC have clearevidence for such phenomenum. This effect Is aalnly present in artificialsystems, as Junctions and point contacts, in any kind of hlgh-Tc oxides.

; It opens a prospect for a new superconductive electronics based on the: time average current-voltage response in the NDR range, instead of the' Josephson oscillations. It allows the use of arrays of Metallic Junctions,| because it avoids the need of phase locking, and the power output can| easily reach several microwatts. The Host relevant possible uses of the! »etaille Josephson junctions as NDR devices are extensively discussed.

'(••

I (1) R. KUmel, U. Gunsenhelaer & R. NIcolsky, Phys. Rev. M 2 , 3992 (1990).| (2) H. Ohta & T. Matsui, presented at 1TS-HTSC III, to appear in Physic* C

I 63

K'1

6P:a34

LOSSFREE AND DISSIPATIVE LATERAL MOTION OF AMAGNET LEVITATED BY A HIGH-T, SUPERCONDUCTOR

T.H. JOHANSEN, H. BRATSBERG and Z.J. YANG.

Department of Physics, University of Oslo.P.O. Box 1048, Blindem, 0316 Oslo 3, Norway.

The levitation force between a permanent magnet and bulk high-Tc supercon-ductors is known to be highly hysteretic for large (>mm) relative displacements.Using harmonic excitations we have studied the lateral component of the forceon a small magnet from a Bi-based superconductor. Applying lateral amplitudesfrom 1/zm up to lmm we find clear evidence for a transition from an elastic (nohysteresis) to an inelastic interaction. The result is interpreted as a flux pinning-depinning effect. Crossover amplitudes up to several /im have been observed.

Magnetic levitation is an area where today one has great promise for applicationsof the new ceramic superconducting materials. The existence of a lossfree rangein amplitude is a very relevant aspect of the levitation phenomenon, as it essen-tially defines limits for how precise levitated objects can be positioned.

6P:a35

Shear mnad attenuation hi layered high-Tc eupreconduetora.

I»E>Dwulyjeiikw

Uoieom Pkfticl Society Lenitukf pro*. S3, F1AN, SU-t 179*4 Moscow, Jtwim

The meat remarkable effects afcmrid be expected for t i — wrmi wave* mpore materials, bat eonw poh/cryatallme aampk* and cryetaUhw of kgrred

iprapertie. -

1. K J A M . WJ».Wiaft«*, M.-G. Xm. M-Levy, Btmai K3arat«, AJCStagh,.S.OMifekr, V.M.Le TMMn»ean. Phys. Rev., l t t# , B4S, a.4, p.3S«f.3. A. Kan. Z.Phyji, B., 1M#, T.7«, n.J, p.Jt7.

64

6P:a36EFFECT OF COMPLEX STRUCTURE OF HIGH TEMPERATURE

SUPERCONDUCTORS ON ITS DYNAMICAL CHARACTERISTICS

A.M.KOSEVICH, E.S.SYRKIN, S.B.FEODOSYEV, AND I.A.GOSPODAREV

B.I.Verkin Institute for Low Temperature Physics &

Ingeneering Ukr. Academy of Sciences, Kharkov, 310164, USSR

The partial distribution functions of the frequencies

calculated on the basis of the simplified model for high-tem-

perature superconductor of YBa^up^ -type. These functions

contain information about the vibrational characteristics of

each layer in the compound under study. The comparison of the-

se functions for the cases S = 0 and S = 1 is carried out.

Calculations are realized by Yacobian matrices techni-

que, based on the construction of the so-called spectral den-

sities. The connection between partial functions of frequency

and spectral densities is determined.

6P:a37

Renormalization of phonon frequencies by electronic carriers inlayered high-temperature superconductorsG. HASTREITER, D. STRAUCH, J. KELLER

Institut fur Theoretische Physik, Universitat Regensburg,W-8400 Regensburg, Germany

It is generally assumed that there are free electronic carriers associated with the CuOjplanes in high-temperature superconductors. Regarding these carriers as being strictlyconfined to the two-dimensional planes but free within these planes we investigate the

coupling of the electronic system to lattice vibrations (the latter within the framework -of a shell model of lattice dynamics). i

We discuss the influence of the electron-phonon interaction in layered supercondutors *on frequencies and eigenvectors of phonons with different polarization and arbitrary 'Iwavevectors. Among others, we find a complete suppression of the LO-TO splitting l

for modes polarized along the conduction planes due to screening by the free carriersand a strong renormalization of some phonon frequencies by particle-hole excitations.Numerical results are presented for YBa2Cu3C>7.

65

6P:a38

MODE-SOFTENING AND STRUCTURAL TRANSITIONS IN LAYEREDOXIDE PEROVSKITES

H. BLASCHKE and G. MEISSNERTheoretische Physik, Universitat Saarbrlicken, Germany

The low-temperature orthorhombic (LTO) phase of some layeredid kit lik L N i O L B C O h i t

p ( ) p yoxide perovskites like LagNiO. , or La2,,.Ba CuO. having twoformula units per primitive ceil may exnioit a further struc-tural transition into a low-temperature tetragonal (LTT) phasewith four units depending on the Ba-doping x or the oxygenexcess 6 respectively. Since these compounds moreover have a 1high-temperature tetragonal (HTT) phase above some elevatedtemperature Tg, we have investigated mode-softening in theLTO phase of the possible sequence of transformations:HTT* LTO* LTT. Estimates for non-universal parameters of anappropriate Ginzburg-Landau theory for a two-component order-parameter, as being obtained from a comparison with experi-ments, are briefly discussed.

6P:a39EXPRESSION FOR THE CRITICAL CURRENT DENSITY OP THEHIQH-TL J>ERATURE SUPERCONDUCTORS

Z. RAJILIC AND D. Lj. MIRJANICFaculty of Technology, University of Banjalulca,D. Mitrova 63 b, 78000 Banjaluka, Yugoslavia

The expression for the critical current density <jc>at zero temperature and zero applied magnetic fieldis derived in the three-dimensional bigausson modelof high-temperature superconductivity based on asystem of non- linear equations with logarithmic non-linearity. The obtained order of magnitude for jo ofsingle-crystal YiBa2CuaO?-x is supported by someexperiments. The derived expression enables us toexplain the experimental fact that jc of a thin epi-taxial film is significantly higher than jc of asingle-crystal sample of the same compound. We canalso describe the simultaneous rise of jc and the ;velocity of sound by some treatments of ceramic ~\YiBa2Cu3O?-x. It is discussed the possibility of jc Aimprovement by an applied oscillating electric field.

66

6P:a40STUDIES OF STRUCTURAL CHANGES IN HIGH TEMPERATURESUPERCONDUCTORS BY ELECTRON ACOUSTIC MICROSCOPY ANDCATHODOLUMINESCENCE

J- Piqueras, P. Fernandez and F. Domfnguez-AdameDpto. Ffsica de Materiales, Facultad de Ffsicas,Universidad Complutense, 28040 Madrid, Spain

Scanning electron acoustic microscopy (SEAM) and

cathodoluminescence (CL) in the scanning electron microscope are used to image

different phases in sintered YBasCu3O7 and BijSrjCaCusC^ and to detect phase

transitions below room temperature. The evolution of the SEAM and CL signals

with temperature, between 85K and 300K, shows the existence of transitions

previously reported in studies of thermal and structural properties of these

materials, and enables the observation of the structural changes with the spatial

resolution inherent to the used microscopy techniques.

6P:a41

ON FIELD-INDUCED GRANULAR BEHAVIOUR IN DEOXYGENATED AND/OR IRRADIATEDHIGH TEMPERATURE SUPERCONDUCTORS

S. A. SERGEENKOVNeutron Physics Laboratory, Joint Institute for Nuclear Research,141980 Dubna, USSR

The experimentally observed1"3 in deoxygenated and/or irradiated high tem-perature superconductors (HTS) correlations between defect flux pinning,anomalous (non-logarithmic) relaxation of magnetization, critical currentenhancement, double-step behaviour of the power-law current-voltages,field-Induced crossover of irreverslblllty line in the H-T plane, paracon-ductivlty and fluctuation-induced diamagnetlsm as well as flicker noisespectrum in HTS SQUIDs vs. applied magnetic field, oxygen deficiency, ir- 1

radiation fluence and dislocation density are discussed via a new model of igranular superconductor with defect-mediated intra/inter-graln boundary Iweak links. ?

l.Daeumling M. et al., Nature 346 (1990) 332. ?2.Gerber Ch. et al., Nature 350 (1991) 279. I3.Clvale L. &t al., Phys.Rev. Lett. 67 (1991) 648. k

67

6P:a42COMPARISON OF THE U(J)-RELATION FOR DIFFERENT HTC-SUPERCONDUCTORS

M.REISSNER AND W.STEINER

Institut fUr Angew?ndte und Technische Physik, T.U.Wien, A-1040, Austria

It has been shown1 that typical distributions of activation energies exist

for the different classes of high temperature superconductors, if these

distributions are determined within a model of Hagen and Griessen2. One of

the basic restrictions in this model is the assumption of a linear

relation between pinning potential U and critical current density J.

It is the aim of this paper to Investigate the U(J)-relation for the

different hTc-materials and to discuss their influence on the distribution

of activation energies.

1. Re I liner H. and Steiner W., Supercond.Scl.Tochnol. (1991) In press.

2.Hagen C.W. and Crlessen R., Studies of High Temperature Superconductors

Vol.3 (1991), ed. A.V.Harllkar (New Vork: Nova Science Publishers) 159.

6P:a43- COMPLEX AC-IMPEDANCE OF HTSC-FILM

AND EFFECT Of ULTRASOUND

A.Voronel, S.Feldberg, School of Physics & Astronomy,Tel-Aviv University, Ramat-Aviv, 69973, Tel-Aviv, Israel, phone

I 972-03-93156469i M.Levin, R.Pogreb, V.Sandornirsky, Research Institute,i College of Judea and Samaria, 44804 , Ariel, Israel, phone5 972-03-9356469

;V Detailed investigation of frequency dependence of HTSC-r film AC-impedance in the range of frequencies from 20Hz up to;.; 13MHz has been performed at low and room temperatures.;i The aim of this investigation was to study a possibility\ to analyze the sophisticated HTSC-film structure by simulationy. with an equivalent electrical circuit (including percolation| network).| The changes of this circuit parameters have been observed| near Tc. For revealing the origin of these changes theI influence of ultrasound on AC-impedance was measured.%. Ultrasound propagation leads to testery of mechanicalfc properties as well.

I 68

6P:a44SUPERCONDUCTING PROPERTIES OF W Si /Si MULTILAYERS

x y

VAVRA I., LOBOTKA P., BEKACKA S., SENDER^ R*Institute of Electrical Engineering, SAS, 842 39 Bratislava, CSFR"institute of Physical Electronics, SAS, 921 01 PieStany, CSFR

The W Si /Si multilayers (ML) with equal layer thickness of W Si and Si (1 mm)x y x ywere prepared by electron beam evaporation in uHxahiohvacuum. Each sample con-tains 10 layer pairs. The composition ratio x:y changed from 4:1 up to 1:6.All the ML's had amorphous structure. Comparing to the W/Si multilayer, whichis superconducting with T =4,21, critical temperature is reduced with increa-sing Si content. At composition ratio 2:1 T is 1,52 K. The multilayers with

chigher Si content are non superconducting. Superconductivity was observedalso in the normal direction on ML at the same temperature.

6P:a45JOSEPHSON EFFECT IN MAGNETIC SUPERCONDUCTOR

J. KUZNlK

Institute of PhysicsCzechoslovak Academy of Sciences, 250 68 Rez, Czechoslovakia

K. ROGACKI

Institute of Low Temperature and Structure ResearchPolish Academy of Sciences, 50-950 Wroclaw, Poland.

We present the first observation of Josephson effect in imagnetic superconductor GdMo Se . Point contacts and break ?

6 8 .j

junctions have been fabricated and measured in the temperature «

range above 1.25 K. Temperature dependence of the Josephson A,

critical current was investigated. An exceptional phenomenon |

- the formation of so called devil's staircase - was observed ;

on junction I-V characteristics after 9.5 GHz microwave

irradiation.

69

6P:a46

ALTERNATIVES TO THE F R O H L I C H TRANSFORMATIONIN SUPERCONDUCTIVITY

M. WAGNERInst. f. Theor. Physik, Univ. Stuttgart, Pfaffenwaldring 57, D-7 Stuttgart 80

One of the early brilliant achievements in superconductivity researchwas Frohlich's transformation of 19521, which deduces an effective electron-electron interaction from the original electron-phonon Hamiltonian. How-ever, this transformation displays two undesired features: a) it cannotbe written in a closed form , and usually is given to 2nd order only b)the effective electron-electron interaction (2nd order) incorporates bothattractive and repulsive terms.As shown earlier2 there exist unitary transformations for the electron-phonon problem which can be given in a closed form. They correspondto the choice of a "moving base" for 2nd quantisation depending on theinstantaneous nuclear displacements Q. Similar transformations may befound which correspond to a base motion in nuclear momentum space P.The relevance of these transformations and combinations thereof forsuperconductivity will be discussed.1. H. Frohlich, Proc. Roy. Soc. A215, (1952), 2212. M. Wagner, Phys. Stat. Sol.(b) ; ;5( l98l) , 617

6P:a47

A THEORY FOR THE EFFECT OF IMPURITIES ON THE RAMAN SPECTRA

OF SUPERCONDUCTORS

Thomas Peter Devereaux

Max-Planck-Institut fur Festkorperforschung, Heisenbergstr. 1, D-7000 Stuttgart 80,

Federal Republic of Germany

A gauge-invariant theory for the effects of impurities on the electronic Raman scatte- 1

ring by pairs of quasiparticles in superconductors will be presented. It will be shown

that the Raman spectrum is strongly affected by impurity scattering due to aniso- ;.-

tropic mass fluctuations, and symmetry dependent line shapes can be obtained for '"l a

anisotropic impurity scattering. For strong impurity scattering it will be shown that I

the peak of the Raman spectrum does not coincide with the energy gap. Implications

for the Raman spectra of the cuprates will be discussed.

70

\-

6P:a48READ-OUT SCHEMES FOR REDUCTION OF FLICKER NOISE IN DC SQUIDS

Staniulav Papez, Peter VrabCekInv titute of measurement science SAS, DufaravsAa cesta 9,842 19 Bratislava.CSFR

There are controversial demands for user qualities ofDC-SQUIDs: the low level of both white and 1/f noise, thesimple read-out electronics and the negligible crosstalks inthe multichannel magnetometrie systems. We analyze the problemof flicker noise restraining and its consequences to the otherrequirements as mentioned above. 1/f noise behaves as fluctu-ations of critical currents or magnetic flux affecting theDC-SQUTD sensor. Common equipment for 1/f noise reduction usedouble-frequency driving - besides of flux modulation, thedriving current is modulated In principle, the read-outelectronics is able to eliminate the fluctuations of criticalcurrents only. Flux fluctuations are strong dependent on thesensor quulity. The ways of compensation of critical currentfluctuations are reviewed and the outstanding problems areindicated.

6P:a49SCALING OF THE VOLUME PINNING FORCE AND THE INFLUENCE OFTHERMALLY ACTIVATED FLUX MOTION IN TYPE-II SUPERCONDUCTORS

L.NIELinstitut fur Metallphysik / Kristall-LaborUniversitat Gottingen, Windausweg 2, 0-H3400 Gdttingen

It is convenient to express the volume pinning force Fp = BJe forconventional hard type-II superconductorsin terms of a scalinglaw Fp = const. .BcjT'fCb), and usually f (b)=bp(l-b)q x. In hightemperature superconductors the critical current and the volumepinning force drop to zero at a field B*(T) which is generallymuch lower than BC2(T). In this contribution the influence ofthermally activated hopping of vortices on the measured volumepinning force is investigated. At high temperatures F, isdetermined not only by the depinning critical current in absenceof thermal activation, jo(B,T) but also by the activation energyU(j/B,T). Therefore, the observation of a scaling law even athigh temperatures implies constraints on models for flux creepand the critical state.

1 Kramer E.J., J.Appl.Phys.44 (1976) 1360

I 71

6P:a50

ANTIFERROMAGNETIC ORDER IN UPt3 UNDER PRESSURE: EVIDENCE FOR A

DIRECT COUPLING TO SUPERCONDUCTIVITY

S.M. Haydend), L. Taillefer®, C. VettierO) and J. FlouquetW

(DH.H. Wills Physics Laboratory, University of Bristol, Bristol, BS8 1TL, UK

(2)Laboratoire Louis-Ned, CNRS, 38042 Grenoble, France

(3)European Synchrotron Radiation Facility, 38043 Grenoble, France

WCentre d'Etudes Nucleates, DRF/SPh, 38041 Grenoble, France

Neutron diffraction is used to show that a hydrostatic pressure of 4.0 ± 0.7 kbar destroys the

antiferromagnctic order in the heavy-fcrmion superconductor UPt3. Combining our results

with previous specific heat measurements, we show directly that there is a strong coupling

between the antiferromagneac and superconducting order parameters in this material. A p-T

diagram is constructed with four ordered phases meeting at a multicritical point

6P:a51

MAGNETIC PROPERTIES OF THE YBaCuO SUPERCONDUCTIVITY POWDERS

M.TIMKO, I.SARGANKOVA, A.ZENTKO, J.KOVAC

Institute of experimental physics, SAS, Solovjevova 47,

043 53 Kosice, Czechoslovakia

The autors have measured the magnetization for a number of

different sized YBaCuO superconductivity powders. Critical

current density was obtained from hysterezis loops based on Ii

the Bean model. The another critical magnetic properties of |

these powders are discussed too. J

72

6P:a52. 0/Zr02/SAPPHIRE LASER DEPOSITION

S.V.Gaponov, E.B.Kluenkov, L.N.MazoInstitute of Applied Physics USSR Academy of Sciences, 46 Uly-anov Str., 603 600 Nizhniy Novgorod, USSRM.Jelinek, L.Jastrabik, L.SoukupInstitute of Physics, Czech.Academy of Sciences, Na Slovance 2180 40 Prague 8V.HnatowitzInstitute of Nuclear Physics, ftez - Prague

Results of YBaCuO and ZrO2 laser deposition on 1102 sapp-hire are presented. Special laser system consisting of twocrossed laser beams of Sid^glass laser was used for the deposi-tion. Laser energy was 2.2 J, repetition rate 1 Hz and laserpulse duration was 30 ns.For ZrO2 laser deposition metallic Zr was used as a target.Quality of Zr0o buffer layer of 100 nm thickness was controlledby RHEED. l

Superconductive YBaCuO layer depsited on ZrO2 buffer was c-axisoriented. For YBaCuO film of 100 nm thickness deposited onZr02/1102 sapphire zero resistance temperature of 89.5 K was

; measured. Results of PIXE and RBS analysis are also published.i

!

6P:a53THERMAL CONDUCTIVITY OF

B. M. ANDERSSON AND B. SUNDQVISTDepartment of Experimental Physics, University of Umea, S-90187 Umea, Sweden.

\ We report data of the thermal conductivity X, on YBa2Cu4Og material, produced

by Hot Isostatic Pressing, in the temperature interval 30-300 K. For temperaturesbelow 100 K, \ was measured by a steady state method. In the temperature range

i from 100 K to 300 K, the thermal diffusivity was measured and X was calculated:. using literature data for the specific heat. Preliminary data show that the thermal\ conductivity increases by a factor of 2 from room temperature down to 100 K. The\ results will be discussed in terms of current theories for high temperatureI superconductors.

73

6P:a54

SUPERCONDUCTING FLUCTUATIONS OF TRANSPORT PROPERTIES

IN YBaCuO THIN FILMS

W.LANG*, G.HEINE*, H.JODLBAUER*. P.SCHWAB*, X.Z.WANG*, D.BÄUERLE*+Ludwig Boltzmann Institut für Festkörperphysik, Kopemikusg.lS, A-1060 Wien, Austria

and Institut für Festkörperphysik, Universität Wien, Austria

'institut für Angewandte Physik, Universität Linz, A-4O4O Linz, Austria

Measurements of the electrical resistivity, the migneioresislance and the Hall effect on

thin films of YBaCuO are reported in the fluctuation regime above T . The films have

been fabricated by pulsed-laser deposition in oxygen atmosphere on MgO substrates. The

rounding of the resistivity curve above T was analyzed in terms of the 2-dimensionaI

Lawrence-Doniach and Maki-Thompson theories for thermodynaniic fluctuations of the super-

conducting phase transition. The results are compared with superconducting parameters

estimated from the analysis of magnetoresistance and Hall effect measurements in the

fluctuation regime.

Supported by Fonds zur Förderung der Wissenschaft. Forschung, Ausiria, grant P8180

\ 6P:a551 MAGNETIC RELAXATION IN TIΠEPITAXIAL THIN YBaCuO THIN FILMS IN: BOTH CONSTANT AND CHANGING MAGNETIC FIELD

s L. POST, M. JIRSA and V. GREGOR

* Institute of Physics, Czechoslovak Academy of Sciences,i Na Slovance 2, CS-180 40 Praha 8, Czechoslovakia<Î The relaxation of the induced magnetic moment m (and closelyit3 related critical current j ) with time measured at constant

I magnetic induction B (conventional relaxation) is compared\; «xt

? at various temperatures with the magnetic moment values m on

i magnetic hysteresis loops recorded by VSM at various rates B =

| dB /dt of sweep (the loop relaxation) using generalized

I relation between sweep rate and time scales. The values ofîr magnetic moment m on hysteresis loops are consistent with

values of m measured by the conventional relaxation in

overlapping range of times. Total range of relaxation times

analyzed by both methods is 10~z to 103 s.

74

6P:a56LOCAL Cu(2) MAGNETIC BEHAVIOUR IN Y0.»71TOYbo.o»Ba2Cu8Ox

AS A F U N C T I O N OF O X Y G E N LEVEL

J.A. HODGES, P. BONVILLE, P. IMBERT, G. J E H A N N OSPEC-DRECAM, Centre d'Etudes de Saday, 91191 Gif-sur-Yvette Prance.

When substituted into YBa2Cu3Oc, a Yb3 + ion experiences a Cu(2) derived molecularfield when its neighbouring Cu(2) moments are magnetically correlated*1'.

We have used 170Yb Mossbauer spectroscopy to examine (up to 70K) the static anddynamic characteristics of this local Cu(2) derived molecular field in the mixed spinglass/superconducting region which is present around z ~ 6.5. For x values at the lowerend of the mixed region, the majority of the Yb 3 + probes evidence local spin glassbehaviour and the fluctuation rates of the local molecular fields decrease progressivelyas the temperature is reduced. As x is increased, an increasing fraction of the probesnow show no detectable molecular fields. We interpret this as evidencing local super-conducting behaviour where at temperatures much lower than the gap, no magneticfluctuations are expected to be present. In the range 6.4 < x < 6.7 we examine therelative evolution of the two subsystems which appear to form an interacting ensemble.

! (1). J.A. Hodges, P. Bonville, P. Imbert, G. Jehanno, Physic* C, to be published.

| 6P:a57v

I STUDIES OF Ca-Th SUBSTITUTION IN YBa2Cu3O7-8 BY RAMAN SCATTERINGI AND CALCULATION OF THE ELECTRON-PHONON INTERACTION.

L.BORJESSON, H.V. PHUONG., T. JARLBORG#, M. ANDERSSON*. AND O. RAPP*Physics Dept, Chalmers Univ. Techn. S-412 96, Goteborg, Sweden, #Dept de Physique de laMatiere Condensed, Univ. de Geneve, 24 Quai Ernest Ansermet, CH-1211 Geneve,Switzerland, and *Solid State Physics, The Royal InsL Techn. S-10044 Stockholm, Sweden.

Ca and Th can be substituted for Y up to x-0.1 in Yi.2xCaxThxBa2Cu3O7-s in dieorthorhombic phase.1 This substitution is iso-electronic with small changes in lattice parameters

; and preserved oxygen concentration. Yet the superconducting Tc decreases by dTc /dx » -130 K,i which is a surprisingly large depression rate. We have investigated mis substitution by neutron

diffraiptinn|2 Raman yaltmng anH cairqiiatirm); pf t|m t&wtrrm phnnnn inlyraninn\ The atomic distance between chain Cu(l) and apex oxygen O(4) and the vibration frequencyI of the « 500 cm-1 Raman mode associated with 0(4), both increase slightly with Ca-Th{• substitution. Both these changes are unusual and opposite in sign to those usually observed in| substitutions in 1:2:3 compounds depressing Tc. The electronic part of the electron phononi interaction n, shows a strong sensitivity to small changes in the Cu(l)-O(4) distance, as| anticipated by previous observations.3 A sizeable decrease of i\ is calculated for increased Cu(l)-I 0(4) distance. We thus find shifts both in a characteristic phonon frequency and in ij in the| directions consistent with the observed decrease of Tc.

I 1. M. Andersson, Z. Hegediis, M. Nygren, and 6 . Rapp, Physica C160,65 (1989).I 2. M. Andenson, 0 . Rapp, and R. Tellgren, Solid State Commun. 81 (1991) (hi press).I 3.T.Jarlborg,SolidSuteCommun.71,669(1989).

I 75

6P:a58

NORMAL STATE HALL ANGLE DETERMINATION IN OXYGEN DEFICIENTEPITAXIAL FILMS.

B. WUYTS, M. MAENHOUDT, Z.X. GAO, S. LIBBRECHT, E. OSQUIGUIL, andY. BRUYNSERAEDELaboratorium voor Vaste Stof-Fysika en Magnétisme, Katholieke Universiteit Leuven, B-3001 Leuven, Belgium. '

Systematic resistivity />(T) and Hall coefficient Rj/(T) measurements in oxygen deficientYBa2Cu3Ûr (6.5 < x < 7) epitaxial films, show that the temperature dependence of the |Hall angle, cot(fl/j) = aT2, is valid for all x-values and irrespective of the temperature ^dependences of p(T) and R«(T). This could indicate the existence of two electronic re-laxation rates, as recently proposed by P.W. Anderson in the framework of the Luttingerliquid model. The slope a varies linearly with Tc, suggesting that a rather than R# is ameasure of the carrier density in the CuO2 planes.

This work is supported by the High Temperature Superconductivity Impulse and Con-certed Action Programs, financed by the Belgian State.

6P:a59

SAW ACOUSTOELECTRIC EFFECTS IN LAYER STRUCTURESWITH HTSC (1;2:3)-F1LM5

M.Levin> R.Pogreb, V.Sandomirsky, College of Judea andSamaria, Research Institute, Ariel, 44804, Center of SolidState Physics, Israel, phone (972>-03-936-64-69

A.Voronel, S.Feldberg, School of Physics and Astronomy,69978, Tel-Aviv University, Israel, phone (972)-03-545-9166

Acoustoelectric effect (AE) was investigated in two kindsof sandwich structures :

a) HTSC-film on piezodielectric substrate (LiNbOs).Surface acoustic wave (SAW, 24 00MHz) propagates along thesurface of piezodielectric.

b) HTSC-film on nonpiezodielectric substrate - air gap -piezodielectric layer. SAW propagates along the surface ofpie^odielectric. The width of air gap should be less then thewavelength of SAW.

In the last structure one can also measure AE at thepresence of static electrical field (field-effect).

Modification of AE is observed at the transition throughfe.

Theoretical analysis of the data allows to separatemechanical and electrical effect of SAW - influence onHTSC-film.

76

6P:a60

INTERACTION OF Pb WITH YBaCuO THIN FILM SURFACE.

T.J.SARAPATKA AND P.MIKUS'IK

J.Heyrovsky Institute of Physical Chemistry andElectrochemistry, Czechoslovak Academy of Sciences,DolejSkova 3, 182 23 Prague 8, Czeohoslovakia

Nature of the chemical interaction between Pb overlayer andYBa2Cu30g g thin film surface is studied by X-ray

photoelectron spectroscopy. It is found that Pb withdrawsoxygen preferentially from high-Tc superconducting (HTSC)

phase where it reduces Cu selectively in a tine comparablewith the Pb deposition time. This fast process is followed bya much slower outdiffusion of oxygen from the deeper layersof the HTSC grains. Results of temperature, vacuum and Arsputtering effects on the YBaCuO thin film surfaces arepresented.

6P:a61

THERMODYNAMIC PROPERTIES OF PHASES IN THE Y-Ba-Cu-0 syste»

I( J. 5ESTAK and C. K. MOISEEV*I Institute of Physics of the Czech Academy of Sciences,| Na Slovance 2, 18040 Praha 8, CSFK and * Institute of/ Metalurgy, Ural Academy of Sciences, Sverdlovsk, Russia

The existence and stability of phases in the Y-Ba-Cu-0 sy-stem is survayed and analysed regarding the effect of con-taminations [1].Basic thermodynamic data are hypotheticallycalculated [2] for 32 possible compounds and compared withthe known data from literature. The role of oxygen ordering-disordering is discussed with respect to local thermodyna-mic conditions (curvature,stress) and formation kinetics

| [3]. The YBCO melt textured processing via fast quenchingI [4] and crystal growth in temperature gradient is included.

':. [1] J.Sestak "Phase diagrams in CuO HTSC",Pure Appl.Chem./ [2] J.Sestak, N.Koga "Problems of YBCO formation and decom-\ position kinetics and mechanism",Thermoch.Acta in printi f3] C.K.Moiseev, J.5estak et al "Calculation of thermodyna-[ mic functions of YBC.0 phases", Thermoch.Acta in print; [4] J.Sestak "Oxide melt fast solidification as a route to: prepare HTSC" in V.Narlikar (ed) "Studies of HTSC",1 p.23, Vol. 7, Nova Science Publ., New York 1991

77

6P:a65CM-SITE REPULSION AND SPIN ORDERING OF ITINERANT ELECTRONS

E. V. KholopovInstitute of Inorganic Chemistry, 630090 Novosibirsk. USSR

The on-site repulsion is a natural type of interaction betweenelectrons in complex modern compounds. As a result, electronstry to avoid one another there. However, only electrons withopposing spins can meet at the same site. Therefore the inter-action at hand can be the reason of spin ordering! leading tothe appropriate modification of the ground-state configurationof electrons in question. He adopt a one-band model here. Thetight-binding approximation is used in the cases when the con-crete form of the band spectrum is required. It is shown t.hatdifferent types of the ground state are admissible in depend-ence on the values of the corresponding parameters of thetask. In particular, if the concentration of electrons in theband of interest is small enough, then the ordinary paramag-netic state is survived. The ferromagnetic case is typical forlarge electron contents. In this event the spin splitting ofthe electron band occurs. Such a state is responsible for theconfined holon statistics discussed earlier. Both of the abovepossibilities compete with an antiferromagnetio spin alignmentof electrons, which corresponds to the spatial separation ofdifferent spin projections. Several types of the antiferromag-netic ordering are proposed and discussed.

6P:a66SPECIFIC HEAT OF MAGNETIC KONDO LATTICES UNDER HIGH PRESSURE

A. EICHLER, E. HANKE, T. KIRSCH, J. MICHAL, and S. SULLOWInstitut f. Technische Physik, TU Braunschweig, Mendelssohnstr. 2,D-3300 Braunschweig, F.R.G.

From measurements of the specific heat under high pressure the pressuredependence of the Kondo temperature as well as of the magnetic orderingtransitions can be determined. By that meanB information on the competitionbetween the Kondo interaction and the RKKY interaction leading to magneticorder can be gained. This competition is very sensitive on the decrease ofthe atomic distances and the resulting change in the hybridization strengthbetween the f-states and the conduction band states.CeAlg, Cebg, and CePb3 have been investigated as representatives of anti-ferromagnetically ordering Kondo lattices. They show heavy fermion charac-ter of different strength and exhibit similarities in some details of the mag-netic structure and phase diagrams. The comparison of the results showsindividual differences, which call an unifying description of these threematerials in question.

78

6P:a67

AGING EFFECT IN SPIN GLASSES REVISITED

P. ERHART, B. SENNING and F. WALDNERPhysics Institute, University, CH-8001 Zurich, Switzerland

The "aging" or "memory" effect is considered to be a strong evidence for a spin glass. Whena sample is, for example, field cooled at time tA, and when later at time ts the field is setto zero, the resulting magnetization m might exhibit a special feature at time tc around*B + (<B — <A) when plotted as a function of the logarithm of a time t' starting at time ta-

A 'minimal global model' will be described which implies either the independent decay of adistribution of activation energies or a single characteristic activation energy U,ff(m) as afunction of the decaying m. A superposition of such decay functions starting at tA or tsdescribes well the shape of the decay measured by Svedlindh et al.1

However, the main goal of this contribution is to show that this effect is rather a conse-quence of the special plotting as a function of the logarithm of the delayed time f, and nota unique indication for a spin glass. Why ? A straightforward calculation reveals that adecay function x(t) which is close to a power law t~h exhibits an extremum in its derivativedz(f= i '+ i l i , ) /d( lnt ' ) in respect to the logarithm of time f = i - < „ at t' « tw/b for arbitrarytw. Thus, if b w 1, an 'aging' or 'memory' peak in dx/d(\nt') is 'seen' around t' ss tw.

Moreover, a decay x(t) ~ 1 — 6 In t will exhibit an extremum of the second derivative aroundt' K tw when plotted accordingly as a function of lnt' , quite similar to measurements insuperconductors.2

1. P. Svedlindh et a/., Phys. Rev. B 35 (1987) 268.2. C. Rossel et al, Phys. Rev. Lett. 62 (1989) 681.

6P:a68

THE GROUND STATE OF FERMION TRIMER

Dr STEFAN SUNARlC, Prof.MASlNSKOG FAKULTETA88000 MOSTAR - YUGOSLAVIA

Dr TULLIO PERSI, Doc.FAKULTETA GRADJEVINSKIH ZNANOSTI51000 BIJEKA - CROATIA

The wave functions of these systems are given as the products

of two particle functions. The general formula for three par-

ticle correlation functions of helium trimers in r-space has

been found in paper 11 | .

In this paper, the general formula for the ground state ener-

gy of fermion trimer (3He) with spin 1/2 has been found.

|1| S.Sunaric and T.Persi: "WAVE FUNCTIONS OF HELIUM TRIMERS11

- in print.

79

6P:a69CYCLOTRON RESONANCE OF ELECTRONS IN THE WIGNER SOLID REGIME

M. BESSON, C. M. ENGELHARDT, E. GORNIK, G. WEIMANNWalter Schottky Institut, TU Munchen, Am Coulombwall, D-8046 Garching

Cyclotron resonance (CR) of specially designed high mobility 2D electron systems has beenstudied systematically in the extreme quantum limit. The measurements are performed with arapid scan Fourier transform spectrometer connected to a 17T superconducting magnetsystem in the temperature range 0.4K to 15K. The samples consist of a one sided modulationdoped GaAs/AlGaAs single quantum well (SQW) and an undoped inversion channel. Thecarriers of the SQW screen the Coulomb potential of the ionized donors, thus leading toextremely high mobilities in the inversion channel, evident from very narrow CR line-widths(0.15cm-1). The free carrier density in the inversion channel is between M0 1 0 cnr 2 and6-1010cnr2. Filling factors down to -1/20 are investigated. Below a critical filling factor-1/10 an additional CR line at the high energy side of the conventional CR is observed for allsamples. The intensity ratio of these two absorption lines depends strongly on temperature.The position of the new CR is compietely independent of temperature in contrast to the con-ventional CR, which shifts systematically with increasing temperature to lower energies. Withincreasing magnetic field and decreasing temperature a complete condensation into the novelCR occurs with a "melting" temperature of about IK. The different temperature behaviour ofthese two resonances indicates the existence of two phases of electrons. The new CR isattributed to a lowered ground state. The energy gap of -4K and the density of states in theground state break down abruptly at the critical filling factor. A further feature of the novelphase is a reduced CR absorption. The new ground state can be interpreted as a magneticallyinduced Wigner crystal.

6P:a70

GROUND STATE ENERGY OF MANY-BODY FERMI SYSTEM BY lSL\ ( i FEEN-BERC-J PERTURBATION THEORY

•f. Kilic. F&rtiltr ftf ScirftfPS att/i Arts i tttrersi/y of Split. Sitlu.andI Persi. Department of Civil Engineering, l.'nivf rsii.y " IRi jeka . Rijefca. Croatia

Hitherto Feenberg perturbation theory was applied oiilv to boson systems. In the presentw».rk we apply tins general method tw ft-riiiiuii systems. \ \v d-Tive :tti txpr 'ssioti fur I lieground state energy of N icirnuenl interacting fennions. It represents a generalization <>(tlie (ji'll-Manii - Brut-ckiier K!M-Bi formula .'which »v;u> ...l.tfiiin -I for ..l.iio< rlfctron ft«i!>)

The relation of our result with Rayleigh - Schrodinger perturbation theory is presentedas well.

The evaluation of our results is done for electron gas and tor a system with short rangerepulsive and longer rangf at tractive potential. Wt- fiuphasi/ . ili.it oijr ri-siilt ii, tin Sr»torder of denominator includes ilirecl and exchange scattering with iincxi'ited partirles"which vu:r<r not coritaineti HI ( ( iM-B) tlifury. Al.so usin^ lk|UiiJ li'liuiu t!ifr<- paranioterbwe find that the same quantity is '1\)% different in comparison with KjM-H) ones.

Af( i-atufatioiis arc p i i f •rineif iti frit- jiani<f<- f,,isis

I 80

6P:a71

EXACT U INFINITE RESULTS FOR THE HUBBARD MODEL ON A 4x4CLUSTER POINTING TOWARDS A FERROMAGNETIC FERMI LIQUIDNEAR HALF-FILLING

G.Chiappe(l) , E.Louis(l), F.Guinea(2) and J.A.Verges(2)(1) Deparlamcnto de Fi'sica Aplicada, Universidad de Alicante, Apartado 99, 03080 Alicante,Spain.(2) Institute) de Ciencia de Materials de Madrid (C-XII), Uiiiversidad Aiitonnnia de Madrid,28049 Madrid, Spain.

The Lanczos method has been used to obtain the groundstale and some excited states of aone-band Hnbbard model of infinite site repulsion on a 4x4 cluster of the square lattice. Allthe fillings have been considered. Calculations are based on an algorithm that selects the wholespace of electron configurations that avoid double electron occupancy. Therefore, our resultsare exact within numerical precision. The analysis of the Brilloiun Zone occupation shows thatnot only the Nagaoka state but also the groundstates of up to five holes produce an emptyingof the upper part of a ferromagnetic band, i.e., the corner of the Drillouin Zone is progresivelyemptied as holes are introduced into the half-filled system. The physical interpretation of theseresults is simple: only one electron per k point is allowed near half-filling. On the other hand,the behaviour of the Hubbard model in the dilute limit, is mor" conventional: approximately twoelectrons occupy the lower part of the one-electron band. This picture remains iclatively exactup to a filling of six electrons.

6P:a72

WARD IDENTITIES AND RESPONSE FUNCTIONS IN THE LUTTINGERLIQUID

C. DI CASTRO and W. METZNERDipartimento di Fisica, Universita "La Sapienza", P.le A. Moro 2, 00185Roma, Italy

High-Tc superconductivity has renewed the interest in non-Fermi-liquid be-havior of interacting electron systems. A classical example is the breakdownof Fermi liquid theory in the one-dimensional case. We show that the field-theoretic renormalization group allows for an efficient exploitation of thesymmetry properties of the systems via the related Ward identities. In par-ticular, the separate charge conservation in low energy scattering processesfor particles near the left and right Fermi point gives rise to i) a vanishing/^-function with a corresponding line of fixed points and non-universal criticalexponents, ii) RPA-like density response, iii) finiteness of the compressibil-ity despite the presence of a singular propagator with anomalous dimension.Possible extensions to higher dimensions favor the method of Ward identitieswith respect to the more traditional bosonization approach.

81

6P:a73

MOMENT EXPANSION OF THE TWO-PARTICLE GREEN

FUNCTION FOR THE HUBBARD HAMILTONIAN

M. KOTRLA AND V. DRCHAL

Institute of Physics, Czechoslovak Academy of Sciences, Prague

Na Slovance 2, CS-180 40 Praha 8, Czechoslovakia

Energy moment expansion of the two-particle Green function for the Hub-

bard Hamiltonian is developed employing equations of motion. We calculate

explicitly first five exact moments. These exact results are used to evaluate

the accuracy of several approximative solutions for the two-particle Green

function which were used in the study of the Auger spectra of transition

metals.

6P:a74PERTURBATION THEORY FOR THE TWO-DIMENSIONAL HUBBARDMODEL: ABSENCE OF QUASIPARTICLE EXCITATIONS

J.Galan and J.A.VergesInstituto de Cicnciade Materials de Madrid (C-XII), Universidad Autouomade Madrid, 28049Madrid, Spain.

The Green function of the two-dimensional Hubbard model has been calculated through thesecond-order selfenergy diagram. Comparing our perturabative total energy results with exactresults on small clusters, we conclude that the approximation works up to U values close to 8.In this way, we extend our previous caiculations(l) up to realistic U values with the advantageof obtaining the Green function of very large clusters of the square lattice (up to 50x50 sites). iThis allows the study of the imaginary part of the selfenergy near the Fermi level. Its behaviour .>;is lineal not only near half-filling (we avoid this last situation due to the appearance of a highly ^degenerate one-electron state that is neither completely occupied nor completely empty) but |also for the most interesting range of hole doping (about 15 percent holes). This behaviour ifturns on to the more conventional quadratic one when doping is large enough. The lineal part %of the imaginary part of the selfenergy -as it also appears in a pcrturbative study of the one- t j |dimensional Hubbard model- precludes the use of the concept of quaaiparticle and, therefore, ;*the conventional Fermi liquid theory. .' '

1. J.Galan and J.A.Vergcs, Phys.Rev.IJ 44, 10093 (1991).

82

6P:a75SELF-CONSISTENT THEORY OF THE ANDERSON LATTICE

J. PETRU

Institute of Physics, Czechoslovak Academy of Sciences, Prague

Na Slovance 2, CS-18040 Praha 8, Czechoslovakia

The periodic Anderson model is studied using the irreducible Green functions method,

which makes possible the derivation of the exact Dyson equation and the exact self-

energy operator. In addition the method gives a generalized mean-field approximation,

which represent a unified and natural concept for a renormalized quasiparticle spectrum

ignoring the finite lifetime effects. The necessity of introducing auxiliary fields, such as

slave-boson is avoided. The formalism is flexible enough to describe the strong coupling in

mixed valence a.nd heavy fermion systems. The results are compared with what is known

from other approaches.

6P:a76ANYON STATES IN CRYSTALS WITH ROTATIONAL DEFECTS

V.A.OSIPOVLaboratory of Theoretical Physics, Joint Itistitute for Nuclear Research, 141980 Dubna,USSR

We show that rotational defects in planar elastic systems can change the statistics ofconducting electrons (holes). The reason is that the disclination flux can, in princi-pie, be fractional. This fraction of a flux is defined fairly well in crystals where thesymmetry of the lattice plays an essential role. In the framework of the gauge theoryof defects we h?ive found an exact topologically non-trivial solution for disclinationvortex. An attractive possibility for semion states in HTSC crystals with disclinationvortices is discussed. Noteworthy that the rotational defects (screw dislocations) wereexperimentally observed1 recently in YBatCuzOis films. The interaction betweenelectrons and acoustic waves is taken into account. As a result, free particles obeyingfractional statistics are found to be available only if their energies are larger than theFermi energy2.

I l.Gerber Ch. et al., Nature 350 (1991) 279.i§ 2,Osipov V.A., Phys.Rer.Lett. (sttbmht<xl}

83

6P:a77

PHASE DIAGRAM OF THE 2-D HUBBARD MODEL.

J. Beenen &: D.M. EdwardsDepartment of Mathematics

Imperial College of Science, Technology & Medicine180 Queen's Gate, London SW7 2BZ, UK

Ferromagnetic and antiferromagnetic phases in the doping (S) vs. interaction (U/t)phase diagram of the 2D Hubbard Model on a square lattice are determined, makinguse of a Green's-function decoupling scheme first introduced by Roth[l].The big advantage of this method is that it is analytic and thus can be applied toinfinitely large lattices.For various values of U/t ranging from 8 to oo graphs of magnetisation, total en-ergies, Fermi level, the location and width of up- and down-spin bands, have beencalculated as function of the doping fraction 6. The results agree qualitatively withthose of variational calculations.An extension of the method, to investigate a possible superconducting phase, isformulated and discussed. We find a gap equation for an order parameter thatmight explain the coexistence of magnetic and superconducting phenomena in highTc materials.

1. L.M. Roth, Phy». R*v. 1S4, no.3. 451 (186»).

6P:a78SINGLE PARTICLE AND OPTICAL GAPS NEAR THE METAL-INSULATOR TRANSITION

R. Raimondi, C. Oastellani, and M. GrilliDipartimento dt Fisica. Univcrsita "La Sapienza", 2, Piazzale Aldo Moro, 00185 Roma, ',Italy.Y. Bang, G. Kotliar, and Z. WangSerin Physics Laboratory. Rutgers University, P.O. Box 849, Piscataway, NJ 08854 USA

We analyze the collective excitations near a Mott-Hubbard and a metal charge transferinsulator transition, using the slave boson technique. We show that the Mott transition ^can be viewed as an exritonic softening, which takes place when the bound state betweenthe lower and upper Hubbard bands reaches zero energy. The exciton energy is related •'to the jump of the chemical potential at zero doping. In a charge transfer insulator this jmode describes a p-d charge fluctuation, i.e. it is a charge transfer exciton. In the single ••band Hubbard model the excitonic resonance describes virtual transitions between the •.lower and the upper Hubbard band. i

84

6P:a79

MOMENTUM DEPENDENCE OF THE SELF-ENERGY FOR THE 2-D HUBBARD MODEL.

C.J.Rhodes and R.L.Jacobs.Department of Mathematics,Imperial College of Science and Technology,180 Queen's Gate, London, SW7 2BZ. United Kingdom.

We have carried out accurate numerical calculations of the frequency and momentum dependenceof the self-energy, £(*,«), for the 2-D Hubbard Model within second order perturbation theoryon U/W for the half-filled and away from half-filled cases. Models of this kind are importantbecause they have been shown to be a good starting point from which to describe many of thenormal-state properties of High Tc superconductors. In our calculation, at half-filling, the nestingof the Fermi surface [1] gives rise to a linear w dependence of H(kj, w) which is the same as that inthe phenomenological marginal Fermi Liquid hypothesis proposed by Varma et.al. [2] to explainmany of the experimental results on the normal-state.The most important new feature of our results in the perfectly nested case is the appearance of astrong low energy peak in ImS(k,ui) when k is off the Fermi surface. The physical origin of thispeak, in terms of contributions to the momentum integrals of disjoint regions of phase-space, isunderstood and will be described. Relevance to recent angle resolved photoemission experiments[3] will be discussed. An explanation of normal-state tunneling results is also possible from ourcalculations.

1. A.Virosztek ind J.Ruvaldi Phyi. Rev. B42 4064 (1990)

2. CMVarma et.al. Phyr Rev. Lett. 63 1996(1989)

3. Takahashi et.al. Phy«. Rev. B39 6636 (1989)

6P:a80

ONE-PARTICLE SPECTRAL DENSITIES IN THE EXTENDED ONE-BANDHUBBARD MODELS.

M.P.L6pez Sancho, J.H.L6pez Sancho.M.C.Refolio and J. RubioInstituto de ciencia de Materlales de Madrid, CSICSerrano 144, 28006-Madrid, Spain

One-particle spectral densities, as well as charge and spincorrelations, of doped and undoped systems, are presented fordifferent size clusters of CuO2 units with periodic boundaryconditions, in extended one-band Hubbard models. A generalizedunrestricted Hartree-Fock calculation, which deals with chargeand spin fluctuations in a self-consistent way, is carried out iincluding intra-atomic and interatomic Coulomb interactions.The results are compared with, and discussed in the light of .•recent Lanczos and Monte Carlo calculations for small *clusters. Good agreement is found for U/t values up to 10 and Idopages of 0.2-0.25. Cluster-size effects are studied. |

II

85

¥••

6P:a81

ANTI-FERROMAGNETIC MOMENTS AND ONE-ELECTRON SPECTRA OF THE2D-HUBB ARD-PETERLS MODEL IN THE SELF-INTERACTION CORRECTED

DENSITY FUNCTIONAL FORMALISM

J.A.MajewskiPhysik Department, Technische Universiffit MUnchen, D-8046 Garching, FRG

We present results for the ground state properties and one-electron excitation spectra in thetwo-dimensional Hubbard-Peierls model near half-filling which incorporates both electron-electron and electron-phonon interactions. We find that the self-interaction corrected localspin-density functional theory (SIC-LSD) gives excellent agreement with exact results onsmall lattices. For infinite systems, the SIC-LSD predicts much larger energy gaps and anti-ferromagnetic moments man the plain LSD method. Noticeably, we find that lattice distortionsdestabilize the antiferromagnetic ground state in 2d and cause the electronic energy gap todecrease.The band structure in the SIC-LSD approximation is calculated in two steps. First, the totalenergy is minimized with a modified conjugate gradient method where off-diagonal Lagrangemultipliers are fully taken into account to guarantee orthogonality of the SIC orbitals. Theresulting Lagrange multipliers are diagonalized and give valence bands. In the second step, acomplete Hamiltonian, including both occupied and empty states, is constructed and the con-duction bands are calculated.

-i

I*

86

6P:bl01

AB INITIO CALCULATIONS OF YTTRIUM DISILICIDE AND INTERFACE WITHSILICON.

L. MAGAUD, J.P. JULIEN, F. CYROT-LACKMANNLEPES - CNRS - BP166 - 38042 Grenoble Cedex 9, France

Ab initio calculations of die electronic structure of Yttrium disilicidc have been performed usingthe LMTO-ASA method. Two different cases have been investigated: stoecheometric YS12 andSilicon deficient YSii.7 where one silicon atom out of every six is missing. We show that themain effect of these vacancies is to shift the Fermi level towards a much lower density region,stabilising this way the structure. The interface of YSi2 with Silicon is also investigated using asupercell technique. Comparison is made with results obtained through a tight-binding scheme.

6P:blO2

SPRAINING INTERMETALLICS FOR FUN AND PROFIT VIA TOTAL ENERGY CALCULATIONS

M.J. MEHL, D.A. PAPACOJSTANTOPOULOS, B.H. KLEIN, L.L. BOXERNaval Research Laboratory, Complex Systems Theory Branch, Washington, D.C.20375-5000 U.S.A.

Density functional based total energy calculations provide highly accu-rate predictions of the elastic moduli of simple metals and binary intermet-allic alloys. The reliability of these results allows us to predict the elas-tic properties of new materials, providing a selection criteria for experi-mentalists. We present a review of the method, and discuss the results of ourstudies of the eleastic properties of intermetalllc systems.

The calculation of elastic moduli involves small strains, changing thelengths of the primitive vectors by less than 10%. large strains can be usedto transform the structure of the crystal. Hi particular, a class of "magic''strains exists, which transform the crystal into itself. He have discovereda correlation between the barrier heights in these lattices and the meltingtemperature. Thus, static lattice calculations may provide information aboutthe solid-liquid phase transition as well as properties of the solid.

87

6P:blO3

AB INITIO ELASTIC CONSTANT AND ELECTRONIC STRUCTURE OFAIP

P. RODRIGUEZ-HERNANDEZ and A. MUNOZDepartamento de Ftsica Fundamental y Experimental, Universidad de La Laguna, E-38204La Laguna (Tenerife) - Spain;

We present a first principles study of electronic and ground state properties of AIPevaluated in the context of the local density formalism, using nonlocal normconservingpseudopotentials. The calculated band structure and lattice constant are found in goodagreement with the existing optical data and with other empirical calculations. We havestudied the elastic properties of AIP by computing the components of the stress tensor forsmall strain using the method developed by Nielsen and Martin'1'. We also obtain somephonon frecuencies at different k points. All the calculations were done with a kineticenergy cutoff of 24 Ryd. Our results give aditional support for the scaling laws proposedfor the elastic modulus and to the empirical predictions for these properties.We acknowledge to the Consejeria de Educacion del Gobierno Autonomo de Canarias forpartial finantial support.

1. O.H. Nielsen and R.M. Martin, Phys. Rev. B 32, 3780 (1985), ibid 32, 3792 (1985).

6P:blO4

NEW DEVELOPEMENTS IN BAND-STRUCTURE METHODSH. BROSS und G.M. FEHRENBACH. Sektion Pysikder Ludwig Maximilian* Universitat Munchen,Theresienrtrafle 37, W-8000 Munich, Fedderal Republic of Germany.

In a variety of problems in solid state physics the validity of the completeness relation isrequired e.g. the evaluation of response functions or of the self energy. However, mostmodern linear methods to calculate the band-structure yield a limited number of excitedstates. Thus the above mentioned pysical properties cannot percisely be calculated. Newmethods are described which are based on suitably chosen large Ritz-ansatzes with theconsequence that the corresponding linear eigenvalue problem generates a large numberof excited states. Our new ideas are illustrated by extensive calculations in the case ofCu.

I*

88

6P:blO5

A METHOD FOR FREE ENERGY CALCULATION AT THE SECOND

ORDER PHASE TRANSITION BELOW CRITICAL TEMPERATURE

I.R. YUKHNOVSKEI, M.P. KOZLOVSKEI, I.V. PYLYOK

Institute for Condensed Matter Physics, 14/16 Drahomanov St.,

LVIV-5, 290005, UKRAINE

A method for explicit calculation of the free energy of three

dimensional I3ing model at T Tc is proposed. In the frames of

this method the order parameter is not to be introduced as an

independent variable, but it is calculated via principles of

statistical mechanics. Calculations with the help of non-gaus-

sian density measure allow to obtain the microscopic analogue

of the Landau free energy expansion in the terms of the order

parameter. General expansions for the coefficients of the ex-

pansion are obtained, their temperature dependence as well as

the dependence on the microscopic parameters of the system is

investigated. Numerical results are obtained for the case of

exponentially decreasing potential and simple cubic lattice.

6P:blO6

ULTRASOFT PSEUDOPOTENTIAL FOR FLUORINE

K. Laasonen, A. Pasquarello and A. Satta*IRRMA, Lausanne, Switzerland

We have generated an ultrasoft pseudopotential for Fluorine on thebasis of Vanderbilt's scheme. We present detailed transferabilitytests on the atom and ab-initio molecular dynamics study of the F2dimer, which show that the new pseudopotential is able to reproduceaccurately the all electron results with a plane wave cutoff as low as24 Ryd.

I 89

6P:blO7FIRST PRINCIPLES CALCULATIONS OF THE STRUCTURAL PROPERTIES OFORDERED INTERMETALLIC ALLOYS

M.J. Mehl*, D.A. Papaconstantopoulos, and B.M. KleinComplex Systems Theory Branch, Naval Research Laboratory,Washington D.C. 20375-5000, USA

First-principles total-energy electronic structure methodsprovide an accurate description of many mechanical propertiesof solids. We focus on our work describing the equations ofstate and elastic moduli of ordered intermetallic alloys. Thesystems studied include many with high melting temperatures (>2000 K) and the Al^Li,, system.

"Current Address: Institut Romand de Recherche Numerique enPhysique des Materiaux, PH-Ecublens, CH-1015 Lausanne,Switzerland

6P:blO8

'Ab-Initio'- Calculations of Phonons in SiC

:: K. KARCH, O. SCHUTT, P. PAVONE, W. WINDL f

;•• ^(Institut fur Theoretische Physik, Universitat Regensburg, Germany)

We present the first realistic 'ab-initio'-results for the phonon dispersion curves andeigenvectors of cubic SiC. The calculations are shown in comparison with the properties

i of Silicon and Diamond.i We used the self-consistent method of Baroni et al.[l], that allows calculations ofi dynamical matrices within the scope of linear-response theory and density-functionali theory.

I" [1] Gianozzi, P., Gironcoli, S., Pavone, P., Baroni, S., Phys. Rev. B 43, 7231 (1991)} • •

I PACS number: 6300

90

6P:blO9

AB-INITIO CALCULATION OF PHONON EIGENVECTORS,

GRUNEISEN PARAMETERS, AND THERMAL EXPANSION COEFFICIENTSOF SEMICONDUCTORS

Pasquale Pavone and Stefano BaroniScuola Internazionale Superiore di Studi Avanzati (SISSA), 1-34014 Trieste

Lattice dynamical properties of semiconductors can be accurately described in the fra-mework of the Density-Functional Perturbation Theory (DFPT). In fact, ab-initio pho-non dispersions of semiconductors calculated by means of DFPT are in excellent agree-ment with experimental data. I1' However, a complete description of lattice dynamics ofcrystals cannot be given by just the phonon frequencies but requires the knowledge ofboth eigenvalues and eigenvectors of the dynamical matrix. To this purpose we presentthe calculation of phonon eigenvectors along some high-symmetry lines in diamond andsome elemental (Si, Ge) ana compound (GaAs, AlAs) semiconductors. As a byproductwe calculate the internal-strain parameter for these materials. As a further application,we present the calculation of the complete dispersions of mode Griineisen parameters.Subsequently, the thermal expansion of such semiconductors can be calculated withinthe so-called Quasi-Harmonic Approximation. Our results reproduce even fine detailsof the peculiar experimental low-temperature behaviour of the thermal-expansion coef-ficient in such tetrahedral semiconductors.

[1] P. Giannozzi, S. de Gironcoli, P. Pavone and S. Baroni, Phys. Rev. B 43, 7231 (1991).

i

| 6P:bllO

| TOWARDS A NEW CLASS OF MODELS FOR LATTICE DYNAMICALI CALCULATIONS IN SEMICONDUCTORS; L. Colombo'1', P. Giannozzi(2)

(1)Dipartimento di Fisica, Universita di Milano, via Celoria 16, I-S01S3 Milano, Italy{2)Scuola Normale Superiore, Piazza Cavalieri, 1-56100 Pita, Italy

Fitting the parameters of a phenomenological model for lattice dynamical calculations

usually requires a data base of experimental phonon frequencies, derived from neutron

scattering or optical spectroscopy data. The bond charge model (BCM)1 belongs to

this class of dynamical models. In the present work we derive a new set of BCM

parameters for bulk GaAs by fitting either phonon frequencies and ionic displacement

patter at, as obtained by first-principles calculations.2 The new release of the BCM

i allows us to reproduce quite satisfactory both the bulk phonon dispersion relations and

j: the displacement pattern for the LO(X) phonon.3 We discuss the application of such

| results to the calculation of lattice dynamical properties of GaAs/AlAs superlattices.

\ 1. W.Weber,Phys.Rev.Bl5,4789(1977);

); 2. P. Giannozzi, S. de Gironcoli, P. Pavone, and S. Baroni, Phys.Rev.B43,7231 (1991)

| 3. D. Strauch and B. Dorner, J. Phys. Condens. Matter 2,1457 (1990)

91

6P:blllSYMMETRIZED SELF-CONSISTENT WEIGHTED DENSITY APPROXIMATION FOREXCHANGE-CORRELATION FUNCTIONAL OF THE ELECTRON GAS.

E.CHACON* and J.E.ALVARELLOS*.+ Instituto de Ciencia de Materiales (CSIC) and Departamento deFlsica de la Materia Condensada (UAH). Cantoblanco. E-28049Madrid, Spain.* Departamento de Flsica Fundamental. UNED. Apartado 60.141. E-28080 Madrid, Spain.

Within the density functional formalism, the original1 self-consistent Weighted Density Approximation provided a direct linkbetween the electron-electron pair distribution function and the Iresponse function of a homogeneous electron gas. That was usedto obtain in a closed form all the bulk properties of theelectron system. The main disadvantage of this theory is that theexchange and correlation (XC) potential out of a jellium surfacedo not recover the correct classical image potential form l/4z,but merely l/2z instead2.Here we present a new approximation, correcting the previousfunctional, by symmetrizing the charge conservation condition.That also makes the new XC functional fully symmetric, as theexact XC functional must be. We report the results for thehomogeneous electron gas. We hope this new form will correct theforementioned misbehaviour of the XC potential.1. E.Chacon and P.Tarazona. Phys.Rev.B 37 (1988) 4013.2. E.Chacon and P.Tarazona. Phys.Rev.B 37 (1988) 4020.

6P:bll2AN EFFICIENT METHOD FOR CALCULATING QUASIPARTICLE ENERGIES IN SEMICONDUCTORS

R. DEL SOLE (a), F. BECHSTEDT <b), G. CAPPELLINI (a), and LUCIA REINING (c)(a) Dipartimento di Fisica, II Universita1 di Roma "Tor Vergata", via della RicercaScientifica, 1-00173 Roma, Italy(b) Friedrich-Schiller-Universitat, Physikalisch-Astronomische Fakultat,Max-Wien-Platz 1, D-6900 Jena, Germany(c) Centre de Calcule Atomique et Moleculaire, Universite' Paris Sud, Bat. 506, Orsay,France

The most serious error in local-density approximation (LDA) calculations of the properties ;of semiconductors and insulators is the discrepancy between the Kohn-Sham eigenvalues and ;.excitation energies. The problem was solved in recent years by treating exchange and <correlation within the GW approximation.1-2 This approach is rather computer-time fconsuming and can be used only for simple systems. -j

aWe present a method for the efficient calculation of the electronic structure of .semiconductors within the GW approximation. It is based on a linear expansion of the *self-energy in E around the LDA values, on the use of a model dielectric function, and on a '.LDA-like treatment of local-field effects. The resulting quasiparticle shifts are in agreementwith the complete GW calculations'-2 within 0.2 eV, in spite of the limited computationaleffort: each k-point takes 15 minutes of Cray-YMP CPU time.

1. M. S. Hybertsen and S. G. Louie, Phys. Rev. S34, 5390 (1986)2. R. W. Godby, M. Schluter and L. J. Sham, Phys. Rev. B37, 10159 (1988)

92

6P:bll3FIRST PRINCIPLES STUDY OF THE STACKING EFFECT ON THE ELECTRONIC

PROPERTIES OF GRAPHITE(S)

J.-C. Charlier, X. Gonze and J.-P. Michenaud.University Catholique de Louvain.Unite* de Physico-Chimie et de Physique des Matfriaux (PCPM).Place Croix du Sud 1 (Banment Boltzmann)B -1348 Louvain-La-Neuve (BELGIUM).

The electronic properties of natural1, simple hexagonal2-3 and rhombohedral4 graphites have

been studied in the framework of the density functional technique, using non-local ionic

pseudopotentials and a large number of plane waves. The band structures, at the Fermi level,

are compared to the corresponding tight-binding models for the three periodic 3D-graphites.

The valence charge densities, the densities of states and the Fermi surfaces are also presented

and compared.

1. J.-C. Chattier, X. Gonze and J.-P. Michenaud, Phys. Rev. B 43,4579 (1991)2. J.-C. Charlier, X. Gonze, J.-P. Michenaud and J.-P. Vigneron, Phys. Rev. B (IS December 1991)3. J.-C. Charlier, J.-P. Michenaud and X. Gonze, submitted to Phys. Rev. B.4. J.-C. Charlier, J.-P. Michenaud and X. Gonze, in preparation.

6P:bll4ii Electronic Structure of Alkaline Earth Oxides

I E.J. Whitehead & D.M. BirdI School of Physics, University of Bath, Bath BA2 7AY, U.K.

Results of ab-initio calculations of the electronic structure and elastic propertiesof alkaline earth oxides will be presented. The calculations use norm-conservingpseudopotentials and a plane-wave basis, together with the local density approx-imation to the exchange-correlation functional. Particular attention will be paidto the change in sign of the Cauchy violation (C12 — cu) as one goes down the se-ries from MgO to BaO. The relationship between these fully quantum mechanical

! calculations and various widely-used semi-empirical models will be discussed.

93

6P:bll5FERROMAGNETIC SPINELS : A FIRST-PRINCIPLES STUDY

A. Continenza Phys. Dept. Univ. L'Aquila, ItalyT.M. de Pascale and F. Meloni, Physics Oept. Univ. Cagliari, Italy

M. Serra Inst. Sup. Physics Univ. Cagliari, Italy

The chromium spinel CdCr2Se4 is a ferromagnetic semiconductorwhich, for its interesting magnetic and electric properties has beenobject of many experimental studies. In particular the negativemagnetoresistance, the red and blue shift and the influence of magneticordering on the Faraday effect have been extensively investigated usingmodels based on electronic structures empirically obtained.We present the first a priori calculation which, in the FLAPWrelativistic scheme furnishes the adequate information to compare thecalculated values with the resonant photoemission spectra and withthe active Raman modes. In particular it has been studied thecontribution of the Cr 3d states to the electronic DOS for the two spinorientations in the equilibrium crystal configuration.

6P:bll6SELF-CONSISTENTLY DETERMINED PROPERTIES OF SOLIDSWITHOUT BAND-STRUCTURE CALCULATIONS.

Pietro Cortona

Dipartimento di Fisica, University degli Studi di Genova, 1-16146 Genova, Italy.

We describe a method of directly determining the charge density and the total energy of solids

without preliminarly calculating the band-structure of the system. The method is based on the

second theorem of Hohenberg and Kohn; it is easy to implement, self-consistent and suggests a

meaning for concepts like "atoms in solids", "crystalline field", "charge transfer", which are J

not, in general, well defined in the context of ab-initio calculations. The results we have .•

obtained for all the alkali-halide crystals are compared with the corresponding experimental data.•/

1. Cortona P., Phys. Rev. B 44 (1991) 8454.

94

6P:bll7SURFACE STRESS THEOREM - GENERALIZED SURFACE VIRJAL THEOREM FOR THEJELLIUM MODEL OF HALFSPACE METALS

J. GRAFENSTEIN1, ft. KASCHNER2, P. ZIESCHEaTU Dresden and MPI FKF Stuttgart, Heisenbergstr. 1, W-7000 Stuttgart 80,2 TU Dresden, Inst. f. Theoret. Physik, Mommsenstr. 13, O-8027 Dresden

The surface virial theorem1 proves to be the trace of a more general tensor relation - the surfacestress theorem2. Due to the symmetry of the problem (semi-infinite jellium) the correspondingtensor quantities have only two independent components: one parallel, the other perpendicularto the surface. The surface stress theorem will be given within many-body theory as well aswithin the LDA of the Kohn-Sham density functional theory. A new sum rule between the fourcontributions of the Lzng-Xohs theory to the surface energy wiS be derived and numericallyillustrated3.1. Vannimenus, J., H.F. Budd, Phys. Rev. B15 (1977) 5302.2. Ziesche, P., R. Kaschner, Solid State Commun. 78 (1991) 703.3. Ziesche, P., J. Grafenstein, subm. to Phys. Rev. B

6P:bll8CRYSTAL BINDING ENERGIES FROM ATOMIC CLUSTER CALCULATIONS

YANG JINLONG*. WANG KELIN*. F. CASULA* G. MULA#

(*)Center for Fundamental Physics;University of Science and Technology of China,Hefei, Anhui 230026, PJL China; (#)Dipartimento di Scienze Fisichedell'Universita' di Cagliari, Via Ospedale 72,1-09124 Cagliari - Italy

A novel parameter-free technique is proposed to estimate the binding energy of acrystal from the knowledge of the binding energy of suitably chosen small atomicclusters, the latter being computed through the use of an all-electron discretevariational method within local-density-functional (LDF) theory. Though not asgood as the direct use of the full method our technique proves itself of accuracycomparable to pseudopotential LDF calculations, with the added benefit of givingdirectly the binding energy instead of the total energy.Test calculations are presented here for several metals and semiconductors, including 1the third row elements from Na to Si and the group IV semiconductors from C to ISn. In all cases the computed values of the binding energy, as well as of the jequilibrium lattice constant are within a few per cent of the experimental data. Last &•but not least it has been possible to do all the calculations by using just VAX-class iminicomputers, namely models DEC 11/750 and 6410. This computational 1advantage with respect to standard calculations could be crucial to their systematic •extension to complex structures, such as e.g. ternary compounds. '

95

6P:bll9CALCULATION OF WANNIER FUNCTIONS FOR d-s BAND OF Cu BY MODIFIED

VARIATIONAL METHOD

P. Kodrak

Institute of Physical Chemistry of the Polish Academy of Sciences,

Kasprzaka 44/52, 01-224 Warsaw, Poland

1 2The modified variational method is used to calculate Wannier v

functions for d-s band of Cu. Calculations have been performed for the

crystal potential given in ref. 3. Energies in high symmetry points in the ^

Brillouin zone calculated with the use of Wannier functions are compared

with that obtained in ref. 3. The effect of the number of nearest neighbour

shells taken into account and other approximations introduced into

calculations are discussed.

1. Kodrak P. and Wojnecki R., J. Phys. C19 (1986) 4011.

2. Modrak P. and Wojnecki R., Phys. Rev. B36 (1987) 5830.

3. Moruzzi V.L., Janak J.F. and Williams A.R., Calculated Electronic

Properties of Metals (Pergamon, New York 1978).

6P:bl21

UNIVERSAL BEHAVIOR IN ELECTRONIC PROPERTIES OF STABLE ICOSAHEDRALPHASES WITH TRANSITION ELEMENTS ?

F.CYROT-LACKMANN, C.BERGER, T.KLEIN, P.LANCO, D.MAYOU, G. TRAMBLY.LEPES - CNRS, BP166 - 38042 Grenoble Cedex 9, France.

iVery high resistivities associated to diamagnetism are measured in stable AlCuFe and AlPdMnpure icosahedral phases. The resistivity that depends strongly on the nominal concentrationsand on the structural quality of the sample reaches up to several thousands nQcm, and is 'correlated to reduced densities of states at the Fermi energy and an estimated low density of >carriers. These behaviors are consistent with the proximity of a metal-insulator transition for ithese high quality quasicrystals. One of the interpretations could be a peculiar band structure j |effect due to a strong interaction between the Fermi surface and the highly symmetrical $Brillouin zone. This is confirmed by abinitio LMTO-AS A calculation of approximants which '-. "are Hume-Rotherey type alloys. ty

96

6P:bl22ABSORPTION SPECTRA OF RARE EARTH DOPED SM OPTICAL FIBERS

MARIE POSPISILOVA. MARTINA SCHNEIDEROVAInstitute of the chemistry of glass and ceramic materials CSAVLipova 5, Praha 2, Czechoslovakia

Absorption spectra of Er, Nd, Tb. Sm doped SM fibers withdifferent core host glass were measured by the cut-back methodin wavelengths from 500 to 1600 nm. Fibers were prepared by MCVDand solution doping techniques in ICGCM. As core host glassesSiO^-AljOj, Si(X,-Ge02-P2O5 and SiO,-Ge02 were used. The influenceof core host glass on absorption properties of rare earth ionsis investigated.

6P:bl23Cluster Matter: Inhomogeneous Materials based upon Clusters

Uwe Kreibig, RWTH Aachen/Germany

In cluster science usually the way from molecule toward thesolid state is discussed in terms of increasing cluster size.Yet, a such transition is as well achieved by increasing thenumber of clusters and forming inhomogeneous material likenanostructured matter, cluster-matrix matter or island films.The ample field of complex topological structures on a nano-,micro- or mesoscopic scale yields material with a broad varietyof physical properties.

Several experimental examples for the transition fromnanoscopic to bulk behavior are presented and discussed toprove the validity of a general description of cluster SMtter.

I 9 7

ft I

6P:bl24SYMMETRY OF A QUASICRYSTAL

C.RIPAMONTIDipartlaento dl Fitica, Univeraita'di Genova, Italy

The space symmetry of a thing is usually regarded as an inherent property,residing in the spatial relations among its parts, consisting in an inva-riance out of a virtual change.This can be said an absolute and individualconception of symmetry. A more general conception, relative and collective,is possible, making no reference to parts or structure of thtj individual.In this relative mode, syametry arises not from an invariance rather from achanging whose discernability however is due to arbitrary,hence irrelevant,settings. It makes possible a representation of a quasicrystal having exac-tly the observed scattering symmetry. This is to be contrasted with the nowcommon representation, of the absolute/individual kind,describing a quasi-crystal as something without symmetry, actually a section of a truly symme-tric thing but with a symmetry impossible in space and1 higher than obser-ved. In the relative mode instead, a quasicrystal is a perfectly symmetricthing,but its symmetry has not be sought immanently in the individual buttranscenclentally in its multiplicity: it is not the space structure of theindividual which is relevant for the understanding of its scattering pro-perties, rather it is the relation among all the equivalent individuals,that is the structure of their manifold. Besides the automorphic structurewhich can be assumed isomorphic to the nondisplaclve part of that of space,it is thij topological structure which is to be uncovered;however the maintopologic;al property -the dimensionality- can be determined on objectivitygrounds:it is a function of the sole scattering symmetry.

6P:bl25A THEORETICAL SIMULATION OF DAMAGE IN COMPOSITE

MATERIALS : A CHAOTIC MODEL

F. hieioni and A VaroneDjpartimento di Scienze Fisiche, Universita' di Cagliari, Italy

F. GinesuDipartimento di Ingegneria Meccanica, Universita' di Cagliari, Italy

Composite filamentary meterials present a particular damageprogression accordingly to the angle orientation of the included fibres.Graphite-peek laminates show a variation of the hysteresis loop areaassociated to the internal strain and are connected with energydissipation due to viscoelastic behaviour.The experimental results are related to a simple theoretical modelbased on a non-linear second order differential equation related to theinstability in chaotic systems. The transition points in theexperimental damping energy diagram are correlated to the criticalpoints in the theoretical bifurcation plot while the power spectrumindicates the possible stable states of the system. Thecorrespondence with the experimental values is very good andsupports the validity of the computational model in the prevision ofthe structural characteristics of composite materials.

98

6P:bl26TIME LAG IN HOMOGENEOUS NUCLEATION: AN ANALYTICAL APPROACH

P. DEMO, Z. KOZISEKInstitute of Physics, Czech. Acad. Sci., Na Slovance 2, 180 40 Praha, Czechoslovakia

Below an equilibrium temperature, the clusters of new phase may be formed with-in the melt. This nucleation process reaches the steady-state regime during certain timelag corresponding to the moment at which the increase of the integrated cluster flux(i.e. the number of critical nuclei appearing through the time of observation) becomeslinear with the time. In order to determine this transient period, we developed principi-ally new method (based on the application of the boundary layer theory combined withthe Green's functions technique) providing to obtain an approximative solution of theFokker-Planck equation with nonconstant coefficients which describes the distributionof clusters at the kinetic level. It is shown that our analytical treatment (applied to theglassy system Li^O^SiO?) is in better agreement with our previous numerical solutionsand also with the accessible experimental data than the other previous approaches.

6P:bl27METASTAHLE STATES AND SPINODALS IN THE BEG MODEL

V.H. BoykoInstitute for Surface Chemistry, 252028, Kiev-28,31 Nauka Ave., Ukraine

The BEG model was first introduced in order to study thethermodynamics of He3- He^ mixtures near the criticalmixing point.It is shown that in the mean-field approximation in the BEGmodel metastable states also exist. One can calculate thelocation of spinodals and describe thermodynamical beharlorof the model in the vicinity of spinodal points. The Ginz-burg criterion which controlls the validity of the mean-field approximation is analyzed. In addition the possibilityof nucleation phenomena within the BEG model is discussed.

I. Blume M., Emery V.J., Griffits R.B.. Fhys. Rev. Aft(1971) 1071. .

99

6P:bl28CRITICAL BEHAVIOR IN THE EXTENDED BEG MODEL

C. BUZANO AND A. PELIZZOLADipartiaento di Fisica, Politecnico di Torino, Italy.

The Cluster Variation Method in the two-site approximation is used toanalyze the critical properties of the spin-1 model characterized bythe extended Blume-Emery-Griffiths (BEG) Hamiltonian

H - -J I S.S.-G I S.2S.2 -C I (S.2S.+S.S.2)+D I S.2-B I S.x 3 j x 3 i ] i D i i

where S. is the z-component of the spin-1 operator at site i(i-1,2,....,N) of a regular lattice and <ij> indicates simulation overnearest-neighbors. We consider J>0; G,C,D positive and negative.Attention is devoted to the role of the parameter C in particular withrespect to the tricritical lines and the reentrant phenomenon. Thebehavior of the pair-correlation functions is examined in typicalregions of the phase diagram.

1 - G. An, J. Stat. Phys. 52 (1988) 727.

6P:bl29ON THE PHASE TRANSITIONS THEORY IN

BINARY SYSTEMS

0. PATSAGAN

Institute for Condensed Matter Physics of the

Ukrainian Academy of Sciences, Dragomanov 14/16,

290005 Lviv, the Ukraine

Phase transitions in the binary continuous aystern are

investigated by means of the collective variables method

with a distinguished reference system. The critical tempera-

tures are obtained for the two-component case of different

size particles and different pairwise potentials in the Ga-

ussian approximation for the grand statistical sum functio-

nal. The phase spaces of collective variables connected with

order parameters are found. The case of the binary symmetri-

cal system is considered in detail.

100

6P:bl30

EFR IN IRRADIATED POLYACETYIENE

O.Hola.Katedra chemickej fyziky CHTF STUf Bratislava

The influence of gamma irradiation on the paramagnetic

properties of polyaeetylene was studied.The samples were exposed

to gamma irradiation up to a dose of 3 MGy.

The BPR line shape was of the Lorentzian type.The calcula-

ted g-factor was closely related to the g-factor of an isolated

spin.The dependences of the E?E- linewidth as well as of the re-

lative concentration of the paramagnetic centres on the radia-

tion dose in the mentioned samples were studied.

6P:bl31ELECTRICAL CONDUCTIVITY AMD ESR LINEVIDTH OF DIFFERENT POLYACETYLEMESTRUCTURES

A. BARTLL, J. FROEHMER', R. ZUZOK* and S. ROTH*'Institut fflr Festkorper- und Werkstofforschung Dresden e.V.Helaholtzstr. 20, D-8027 Dresden

*Max~Planck-Institut fflr FestkorperforschungHeisenbergstr. 1, D-7000 Stuttgart 80

The electrical conductivity in highly conducting polyacttylene after dopingis strongly influenced by the preparation aethods. For intonation aboutthe correlation between the length of tb« undisturbed conjugated chainsegments and the electrical conductivity defined concentrations ofadditional conjugation breaking defects were introduced into the Materialsby cheaical aethods. The decrease of the s»an conjugation length vasstudied by electron spin resonance and electrical conductivity. In the tvoinvestigated "standard" and "new" polyacetylene types with increasingdefect concentration the electrical conductivity decreases drasticallyvhile the ESR linevidth increases. From ESR aeasureaents follows that athigh defect concentrations the aean conjugation length in "now"polyacetylene is larger than in "standard" polyacetylene.

101

6P:bl32KIRCHHOFF'S THEOREM IN LATTICE MODELS OF POLYMERS

E.I. KORNILOV and V.B. PRIEZZHEVJoint Institute for Nuclear Research, P.O. Box 79, Moscow 101000, USSR

Graphical representation of physical objects plays the important role in var-ious problems of statistical physics. So, a solution of linear polymers maybe represented in various cases as a system of lines (interacting or nonin- >teracting, directed or nonmarked, closed or disconnected). Their statisticaldescription is hard because of excluded volume effects even in absence ofother kinds of interactions. Most frequently the lattice models of polymersare considered in which the sites and edges of a lattice are identified withpolymer atoms and chemical bonds, respectively.We discuss three kinds of lattice models of polymers which partition andcorrelation functions may be calculated by the Kirchhoff theorem: thelattice model of rooted branched polymers having an exact solution in alldimensions, the model of biomembrane polymers and the model of ringpolymers.

6P:bl33DIELECTRIC AND MECHANICAL BEHAVIOUR OF POLYURETHANE NETWORKS

J.NEDBAL. H.ILAVSKY* and J.FAHNRICHFaculty of Mathematics and Physics, Charles University, Prague,V Holesovtckach 2, 180 OO Praha 8+Institute of Macromolecular Chemistry, Czechoslovak Academy ofSclencies, Prague, Heyrovskeho naa.2, 162 OO Praha 6

The effect of the initial composition on dielectric and dynamic•echanlcal behaviour of chemically crosslInked polyurethane :networks prepared from poly(oxypropylene)dlols (PD,Hn>400 and2OOO) and tris(4-isocyanaophenyl)ester of ttilophosphorlc acid '(TI, Mn-465) was Measured. Samples with various ratios of •»reactive groups r-tOHJPD/tNCOlTI-0.5-1.8 were prepared to the |highest possible conversions of Minority groups. The shape and ';frequency position of the both complex peraitlvity and complex Ishear compliance In the main transition region are affected by ithe ratio r,I.e. by the concentration of elastlcally active -network chains (EAMC). The shape of shear compliance on 'frequency depends on detailed structure of IANC. The positionand magnitude of the dielectric measured transition correlateswith the concentration of lsooyanate groups In the system. Theshape of dielectric spectra Is affected by the polarity of thechain and by the structure of EARCs.

102

6P:bl34ELECTRICAL PROPERTIES OF POLYMER COMPOSITES

ANDERS LUNDINPhysics department., University of UmeS, 90187 Ume£, Sweden

The electrical resistivity of conducting polymer composites, consisting of a polymer matrixmixed with different amounts and kinds of carbon blacks, has been measured as a functionof temperature and pressure. In order to measure the true temperature dependence of theresistivity the measurements must be carried out under constant volume. For that purposemeasurements of compressibility at different temperatures have to be performed. So far thecompressibility has been measured for polyethylene mixed with different amounts and kindsof carbon blacks at room temperature. The compressibility measurements have beencarried out in a piston - cylinder device.

6P:bl35PHOTOEXCITATION DYNAMICS IN CONJUGATED POLYMER CRYSTALS

IGOR ZOZULENKOInstitute for Theoretical Phytict, Acaiemf of Sciences of Ukraine, BS814S, Kit*, Ukraine

Recombination kinetics of photoinjected charge carrier* in qnati-one-dimensional condncting• polymers is studied. The dynamics of a correlated pair of photoexcitations is considered within; the model of the one-dimensional diffusion motion of qnatiparticles in segments of a polymer

chain confined by the defects (traps). The distribution function and the survival probabil-ity of a recombining pair in a confined segment, and the averaged survival probability in apolymer chain with the random trap distribution are calculated '. The results obtained anassociated with the observed characteristics, such as transient photocurent decay, kinetics of

; photoindnced changes in optical absorption (or reflectivity), and delayed fluorescence caused( by the charge carrier recombination 2. It is shown that an influence of the defects leads to; the acceleration of the pkotocurent decay, namely, the usual power-law dependence <x t"1/2

t describing the geminate recombination kinetics on an infinite chain , on times ~ (10wac3W)~i

(W is the diffusion rate, c is the trap concentration) is changed by a fatter exponential-like .dependence oc exp{-ti/3). The delayed fluorescence decay caused by the recombination of ?

•- photoexcitations is shown to follow the similar exponential-like dependence. On the contrast, \' the photoinduced absorption decay is slowsd-dowa due to the trapping of photoezcitatious by \K defecU. Ii 1| 1. Zoiulenko I.V., Solid State Common. 76 (1990) 1035; Synth.Het. 43 (1991) 3365. fj 2. Zosnlenko I., Phys.Rev.B, submitted. \

103

6P:bl36PRESSURE DEPENDENCE OF ELECTRICAL CONDUCTIVITY OF THE

CONDUCTING POLYMERS

P. FEDORKO. V.SKAKALOVA. S.KOglNA. V.LAUR1NC

Dept. of Physics. Faculty of Chemical Technology. Slovak

Technical University, CS-81237 Bratislava, Czechoslovakia

Pressure dependences of the DC conductivity of doped

polypyrrole, polyacetylene and polythiophene were measured at J

various temperatures under hydrostatic pressure. Behaviour of

the samples strongly depends on the temperature and pressure

range. Results are interpreted in the frame of a model

supposing two limiting transport mechanisms parallel to each

other: transport through random contacts between parallel

neighbour fibers and transport through disordered regions of

the fibers intergrowth.

6P:bl37RELAXATION OF CONDUCTIVITY OF POLYPYRROLE UNDER PRESSURE

V.SKAKALOVA, P. FEDORKO, J.ANHUS. *M. OHASTOVA. S. BALOCH. *D.WALTON

Dept. of Physics, Fac. of Chem. Technology, Slovak Techn.

University, CS-812 37 Bratislava. Czechoslovakia

*Polymer Institute, Slovak Academy of Science* CS-84236

Bratislava \

'Dept. of Appl. Phys. Science. Coventry Polytechnic. Priory

Street Coventry CVT 5FB, UK

The temperature and time dependences of the electrical .-

conductivity of electrochemically prepared polypyrrole at ;

various hydrostatic pressure were studied. Silicone oil and Ar £

were used as hydrostatic pressure medium. It was found that I;

while at low temperatures pressure changes were followed \ •>

immediately by changes in the electrical conductivity, at =

higher temperatures these changes presented slow relaxation

character. From the DSC measurements the minimum relaxation

temperature was found to be -9.5 °c.

104

6P:bl38NEW POLYMERIC COMPOSITES

R. KUZEL, J. KUBAT+, I. KRIVKA, J. PROKES, P. NOZAR

Fac.of Math.and Phys..Charles Univ.,Ke Karlovu 5, 12116 Prague 2

Dept.of Polymeric Materials, Chalmers Univ.of Techn..Gothenburg

New polymeric composites are proposed containing polyethylene or

polystyrene and precious metals (Au, Pd, Ag) or RuO2 in powder

form of regular spherical particles or small single crystals,

instead of carbon black used before. These systems show unusual

temperature dependences of resistivity (20-400 K ) , where sudden

steps of electric resistivity appear at low temperatures, and at

elevated temperatures there is a certain structure observed. The

resistivity dependence on the contents of conductive component

conforms to the percolation theory indicating also all the pa-

rameters describing blending curves. The results achieved with

* various polymeric composites filled with carbon black or ingre-

| dients mentioned above are discussed and mutually compared.

j 6P:bl39| DIELECTRIC PROPERTIES OF POLYMERIC COMPOSITES

J. KUBAT+, J. PROKES, R. KUZEL, I. KRIVKA, 0. STEFAN+Dept.of Polymeric Materials,Chalmers Univ.of Techn..Gothenburg

Fac.of Math.and Phys..Charles Univ.,Ke Karlovu 5, 12116 Prague 2

Heterogeneous systems based on polymeric materials (chloropre-

ne rubber, polyethylene, polystyrene) filled with various con-

tents of carbon black, and especially with powders of precious

metals and some oxides are studied by measuring the capacitance J

r and conductivity of capacitors at various temperature and fre- 5

. quencies. Cole-Cole semi-circles enable to ascertain all the pa- j

| rameters of the filled dielectric with permittivity depending |

f on the ingredient contents. There are some composites manifes- 3

!• ting sudden decrease in capacitance and distinctive peaks in the ;

i conductivity at certain temperatures. With regard to these and

other effects, various temperature dependences on the used

| filling and polymer type are discussed.

! 105

6P:bl40

CORRELATION EFFECTS AND STRUCTURE OFCRYSTALLINE LIQUIDS (BLUE PHASES).

E.DEMIKHOVUniversity of Paderborn, Physical Chemistry (Fbl3)

Warburger Str.lOO, PB1621, 4790 Paderborn, Germany

An approach to the investigation of short range correlations in isotro-pic liquid of high chiral liquid crystals is presented(l-2). In the frameworkof this approach quantitative description of fluctuation phenomena in thevicinity of the phase transition isotropic liquid- blue phase is given. Theenergy gap between chiral fluctuation modes in isotropic liquid leads tothe anomalous growth of the correrlation length of plane spiral mode inthe vicinity of the blue phases and to the experimentally observed in (2)peculiarity of the optical activity. Connection between short range orderin the isotropic liquid and structure of crystalline liquids Is discussed.The effect of change of the BPI structure under the influence of smecticfluctuations is observed. Fluctuation effects in ferroelectric liquid crystalsare discussed.

l.V.Filev, JETP Lett. 37, 703 (1983).2.E.Demikhov, V.Dolganov, JETP Lett. 38,445 (1983), Sov.Phys. Cry-stalogr. 34(5),723 (1989).

6P:bl41FERROELECTRICITY IN LIQUID CRYSTALSINFLUENCED BY THE SUBSTANCE CHIRALITY

M. GLOGAROVA, CH. DESTRADE*, J.P. MARCEROU+,J.J. BONVENT , H.T. NGUYEN

Institute of Physics, Czechoslovak Acad. Sci.,Na Slovance 2, 18040 Prague 8, Czechoslovakia

Centre de Recherches Paul Pascal,Chateau Brivazac, 33600 Pessac, France

The left and right handed versions of a chiral SmC material ha-ve been mixed to change the substance chirality. The dielectricand electroclinic properties measured simultaneously on the miy-tures allow to determine first three coefficients in the freeenergy describing the phase transition and the viscosity connec-ted with the soft mode. It has been shown that C coefficient dri-ving the linear interaction CP-9- between the polarization (P)and the phase transition parameter (tilt angle •©•) is the onlychirality dependent coefficient. It depends linearly on the con-centration (n) of the left and right handed version. As a con-sequence of this dependence, the, phase transition temperatureT is shifted with n as A T — n .

The decrease of spontaneous polarization when the chirali-ty is lowered is quantitatively explained by the lowering ofCPO- coupling.

106

6P:bl42POLAR LIOUID CRYSTALS IN THE NGN-UNIAXIAL MOLECULES MODEL

K. Szumiiin and J.J. Milczarek* Institute of Physics. Warsaw Technical University.KoszyKOwa 75. 00-662 Warsaw. Poland* * Institute of Atomic Energy. Dept.E-VI. Swierk.05-400 Otwock. Poland

A general systematic approach to the problem of possible polarorderings in the systems composed of polar non-uniaxial mesoge-nic moiecules is developed. A model interaction potential forelongated molecules with the dipoie moments pointing in somefixed directions in respect to the long axis of the molecule isdesigned. The approach is based on the diagram expansion methodof the free energy of the system in terms of the one-particledistribution function. The systematic procedure is used todetermine the set of the system order parameters for giveninteraction potential. The possible kinds of phase diagrams inthe temperature - molecular density plane are analyzed for themodel interaction potential. The obtained phase diagramsexhibit the phase transition lines of the first and second kindbetween polar (ferro- and antiferroelectric) and non-polarsmectic phases. The interaction potential parameters can bechosen to give the phase diagrams comparable to those obtainedexperimentally.

6P:bl43

ON THE OPTICAL NOISE IN PLANAR NEMATIC LIQUID

CRYSTALS NEAR THE FREEDERICKSZ TRANSITION

P. Allia, P. Galatola, C. Oldano, P. Taverna-Valabrega, L. Trossi

Physics Dept., Politecnico di Torino, I -10129 Torino, Italy

Consorzio INFM, Research Unit of Torino Politecnico

Room-temperature measurements of the stationary noise of monochromatic light scattered by,

or transmitted through a sample of BDH K15 planar nematic liquid crystal, have been performed

as functions of the applied voltage near the electrically induced Freedericksz transition. The

critical voltage for the transition has been detected by an interferometric technique. The

low-frequency spectral density of the transmitted-light noise displays a well-defined maximum

at the critical voltage, according to the views about critical dynamics in these systems. Such a

noise anomaly is hidden in light-scattering experiments. The different performances of the

considered techniques are explained in terms of the liquid crystal's optical properties.

>. * 1 0 7*, • I ?

6P:bl44ON THE SWITCHING FROM THREE DIMENSIONAL TO ONE DIMENSIONALBEHAVIOUR IN A MODEL LIQUID CRYSTAL

C.CHICCOLI", P.PASINI0, F. SEMERIAa, C.ZANNONI4

a)INFN Sezione di Bologna and CNAF, Viale Ercolani 8, Bologna, 40138, Italy.b)Dipart. di Chimica Fisica ed Inorganica, Viale Risorgimento 4, Bologna, 40136, Italy.

A Monte Carle computer simulation of a modified Lebwhol-Lasher lattice model is presented.The angular part of the pair potential is a second Legendre polynomial of the relative orienta-tion between the two particles, like that of the Lebwhol-Lasher model. Each particle interactswith its six nearest neighbours with an attractive anisotropic potential differing in strengthfor the four horizontal and the two vertical neighbours. Various values of the out-of-plane toin-plane coupling ratio £ have been considered, i.e. f = 0.5,0.2,0.1,0.05,0.01. The lattercase is close to the limit where the system reduces to a set of one dimensional lattices whichhave no phase transition as shown analytically by Vuillermot and Romerio [2]. Comparisonsare made with available simulations [3] and with mean field theory. The system mimics in asimple way what we could have in a columnar system where the interaction between moleculesin different columns could be more and more weak compared to the one between particles inthe same column.

1. P.A. Lebwohl, G. Lasher , Phys Rev. A6, (1972) 426.2. P.A. Vuillermot and M.V. Romerio, J. Phys. C6 (1973) 2922.3. C. Chiccoli, P. Pasini and C. Zannoni, Liquid Crystals, 3, (1988) 363.

6P:bl45THERMOCHROMIC VO2 SPECIMENS MORPHOLOGY RELATED TOVARIOUS ELABORATION TECHNIQUES AND W CONCENTRATION .

J.C. Rakotoniaina'^.R.Mokrani-Tamellin'.J.R.Gavarri'.W.Chodkiewicz4, G.Vacquiei^andC.Cesari3

!LMPV, 3GMET et "RCMO, Universite de Toulon, BP 132,83957 La Garde Ccdex, France.2LCM, Universite de Provence, 3 Place Victor Hugo, 13000 Marseille, France.

We are investigating the properties of doped VO2 samples elaborated by dry processes(classical powder metallurgy ) and those of undoped samples prepared through a liquid phase(wet process ). The aim of these experiments is to elaborate VO2 specimens with small grainsizes for applications as pigments in thermochromic filters or coatings.

Concerning the wet process many reactives have been checked: a) V2O5 + oxalic acidb)V2O5 + ammoniac c) NH4VO3 + chlorydric acid and d) NH4VO3 + hydroxylammoniumchloride. In every case the conditions of elaboration of VO2 ( concentration and temperature)have been determined and lead to a granulometry which is 10 to 50 times less than in the dryprocess case.

For the undoped specimens, this morphology is confirmed by SEM experiments.However, 2 different phases are exhibited: a (3 monoclinic phase with rough shaped grains andan a rutile phase with regularly crystallized grains, of high interest for thermochromicapplications.

The doped samples show SEM images with a crystalline type granulometry. X-Raysanalysis prove that W concentration is higher at the edge of the grains. The overallconcentration agrees with the chemical composition; the highly doped samples exhibit specificgrain shapes.

108

6P:bl46THE ATOMIC AND ELECTRONIC STRUCTURE OF SELF-TRAPPED HOLES IN

CORUNDUM («-Al2O3) CRYSTALS

E.A.KOTOMIN* I.A.TALE* P.W.M.JACOBS5

Institute for Solid State Physics, University of Latvia, Riga

'chemistry Dept, University of Western Ontario, London, Canada

Despite its technological, scintillation and catalyticimportance, the electronic structure of defects in corundumcrystals is not weii-studied, especially theoretically. Thispaper deals with the energetics, atomic and electronicstructure of the self-trapped hole (STH) and its migrationproperties. Experimentally, it is observed that after suddensmall temperature increase there is a long ( 100 s) time delayin the luminescence increase. These experiments are discussedin terms of diffusion-conrtolled small- polaron (STH)recombination. To specify its microstructure, combined semi-empirical (INDO) and atom-atom potential methods were used. Itis shown to be similar to the STH (V centre) in alkali halides.Optical properties and migration mecnanism of STH are discussed.

6P:bl47SOME PROPERTIES OF RuO2 THICK FILM RESISTORS DOWN TO 50 mK

I.BATKO, K.FLACHBART, M.SOMORA1, D.VANICKtf1, K.WINZER2

Institute of Experimental Physics, Slovak Academy of Sciences,

043 53 Kosice, CSFR; faculty of Electrical Engineering,

Technical University, 043 89 Kosice, CSFR; I.Physikalisches

Institut, Universitat Gb'ttingen, 3400 Gbttingen, FRG.

In the contribution properties of some RuO« resistors prepared

by screen printing have been studied between 50 mK and 4.2 K

and in magnetic fields up to 12 T. The sensitivity dR/RdT of

the resistors is comparable with that of germanium sensors

used in this temperatures range and the magnetoresistance

AR(B) /R(0) is about 6 X in the field of 12 T and at tempe-

ratures T v> 500 mK.

109

6P:bl48DEUTERATION EFFECT ON COUPLED MODES IN A Rbl-XNH4XH2PO4 DIPOLARGLASS

F.MOUSSA *and E.COURTENS** .* Laboratoiie L6on Brillouin CENSaclay F 91191 Gif-sur-Yvette Cedex FRANCE** IBM Zurih Research Laboratoiy,CH8803 Riischlikon SWITZERLAND

Transverse acoustic phonons propagating in the basal plane (a,b) of mixed crystals of RADP aremeasured by mean of inelastic neutron scattering on protonated (x=0.25) and deuterated (x =0.62) RAnP ( from room till low temperatures,

An anomalous temperature behavior of the damping of the phonons is observed on(H)RADPl.A strong effect is induced by deuteration : phonons in (D)RADP behave normallyin the same range of temperature. The former experiments have been well explained by themodel of the piezoelectric coupling built to interpret the dielectric constant and Brillouinscattering measurements^. The results jjiven by these techniques on deuterated sample lead to adistribution of energy barriers much higher than for the protonated sample^. This agrees verywell with neutron data which confirm in turn the strong effect of deuteration on the dynamics ofthis glassy phase4.

1. F. Mouss&.E. Courtens, T. Lebihen. 7th ICMF Dijon 91 to be published.2 E. Courteiis.R. Vacheron and Y. Dagom Phys. Rev. B 33 (1986) 7625 and Phvs. Rev B 36(1987)3183 E. Courtens Phys. Rev. B 33 (1986) 29754. J.F. Berret, M. Meissner, S. K. Watson, R. O. Pohl, E. Courtens, Phys; Rev. Let. 67(1991)93.

6P:bl49

The Pressure Dependence of Phase Shift of Photoacustic Signal in

Ruby as New Method for Pressure Measurement

B.R.Jovamic. Lj.D.Zekovic'and B.Radenkovic*

Laboratory of Interdisciplinary Research, Institute of Fhysic*11OO1 Be.Ograd , P.O.Bon 57 , Yugoslavia<i> Lj.D.Zekovic Depeartment of Metrology, Fhysical Faculty, P.O.

Box 57, 11OO1 Belgrade , Yugoslavia<2> B.Radenkovic, FON, P.O.Box 74O, X1OO1 Belgrade, Yugoslavia

Abstract This paper considered new method for measuring pressure

(up to 200 kbar) in ruby by measuring the phase shift A6 of

photoacustic signal. Determining the pressure in samples based on

.-iieaBurernent the phase of photoacustic signal at two different

excited wavelength and than calculated pressure usjing procedure

in this paper.

1. ft.S.Cfuimby and W.it.Ysn, J.&ppl.Ptiys.Si. (19BO), t?BO.

110

6P:bl503OLID ON SOLID CELLULAR AUTOMATA: GROWTH OF Ta-OXIDE PARTICLES IN THENONSTATIOMARY THERMAL FIELD

3. LUGOMERRuder Boskovic Institute, Bijenica c. 54, 41000 Zagreb, CroatiaM. KERENOVIC and M. STIPANCICPedagogical Academy, Univ. of Banja LuKa, 78000 Banja Luka, BiH

Oxidation of Ta in the nonstationary thermal fieid generates various kinaot the oxide particles (local structures) which grow faster thansurrounding. They represent the "sol id-on-soli a" cellular automata, i.e.trie seif organized objects whose structure and morphology depend or. theneating rate /<<(i=AT/At). At the 6-scale 2. 10 K/min, they grow on tnenexagonai basis as a multnayered structures, every layer of whichrepresents a 2D-Archimedean spiral, with the origin at the dislocationcore.At me (j-scaie 20 K/min i 0 £ 50 K/mm, the sample surface is divided intothe oasins of homogeneous (1) anu in Homogeneous (21, oxide nucieation.In tne type (1) of basin, the hexagonal oxide structures develop, while intn<? type (2) develops a combination of the hexagonal and the roll type ofstructures. They represent fingerprints of t!>e Benard air convection cells.in addition, the "asymmetric-6-petal flower'1 like particle with the volcanovertica' crossection develops iaround the screw dislocation core; whoseoetaiS represent a commensurate isoicale

6P:bl51

New method for measuring pressure in alexandrite (BeAlJD

Lj.D.Zekovic *, B.R.JovanicB.Radenkovic2 and V.V.Urosevic

Laboratory of Interdisciplinary Research, Institute of Physics ,11OO1 Beograd , P.O.Box 57 , Yugoslavia<»> Lj.D.Zekovic Depeartment of Metrology, Physical Faculty, P.O.

Box 57, 11OO1 Belgrade , Yugoslavia«z> B.Radenkovic, FON, P.O.Box 74O, 11OOX Belgrade, Yugoslavia

Abstract This paper considered new method for measuring of applied

pressure in alexandrite by measuring the phase chift 6 of

photoacustic signal. Method based on theoretical found dependence i

of 6 upon pressure. :|

M.L.Shand, J.Appl.Phys., 54 (1983), 2602 J

J.Liu, R.Tang, Y.Wang, W.Jia, Y.Shang and S.He, 40 & 41 U9BB) 419 |

111

6P:bl52VTBRATIONAL DYNAMICS IN AMORPHOUS SILICA BYLIGHT SCATTERING MEASUREMENTS

P.Benassi, A.Fontana, L.M.Gratton, M.Montagna, O.Pilla and G.VilianiDipartimento di Fisica, Univcrsita' di Trento, Povo, Trento, 1-38050, Italy.

In recent years the low frequency light scattering in glasses has been theobject of many experimental and theoretical works. Roughly speaking, twomain contributions have been identified in the low frequency light scatteringspectrum: the disorder induced one-phonon density of states and a "lightscttering excess" which has been observed in many glassy systems. From anexperimental point of view, one of the most serious problems is to determinethe low frequency spectral shape of the scattered light.

We present light scattering data in amorphous silica in the full spectralrange of interest (i.e. 0.2 cm"1 < w < 250 cm"1), thus obtaining the shapeand the intensity of the spectrum as a function of temperature. The datashow the typical Bose Einstein behaviour above 60 cm"1, while we observean anomalous behaviour from 60 cm"1 down to 1 cm'1. We try to providea microscopic description of the low frequency vibrational modes on thebasis that harmonic excitations coexist with anharmonic ones.

6P:bl53

TRANSPORT PROPERTIES IN Nb-DOPED BARIUM TITANATE CERAMICS ANDSINGLE CRYSTALS: A COMPARISON.

C.Gillot and J.-P. Michenaud.University Catholique de Louvain.Unite1 de Physico-Chimie et de Physique des Matenaux (PCPM).Place Croix du Sud 1 (Batimcnt Boltzmann)B -1348 Louvain-La-Neuve (BELGIUM).

Doped BaTK>3 single crystals and ceramics exhibit anomalous electrical transport properties,mainly due to their ferroelectric character. In ceramics, the role of grain boundanes in thetransport properties remains puzzling. In this study, we present and compare measurements ofelectrical resistivity and thermopower in No-doped samples in a wide range of temperature(77Kto 4S0K) in order to separate the bulk from the grain boundary contribution. Phasetransitions are responsible for abrupt changes in transport properties.

112

6P:bl54

EELS STUDY OF SINGLE-CRYSTALLINE NIO(IOO)

A. GORSCHLUTER, C. HENIG

Physikalisches Institut der Universitit Munster, 4400 Munster, Germany

We present a detailed EELS study of NiO(lOO) cleaved in UHV. Primary energies ran-

ged from 1200eV down to lOOeV. Angular dependent measurements allow to distinguish

between surface and bulk contributions. Analogous measurements at thin oxidized poly-

crystalline Ni-films show the influence of disordered systems. The most intense features in

NiO loss spectra are caused by plasmon losses and 0 2p-excitations. These EELS spectra

are used to suppress structures in the spectra of other electron spectroscopic measure-

ments (e.g. BIS, APS).

6P:bl55OPTICAL PROPERTIES AND EPK CENTERS IN CUBIC .STABILIZED ZIRCONIA

C.B. AZZONI and A. PALEARIDipartimento di Fisica "A. Voltn" del 1'Universita' di Paviavia Bassi 6, 1-27100 Pavia, ItalyThe study of EPR defects induced either by different reductiontreatments or by X and UV irradiations in yttria stabilizedzirconia (YZS) allows us also to give some insight to the originof the optical properties of this material: the yield and thermalstability properties of EPR centers in treated samples suggest adistinction of the optical absorption in two components (at 375 nmand 480 rim) only one of which (375 nm) seems related to theparamagnetic center Zr3* sixfold-coordinated. On the other handthe excitation spectrum of the intrinsic photoluminesce (PL) ofYSZ corresponds fairly closely the 375 nm absorption band inducedby treatments. This suggests to identify the luminescent centerswith the defects responsible of this optical absorption ratherthan with other centers which give rise to the yellowishcoloration due to the 'i80 nm band well characterized in reducedsamples. Nevertheless this PL is also observable in as receivedcrystals, where no detectable optical absorption arises fromintrinsic defects, exciting near l.Jie absorption edge (e.g. 308 nmfrom an excimer laser). In this case one observes that 375 nm bandgrows in the optical spectrum for prolonged excitation: thisprocess may bo represented as radiative relaxation following thecreation of new centers. Radiation with lower energy (e.g. 458 nmfrom a argon-krypton laser) does not excite intrinsic PL in asreceived samples, but only in the samples where some defects areinduced by reduction or irradiation treatments: in this case thePL represents n relaxation of selective intracenter excitation.

113

6P:bl56

THE ORIENTATION OF YIG PARTICLES IN A VISCOUS MEDIUM Bit HEADS 0 7TOE MAGNETIC IMPULSES FORMING THE CONFIGURATION OF THE DIRECTIONS < l l l >

J . KOLOVHAT

Faculty of Mathaoatiea »nd Physics, Charles University,Ke Karlovu 5, 12116 Prague, Czechoslovakia

The viscous solidifying medium and the multiple repetition of the setof magnetic Impulses (Pig.) allow to attain the particle orientation accordingto the easy direction* <1H> of VIC Thestronger are the magnetic impulses, the betteris the suppression of the shape anisotropy.at each individual particle. The directionsof easy magnetisation in all particles arenearly parallel In the solidified epoxlderesin. The theoretical proof of such resultfor extremely high fields, the computationalsimulation of the orientation procedure andthe FUR experiment demonstrate the possibilityof such kind of the particle orientation.The powder particles of YIG are regarded tobe noninteracting single crystals of all possible ellipsoidal forma with randomorientations of crystal axes.

6P:bl57

STUDY OF THE PHASE TRANSITION OF DOPED KTaO3 BY OPTICALTECHNIQUES

G.P. BANFI*, P. CALVI, P. CAMAGNI, E. GIULOTTO, G. SAMOGGIADip. di Fisica "A. Volta" dell'Universita. 27100 Pavia. Italy•Dip. di Elettronica dell'Universita, 27100 Pavia. Italy

In order to clarify the nature of the phase transition of KTaO.vLi, we have performed Raman,second harmonic generation (SHG) and birefringence experiments. By means of Ramanspectroscopy the intensities and lineshapes of the transverse optic modes were studied as afunction of temperature, in field-cooling (f.c.) and zero-field-cooling (z.f.c.) conditions.Combined measurements of birefringence and SHG allowed the direct estimate of the polarcorrelation length in f.c. and z.f.c. samples. Below the transition region, all the experimentsconfirm an inherent limitation in the growth and cooperative ordering of polar domains. Thisseems to emphasize the dipole-glass character of the transition in this category of compounds.Preliminary results on KTaChtNb are also presented.

114

6P:bl58

OPTICAL ACTIVITY OF FERROELECTRIC TGS CRYSTALS

O.S.KUSHNIR, Y.I.SHOPA AND O.G.VLOKH

Lviv State University, Phys. Dept., Lomonosova st., 8

290005, Lviv, Ukraine

A new optical method for simultaneous measuring all the com-

ponents of optical activity, birefringence and optical indi-

catrix rotation is developed, basing on analysis of the pola-

rization characteristics of the light passed through a crys-

tal sample. The temperature dependencies of gyration compo-

nents g,T and goo as well as birefringent properties of TGJS

crystals are studied both in ferroelectric and paraelectric

phases. The obtained results are explained in the framework

of a phenomenological theory.

6P:bl59

OPTICAL REFLECTANCE DATA OF NiO AND Li:NiO SINGLE CRYSTALS INTHE RANGE 4 TO 30 eV oo.

F.PARMIGIANI*, A.REVCOLEVSCHI*, L.SANGALETTI®, M.SCAGLIOTTI*,N.ZEMA§*C1SE S.p.A., P.O.Box 12081, 20100 Milano, Italy; # Universite de Paris XI, 94105Orsay, France; @ Dipartimento di Fisica A.Volta, 27100 Pavia, Italy; §ISM-CNR, 0044Frascati, Roma, Italy

The RT reflectivity of high quality NiO and 0.8% Lithium-doped NiO single crystals hasbeen measured in the range 4 to 30 eV, Reflectivity data have been analyzed through KKtransforms so as to obtain the values of dielectric constants. Vacuum cleaved fragmentsof the same crystals, examined through an XPS probe, resulted to be free from anycontamination or segregated phases. Owing to the imperfect smoothness of crystalsurfaces, it has not been possible in the case of Li:NiO to obtain an absolutedetermination of reflectivity. Nevertheless a qualitative difference between the two spectracan be appreciated. This concerns expecially the 4 eV peak, corresponding to thefundamental absorption onset, and the structure in the 5.5-7.5 eV range. Thesedifferences are attributed to a decrease in the O2p-Ni3d charge-transfer transitionstrength in Li-doped NiO with respect to undoped NiO, due to the creation of O2p holesfollowing Ni2+ substitution by Li+. This interpretation is found to be in agreement withother spectroscopic studies.

00 Work performed under EEC GRANT NJOUE-0058-I.

115

6P:bl60OPTICAL REFLECTANCE AND XPS SPECTRA OF YTTRIUM STABILIZED ZIRCONIA

P.CAMAGNI®,F.PARMIGIANI*,G.SAMOGGIA®,L.SANGALETTI(SM.SCAGLIOTTI*,N.ZEMA*® Dipartimento di Rsica A.Volta, 27100 Pavia; *CISE S.p.A., P.O.Box 12081,20100 Milano;'ISM-CNR, 0044 Frascati, Roma.Italy

Yttrium stabilized zirconia (YSZ) is a good ionic conductor, owing to the large number ofstoichiometric vacancies brought about by Y-doping. The high degree of lattice disorder hasstrong repercussions on many physical properties. In this paper we present a study of theelectronic structure of YSZ single crystals of varying Yttrium concentration, performed throughreflectivity and high resolution XPS measurements. Reflectivity data, in the range 4 to 30 eV,have been analysed through KK transforms so as to obtain the value of the complex dielectricconstants and the electron effective number. Reflectivity is practically unaffected by Y-doping inthe region corresponding to the fundamental absorption edge. On the contrary, the first interbandstructure, ranging from 6 to 9 eV, is found to narrow on increasing the Y content. This is seento correlate with a narrowing of the valence band, observed in the corresponding range of theXPS spectra. The general trend is consistent with some kind of ordering process, taking place inthe vacancy system at higher concentrations.

6P:bl61VUV REFLECTIVITY ON Si02

C. BDBIO (a,b) and W. CZAJA (a)(a) I.P.A., Dep. Physique. EPFL, CH-1.015 Lausanne, Switzerland.(b) It/L. Fisica, Univ. Pavia,, Via Bassi 6, 27100 Pavia, Italy.

Reflectivity spectra of crystalline and amorphous Si02 in thevacuum ultraviolet range of energies and at Differenttemperatures, ranging between 400 K and 30 K, show bothdifferences and similarities depending on their modification.The spectra show also a dependence on the crystallineorientation of the samples. The structures observed have beenanalysed and there is evidence of a plasma edge in crystallineSi02. The Kramers Kronig spectra obtained from the reflectivityhave been compared with previous absorption measurements.

116

6P:bl62

STUDY OF THE OPTICAL ABSORPTION EDGE OF YTTRIUM-STABILIZEDZ1RCON1A

P.CAMAGNI®, P.GALINETTO®, G.SAMOGGIA®, N.ZEMA*^Dipartimento di Fisica A.Volta, 27100 Pavia;# ISM-CNR, 2044 Frascati, Roma,ltaly

A detailed study of the fundamental absorption edge of yttria-stabilized zirconia (YSZ) singlecrystals has been performed for different contents of the yttrium ion, between 12 and 24at%.Two distinct regions are observed.Below 5 eV, absorption grows with an exponentialUrbach iaw = expphv, whose slope is nearly independent of temperature and Yttriumconcentration, while the strength is markedly dependent on the latter parameter. Excitation inthis region produces a luminescent emission, which is interpreted in terms of transitionsbetween extended and disorder-induced localized states. At energies > 5.2 eV, a widestructureless luminescence is observed, which can be connected to the decay of the self-trapped exciton, hence to the onset of direct transitions. The analysis of these phenomena,extended to reduced and irradiated crystals, provides new insight on the electronic transitionsof this highly defective system.

6P:bl63

ADVANCES IN EMISSION KINETICS ANALYSIS OF HEAVY ns2 IONS INALKALI HALIDE CRYSTALS.

M.NIKL,1 J.HLINKA'K. POLAK'E.MIHOKOVA^P.FABENlfc P. PAZZI,2L. SALVINI3

1/Inatitute of Physics,Cukrovarnicka 10, 162 00 Prague,CSFR

2/I.R.O.E. del CNR, Via Panciatichi 64, 50127 Firenze, ITALY

Our results in theoretical Modeling of emission kinetics of Tl*

and Pb2* centers in KX(X-Cl,Br,I) and Tl* in Csl crystals arc

reviewed. Multiphonon processes are included in nonradiative

transitions between radiative and aetastable levels in a single

excited state ainiaua. The deviations froa single exponential

course at 4.2 K in case of slow coaponent decay curve of both

Tl* and Pb3* in KX(X-Cl,Br,I) are revealed and explained by

slow relaxation process of setting up autual distance between

radiative and aetastable levels. The paraaeters of nonradiative

energy transfer processes between non-equivalent Jahn-Teller

excited state ainiaa were found for KX:T1(Z-Br,I) and CsI:Tl.

117

6P:bl64RED LUMINESCENCE OF STRUCTURAL DEFECTS IN Hg2Cl2 CRYSTALS

Z.BRYKNAR, A.KOfiAKOVA, P.JIROUSEKCzech Technical University in Prague, Brehova 7, U S 19 Praha 1

In this work, we focused our attention on the red luminescenceof Hg2Cl2, as up to now no successful attempt to explain thisemission has been made. We wished to define, whether the redemission is of an intrinsic nature or whether it belongs tothe structural defects of crystals. For this reason we stu-died the following effects on Hg2Cl2 single crystals: X-ray jexcited luminescence, slow-curve of the thermally stimulatedluminescence , and emission and excitation spectra of lumines-cence conventionally excited by UV lamp.

The results of the Hg2Cl2 red luminescence measurements can besummed up as follows: a) Luminescence of Hg2Cl2 In the redspectral region excited either with X-ray or UV light origina-tes from the structural defects of the crystals and it is notof the intrinsic nature, b) The thermally stimulated luminesce-nce of Hg2Cl2 was observed for the first time and Its emi-ssion spectrum was found in the red spectral region, as well.It is assumed that this luminescence also originates fromstructural defects of crystals.

6P:bl65PHOTOEMISSION SPECTROMICROSCOPY INVESTIGATION OF SnOx-BASED GAS

SENSORS.

D. Rosenfeld, P. Almeras, C. Coluzza, F. Gozzo, R. Sanjinfs, and G. Margaritondo

IPA-Departement de Physique, PHB-Ecublens, 1015 Lausanne, Switzerland ;

The SnOx films are an interesting material because of their widespread technological

applications. The performances of tin oxide-based devices arc strongly related to the structure ;|

and to the oxidation state of the films. The spatial homogeneity of both such characteristics are ;

also crucial. Thereby, photoemission studies of the valence band and core levels of these films '.

are of great interest in order to characterize the microstructure and to understand their electrical £Hi

properties. JgIn the present study, X-ray photoemission spectromicroscopy has been used to investigated the | |

active area (SnO x thin films deposited by DC sputtering) of gas sensors. The degree of j |

oxidation and the homogeneity of films have been analyzed by using a high lateral resolution ty

mode ( 30 micron) with an energy resolution of 0.4 eV on the total spectrum. We will also \

report the results on the interaction of H2, H2O, and CO gases with the surface of SnOx films

in miniaturized integrated gas sensors. These results have been related to the electrical transport

properties of the same devices in order to clarified the contribution of the chemisorbed species.

118

6P:bl69

ELECTRIC BIREFRINGENCE MEASUREMENTS OF AQUEOUS FD-V1RUS-SOLUTIONS

Bansgexd Kraaer and Reinhart Weber

Fakultat fiir Physik, Dniversitat Konstanz, 7750 Konstanx,Germany

Aqueous solutions of rodlike fd-virus particles (length l=880nm, diameter d=9nm) areexamined by the transient electric birefringence method. A special experimental setup isused, which allows a very sensitive variation of the screened Coulomb interactionbetween the particles. The birefringence signal is measured as a function of the virusparticle concentration and the ionic strength of the solution. For low applied electricfield strength it is demonstrated that anomalous birefringence is an effect of the stericand electrostatic interactions between the fd-virus particles. It is shown that thisbehavior is correlated to a decrease of the rotational diffusion constant Dp. In the caseof high ionic strength the deduced values of D R are in agreement with the theory ofTeraoka and Hayakawa [1] up to a concentration of 8c* (c* is the overlapconcentration), at larger concentrations the values are significantly higher thanpredicted.

[1] Teraoka, I.; Hayakawa, R., J. Chem. Phys., 1989,91,2643.

6P.bl70MONTE CARLO SMULATION8 OF CLOSED DNA MOLECULES.

MARCO BOTTA, GIUSEPPE CHIRICO AND GIANCARLO BALDINI.

Dipartlmento dl Flsica. Untversita' degli Studl di Milano, via Celoria 16. 20133Mllano.

The structure of closed DNA molecules plays an Important role in the understanding ofmany aspects of the DNA activity. We are using a Monte Carlo Approach in order tosimulate the possible conformation in solution. The DNA is modelled by a B-spllne (1) curveand the energy is computed from the known values of the bending and torsional rigidity,and the topological constraints (linking number). The average conformation results in ainterwound structure where two different parts (double helix filaments) of the closed DNAmolecule interwine one around the other. The statistical ensemble is then used to computethe average values of several quantites, like diffusion coefficients or radii of gyration, and agood agreement is found with experimental results.

1. Hao M. Olson W.K.. biopolymers. 28 (1989) 873-900.

119

6P:bl71MICROSCOPIC BASIS FOR SUPERIOHIC CHARGE TRANSPORT MODEL INBIOLOGICAL MEMBRANE CHANNELS

RAKITIN A. S.Institute of New Physical and Applied ProblemsAcadamy of sciences of UKraineUntzKogo 11-47. 252035 Kiev, UKraine

The idea of the "superionic origin"1 of charge transport me-chanism in biological membranes is developed. The microsco-pic analysis is carried out*in the frameworK of "unstableFrencel couples model". It is shown that a sharp enhance-ment of ionic channel penetrability may taKe Place due to aferroelectric-superionic phase transition caused by "perco-lating" ion electrostatic field effect. The microscopic eq-uation of state is derived. An appropriate temperature andfield dependences are obtained and discussed.

1. Leuchtag H. R. , Int. Biophys. Congr. (1990) 5.1.13.2. RaKitin A. S., 1 UKr. Symp. Phys. Techn. MM/SMM RW

(1991)11.121.

6P:bl72EVIDENCE OF HEMOGLOBIN DISSOCIATION FROM LIGHT SCATTERING

LORENZO LUNELLI. NICOLO' ROMANI and GIANCARLO BALDINIDipartimento di Fisica. Universita degli Studi. Via Celoria 16 . 20133 Milano, Italy.

Hemoglobin, a tetramer protein, binds O2 . CO and other small molecules in a cooperativefashion. Under extreme conditions of pH or ionic strength it can dissociate into dimersaccording to (a p ) 2 - * 2 (a p).

Dynamic light scattering experiments under way show that the hydrodynamic radius of the •tetramer is 6.5 nm whereas values of 5.3 nm are observed at pH.6 corresponding to a 0.93dissociation fraction. The measures show also that high ionic strength inhibits the :dissociation of Hb-CO at acid and alkaline pH but it favours dissociation at neutral pH.

Light scattering measurements of Hb-O2 are underway at different stages of oxygen binding fsince tetramer to dimer dissociation is expected to occur near oxygen saturation. ' %

••'i

1. Bucci E.. Frontlcelli C. and Gryczynski Z.. Biochemistry 30 (1991) 3195. >Y

120

6P:bl73

BROWNINAN DYNAMICS OF CLOSED DNA MOLECULES.

Giuseppe Chlrico, Jorg Langowski*

Dipartlmento dl Fisica, Universita' degli Studl di Milano, via Celorla 16, 20133Mllano.• EMBL, Grenobel Outstation, Avenue des Martyrs, 38000 Grenoble, France.

The dynamics and the structure of closed DNA molecules play a major role in DNA activity.We are studying the brownian dynamics of large DNA molecules (up to lum) modellingthem as non-adjacent string of beads (1). The torsional-bending coupling, essential forthese closed molecules, is computed here from suitable potentials, and implemented in aFortran program on a parallel machine (STARDENT 3000). The use of the proper couplingallows the study of the writhing of a relaxed (i.e. un-stressed) DNA molecule undertorsional stresses. This method seems promising for the direct computation of DNAdynamical properties, such as dynamic light scattering correlation functions, orfluorescence polarization aiiisotropy decays etc.., of large DNA molecules.

1. G.Chirico, J. Langowski, Macromolecules, January 1992, in press.

6P:bl74

RHEOLOGICAL PROPERTIES OF SUSPENSIONS OF INTERACTING RODLIKE FD-VIRUSPARTICLES

Christian Graf and Reinhart Weber

Fakultat fur Physik, Dniversitat Konstanz, 7750 Konstanz,Germany

Low shear ( 7 = 1 1/s) and shearrate dependent (1 1/s < 7 < 100 1/s) viscositymeasurements on aqueous suspensions of rodlike fd-virus particles (length = 880 run,diameter = 9 nm) below and above the overlap concentration c* = 1 particle/L^ arepresented. In suspensions, where the Coulomb interaction is screened by added salt, theparticle concentration dependence of the low shear viscosity r\ follows in a firstapproximation the reciprocal of the rotational diffusion constant D r . For concentrationshigher than 20 c these samples reveal a pronounced non-Newtonian rheologicalbehavior. If the ionic strength of the suspensions is decreased, the virus particles areadditionally interacting via Coulomb forces. Using a tube pump system containing ionexchange resin, the low shear viscosity 11 as well as the shear rate dependence aremeasured continuously as a function of the conductivity of the suspension, respectivelyits ionic strength. Due to the structural ordering of the virus particles in this case astrong increase in the low shear viscosity is observed. This is accompanied by non-Newtonian behavior c e n at particle concentrations lower than 0.5 c*, especially at theminimal ionic strength of approximately 0.5* 10~6 M. These results are compared with

i available theories.

121

6P:c201

LUMINESCENCE FROM SILICON DOPED WITH Cu AND Fe ANDEXTENSIVE DEFECT DECORATION

M.C. CARMO, M. LIMADepartamento de Fisica, Universidade de Aveiro, 3800 Aveiro, Portugal

Extensive defects are known as segregation sites for impurities in silicon thusaffecting the yield properties of devices. Transition metals are also fearfulcontaminants in IC technology due to the fact that they complex with electricalactive impurities.

In this work we have studied ways of segregating transition metal impurities inselected parts of the crystal by high resolution spectroscopy. We followed the effectof extensive induced transition metal associated luminescence bands|1,2| and alsostudied the annealing properties of these bands in the presence of extensivedefects under controlled experimental conditions.

1. M.I.. Calao, M.C. Carmo, Physica Scripta 38 (1988) 455.2. M.C. Carmo et al, Mat. Res. Soc. Symp. Proc. vol. 138. (1989) 221.

6P:c202SPATIAL SENSITIVITY REVERSAL IN A MODIFIED DLTS

I. Thurzo, V. NadaZdyInstitute of Physics, Slovak Academy of Sciences, Dubravskacesta 9, 842 28 Bratislava, Czechoslovakia

The modified charge DLTS scheme benefits from the feedback

charge method (T.J. Mego 1986), designed originally for

quasistatic CV measurements. In addition to the conventional

train of filling pulses in DLTS, there is a couple of probing

pulses of equal amplitudes aU^kT/q which is applied to the

sample during each excitation cycle. Positioning the latter at

points in time t, and t« with respect to the trailing edge of a

filling pulse, a suitable sampling circuitry makes it possible

to assess the "instantaneous" capacitances C(t,), C(t?) which

represent equivalents of their high-frequency counterparts. In

this way we obtain the signal AC=C(t,)-C(t2) corresponding to

the standard capacitance DLTS with its optimum sensitivity for

bulk trap detection, as opposed to conventional charge DLTS

schemes.

122

6Px203IMAGING OF DEFECTS IN GaAs:In BY SCANNING ELECTRON ACOUSTICMICROSCOPY

B. Mendez and J. PiquerasDpto. Fisica de Materiales, Facultad de Fisicas, UniversidadComplutense, 28040 Madrid, Spain

The application of scanning electron acoustic microscopy (SEAM)to the characterization of low dislocation density GaAs:In hasbeen investigated. The material shows a high SEAM signal thatallows to image structural defects. In samples with (110)orientation, dislocations with a structured contrast possiblyrelated to precipitates are observed. Single dislocations are notimaged by SEAM in GaAs with other dopants1. Measurements havebeen complemented with cathodolflsinMcanoe in the scanningelctron microscope of the same saaple areas.

1. B. Mendez and J. Piqueras, accepted in Appl.Phys.Lett>

6P:c204META-STABLE DEFECTS IN SILICON

NICHOLAS A. SULIMOVGeneral Fhysics Institute of the USSR Acadaty of Sciences,117942, Vavilov street 38, Moscow, USSR.

The paper reveals variations of volume electro-physical parameters ofthe boron and phosphorus doped Si wafers grown by Czochralsky method underelectron irradiation (E=25kev). The experiments on elastic IR light scat-tering, microwave-photo conductivity and DLTS were carried out. The varia-tions of charge states of large-scale impurity clusters, volume non-equi-librium carrier lifetime and DLTS spectra take place. The model of meta-stable defects responsible for the variations is discussed.

i123

6P:c205

NATURE OF POINT DEFECTS IN Bi2_xInJ £Te3 CRYSTALS

J.HORA'K1 and Z.STARf2

11nstitute of Chemical Technology, 532 10 Pardubice, SsFR2Joint Laboratory of Solid State Chemistry Czech.Acad.Sci.and Inst.Chem.Technology, 532 10 Pardubice, CSFR

Transport coefficients (el.conductivity, Hall constant, See- jbeck coefficient) and plasma resonance frequency of Bi, In^Tecrystals with a various value of x have been determined.

Using the calculated bonding parameters a model has beenproposed which allows to explain the relations between the in-creasing content of incorporated In atoms and the decrease ofantisite defects concentration in the p-type crystals; theelectrical conductivity of n-Big^In^Te, (for x>0.1) is pro-bably associated with an increase in the concentration ofTe-vacancies.

6P:c206INVESTIGATION BY THERMOLUMINESCENT EXPERIMENTS OF POINT DEFECTS IN

ALUMINO-SILICATE LATTICES

P. BROVETTO, A. DELUNAS, V. MAXIA, M. SALIS and 6. SPANO

Gruppo Nazionale dt struttura del la Materta - Cagliari, Italy

IstHuto di Fisica Supertore dell" Universita - Cagllart, Italy

The thermolumtnescent emission of solids belonging to A1,O,-SiO, and

Al,Oj - MgO -SiOa systems has been recorded simultaneously versus temperature |

and wavelength In the ranges from 300 to 700 K and from 375 to 750 nm, "respectively. The emission patterns of x-ray activated synthetic samples of ?mullite and cordtertte are characterized along the temperature axis by a broad |band extending from 350 to 700 K. The spectral composition shows bands at 710, j

630 and 460 nm. The analysis of data and their comparison with results obtained |

when studing the thermoiuminescent emission of alumina' evident late the role ••

of lacunar sites and lattice voids in originating points defects responsible for

carrier trapping in the lattice.

I. Brovetto P., Delunas A., Maxia V., Spano 6., liazza D. and Valllno li . , NuovoCimento D l l (1989) 1657.

124

6P:c207

THE EFFECT OF ELECTRON IRRADIATION DOSE ON THE PROFILE OFTHE INTRODUCED DEFECTS IN GaAs VPE LAYERS

C D . Kourkoutas *. B. Kovacs+. P. C. Euthymiou. B. Szentpa 1 i +.KSomogyi+.P.C.Banbury** and G.E.Zardas

Sol.St.Section,Phys.Dept.Athens Univ..104 Solonos Str.Athens10680.Greece.* Dept.of Phys.,Chem.and Mater.Techn.TEI Athens,12 Ag.Spyridonos.Egaleo 12243.Attiki.Greece.+ Res.Inst.forTechn.Phys.H1325.Budapest.Hungary.** Physics Dept.Reading U-niv.Reading,England.

We study the profile of the introduced by 0.65 MeV electronirradiation defects in^aAs VPE layers.The irradiation dosewas 6X10™ el/cn£-l .8x10*^1/cm*.The concentration and thecon-ductivity profiles up to 2 pm have been measured.The condu-ctivity undergoes a significant decrease at irradiation do-ses greater than 10 el/cm .The dominant role of a shallow e-lectron trap,probably E2 [ll.is indicated by the demperaturedependence of the conductivity in the measuring region 190K-300K.The concentration of the dominant electron trap increa-ses vs depth in all cases.Heat treatment at 300° C does notaffect the trap concentration,while that performed at 400*Ccauses 50% recovery.[1] D.Pons and J.C.Bourgoin,J.Phys.C18,3839.(1985)

6P:c208ELECTRICAL PROPERTIES OF ION IMPLANTATION INDUCED DEFECTS IN SILICON

P. HAZDRAW, V. HASLAR"" and M. KEJHARW

'•'Department of Microelectronics, Faculty of Electrical Engineering, Czech Technical University Prague,Technicka 2, 166 27 Prague 6, Czechoslovakia

(b>Laboratory of Ion Implantation, Faculty of Electrical Engineering, Czech Technical University Prague,Technicka 2,166 27 Prague 6, Czechoslovakia

Generation and recovery of ion implantation induced crystalline defects in silicon and determination of theirinfluence on silicon electronic structure and transport properties are presented in this paper. The ionimplantation of "Si* ions into phosphorus doped ( ND ~ 13x10" cm"3) <100> oriented Czochralslti-grownn-type silicon was utilized for investigation of crystalline defects created by medium mass energetic ionirradiation. Wide spectrum of implantation temperatures ranging from 120 K to 820 K, doses of 5x10* cm"3

to bclO13 cm"2, implantation energies 160 and 400 keV and subsequent isochronal annealing in temperaturerange from 370 K to 870 K was used for detailed identification of created defects and determination of theimplantation conditions influence on defect generation rate and stability. Created defects and their influenceon electrical properties of semiconductor material ( deep level structure, generation and recombinationphenomena, carrier concentration) were investigated using Deep Level Transient Spectroscopy and otherelectrical methods ( I-V, C-V ) applied on special ultra-shallow test p*n diode structures. Semiconductordevice simulator involving a novel and more accurate model of thermal generation and recombination wasutilized for detailed experimental data interpretation. Up to eleven deep level centres were identified andattributed to different defect structures. The crucial mechanisms of individual defect generation and theirdependence on irradiation conditions were established as well as thermal stability of defects produced.

125

6P:c209INTERACTION OF IMPURITIES IN CUPROUS OXIDE

R. KUZEL, F.L. WEICHMAN+

Fac.of Math.and Phys..Charles Univ.,Ke Karlovu 5, 12116 Prague 2+Dept. of Physics,.University of Alberta, Edmonton, Canada

As late as over 30 years ago, the formation of complexes in cup-

rous oxide when heated, and their dissociation when illuminated, ):

were assumed. However, the point of view of some authors diffe-

red in this question. Our detailed measurements of Hall coef-

ficient temperature dependence of samples containing various im-

purity concentration enabled to prove uniquely the formation of

both simple copper vacancies (acceptors), and their complexes.

Based on performed measurements, a new method of indicating the

concentration of not only simple vacancies and their complexes,

but also of compensating donors, without having reached the tem-

perature region of the current carrier saturation, was proposed.

The activation energy of the complex dissocation was determined.

6P:c210DEEP LEVELS IN SILICON AFTER NEUTRON IRRADIATION

J.Mudrort,P.Sutta,IL.Macko

Department of Physics,Faculty of Applied Electronics, /

Technical University,031 19 Liptovsky Mikulas,CSFR j

D.Pogany ,P.liacko,P.Bal lo ••

Department of Physics,Faculty of Electrical Engineering, />

Slovak Technical University,812 19 Bratislava,CSFR j{

DLTS spectra of silicon p-n junctions Mere measured before M

and after neutron irradiation (average energy En=l MeV,flux '§

density 1=1.10**-l.1023cm-2).Seven peaks which correspond a

with point defects in silicon caused by fast neutrons have '•','

been detected.The decrease of switching time <trr=16O ns at

!*=0,trr=7 ns at 1=1.10**cm-s > was observed. v

126

6P:c211APPLICATION OF A NEW METHOD TO MEASURE MFiCTS IN SKMIOOHDOCTORS.

Laazld DdzaaResearch Institute for Technical Physicsof the Hungarian Academy of SciencesBudapest 1325 P.O. Box 76

A new Method is used to investigate VaOs and silicon samples. Freecarrier Mission or dielectric relaxation transients of electricallyactive defects in semiconductor or insulator samples can be Measuredby the Method typically in the 16 us -1 ms time constant range. (1) Bythis new deep level spsctroscopy technique the frequency dependence ofthe saMple capacitance and the DC leakage can be also determined in athe SBMB Measuring setup. The relaxation of the defects is Monitoredby the voltage transient generated on the saMple capacitance. Thevoltage transient is Measured by a large input *T~*»~»- oscilloscope.The excitation pulses are suppressed by connecting a compensatingbranch to the sample and feeding this branch with compensating pulses.It is shown that the Method is very useful in identification ofdifferent origin relaxations in the samples.

1 L. Ddzsa Solid State Blectronics, accepted for publication

6P:c212

ENERGY TRANSFER BETWEEN Ni2 * AND CU + CENTRES IN ZnS

P. Thurian, R. Heitz. T. Jentzsch, A. Hoffmann and I. BroserInstitut fur FestkdrperphysikderTU-Berlin. 1000 Berlin 12,Hardenbergstr.36,

Germany

The PL and PLE of ZnS crystals doped simultaniously with copper and nickel isinvestigated. Both Ni2 + and Cu2* impurities show a acceptor type chargetransfer band (CTB) in PLE peaking at 2.60eV and 1.70eV, respectively. It turnedout that the Cu2 + luminescence is additionally excited during light absorption inthe CTB of Ni2 +. This is due to an energy transfer by photoexcited holes betweenNi2 + and Cu + centres. The threshold energy of this process yields an accuratevalue for the deep Ni2 + acceptor at 2.533eV above the valence band. In the lowenergy onset of these CTBs sharp resonances are observed, revealing newexcitation processes of these centres'. They include binding of an hole by atransition metal forming an "external" excited state of the impurity. The bindingenergies of these (Cu+]h) and (Ni + ,h) states are determined to be 119meV and96meV, respectively. These results are compared with the excitation mechanismsof the visible Cu-related luminescence bands (Cu-B, Cu-G, Cu-R).

1 R. Heitz, A. Hoffmann, P. Thurian and I.Broser, to be published in J.Phys. C, Jan.1992

127

6P:c213INVESTIGATION OF DEEP LEVELS IN SILICON

J. PROKES, 0. STEFAN

Faculty of Mathematics and Physics, Charles University

Ke Karlovu 5, 121 16 Prague 2, Czechoslovakia

Deep levels in a float-zone grown silicon were studied by

means of capacitance methods. The material of n-type doped

with different elements (Co, Fe, Cr, Au, Ag, Pt, Pd), irra-

diated with high energy electrons and reference one were

available. Abrupt and graded p+-n junctions were formed by

diffusion of Al and both fast and slow cooling were employed.

Common features were found for different materials and espe-

cially the origin of E -0.54 eV level is discussed. It seemsc

to be connected with a native defect but the influence of

doping is not negligible.

6P:c214

JAHN-TELLER EFFECT ON THE EL2 CENTER UNDER UNIAXIAL STRESS

Liana Martinclli* and Giuseppe Pastori Parravicini***Dipartimento di Fisica, Universita' di Pisa, GNSM and INFM, piazza Torricelli 2,56125 Pisa, Italy**Dipartimento di Fisica "A. Volta", Universita' di Pavia, via A. Bassi 6,27100 Pavia.

Piezospectroscopic experiments on the 8378 cm"1 zcro-phonon line (ZPL) of the EL2defect in AsGa suggest that the EL2 center is an arsenic antisite AsQa defect, oftethraedral T<j symmetry, subjected to a small lattice relaxation. By means of therecursion method we have studied the vibronic levels of this defect and the opticalproperties associated with the A]-»T2 transition energy. In our model we haveincluded on the same footing both the Jahn-Teller coupling on the T2 degenerateelectronic states and the effect of the uniaxial stress along several crystal directions. Thephonon mode, useful to explain the replicas of the ZPL and the behaviour of the stress-split sublevels of the T2 states, has X2 symmetry. Our calculations provide a reasonableagreement with the experimental splitting and also allow to predict the behaviour understress of the replicas of the ZPL.

128

6P:c215

PARAELECTR1C RESONANCE OF PHOTO-EXCITED Sn RELATEDDX CENTERS IN A^Ga^As AT LOW TEMPERATURES

K.ZDANSKY and A.R.PEAKERInstitute of Radio Engineering and ElectronicsCzechoslovak Academy of SciencesChaberska 57, 182 51 Praha 8, Czechoslovakia andCentre for Electronic Materials, University of ManchesterInstitute of Science and TechnologyP.O.Box SS, Manchester M60 IQD, England

Frequency dependences of photo-excited capacitance and conductance ofGaAs/Ali-Gai-jAs heterostructure diodes prepared by liquid phase epitaxyhave been measured at low temperatures down to 25 K.It has been foundthat these dependences exhibit a resonance in the frequency range of onesor tens of KHz depending on the temperature.lt has been proposed that theresonance is caused by hindered rotations of S'n related DX centers in thefree carrier frozen AlxGa\^zAs layer which are driven parametrically by theoscilating electric field of the measuring equipment.

6P:c216

THE CONSEQUENCES OF THE FREE-CARRIER ENTROPY FOR TIGHTLY BOUNDDEFECT STATES IN SEMICONDUCTORS

D. H. COBDENt, L. MARTIN-MORENOt, AND M. J. UREN+ttThe Cavendish Laboratory, Madingley Road, Cambridge CB3 OHE, United Kingdom

ttDRA Electronics, St Andrew's Road, Malvem, Worcestershire WR14 3PS, United Kingdom

We show how the energetics of electron capture to a tightly-bound ("deep") defect state in asemiconductor can be strongly influenced by the interaction of the defect with the free carriersin its vicinity. In particular, the entropy of the carriers can lead to a large temperaturedependence of the measured defect energy level. This may explain several anomalies reportedin the literature on deep levels in silicon and oxide defects in MOSFETs. We have modelled theeffect by calculating the statististical mechanics of the local conduction band states as modifiedby the screened defect potential.

129

6P:c217VANADIUM LEVEL AND PHOTOCONDUCTIVITY IN n-InP UNDER PRESSURE

A.K. SAXENADepartment of Electronics and Computer EngineeringUniversity of Roorkee.Roorkee 247 667 (UP),India

Resistance and Hall effect in V doped n-InP have been measuredas a function of hydrostatic pressure upto 50 kbar. The PCresponse from the sample in Bridgmann ring has been used toprecisely measure the pressure and the results show that Thas a coefficient of (8.2+p.2)meV/kbar. An increase inresistance by about four orders is due to electron trap out toV - level as this is pushed into the band gap with pressure. Atatmospheric pressure, its energy is estimated to be (0.16^0.04)eV above p -This is the first measurement of V level in InPreported so far. V and other 3d transition metal impurities inGaAs,InP,GaAlAs, GaAsP and GalnAsP seem to conform to the vacuumlinked model of Ledebo and Ridley. At atmospheric pressure, thephotolumlenscence spectra did not show any energy levels at 300and 77K. Also no deep lying level could be detected either byDLTS or temperature dependent Hall effect. This permitted us toanalyse the results on InP band structure and the V level only.The V level in GaAs has been reported to lie 0.150 eV below rfrom electrical transport measurements. The energy positions ofV level in GaAs and InP, thus, require conduction and valenceband discontinuities of 0.31 and 0.20 eV,respectively.

6P:c218PECULIARITIES OF THERMOSTIMULATED CURRENTS IN SEMIINSULATING

GaAs AND InP:Fe

E. KLIER, F.L. WEICHMAN +

Fac.of Math.and Phys..Charles Univ.,Ke Karlovu 5, 12116 Prague 2+Dept. of Physics, University of Alberta, Edmonton, Canada

Variations of TSC spectra due to different experimental condi-

?• tions have been studied and interpreted. The peculiar effects ;

.; include: 1) Quenching of TSC by high electric fields. 2) Drastic ••*

f changes of TSC spectra with variation of spectral composition 1

I of exciting light and exposure time. 3) Instabilities- and oscil- .'

t lations observed in TSC spectra. Interpretation of these pheno- J

;• mena is based on the assumptions of high field domains (travel- ~k

R ling or stationary), separation of surface and bulk traps and

|vi transitions between bistable configurations of compound defects,••'' •* 1

possibly including transitions EL 2£*EL 2 in GaAs .

1. Kiliulis R. et al., phys. stat. sol. (a) 1J!7 (1991) 415.

130

6P:c219

LOW TEMPERATURE DX CENTER IONIZATION BY FORWARD BIASING AIGaAsSCHOTTKY BARRIERS

R. MOSCA, E. GOMBIA, C. GHEZZI , P. FRIGERI , A. BOSACCHI and S. FRANCHIIstituto MASPEC del Consiglio Nazionale delle Ricerche, Via Chiavari 18/A, 43100Parma, Italy*Dipartimento di Fisica, Université degli Studi di Parma, Viale delle Scienze,43100 Parma, Italy

OX centers are known to control the electrical conductivity of n-type AlxGai -xAs(x>0.22) and to cause deleterious effects in HEMT devices. At low temperature thecharge state of the center is frozen and it can only by changed by photoexciting orby warming the sample.In this work we study the DX center in Schottky barriers prepared on MBE Si-doped AIGaAs. We show that at low temperature the spatial distribution ofpositively charged DX centers near the Schottky contact can be changed by theapplication of forward biases. The phenomenon is not originated by thermaleffects. Preliminary results suggest that for x-0.25 the charge state of the DXcenter begins to change at a bias of about 0.9 V.The influence of the metal species (Au, AI) used for the Schottky contact and of theAlAs mole fraction is considered and the possible origin of this effect is discussed.

6P:c220EVIDENCE FOR THE ROLE OF SPATIAL DISTRIBUTION OF CHARGED

IMPURITIES ON THE ELECTRON MOBILITY IN AI ,Ga ( 1 . s )As

CONTAINING DX-CENTERS

P.L.Coz, C.Ghezzi, A.Parisini

Dipartimento di Fisica - Universita' di Parma - Viale delle Scienze - 43100 Parma

The electron density n and the Hall mobility fi have been measured during electron

capture transients by DX centers or photoexcitation processes performed at different tem-

peratures (IK < T < 140HT) in AI.Ga (1_a)As Si-doped MBE samples.

It is shown that p is not a single value function of n, /* being larger if a given value of n a

reached through capture rather than photoionization processes. This difference is reduced

by lowering the Si-doping level.

The result is interpreted as due to spatial correlation between charges at the impurity cen-

I ters. It is shown that during the fast initial stage of the capture the charges arrange to

I minimize the effect of Coulomb scattering, but the contrary happens during the slow final

f, stage of the capture process.

131

6P:c221TEMPERATURE DEPENDENCE OF THE PHOTOQUENCHING OF EL2 LEVEL INSEMIINSULATING GaAs

M.CHAFAI1,A.ALVAREZx,J.JIMENEZ1,J.PASCUAL2

l .Ffa ica de la Hateria Condenaada,Facultad de Ciencias and ETSII, 47011Valladolid .Spain2.Fiaica Aplicada,Facultat de Cienciea, Universitat Aut6noma de Barcelona,08193 Bellaterra (Barcelona) ,Spain

Semiinsulating GaAs presents a high technological interest as asubstrate for high speed microelectronics. The high resistivityis due to a native midgap donor, the so-called EL2 level.Besides its technological importance this level is characterizedby a large lattice relaxation under photoexcitation at lowtemperature with subband gap light that results in thetransformation into a jnetastaJble state,EL2*. Recently we haveobserved that there exists a thermal hysteresis between theoptically induced EL2-EL2* transformation (PQ) and. the thermally

assisted EL2-EL2* reverse transition (TR). In fact PQ cannot begenerally achieved above 85K, while TR is only achieved at 120-130K. This is discussed in terms of an actuator level. A, whichdepending on its charge state can trigger the transition to themetastable state (PQ) or not. From the temperature dependence ofthe photoquenching is deduced that this level is thermallyemptied between 85 and 100 K; therefore it is estimated to lieless than 200 meV from the corresponding free band.

6P:c222DEEP ZR- AND HF- RELATED LEVELS IN INP

H. Schefflera, N. Baberb, T. Wolfa, A. Knecht a, D. Bimberg a , J. WinterfeW c,and H. Schumann c

a Institut fur Festkorperphysik, Technische Universitat Berlin, Hardenbergstr. 36,I W1000 Berlin 12, Germany' b Semiconductor Physics Laboratory, Department of Physics, Quaid-i-Azam-

University, Islamabad, Pakistan0 Institut fur Anorganische und analytische Chemie, Technische Universitat Berlin,

Str. d. 17. Juni 115, W1000 Berlin 12, Germany

; Although deep levels caused by 3d transition metals (TMs) in InP have been the subject of \extensive studies, little is known about the properties of the heavier 4<j and 5d TMs. We ;

I carried out comparative Deep Level Transient Spectroscopy on n-lnP:Si codoped with the «[ isovalem 3d, 4d, and 5d TMs (Ti, Zr, Hi). The samples were prepared both by Metalorganic \i Chemical Vapour Deposition and ion-implantation. While the deep Ti donor is situated at <-I Ec-0.59eV, Zr and Hf were found to give rise to deep levels with activation energies of '*i 0.53 and 0.46eV, respectively. These levels were not present in reference samples. So it >| appears that the activation energy of TM-related levels is slightly reduced going down in•• this column of the periodic table of elements (3d to 4d and 5d), in agreement with trends of

the predicted activation energies of heavy TMs calculated for GaAs and GaP1.

1. N. Makiuchi, T.C. Macedo, M.J. CaWas and A. Fazzio; Defect and Diffusion ForumVol. 62/63 (1989), p.145

132

6P:c223EPR STUDY OF TRIPLET JV»3+ CENTRES IN NaCl SINGLE CRYSTALS

A.G.BADALJANA.F.Ioffe Physical-Technical Institute,Sankt Peterburg,RussiaJ.ROSAInstitute of Physics, Czechoslovak Acad. of Sci., Na Slovance 2,180 40 Prague 8, Czechoslovakia

The X-band paramagnetic resonance of NaCl single crystals doped by Ni has been studied at 5K.The EPR spectrum shows a remarkable angular variation of a fine structure, on the basis of which twogroups of fine structure lines can be distinguished, one with rhombic symmetry (A) and the other withaxial symmetry (B).

Both parts of the spectrum are described by the following Hamiltonian:

% = g.pH.S, + g.pH.S, + g¥0H$S, + D[St* - ^S(S +1)] + E{Sm - St)

with effective spin 5 = 1 and rhombic parameters for (A) and axial for (B) parts:

(A) :D = 55.5 ± 0.3 GHz; E = 18.1 ± 0.3 GHz; g, = 2.52 ± 0.04; g, - 2.62 ± 0.04

(B):D = 76.7 ±0 .3 GHz; E = 0; g. = ya; y . = y, = yj.; gt = 2.14 ± 0.03; y x = 2.14 ± 0.03.

The spectrum comes from Ni2+ ions (3d*, 5 = 1 , triplet state) which redundant positive charge iscompensated by cation vacancies in two different positions. The rhombic centre is created by Ni3+ ionwith a cation vacancy in the second neighbour position along the (110) direction, the axial centre is

> formed by Ni*+ ion with a cation vacancy in the third coordination sphere on the (100) axis.

}

| 6P:c224I ELECTRON SPIN RESONANCE SPECTROSCOPY OF SILVER DOPED SILICON

N.T. SON, V.E. KUSTOV, T. GREGORKIEWICZ AND C.A.J. AMMERLAANVan der Waals-Zeeman Laboratorium der Universiteit van Amsterdam,Valckenierstraat 65, NL-1018 XE Amsterdam, The Netherlands

The first observation of silver in silicon by electron paramagnetic resonance (EPR) isreported. In silver doped silicon several new EPR spectra were observed.

Three of these, which are labelled Si-NL42, Si-NL43 and Si-NL44, exhibit a hyperfinestructure with twofold splitting due to a nuclear spin 1=1/2. The spectra Si-NL42 and Si-NL43 have the trigonal symmetry and can be described by an effective electron spin S = l / 2and a nuclear spin 1=1/2. From the shift of the hyperfine lines observed in the samples dopedwith the enriched 107Ag and lwAg isotopes, both centres are confirmed to be silver related.

} By observing the hyperfine interaction due to "Fe (1=1/2) in a sample co-doped with "Fe; isotope, the spectrum Si-NL42 is identified as FeAg pair. The spectrum Si-NL44 with the[ isotropic value g=1.9736 and an isotropic hyperfine splitting of S MHz was observed in aI sample doped with l07Ag. A candidate for interpretation of this high-symmetry spectrum is| the isolated interstitial silver impurity.

The other EPR spectra have trigonal symmetry, but have no resolved hyperfine structure. Allthese centres can be described as a paramagnetic system with a spin S—1/2 and rather highg-values, as well as by a spin S=5/2 and g-values close to g = 2 .

133

6P:c225STUDY OF Si RELATED DEFECT IN GaAs BY LVM SFECTROSCOPY

M.ZAVETOVA, J.PASTRRAK, J.OSWALD

Institute of Physics, Czechosl. Acad. Sci., 162 00 Praha, CSFR

Silicon as a doping element in GaAs crystals has a specific te-

chnological inportance. In highly doped samples (> 5.1018cm~3)

besides common shallow donors SiQ also acceptors Si. and com- )

plezes are formed. Luminescence topography, the spatial changes

of the luminescence intensity, both at 860 nm (at RT) and in

the broad bands at 915 nm and 1034 nm (at Be temperatures),

showed the inhomogeneities of the samples measured. High reso-

lution localized vibrational mode (LVM) spectroscopy proved

that these macrodefects are connected with distribution of Si.

More, LVM spectra give the possibility to determine the type of

defects and their respective concentration.

6P:c226EFFECTS OF ISOTOPIC DISORDER ON THE VIBRATIONAL PROPERTIES OFGE: A COMPARISON OF 70GE, 74GE, 76GE, AND NATURAL GE.

H.D. FUCHS, C.H. GREIN, R.I. DEVLEN, J. KUHL, and M. CARDONAMax-Planck-Institut fur Festkorperforschung, Heisenbergstr. 1, 7000 Stuttgart, Ger-many. :

High-resolution Raman spectra, time-resolved picosecond Raman spectra, and infraredtransmission (ir) spectra of isotopically enriched 70Ge, 74Ge, and 76Ge as well as naturalGe were measured and compared to theoretical calculations using the self consistent Born •approximation and the coherent potential approximation. The broadening of the Raman *line in the frequency domain was found to be predominantly caused by the anharmonic "decay of optical phonons, resulting in a line broadening which is inversely proportional ••<}to the average isotopic mass. From the phonon linewidths the anharmonic decay time of ijoptical phonons in Ge at 80K was determined to be 6.1ps±0.1. Comparison of the time j{and frequency domain measurements, taken with the same samples, allowed the deter- k'mination of the phonon generation time. The Raman line broadening due to isotopic 'fdisorder in natural Ge is negligible because of the vanishing phonon density of states at 'jthe Brillouin zone center. As opposed to the Raman experiments, where q ~ 0-phononsare probed, the q = 0-phonon lines observed in the ir experiments arc broadened as well :.as shifted in energy due to isotopic disorder, in excellent agreement with theory.

134

6P:c227

Doping Dependence of the RecombinationKinetics of CdSrln

Ch.Fricke, R.Heitz, A.Hoffmann, and I BroserInstitut f Or Festkdrperphysik, Technische Universitat Berlin

The dynamical behaviour of the near band gap luminescence in CdS:ln crystals ispresented for a wide ranged Indium concentration.At low excitation densities and In-concentrations of < 10'* cm-3 a lifetime of 100ps1 for the (D°,X) complex is observed. For In-concentrations of some 10i?cm-3 abroad luminescence band develops and decays within 25 ps. This can be explainedby a distortion of the electronic structure due the high doping. The degeneracy ofthe conduction band at higher doping levels near the metal-semiconductortransition (Nm > 1019 cm-3) results in radiative band-to-band transitions. Thecorresponding luminescence band decays non exponentiallly within a fewhundred ps.At high excitation densities the luminescence dynamics change, amultiexponential behaviour for low and medium Nin is observed. Theluminescence decay time for highest Nm correspond to those for low excitationdensities.The similiar effects of photo- and doping-induced charge carriers on theluminescence dynamics are discussed.

' R.Heitz et al. .Material Science Forum, vol 83-87, (1992)

6P:c228NONriWNELING CHARACTER OF THE TRAHSPORT PROCESS IM HIGH-T, SUPERCONDUCTORS

Roberto NlcolskyInstltuto de Fislca, Universidade Federal do Rio de JaneiroC.P. 68528, Fax: + 55 21 280-7693, Rio de Janeiro 21945, Brazil

The nonlinear current-voltage characteristics (CVC) of high temperaturesuperconductors are analysed In order to determine which kind of transportprocess Is dominant across the Intrinsic Interfaces in those materials.The CVC of grain boundaries, twinning planes and CuCte double planes arediscussed under the classical Josephson tunneling theory and the recenttheory for superconductor-normal metal-superconductor Junctions. The useof the resistively-shunted-Junction model by Beveral authors for fittingthe data is also commented. The results of sceclfic experiments designedto test the nature of YBCO grain boundaries .are presented as well asothers from the literature, as the recent ones on c axis conductance inthe mixed state. In conclusion, it is shown thav" the CVC of all kind ofIntrinsic interfaces are consistent with the metallic conductance, Insteadof the tunneling one, as the transport process In hlgh-Tc superconductors.

( D R . KfbMel, U. Gunsenhelmer & R. Nlcolsky, Phys. Rev. M 2 , 3992 (1990).(2) R. Nlcolsky, L. Ghlvelder, P. Pureur & S. Reich, in preparation.(3) R. Kleiner, F. Stelnmeyer, G. Kunkel & P. MUller, preprint (1991).

135

6P:c229ELECTRON-PHONON INTERACTION IN HIGH TEMPERATURE SUPERCONDUCTORS:TUNNELING AND OTHER EXPERIMENTS

M.A.Belogolovslcii, V.K.SvistunovDonetsk Physico-Technioal Institute., Ukrainian Academy cfSciences, R.Luxemburg, 72, Donetsk 340114, Ukraine

The current status of experimental investigations of theelectron-phonon Interaction characteristics in M g V T ^superconductors is reviewed. Emphasis is put on tunnelingspectroscopy results which are central r,o Identification cfthe pairing-mediating excitations In the Layered euprai:ecompounds. The determination of the ele:.t,ron-phonon spectralfunction with its implications on the theory ofsuperconductivity in these materials are discussed. An atu.-mpr.to compare tunneling results with those from measurements ufthe nuclear spin relaxation rate, specific heat, thfrmopower,electrical resistivity. Infrared reflectivity, neutron andRaman scattering is presented.

6P:c230ELECTRON-PHONON COUPLING IN THE TUNNELING CHARACTERISTICS

OF SUPERCONDUCTING Ba K BiO AND Bi Sr Ca Cu 01 - x X 3 Z 2 1 2 8 + X

r.SAMUELY*, S.I.VEDENEEV*, A. G. M. JANSEN , P. VVDER

Institute of Experimental Physics, CS-04353 Kosice

P.N.Lebedev Physical Institute, Moscow

Max-Pianck-Institut fur Festkorperforschung, Grenoble

The conductance of Ba K BiO tunneling junctions as welll-x X 3

as Bi Sr Ca Cu 0 junctions shows in the best examples a

sharp gap singularity with a small broadening. A value of

the zero-bias conductance is bigger than 10, respectively

20X from the peak value. This discrepancy with the clasical

BCS behavior is ascribed to parallel tunneling to the normal

regions present in the oxide superconductors. The analysis

of additional structures at voltages above A/e in terms of

strong coupling effects yields the interaction function

« F(ui) with the structure at energies corresponding to

phonon density of states F(u).

136

6P:c231MEASUREMENT OF VORTEX DISSIPATION IN SINGLECRYSTALLINE

L.LEGRAND*. I. ROSENMAN*. Ch. SIMON* and G. COLLIN**

*Groupc de Physique des Solidcs, Univcrsitcs Paris 7 et 6, Tour 23-2, Place Jussieu

75251 Paris cedex 05, France.

**Laboratoire de Physique des Solides, Universitd d'Orsay, Orsay, France.

We have measured the instabilities in the temperature variation induced by thedissipation due to the vortex movements, in a singlecrystalline YBa2Cu3<37thermally isolated, in a slowly varying magnetic field, up to ST. Threefeatures appear periodically: a regular increase of the temperature and anoscillatory regime followed by a large temperature jump. We interprete mis interms of critical state penetration, relaxation oscillations of the temperatureresulting from out-of-equilibrium vortex distribution, and flux jump. Theseinstabilities are also seen in the DC magnetization derivative. We have alsostudied the dissipation by AC susceptibility measurements, and obtained the"irreversibilty line".

6P:c235COMPUTER SIMULATION OF GLASS TRANSITION

Boscolo Roberta (1-2> and Roy L. Jacobs <2>( 1 ) Dipartimento di Fisica "Galileo Galilei",

via Marzolo 8,1-35125 Padova, Italy

*2' Mathemathics Department, Imperial College,

180 Queens Gate, London SW7 (UK)

We have carried out computer simulations in a model of a transition-metal-boride glass (Ni84B24) with the aim of observing and understanding the glass transi-tion. The transition-metal-boride glass was obtained quenching the molten formthroughout a series of simulations at different temperatures. Various quantitiessuch the specific heat and the mean-square displacement show physically significantchanges in behaviour near the transition. This behaviour is examined and analysed.

137

6P:c236THE GLASS TRANSITION: A SUPERLATTICE OF CLUSTERS FORMATION

V.BOUDA

Czech Technical University, TechnickS 2, 166 27 Praha 6, CSFR

The new model of the glass transition is based on the existence

of molecular clusters. At the melting point Tm, they are "dense

random packed". When cooling down below the temperature T , the

gradual free volume contraction of the amorphous rest causes the

rearrangement of clusters to the denser cofiguration till their

formation in a superlattice at the glass transition temperature

T . A question whether the glass transition id a purely kinetic

phenomenon or whether there exists an underlying thersiodynamic

transition can be answered. Two ordering parameters on the

molecular and supermolecular levels, the Kauzman paradox, the

physical meaning of the free volume in the WLF equation, the ratio

T_/T , the crazing phenomenon and the brittle-ductile transition

can be explained by this theory.

6P:c237THE A4 GLASS TRANSITION SINGULARITY

S. FLACH1, W. GOTZE2 and L. SJdGREN3

1 Institut fur Theoretische Physik, Technische Universitat Dresden2 Physik Department, Technische Universitat Miinchen3 Institute of Theoretical Physics, Chalmers University of Technology, Goteborg

Formulae for the /9-relaxation process as obtained within the mode coupling theoryfor the dynamics of supercooled liquids are derived for states near an A4 glass tran-sition singularity. A discussion of the expected anomalies of susceptibility spectrais presented. In particular the parameter regions of (l/f)-noise, for spectra exhibit-ing two minima and regions of linear variations in ln(l/f) are identified. The resultsare used to interprete quantitatively dielectric data of the following polymeric systems:polychlorotrifluoroethylene (PCTFE), polyhexamethylene sebacamide (nylon 610), po-lyoxymethylene (delrin) and polyparaethylene oxybenzoate (PEOB).

138

6P:c238

THE INFLUENCE OF ACTIVATED HOPPING ON 0 - RELAXATION

A. Latz, M. Fuchs and S. Hildebrandt

Physik-Department, Technische Univeraitdt Munchen, D-80J6 Garching, FRG

The Mode Coupling Theory (MCT) of the glass transition has shown that the

frequency range between the a - peak and microscopic excitations exhibits universal

features. If activated hopping processes are neglected this so called fi - relaxation is

described by a one parameter scaling law. The shape of the spectrum depends on one

material dependent number A. This picture has got support from experiments, e.g.

[1]. Under the influence of activated hopping processes the /? - spectrum has to be

generalized to a two parameter scaling law [2]. We have solved the MCT equations for

the two parameter scaling law numerically and analytically. The divergence of the time

scales of the idealized glass transition is cut off depending on one hopping parameter 6.

A characteristic narrowing of the /?- minimum is found.

1. N.J. Tao, G. Li and H.Z. Cummins, Phys.Rev.Lett ££ (1991) 1334

2. W. Gotze and L. Sjogren, Z.Phys.B §§_ (1987) 415

6P:c239HULTIPARAHETER TREATMENT OF GLASS TRANSITION KINETICS

J.FAHNRICH. H. SLAHAFaculty of Hatheaatlos and Physios, Charles University, PragueV Holesovlckach 2, ISO 00 Praha 8. Czechoslovakia

In * lsotheraal voluse relaxation curves have been calcula-ted on tne basis of the miltlparameter theory In the glasstransition region for sose relaxation tlae distributions. Thedistributions were treated as homogeneous, in the sense of thetherslnology used In a. The correspondence with expertsent*1results was not quite satisfactory. In the present contributionbetter agreement Is achieved with calculations for a Bore gene-ral aodel, where the relaxation tlse distribution Is taken ina cosblned way, partly as homogeneous and partly as heteroge-

1. Ng D.,Aklonls J.J. In Ngal K.L.. Wright G.B., Relaxations Incoaplex system (contributions froa the workshop "RelaxationsIn Disordered Systeas' in Blackburg, Virginia. July 1983) p.53.2. Bakule R. et al.,Colloid Polya.Sel 266(1991)665.

139

6P:c240HALIOE-CHALCOGENIOE GLASSES Te3IxSe4

3. Brydl, 2. Cimpl, F. Kosek

University of Chemical Technology; njm. Cs. legif 565

532 10 Pardubice, Czechoslovakia

The glasses type Te,IxSe4 (1=1,5-5) were prepared. The samples

for transmission measurement were prepared by both mechanical

furbishing and influencing of pressure on sample at the tempe-

rature 338 K. The transmission in IR region wasn't dependent '

expressively on method of preparation of the sample nor on con-

tents of iodine. The position of absorption edge didn't show

linear dependence on quantity of iodine. The density decreased

with increasing contents of iodine. The water nor normal atmos-

pheric conditions don't act corrosively on surface of samples.

6P:c241EXAFS STUDY OF LOCAL ORDER IN *Bi,Os.yGeO, GLASSES

G. ANTONIOLI1, P.P. LOTTICI1,1. MANZINI1, G. GNAPPI* and A. MONTENERO2

1 Dipartimento di Fisica and GNSM-INFM, ' Istituto di Strutturistica Cbimica, Uni-versita di Parma, Viale delle Scienze, 43100 PARMA, Italy

Gennania-based glasses containing lead and bismuth oxides are promising materials foroptical waveguides with low losses in the infrared region at wavelengths greater than3/un 1. These glasses are also interesting for fiber-optic amplifiers and oscillators byemploying stimulated Raman Scattering '. Here we report an EXAFS study of differ-ent compositions of the glass xBijOa-yGeOj at the Ge K-edge, through a comparisonwith four and six fold coordinated Ge in o-quartz GeOj and rutile GeO2, respectively.It is found that the local structure around the germanium atoms has small but signifi-cant changes with composition. While the coordination number is four at all bismuthconcentrations, the distances and the EXAFS Debye-Waller like factor show a non \linear change. The results are interpreted on the basis of the existing models for the '"structure of the germanate glasses. The EXAFS results are compared with Raman -|and IR data which confirm the anomalous nonlinear change with composition in the 4local structure of the glass. d'

1. K.Nassau, D.L.Wood and D.L.Chadwick, Appl.Optics, 21 (1982) 42762. M.E.Lines, A.E.MiUer, K.Nassau, K.B.Lyons, J.Non-Cryst.Solids 89 (1987) 163

140

6P:c242GLASS COMPOSITES - HETEROGENEOUS SYSTEMS

I. KRIVKA, 0. STEFAN, R. KUZEL, J. KUBAT+, D. RAFAJA

Fac.of Math.and Phys..Charles Univ.,Ke Karlovu 5, 12116 Prague 2+Dept.of Polymeric Materials, Chalmers Univ.of Techn..Gothenburg

Various heterogener is percolating systems based on a glas matrix

containing metal oxide particles - RuO_ and CdO - are studied by

means of complex measurements including the resistance-RuO_ con-

tents, resistance-voltage and resistance-temperature characte-

ristics. The experimental results are compared to computer simu-

lation data and the blending curves are described by the perco-

lation theory. The interesting dependences of resistance on vol-

tage for samples with P.uO2 contents close to percolation criti-

cal volume are explained by means of the Frank-Poole effect and

theoretical concepts used as a base of simulations, especially

those concerning a conductivity mechanism are discussed. These

systems have a wide application in hybrid microelectronics.

6P:c243

LINEAR AND NONLINEAR ACOUSTIC PROPERTIES OF RARE EARTHPHOSPHATE GLASSES.

H.B. Senin, Q. Wang, R.CJ. Draper, G.A. Saunders, P.J. Ford and M. Cankurtaran.School of Physics, University of Bath, Claverton Down, Bath BA2 7AY, UK.

Ultrasonic techniques have been used to study the acoustic properties of rare earth phosphateglasses containing high concentrations of Eu, Gd, La, Nd, Pr and Sm in the temperature rangebetween 300K and 10K. The elastic stiffnesses C,, and C« continue to increase anomalouslyat low temperatures and the ultrasonic attenuation is characterized by broad peaks due tothermally activated structural relaxations which correspond to activation energies of dieArrhenius type. When compressed, these glasses show a wide range of elastic behaviour. ForSm and Eu glasses (tKVdP)*, and (dCydPV* are anomalously negative but are positivefor the La, Gd and Nd glasses. The pressure derivative (dB/dP^ofthe bulk modulus is small,or even negative for Sm and Eu glasses. These glasses therefore show the remarkable propertythat when compressed they become easier to squeeze. It is suggested that the anomalous elasticbehaviour under pressure is associated with soft bending vibrations of the phosphate tetrahedraor alternatively due to the motion of the network modifiers present in these glasses.

I 141

6P;c244

RAMAN CHARACTERIZATION OF GEL-DERIVED TITANIA GLASS

P.P. LOTTICI1, D. BERSANI1, M. BRAGHINI* and A. MONTENERO*1 Dipartimento di Fisica and GNSM-INFM, 2 Istituto di Strutturistica Chimica, Uni-versita di Parma, Viale delle Scienze, 43100 PARMA, Italy

The preparation by sol-gel technique of bulk amorphous TiOj and its characterizationby means of Raman spectroscopy is reported. The Raman spectrum of the TiOj geldried at 120 °C confirms its amorphous nature l . The transformation of the powderboth by controlled thermal treatment and by laser induced heating in the anatase (at360 °C) had rutile (at 750 °C) crystalline forms is studied. Whereas the results onphase transformation on titania thin films are not clearly understood J, our resultson titania powder indicate that both for heat treatment and laser induced heatingthe phase transformation sequence is amorphous to anatase and anatase to rutile. TheRaman spectrum of the btookite (a third TiO7 natural occurring form ) is also presentedfor a comparison. The anatase Raman peaks show an unusual red-shift during thecrystallization process which is interpreted as a pressure effect on the microcrystals.The Raman results are compared with those obtained on amorphous thin films of TiOiand the dependence of the anatase and rutile Raman frequencies and linewidths on theincident laser power is reported, extending previous temperature results,

1. Lj.D.Arsov, C.Kormann and W.Plieth, J.Raman Spectrosc. 22 (1991) 573.2. L.S.Hsu, R.Solanlri, G.J.Collins and C.Y.She, Appl.Phys.Lett. 45 (1984) 1065.

142

7P:al

A POSSIBLE NEW HIGHLY STABLE FULLERITE CLUSTER: Li12C60

JORGE KOHANOFF, WANDA ANDREONI AND M1CHELE PARRINELLOIBM Research Division, Zurich Research Laboratory, CH-8803 Riischlikon.

Recent electrochemical evidence1 seems to indicate that in the solid stateit is possible to obtain a stable compound of stoichiometry Li^Ceo- Promptedby these findings we have investigated the possibility that Li^Ceo might existas a stable cluster, by ab-initio molecular dynamics2. Our results show that astructure with lh symmetry is stable, also corresponding to a HOMO-LUMOgap of the same order as that of Ceo (about 1.4 eV). In analogy with the caseof Li intercalated graphite (e.g. LiCe), the presence of the Li atoms induces apolarization of the valence states already filled in Ceo, giving rise to a weakeningof the double bonds. As a consequence a graphilizalion of the bonds takes place,in the sense that the splitting of the two bond lengths decreases from 0.06 A inundoped C60 (139 A ; 1.45 A) to 0.01 A (1.445 A ; 1.435 A). We analyzethe charge distribution of the states occupied by the Li electrons (HOMO),compared to those of the LUMO of C6o- Our findings are at odds with simplifiedmodels of fullerenes stability.

1. Chabre Y., Djurado D., Armand M., Romanow W.R., Coustel N., Mc-Cauley J.P., Fischer J.E. and Smith A.B., io be published

2. Car R. and Parrinello M., Phys. Rev. Lett. 55, 2471 (1985)

7P:a2A NOTE ON C UNDER HIGH PRESSURE

VI adan Cel ebonovi <t

Inst.of Physics,P.O.B.57,11001 BeograC,Serbia,Yugoslavia

Solid C i s attracting attention for a variety of reasons,ran-oo

ging from interstellar absorption to high T superconductivity1.2 °

Starting from recent experimental data ,and using the classical *

theory of dense matter proposed by P. Savid and R. Kasanin',1 have \

calculated values of pressure at which phase transitions can be \

expected. The results,P = .37 GPa and 15 GPa are in excellent ,Jt r 4 5 "*

agreement with experiments. '1. Huffman,D.R. .Physics Today,44 C1991D 22.

Z. Fleming,R.M. . e t . a l . .Nature.352 C19913 701.

3.Celebonovic,V..Earth,Moon and Planets,45 C19893 291.

4.Kriza,G. . e t . a l . .J.Phys.I France,1 C19913 1361.

S.Nunez-Regueiro.M..et.al..Nature,354 C19O13 289.

143

7P:a3MULTIPOLE POLARIZATION WAVES AND VAN DER WAALS COHESION OF CfioFULLERITE

Ph. Lambin, A.A. Lucas and J.-P. VigneronInstitute for Studies in Interface Sciences, Faculty's Universitaires Notrc-Damc de la Paix,61 rue de Bruxelles, B5000 Namur, Belgium.

In view of computing the van der Waals cohesive energy of C o fullerite, a classical modelconsisting of a spherical dielectric shell of finite thickness is used to simulate the dynamicalpolarizability properties of the Qn molecule. The material of the shell is an isotropic continuumwhose dielectric function represents the large o-plasmon resonance observed in all carbonmodifications around 20-30 eV. The eigenmodes of the polarization fluctuations on such ahollow molecule consist of multipolar surface plasmons of angular momentum /. In the solid,the quasi-static interaction between the surface plasmons on different molecules createsmultipolar polarization waves. Their dispersion relations are calculated throughout the first-Brillouin zones of the fee and hep lattices, up to high values of the angular momentum. Theattractive part of the cohesive energy of the crystal is obtained from the zero-point energy of thepolarization waves. For reasonable values of the shell parameters, adjusted to reproduceultraviolet spectroscopic data, the van der Waals binding energy is found to be around 2 eV. Nosignificant difference is found between the cohesion of the fee and hep lattices at any multipolarorder. The repulsive part of the cohesion and the phenomenon of ordering of the molecularorientation at low temperature, which can be attributed to weaker angularly corrugatedinteractions in the intermolecular contact areas, are not considered in the present work.

7P:a4ESR AND MAGNETIC STUDIES OF Rb AND K DOPED €„

P. Byszewski '•', J. Stankowski ', M. Baran ', R. Jabloriski \ Z. Trybula J,W. Kcmpiriski»1 fnst. of Physics, Polish Acad. of Sci., Al. Lotnikdw 32, PL-02-668 Warsaw, PolandJ Inst. of Molecular Physics, Polish Acad. of Sci., Poznari, Poland' Inst. of Electronic Materials Technology, Warsaw, Poland4 Res. and Develop. Center of Vacuum Electronics, Warsaw, Poland

Qo powder prepared in various conditions were doped with potassium and rubidium insealed ampoules filled with helium. After annealing in various conditions of heattreatment the samples were measured by means of ESR spectrometer and SQUIDmagnetometer. Superconducting properties were detected observing microwave absorptionand measuring low magnetic field susceptibility. The ESR measurement's made at 4.2 Kand up to room temperature show, that in samples exhibiting superconducting properties.two various electron states with different g-factor and different line width were createdby alkali metals doping. It was observed strong dependence of these parameters onannealing procedure and dopants concentration. Prom low field susceptibilitymeasurements critical temperatures and first critical fields were determined for variousdopants concentration and annealing procedures and some attempts were made to estimatethe critical current density.

144

7P:a5FIELD-INDUCED MAGNETIC PHASE TRANSITIONS AND ELECTRICAL

RESISTIVITY IN SOME RARE-EARTH INTERMETALLICS

N. V. BARANOV, P. E. HARKIN, E. V. SINITSYN

Ural State University, 620083 Ekaterinburg, Russia

Field-induced magnetic phase transitions have been studied

on single crystals of R G a2'

R 3 C o an<* R C u2 compounds.

Significant variations of the electrical resistivity were

observed in the regions of the field-induced magnetic phase

transitions. These effects are explained by substantial

deformations of the Fermi surface due to the s-f interaction

during the rearrangements of the magnetic structure. An

anomalous increase of the electrical resistivity was found in

the intermediate state during first-order phase transitions in

which domains of different magnetic phases coexist. This

anomaly is connected with the scattering of s-electrons from

! the interphase boundaries in the intermediate states.

I 7P:a6• CRYSTALLOGRAPHIC AMD PHYSICAL PROPERTIES OFI C«(G«,Si)2_z SOLID SOLUTIONS.

N.Boutarek, R.Madar',* I.N.P.G.,E.N.S.P.G, BP46, 38402 St Martin d'HeresB.Lambert-Andron, S.Auffret and J.Pierre ** C.N.R.S, 166X, 38042 Grenoble, France

Several studies were untertaken on Ce(Ge,Si)2-x solutions,where hybridization between the 4f electron and the conductionband varies with Si content. Superstructures of the tetragonalThSi2 type structure were observed, with ordering of Si, Geand vacancies; for some compositions, Ce atoms have twodifferent environments, with a succession of Si polyedra andGe/vacancies polyedra.Crystallographic transitions were evidenced in the temperature

; range 50 to 200 K, from both crystallographic and resistivitydata.Magnetic properties were compared to those of CeSi2_x systems,pointing the respective influences of vacancies and cellvolume on the hybridization and Curie temperature in thesesolutions.Crystal field parameters are also dependent on hybridizationstrength.

145

7P:a7INTERNAL MAGNETOSTRICTION ABOVE THE VERWEY TRANSITION IN

STOICHIOMETRIC MAGNETITE

G. GaleczkiIl.Phys. Inst., Univ. Koln, Ziilpicher Str. 77, 5 Koln 41

The historical Verwey transition at about 119 K is but one amongmany other remarkable properties of pure, stoichiometricmagnetite: non-monotonous Mossbauer line rearrangements,spontaneous magnetization reversals, multi-stage phonon-softening /I/ between 85 and 150 K. Within the cubic spinelstructure, the oxygen anions -which are larger compared to theiron cations- form a slightly distorted fee lattice, with theoxygen parameter u larger than 0.375. X-ray diffraction lineintensity ratios reveal now a non-monotonous temperaturevariation of u(T) in the cubic phase above 119 K, while theunit-cell parameter changes smoothly with increasingtemperature. This is a direct manifestation of the internalmagnetostriction predicted in 1963 by E.R.Callen and H.B.Callen/2/ and represents the static limit of the phonon-softeningprocess. The results agree qualitatively with the co-operativeJahn-Teller transition model of Chakraverty /3/,too.

/1/G.Galeczki, R.Buckwald and A.Hirsch Sol.St.Comm.23(1977)201/2/E.R.Callen and H.B.Callen, Phys.Rev. 129(1963)578/3/B.K.Chakraverty, Sol.St.Comm.15(1974)1271

7P:a8A TRANSPORT STUDY OF TEE a TO o-PHASE TRANSFOMATION IN FE-CR-SX ALLOYS

M. H. AHADO AND J. B. SOOSA, Physics Center, University of Porto (MIC) and IFIHDP, P-4000 Porto, Portugal

B. F. 0. COSTA AND N. AYRES DE CAMPOS, Physics Department, University of Coiibra, P-3000 Coiibra, Portugal

S. H. DOBIEL, Institute of Physics and Nuclear Techniques, PL-30059 Krakow, Poland

Arc ielted Fe-Cr alloys with stall aiounts of Sn bave recently been under study by Hossbauertechnics, in order to investigate the effect of Sn in tbe kinetics of a to o phase transformation [1].He report here the results of high resolution transport leasureients ( p , dp/dT) on identical alloys.

The leasureients bave been done over a vide range of teiperatures (4 - 300° K) for a set of saipleswith coiposition Fe53 X r ^ jSn3 5. Tbe composition has been detenined by iicroprobe analysis. The ct toophase transformation'has been performed by annealing at 700° C for different periods. Structures rangingfroi the pure a -phase to heavy a / o mixing and up to an aliost pure o -phase bave thereby been obtained.57Fe Hossbauer spectroscopy was used to identify the o and a phases, and to evaluate tbe fraction of the ophase present in each saiple.

Tbe transport coefficient dp/dT reveals great sensitivity to the relative aiounts of a / o phasespresent. Besides the usual Bloch-Gruneisen contribution due to electron-pbonon scattering, dp/dT revealsimportant deviations to this law at low teiperatures. This behaviour is attributable to tbe existence ofdifferent magnetic excitations (and electron-spin scattering) and corresponding teiperature dependance insamples with different a / o relative aiounts.

[1] - B. F. 0. Costa et al. (these proceedings)

146

|.,

7P:a9ELECTRON TRANSPORT AND DILATOMETRIC STUDY OF CRYSTALLIZATION

IN Fa - BASED AMORPHOUS ALLOYS

K. Pçkala <#Phys. Inst., Warsaw Tech. Un., PL), M.(•Cham. Dapt., Un. of Warsaw), V. Ocelik (Inat. of Exp. Phys.,Koäice, CS), P. Ja«kiewicz <#), R. Rataj (•>, T. Kulik <#>

Amorphous alloy. Fa77>;.Si13_5B9. F ^ ^ C u ^ i ^ ^ B , ,

Er*74.5Nb3Si13.5B9' F*73.5CulNb3Si13.5B9 a n d

Fe__ _Cu_Ta_Si _B_ transforming during annaallng to tha

nanocrystallina phasa wara studied by uani of electricalraaistivlty, thamoalactric powar, magnatization anddilatometric methods.The magnetic and structural contributionsto tha electrical resistivity and thermoelectric power wereseparated in tha ferro- and paramagnetic states and related tothe alloy composition. Nucleation rate, growth dimensionalityand a growth controlling mechanism were determined by means ofthe Johnson-Mehl-Avrami analysis. An influence of therelaxation phenomena onto the properties of the alloys isdiscussed.

7P:alO

RESISTIVITY SATURATION UNDER HIGH FRESSURE: fee La

BERTIL SUNDQVISTDepartment of Experimental Physics, Umea University, S-90187 Umeâ, Sweden

The electrical resistivity of fee La has been measured as a function of temperature Tand pressure p, in the metastable state between 70 and 300 K and in the normalstable state between 500 and 650 K, and at pressures up to 1 GPa (10 kbar). A largebut smooth change in pressure coefficient a = dlnp/dp with T is observed. At lowT a is positive, with a value near +2 %/GPa at 70 K, but at higher temperatures abecomes negative, reaching a value of -4%/GPa at 650 K. Reactions between thesample and the pressure medium prevented us from reaching temperatures abovethis. Both the temperature dependence and the pressure dependence of the resistivitycould be surprisingly well described by the phenomenological "parallell resistance"theory for resistivity saturation in highly resistive metals.

147

7P:all

TRANSPORT PROPERTIES OF (Nd2-xSrx)Ni04+S COMPOUNDS.METAL - INSULATOR AND ANTIFERROMAGNETIC TRANSITIONS

J.M. Moreira, J.A. Mendes and J.B. SousaCentra de Ffcica da Universidade do Porto (INIC) and IFIMUP, 4000 Porto - PortugalM.P.S. Kumar and S. B. PalmerPhysics Department, University of Warwick, Coventry CV4-7AL, U.K.

A series of compounds (NdxSr2-x) NK>4+5 with x= 1.05, 1.40, 1.45 and 1.60 have beeninvestigated with high resolution resistivity measurements (p, dp/dT) over the temperaturerange 4K-300K.In all cases, the resistivity increases by several orders of magnitude at sufficiently and |characteristic temperatures (T*), indicating the approach of an insulating phase. T* rises as theelectron concentration increases, when Nd (trivalent) progressively replaces Sr (divalent). Forexamplc,T* < 5K when x= 1.05, and T* -15K for x= 1.40 (and x= 1.45). The case of x= 1.6is rather special, having a much higher T* value (-40K) and giving an unusual succession ofdifferent phase transitions: (i) At the conducting-insulating transition we observe a para-antiferromagnetic transition, producing a very sharp increase of p as T~»TN from above andleading to characteristic critical behaviour in dp/dT at T N = 37.7K. Below TN, p has a fairlyhigh value (-^xlO^xm) but increases only very slowly as T decreases; (ii) At Tci= 25.7K aweak lst-order phase transition is observed in p (Ap/p -0.3%), leading to an unexpecteddecrease of p for T<Tci; (iii) Finally, at Tc2= 1 IK, p suddenly levels off and keeps a constantvalue down to be lowest measured temperatures.

7P:al2EFFECT OF CONDUCTION ELECTRONS ON THE PARAMAGNETIC SUSCEPTIBI-

LITY OF RARE EARTH INTERMETALLICS

S.ZAJAC and F.PESEK

Faculty of Mathematics and Physics of the Charles University,

Ke Karlovu 3, 121 16 Praha 2, Czechoslovakia

Paramagnetic susceptibility of rare earth intermetallies is '*

calculated in the model of the crystal-field split 4f-ions 'j

interacting with conduction electrons by exchange coupling. V;

The calculation is made on the basis of thermodynamic pertur- |'

bation theory to the second order. Analytical formulas for

susceptibility in zero and nonzero magnetic field are given.

The effect of conduction electrons on the temperature depen-

dence of susceptibility is shown.

148

'A **

7P:al3RESISTIVITY MEASUREMENTS OF NdaFHi.*B BASED SINTERED MAGNETS

M.A.Sa,J.M.Machado da Silva,J.B.OliveiraCentra de Fisica Universidade Porto, 4000 Porto, Portugal

Resistivity measurements £(T) from He* temperatures up tos 900K were made in several sintered NdzFe^B based magnets(NdisFe^Be,; Ndi&Fe-7«.BB and Ndi«. »Dyi.. oNbiFe^&B^ ) submitted tovarious previous heat treatment and in different magnetizationstate.

The striking feature of all the results is the curvatureof the resistivity for temperatures just below Tc, thederivative S(/6T showing an inverse X-type anomaly as T->Tcwith 6f/8T<0 just below Tc.

Thermal expansion measurements on NdzFemB show an invartype anomalv around Tc. The pronounced effect in the curvatureof the reaistivity for all the samples is similar in shape tothe thermal expansion, suggesting that the resistivityreflects, in the vicinity of Tc, the invar effect of the matrixNd^Fei-iB. Furthermore the two extra phases presented inNdm.nDyi .raNbiFei'faB/ do not change appreciably the resistivityof the alloy when compared with that of Ndx&Fe^&Bs; this i«consistent with the fact that the remanence is approximatelythe same in both materials.

7P:al4A SOLVABLE MODEL OF MOSSBAUER SCATTERING

B.S. PAVLOV,Institute for Physics, Petersburg University, 198 904 St. Petersburg, USSR.A.A. POKRDVSKIY,Physical Faculty of Petersburg University, 198 904 St. Petersburg, USSR.

Solvable model of Mossbauer scattering (recoilless scattering of ganroa-rays by latent nucleus) is built using methods of operator extensions theory.Scattering cross section thus obtained correctly describes the main featuresof Mossbauer scattering. It coincides with generally accepted Lorentz reso-nance cross section in the first order of perturbation theory. The Debye-Waller factor was obtained from mathematically rigorously calculated scat-tering cross section. The model may be useful for theoretical study ofMossbauer scattering en soft molecules and in liquids.

I4 149

7P:al5EFFECT OF ROLLINS AND HEAT TREATMENT ON THE IRREVERSIBLE MAGNETIZATION INNICKEL-CHROMrUM WIRE

A.H. WRFIKPhysics Department, Faculty of Science Ain-Shams University, Abbasia -Cairo, Egypt.

The mean potential difference (\fe) of Barkhausen jumps and the frequen-cy of the cluster of jumps (FB) were measured as a function of the percent-age of thickness reduction. The increase of the percentage of thickness re-duction up to 55% causes the decrease of V B and F B Vg vanishes at a certainvalues of the magnetizing frequencies. The vanishing magnetizing frequencydepends on the percentage of thickness reduction. The vanishing of V Q isattributed to the produced eddy current in the sample. The heat treatmenthas a considerable effect on both VQ and the vanishing magnetizing frequency.

7P:al6MAGNETOMETR FOR DETERMINATION OF THE ft VALUES AND ORIENTATIONS.A.N.BAZHAN.P.L.Kapitza Institute for Physycal Problems, Academy of Scien-ces the USSR, Moscow, USSR.

The magnetometr with vabrating sample is described whichallows measerements of the sample magnetic moments not onlyalong the applyed magnetic feald, as usual, but along three mu-tually perpendicular directions, along applyed magnetic fealdand perpendicular to it, in 2-300K temperature range and in ma-gnetic field ranging--up to the 75 kOe. The sensitivity of thisinstrument is x »10 . In the given construction the sample vi-brates perpendicular to the magnetic field, n||OX. The axes ofthree pairs of OX, OY, OZ measurement coils are parallel to thedirraction of the sample motion -OZ. For such investigations itis necessery to clarify how to arrange the coils in order toinvestigate the X,Y,Z components of ft separately, [1,2]. Compa-ring the directions of the magnetic lines of force for "HT||OX,M||OY, TifJOZ, we can choos the optimal geometric dimantions ofcoils. When the sample "RtJjOX only, the ratio of the signals ofthe Y,Z and X measering coils in the instrument is «,, _/«„ «

O J[ , & A

10 . The posibilities of magnetometr in investigations of"spin-flop" transitions in Cr?0o antiferromagnets, when H ap-yed along antiferromagnetic vector are demonstrated. v

S.Foner. The Rev. of Scient. Instr. 1969, v.30, p.691. ?.N.Bazhan, A.S.Borovik-Romanov, N.M.Kreines. Instr. and <

Exp. Techniques. 1973, v.16, p.261. ;|-

plyed alon111. S.Fon[2J. A.N.]

150

7P:al7REMANENT MAGNETISATION AND REMAGNETISATION MEASUREMENTS ONDISPERSION OF FINE HAEMATITE PARTICLES

EDUARD PETROVSKV*. PAVEL HEJDA*. TOMAS ZELINKA*. JAN SUBRT**

* Geophysical Institute, Czechoslovak Academy of Sciences, Bo&if II, 141 31 Praha 4,Czechoslovakia

** Institute of Inorganic Chemistry, Czechoslovak Academy of Sciences, 250 68 Rei uPrahy, Czechoslovakia

Artificial samples of fine-grained haematite (a-Fe2O3) were subjected to isothennal remanentmagnetisation and remagnetisation measurements with a view to examine the expression ofdifferent magnetic-treatment history in the remanence behaviour. Emphasize is put on theassessment of interparticle magnetic interactions based on differential remanence (Wohlfarth'sformula). In general, negative interactions yielding a net-demagnetising effect (the sample iseasier to demagnetise than to magnetise) were observed. Alternating-field cleaning slightlyenhanced the degree of correlation in the resulting magnetic microstructure. On the otherhand, differential remanence discriminates clearly between different direct-currentremagnetisation procedures.

7P:al3SIZE EFFECT AND TEMPERATURE DEPENDENCE OF A LOW-ENERGYELECTRONIC TRANSITION IN BISMUTH

Valentina De Renzi", Maria Grazia Betti* and Carlo Mariania( a ) Dipartimento di Fisica, Universita di Modena, via Campi 213/A, 1-41100Modena; <"> Istituto di Struttura della Materia, C.N.R., via Fermi 38,1 - 00044Ftascati

Ultra-thin crystalline films of Bi (240-900 A) were grown on GaAs(llO) at roomtemperature (RT) and investigated by high-resolution electron-energy-loss spec-troecopy (HREELS). An electronic transition typical of bismuth is singled out atabout 50 meV and shown to depend on the film thickness. Its energy shift is as-cribed to the Fermi level shift induced by a quantum-size-effect. Moreover, it isfound to depend on temperature, presenting a red-shift on lowering the tempera-ture from 295 to 110 K. Such a behaviour is explained mainly as due to the thermalbroadening of the Fermi edge, by using an appropriate dielectric model.

151

7P:al9PARAMAGNETIC SUSCEPTIBILITY AND MAGNETIC PHASE DIAGRAM OF TMCU2

SVOBODA1 P., DIVIs1 M., ANDREEV2 A.V., BARANOV2 N.V., MALETTA3 H.1) Charles University, Department of Metal Physics, Ke Karlovu 5, 121 16Prague 2, Czechoslovakia2) Ural State University, Lenin av. 51, Yekaterinburg, Russia3) Hahn-Meitner Institut, Berlin GmbH, 1000 Berlin 39, Germany

The single crystal of TmCu orthorhombic intermetallic compound has beenprepared and its magnetic properties have been studied by means ofmagnetization and magnetoresistance measurements. The pronounced magneticanisotropy determined by magnetization measurements revealed the b - axisas an easy axis in the magnetically ordered state (T = 6.3K) as well as in

the paramagnetic state. The static magnetic susceptibility was calculatedusing crystal field hamiltonian and compared with our experimental data.This allow us to test the reliability of previously published sets ofcrystal field parameters [1,2]. The low temperature magnetic phase diagramof TmCu was finaly deduced.

[1] Sfoa V. et al, J.Phys.rCondens.Matter 1 (1989)10153[2] Gubbens P. et al, J Magn.&Magn.Mater, in press

7P:a20STRUCTURAL PROPERTIES AND ESR OF THE (Gd-R)Cu_Sn-

COMPOUNDS.

K. KACZMARSKA,A.SLEBARSKI,A.STARCZEWSKA

Institute of Physics,Silesian University40-007 Katowice, Uniwersytecka 4

The new rare earth ternary compounds YCu2Sn2, LaCu_Sn2, f,

LuCu2Sn2 and o.Oi^O.o^a 8 1^ (R"y»La»I'U) have been J

prepared by arc melting, x-ray diffraction measurements of f|

the powder samples are performed in the room temperature. I

3+ «r

The ESR on Gd ions in GdQ 0 , R 0 o qCu 2Sn_ shows that the (?.

strong bottleneck in the GdCu2Sn2 compound is partly opened •"

by replacing 90% gadolinium with La,Y and Lu.

152

7P:a21

THE MAGNETISATION OF TERBIUM IN GOLD SINGLE CRYSTALS.

D. St. P. BUNBURY, C. CARBONI, R. G. GRAHAM AND M. A. H. McCAUSLANDThe Schuster Laboratory, The University, Manchester M13 9PL, UK

The work to be described part of a continuing study of the magnetic behaviour ofrare-earth ions as dilute substituents in Pauli paramagnetic hosts1. The particular focusof the present work is to clarify the crystal-field splitting of Tb*+ in gold. The work ofBieaney (private communication) indicates that the crystal field in this system is close toa point at which the Tz, T3 and rf"> states meet. However, the nature of the groundstate has not yet been unequivocally established, and there exist no reliable crystal-fieldparameters in the published literature.

We have measured the magnetization of oriented single crystals of gold containing 0.5%Tb. The measurements were made in the temperature range 3 K to 100 K, byvibrating-sampfe magnetometry, with fields up to 12 T applied along the twofold,threefold and fourfold symmetry axes. Our results do not support earlier estimates ofcrystal-field splittings. A more satisfactory fit to our data is given by the followingcrystal-field parameters: B4 = -8.6 x 10 3 K, B, = - 1 . 6 x 1 0 * K.

1. Reid B, at al. Physica B 174 (1991) 39

7P:a22

ENHANCED NUCLEAR MAGNETISM IN HOLMIUM ORTHOALUMINATE: AN NMRSTUDY

S. M. WARNER, D. St. P. BUNBURY, C. CARBONI, R. G. GRAHAM ANDM. A. H. McCAUSLANDThe Schuster Laboratory, The University, Manchester Ml 3 9PL, UK

Holmium orthoaluminate. HoAI03, is a van Vleck paramagnet with highly anisotropicproperties at and below liquid-helium temperatures. At 0.16 K it undergoes a hyperfine-induced phase transition to a four-suWattice antiferromagnet1. The general features ofthe ordered phase have been described in terms of a simple two-level mean-field model1. .

The work to be described is an NMR study of the enhanced nuclear magnetism of '••Ho ;in a regime where the field-dependence of the parent H o " moment is highly non-linear. <•Its purpose to test the accuracy of published crystal-field parameters3 and to investigate |the dynamics of the coupled electronic-nuclear spin system. The measurements are [Ibeing made by high-speed spin-echo spectroscopy, in fields up to 8 T. Preliminary iresults at 4.2 K show strong NMR spectra, with partly-resolved quadruple structure, in *|the 4 to 5 GHz range. Transverse relaxation is rapid and non-exponential, on a ftime-scale of ~ 1 /is; the spin-lattice relaxation time at 4.2 K is ~ 15 ps. |

1. Hammann J. and Ocio M., Acta. Cryst. A 33 (1977) 975. :

2. Hammann J. and Ocio M., J . Magn. Magn. Mater. 15-18 (1980) 39.3. Karayianis N., Wortmann D. and Morrison C. Solid State Commun. I t (1976) 1299.

153

7P:a23BEHAVIOUR OF UNiAl IN HIGH MAGNETIC FIELDS

L. HAVELA, H. NAKOTTE. E. BROCK, F.R. DE BOER, V. SECHOVSKY*.H.P. VAN DER MEULEN, A. A. MENOVSKYVan der Waals-Zeeman Laboratorlum, University of Amsterdam,Valckenierstraat 65, 1018 XE Amsterdam•Department of Metal Physics, Charles University, Ke Karlovu 5,

CS-121 16 Prague 2

UNiAl belongs to those uranium intermetallic compounds, in which the Iincipient magnetism and enhanced ^-coefficient of the electronic specificheat point to a moderate delocalization of the Sf electronic states. It Isantiferromagnetic below TN-19 K; a ferromagnetic alignment can be achievedin fields above 11 T. Here we describe the effects of magnetic fields up to35 T on magnetic, transport and thermodynamic properties, studied on high-quality single crystals. It turns out that the jr-coefficient progressivelyincreases from the zero-field value (167 mj/mol K ) up to the maximum value(260 mJ/mol K ) found in B - 12 T. The shape of the C/TiT) dependence,which shows a pronounced low-temperature upturn, points to a T lnT term.This upturn can be suppressed only in the field B = 20 T, where r is lowerthan in 0 T. The resistance is strongly reduced by the metamagnetictransition. The results are discussed in terms of on-site spin-fluctuationsdestabilizing the 5/-moments and inter-site correlations of the 5/.rmoments.

7P:a24MAGNETIZATION PROCESSES IN STRESS-ANNEALED METALLIC GLASS

K. ZAVfiTA, O.V. NIELSEN1, K. JOREK

Inst. of Physics, Czechosl. Acad. Sci., 162 00 Praha 6, CSFR

Dept. of Electrophysics, The Techn. Univ. of Denmark, DK-28OO Lyngby

We investigated the connection between the characteristics of the magne-

tization curves and the surface magnetic domain structure of a low mag-

netostrictive metallic glass after heat treatment. Ribbons of the compo-

sition COgg jFe^ j S i ^ B ^ were prepared by single roller quenching in <

vacuum. The anneaiing at 340 °C for 1 h with tensile stress of 200 MPa

applied along the ribbon axis produced a hard axis in the stress direct- ~

ion. The anomalous parts of the ribbon showed distinct values of remanence |

up to 80 mT and connected "coercive fields" of about 0.1 mT. Observations i =

of the magnetic domain structure at the shiny surface of the ribbon by i

means of SEM confirmed different magnetization processes in the ordinary

and anomalous parts of the ribbon with participation of domain wall move-

ments in the latter case. This was accompanied by the by deviation of the

easy axis from the transverse direction.

154

7P:a25THE COERCIVE PROPERTIES OF CONSTRICTED MAGNETIC DOMAIN WALLS

I.TOMAS. G.VERTESY* and L.POSTInstitute of Physics, Czechoslovak Academy of Sciences,Na Slovance 2, CS-180 40 Praha 8, Czechoslovakia

Central Research Institute for Physics,P.O.Box 49, H-1525 Budapest 114, Hungary

The relation between the domain vail coercive field and the

local constrictive forces as seen by the magnetic domain walls

was analytically expressed via effective local magnetic field

gradients. For stripe and bubble domain structures these

gradients were computed. The theoretical results agree very

well with the measurements of the domain wall coercive field of

close packed bubble domain structures in LPE magnetic garnet

films using (i) the magneto-optical low frequency DW

oscillation method, and (ii> the method based on analysis of

quasistatic hysteresis loops. Practically zero domain wall

coercive field can be achieved if the domain walls are packed

to one another enough.

7P:a26ELECTRONIC STRUCTURE PROPERTIES OF Zn-OXIDE SPINELS FROM67Zn M6SSBAUER SPECTROSCOPY

W.POTZEL, G.M.KALVIUS, W.SCHIESSL, H. KARZEL, M. STEINERPhysik Department, Technische Universitat Munchen, D-8046 Garching, GermanyI.HALEVY, J.GALInst. Nucl. Engineering, Ben Gurion University, ISR-84190 Beer Sheva, IsraelW. SCHAFER, G.WILLMineralogisches Institut, Universitat, D-5300 Bonn, Germany

The high resolution 93 keV Mossbauer transition in 67Zn was used to study the normalspinels ZnAl2O4 and ZnFe3O« and the inverse spinels Zn3SnO«.The tetragonal A site,occupied by Zn in normal spinels has an electronic configuration close to the Zn sitein Z11O2 and shows little distortion. Bringing Zn on the octahedral B site reveals amuch stronger distortion an a less covalent bond. In the inverse spinels the A and theB site are occupied by Zn and now both show strong and non-uniform distortions. Inthe magnetic spinel ZnFejO^ we observe below Tjy = 10.6 K a transferred magneticfield at the Zn nuclei (Bjj > « IT at 4.2 K). This is the first observation of the nuclearZeeman splitting in *7Zn in an internal field. Dipolar lattice sums show that the fieldmust be transferred from Fe by superexchange via 0 .

155

7P:a27MOSSBAUER SPECTROSCOPE ON LASER IRRADIATED AMORPHOUSSXSTEM

D.SOHESCU.M.SORESCt^.A.HENING.I.N.MIHAILESCu^D.BARBInstitute of Atomic Physics,769oo Bucharest,Romania•Polytechnical Institute Bucharest,772o6 Bucharest,Romania

Multipulse excimer laaer irradiation ( -2'»8 nm,^=2o ns)has boen performed on samples of 'eni^ix r5i, -

cp (METGLAS

26o5 SC) cut from the ribbon roll 2o pn thick. Energy

densities of about lo mJ/mnr were available by beam focusing

to o spot size of a few mm , followed by laser beam scanningof the sample surface.Room temperature Mossbauer spectra of samples irradiatedwith 25; 5o and 75 laser pulses per spot, at a repetitionrate of lo Ha, were collected using a constant accelerationspectrometer, with the gamma ray perpendicular to the ribbonplane, in the conventional transmission geometry. Leastsquares fitting has been performed in the assumption ofGaussian lineshapes. The areal intensity ratio of the secondto the first lines of the Mossbauer spectra hns beendetermined and the corresponding changes of spin textureand magnetic anisotropy were found to depend on the numberof applied laser pulses.

7P:a28% HOSSBAUER STUDY OF TBE IU'lOOKE OF SN OH THE FOHUTIOX OF THE SIGMA PEASE IN FE-CR ALLOTS

B. F. 0. COSTA, S. M. DOBIEL* and K. AYKES DE CAMPOSPhysics Department, Universityof Coiibra, P-3000 Coimbra, Portugal•Institute of Physics and Nuclear Techniques, PL-30059 Krakow, Poland

Tbe existence of tbe sigia phase in alloys of transition letals is interesting both froi thescientific and technological point of view. It is well known that its presence in austenitic and ferriticsteels dramatically deteriorates their mechanical properties. Among many alloys in which the sigia phaseoccurs, Fe-Cr systei is particularly important because of the role it plays in steel industry. Addition ofa third element influences both the rate of tbe phase formation kinetics and its range in the phase diagram.Froi the up-to-date studies it follows that tbe so called steel making elements, namely Kn, Ho, si, Co, Ti,Zr, Mb, V and H not only accelerate toe formation of tbe sigia phase but they also extend its range ofexistence.

Here we report on tbe effect of Sn on tbe kinetics of tbe fonation of the sigia phase in differentseries of Fe^SiuCr, alloys containing: a) 2=44.5 at* i) y=0.9 att ii) y-2.1 att; b) 2=43.0 att i) y-1.95att ii) y=3.7 att iii) y=4.75 att; and c) z=42.0 att y=5.6 att, which chemical composition was determinedby microprobe analysis. Transformation of tbe alloys into tbe sigma phase was done by annealing u vacuumat temperature T=700 °c for t=0.25-l20 h. The identification of tbe phases was carried out by ''re-siteHossbauer spectroscope which is a suitable method for this purpose [lj. It was found that tbe addition ofsn significantly retards the alpha to sigia phase transformation. This inhibiting effect will be discussedin tens of alloy - stabilizing factors, namely (a) electronic factor and (b) sire factor.

The intiuence of tin on the licrostructure of Fe-Cr-Sn alloy will also be presented and the kineticsof the sigia phase foriation will be described in the fraie of the Johnson-Mehl equation.

[1] E. Japa et al., J. Phys. F, 12 (1982) L159.

156

7P:a29

TRENDS IN THE MAGNETIC ORDERING TEMPERATURES OFURANIUM-TRANSITION METAL-SILICON (GERMANIUM) 1-2-2COMPOUNDS

T. Endstra, G.J. Nieuwenhuys and J.A. MydoehKamerlingh Onnes Laboratory, Leiden University,P.O. Box 9506, 2300 RA Leiden, The Netherlands.

Many compounds of the UT2Si2 and UT2Ge2 series show (anti)ferromagneticordering. The ordering temperature is a complex function of the overlap betweend and / bands: it increases with the overlap for small values, but decreases atlarge values of the overlap, due to the strong hybridization. Combining roughrigid band arguments1 for the hybridization strength with the schematic phasediagram for a Kondo lattice2, we can qualitatively explain the trends in the or-dering for almost all compounds in the series, except for T = Mn, since Mn itselfcarries a magnetic moment.

1. W.A. Harrison and G.K. Straub, Phys. Rev. B 36 (1987) 2695.2. S. Doniach, in Valence Instabilities and Related Narrow-Band Phenomena,edited by R.D. Parks (Plenum, New York, 1977), p. 169.

7P:a30STUDY OF TIE MAGNETIC PUSE DIAG1AM OF InSi CLOSE TO TIE CUTICALTEIPE11TU1E

C. Gregory and If. BernhoeftDepartment of Physics, University of Durham, Durham, U.K.B. Lebech, P. larris, J. Skov Pedersen and I. lortenaenDepartment of Solid State Physics, liso National Laboratory, Denmark.

Following a detailed magnetisation study of InSi close to the criticaltemperature1, various details of the magnetic phase diagram including theso-called 'Phase A' have been studied by small angle neutron scattering.

From the results we observe that in 'Phase A* the helix undergoes a "flip"from the [001] applied field direction to the [100] direction which liesperpendicular to the applied field. The helix then returns to the [001]direction as the field is further increased above the Phase A boundary.

1. C.J. Gregory, D.B. Lambrick and lC.t. Bernhoeft (1992). 'MagnetisationStudy of the Magnetic Phase Diagram of InSi' Proc. ICM 91.

157

7P:a31TEMPERATURE-DEPENDENT QUASIPARTICLE PHOTOEMISSION IN NI AND FE*

J. BRAUNa, G. BORSTELa AND W. NOLTINGb

aDept. of Physics, Univ. of Osnabriick, 4500 Osnabrflck, FRGbDept. of Physics, Univ. of Valladolid, 47005 Valladolid, Spain

The influence of both electron correlations and phonons on thetemperature-dependence of ultraviolet photoemission spectra offerromagnetic nickel and iron is investigated. The spin- andtemperature-dependent quasiparticle photo-current is calcula-ted in the framework of a generalized one-step-model of photo-emission. Phonons are taken into account via temperature-de-pendent phase shifts. The hole-state of photoemission is de-scribed by an energy-, spin-, temperature- and band-dependentquasiparticle propagator, which rests on a combination of den-sity functional theory and a inultiband model of magnetism.Here we present spin-polarized and temperature-dependent pho-toemission spectra for Ni and Fe. The theoretical photoemis-sion results are in excellent agreement with the experiment.

*Work supported by the Deutsche Forschungsgemeinschaft

7P:a32THERMAL EXPANSION ANOMALIES AT SPIN REORIENTATION IN Tm2Co7

A. V. ANDREEV, S. M. ZADVORKIN, E. N. TARASOV

Permanent Magnets Laboratory, Ural State University

620083 Ekaterinburg, Russia

The spin reorientation from the uniaxial anisotropy (above

45 K) to the cone of easy-magnetization axes (below 45 K) has

been observed by means of magnetization measurements on

strongly aligned polycrystals of Tm_Co_ intermetallic compound.

The X-ray diffraction study of the thermal expansion shows that

at spin reorientation the rhombohedral lattice of the compound

undergoes a noticeable volume magnetostrictive deformation

i(-1*10* ) as well as the orthorhombic distortion within the "i

-3 *

basal plane up to 3.5*10 in the cone range. The results are

discussed in terms of two Tm and one Co magnetic sublattices

with noncollinearity between the Tm sublattices at low

temperatures as a reason for the spin-reorientation transition.

158

7P:a33

CURIE TEMPERATURE OP TWO-COMPONENT AMORPHOUS

FERROMAGNET

I.P.HARGOLYTCH

Institut for Condensed Matter Physics of the Ukrainian

Academy of Sciences, Dragomanov Str. 14/16, 290005 Lviv,

the Ukraine.

The Curie temperature of two-component amorphous ferromag-

net is found using the expansion of the free energy in powers

of order parameter. For the model with liquid-type disorder

introduced via hard spheres structure factor the explicit

expression for the concentration dependence of ferromagnetic

ordering temperabure is obtained.

7P:a34

THERMODYNAMICS OF QUANTUM EASY-PLANE FERROMAGNETIC CHAINS

ALESSANDRO CUCCOLI, VALERIO TOGNETTI, PAOLA VERRUCCHIDipartimento di Fisica, Universita di Firenze, Largo E. Fermi 2, I-50125 Firenze, Italy.RUGGERO VAIAIstituto di Elettronica Quantistica C.N.R., Via Panciatichi 56/30, I-50127 Firenze, Italy.

The subject of the paper is the ferromagnetic chain with applied Zeeman field and single-site easy-plane anisotropy. By means of the Villain transformation the Hamiltonian is expressed in terms ofcanonical operators. A new method1 for defining an effective classical Hamiltonian is then used. Inthis way the properties of the quantum system are expressed by classical-like formulas. The effectiveHamiltonian can be cast into the form of the original one, with suitably renormalized parameterswhich describe the contribution due to quantum fluctuations. It is shown how quantum thermody-namic averages are calculated by the classical Transfer Matrix method, with a few examples. Theapplication to the real compound CsNiF3 is considered. The experimentally measured specific heat,magnetization and susceptibility are very well reproduced with a simple computation, demonstratingthe power of the new method. In addition, comparison with the quantum results of the sine-Gordon(SG) model and of the planar model is made, showing that the nonlinearity of the exchange term(which is neglected in SG) plays a relevant role, so that the nonlinear thermodynamic behavior ofthe spin chain only qualitatively can be explained in terms of SG solitons.

1. Cuccoli A., Tognetti V., Verrucchi P. and Vaia R., Preprint (Universita di Firenze, 1991).

159

7P:a35THERMAL STABILITY OF Dy AND Tb DOPED Nd-Fe-B MAGNETS

S.SZYMURA(1) Yu.M.RABINOVICH*2) V.V.SERGEEV^ H.BALA(3* and L.V.POTAPOVA*2'

(1) Institute of Physics and (3) Institute of Chemistry, Technical Universityof Czestochowa, PL-42-200 Czestochowa; (2) All-Union Science-Research Insti-

tute of Electronechanics (VNIIEM) - 107817 Moscow

The elevated temperature (300 - 400 K) performance of the sintered 1 ( r C tmagnets with Nd partly substituted by Dy or Tb (up to 6 at.l)has been studied.Both elements enhance very effectively the coercivity as well as decrease bothtemperature coefficients of spontaneous magnetization and coercivity of thesintered Nd-Fe-B type magnets.The effect of the above elements (RE) on hard magnetic properties of sinteredNd(RE)-Fe-B magnets as a function of temperature is also discussed.

7P:a36MAGNETOCALORIC EFFECT IN NANOCRYSTALLINE MATERIAL.

Z.KALVAInstitute of Physics, Czech.Acad.Sci..Cukrovarnicka 10,CS-16040 Praha 6, CSFR.

Nanocrystalline materials could be a realistic example forapplication of theories which use localized magnetic moments.A superferromagnetic interaction between nanocrystals is expec-ted mainly because the shape of temperature dependence of thesaturation magnetization. The physical origin of this interacti-on is discussed. Magnetocaloric experiments could lead to bet-ter understanding of the excitations of nanocrystalline magne-tic materials. For the adiabatically isolated sample there willbe in the invariant total summa of phonon and magnon entropiesterms of the same magnitude. The dependence of the energy ofmagnon on the external magnetic field is not the same for amor-phous interface and for the crystallised nanocrystals. Magneto-caloric behavior of discussed nanocrystalline material will benonhomogenies. On the boundaries of nanocrystals is possible toexpect temperature gradients, which could be visible with moresophistical fotoelasticity experiments.

160

7P:a37MAGNETIC FLUCTUATIONS IN THE VICINITY OF FIRST-ORDER PHASETRANSITION IN A Mn(lOfcGe) ALLOY

J.J. Milczarek. E. Jaworska. K. MikkeInstitute of Atomic Energy, Swierk. 05-400 Otwock. Poland

The manganese alloys of high Mn (~ 90*) content undergo thefirst order phase transition from the antiferromagnetic (AFI)state with fct (c<a) structure to paramagnetic fee structure.It is suggested that the structural phase transition is drivenby the change in magnetic order of these alloys. The tempe-rature dependence of the order parameter and its fluctuationsin the vicinity of the phase transformation in a Mn(10%Ge)alloy were studied by neutron diffraction performed in a tripleaxis neutron spectrometer. The discontinuous character of thephase transition was confirmed by observation of the jump inthe order parameter occuring at the T N « 492.5 K. Thetransverse and longitudinal components of the magnetizationfluctuations were studied. The maximum of the transversecomponent of the generalized susceptibility tensor was detectedat the TN, jbut no changes in the correlation length for thatcomponent were found. The strong anomaly of the longitudinalcomponent found near TN stems from almost critical temperaturedependence of the correlation length of longitudinalfluctuations.

7P:a41

THERMODYNAMICS OF WHITE PHOSPHORUS IN BENZOIC SOLUTIONS

AS A FUNCTION OF CONCENTRATION AND TEMPERATURE

H. Craubner

Max Planck-lnstitut flir Festkdrperforschung,

Heisenberg-Str. 1, D-7000 Stuttgart 80, Germany

Solutions of white phosphorus (PyJii benzene were investigated densimetrically. The

densities of solvent and solutions were measured as functions of composition and tempera-

ture in the range from 280 to 340 K at an N , pressure of 1 bar. The results were used to

calculate the partial sp volumes of both benzene and P as functions of concentration

and temperature. The limiting values at infinite dilution of densities and partial volu-

mes of P are given as functions of temperature. It is shown that in the case of suffi-w

ciently dilute solutions benzene as the solvent approaches closely to ideal behavior and

obeys Raoult's law. The behavior of P , however, is in fact nonideal, but may be de-

scribed as pseudo-ideal, satisfying Henry's law. The results obtained thus are applied

to evaluate the corresponding partial molar thermodynamic functions, as well as the to-

tal thermodynamic functions of mixing in dependence on composition and temperature.

161

7P:a42

QUASICONSERVED VARIABLES AND LIGHT SCATTERING IN VISCOELASTICLIQUIDS

V.I. MOTORIN, P. BEZOT, C. HESSE-BEZOTLaboratoire de Physique de la Matiere Condensee - CNRS - URA 190University de Nice Sophia Antipolis - BP 71 - 06108 NICE CEDEX 2(France)

A way to choose the variable for the macroscopic description ofthe behavior of the physical systems is suggested. Using this way it is ,possible in particular, to determine the dependence of the macroscopic 'equations on the wave vector k in the whole macroscopic range.Applying this approach, the spectrum of the depolarized (VH) lightscattering in viscous liquids is related to such phenomena as glasstransition, viscoelastic transition and critical temperature for"fragile" liquids. The theory is compared with the experiment. It isshown that the main features of the VH spectrum, its temperature andk dependence can be explained independently of any specific model.

7P:a43

EXPERIMENTAL STUDY OP SOME MESOMORPHIC SAMPLES OF FAIT* ACIDSAND MIXTURES

MIHAE1A DUMlTflU* MARIA HCNCIUC, GABRI3L A. DUMITRUPolytechnical Institute Bucharest, Splaiul Independence! 313,Bucharest 77206, Romania ;

A study of the arrachidonic acid-a unsuturated fatty acid-and

of their mixtures with cholesterol and with other fatty acidc

( arrachidic and elaidic ) is presented.

Between some temperature values these substances,belonging to >3

the biological memorane, present a liquid crystal smectic C .;'

texture, influenced 'jy the cholesterol percentage. |

Plots of the dependences of the current through the samplas •'£.

versus the applied voltage anJ tiris and of the relaxation ti«:e "i ;

ftm.1 electric frpnc? charge on the cholesterol percentage were f

performed v.v& discussed.An external scl'f-fu-cusing. 01 a low po-

wer laser beain (He-He) was emplia^ized, too.

162

7P:a44

TEMPERATURE AND CONCENTRATION DEPENDENCE OF ORIENTATIONAL

CORRELATIONS OP NITRATE IONS IN Cu(NOs)2 AQUEOUS SOLUTIONS

M.P. Fontana, Dipartimento di Fisica, Universita di Parma, Parma, Italy

B. Rosi-Schwartz, Thompson Physical Laboratory, University of Reading, Reading, U.K.

N. Micali, Istituto di Tecniche spettroscopiche CNR, Messina, Italy

We report new results on the dynamics of orientational correlations of molecules in

highly concentrated aqueous solutions of Cu(NO3)2. We determined both single-particle

and pair reorientational relaxation times of the nitrate ion as a function of concentration

and temperature by coupled Raman and depolarized Rayleigh-wing spectroscopy measure-

ments. The ratio of the relaxation times, which is interpreted as a generalized Kirkwood

factor, features a nonmonotonic behavior ar room temperature as a function of concen-

tration, i.e. average interionic separation. At high (75 C) and low (10 C) temperatures

the anomaly disappears.

7P:a45

sus MUTSIS or sou Guuosin mirans 11 n n DIIOTID SOMTIMS

P. CUSOGBI2, K. CIURI1, t. IUIUI1 , G.P. SrUtt3

1) Iititito di Fitica Jedica, OiiuniU di Jticou, Italy lid Libontoire Hot Irilloiii ( l i t . CU-CHS),

CD Saclay, Sif-iir-Uette.

2) I it iUt Fir restioiperforickiie. i n , Jillek, Ceruij.

3) Dipirtiieito di Ckiaica Otfiiici, Di inniU di solojia, Italy.

The ljotropic poljiorpkiii of t ici it i of fiauii ie derint im ku beei receatly iatestigated by i-ray

diffiactioi aid optical aicroscopy. Ike reialti sitgeit a itnctirt foried by rod-iiaped t f fr i f i ta

coaititited of a itickiig of tetiaieii. It it n i l l ion that, i i coitrast to all otker nclt ic acid

coistitieatt, tie giaioiiie it able to self-associate iito stable tt iutirei (at }tl aid fibari). tki

COMOI basic building block is a tetraier, i .e. a plaiar u i t foned by foir giaiiui , kydrojei beaded i i

a Hoogsteei aode. SUS iirestigatioas oi tke isotropic pkase vere tiviitgtd to aulyse tae anrtfatloi

process: tke experiaeits were peifoned at tke reactor Oipkee (LU, Saclay) by isi if tki tin

spectroutei. It preseat i n e son preliaiiaiy u n i t s obtaiiad vitt suples i i rtirt tke coientntioi of

S H I lover tkai 21 (»/»).

163

7P:a46

INFLUENCE OP THE MAGNETIC PIEID ON THE STRUCTURE

OP LIQUID TWO-COMPONENT MAGNET

I.O.VAKARCHUK (a), I.F.MARGOLYCH (b)

Ivan Pranko Lviv University (a), Dragomanov Str.12,

290005 Lviv the Ukraine

Institute for Condensed Matter Physics of the Ukrainian

Academy of Sciences (b), Dragomanov Str.14/16,

290005 Lviv, the Ukraine

The partial structure factors of many-component liquid mag-

net and the full structure factor of the two-component one are

calculated in random phase approximation. The influence of the

external magnetic field and exchange interactions between

atoms on the structure functions of the two-component case is

investigated.

7P:a47

THREE-BODY DISTRIBUTION FUNCTION IN LIQUIDS

A. Di Cicco* and A. Filipponi+* Diparnmcnto di Matematica e Fisica, Universita di Camerino, Via Madonna delle Carceri 62032Camcrino (MC), Italy+ Dipartimento di Fisica, Universita dell'Aquila, Via Vetoio, Coppito (AQ), Italy.

X-ray absorption spectroscopy (X.A.S.), interpreted in the frame of the multiple-scatteringtheory, represents an unique probe of the three-body distribution function. A detailed study ofthree-body terms has been recently carried out in the case of amorphous silicon.! 1] In this caseX.A.S. provided a reliable determination of the three-body parameters, evaluated in the Gaussianapproximation. The application of this technique to disordered systems is complementary to thestandard X-ray and neutron scattering techniques, which probe only the pair distribution function.

We present a X-ray absorption investigation of liquid gallium (1-Ga), carried out at severaltemperatures in liquid, supercooled and crystalline phases. Crystalline gallium is an interestingsystem which shows a low melting point and coexisting covalent and metallic characters. Previousdiffraction analysis of 1-Ga reported a low number of first neighbors (about 9) as compared withother liquid metals which show local close-packing (about 12). Multiple-scattering data-analysis [2]has shown for the first time the presence of a detectable three-body signal in the liquid phase. Thissignal is interpreted by means of an antsotropic local model which is in agreement with the existingdiffraction measurements.

Re<*rences:1] A. Filipponi, A. Di Cicco, M. Benfatto, C.R. Natoli, Europhysics Letters 13,319 (1990).2] A. Filipponi, A. Di Cicco, T.A. Tyson, and C.R. Natoli, Solid State Commun. 78, 265(1991).

164

7P:a48

S T U D Y OF T H E ELECTRIC CONDUCTIVITY OF MOLTEN SALTS

M. RODOVA, K. NITSCH, P. DEMO, Z. KO&SEKInstitute of Physics, Czech. Acad. Sd., Cukrovarnicla 10,162 00 Prague 6

The present paper deals with the study of molten PbCl2, AgCl and eutectic mixtureof AgCl and PbClj (40.8 % PbCh) by means of electric conductivity measurement. Weconcentrated at the temperature range 20 K over and bellow the melting point becausethe most interesting information can be received at the temperature near that point.The measurements were performed at various cooling rates to full freezing of a melt.Simultaneously the undercooling was determined. The differences in the shapes of theconductivity dependencies confirm unlike behaviour of the molten PbCl% and AgCl nearthe freezing point. We assume PhCl% at well as AgCl are dissociated in the melt butP&+ ions in contrary to Ag+ react with Cl~ forming complex anions. To verify thishypothesis we performed some model calculations and the results achieved are discussed.

7P:a49

ALKALI METAL LIQUIDS :

TOWARDS A LAW OF CORRESPONDING STATES

U. Balucani1 , A. Torcin? and R.Vallawi3

1 - I.E.Q. - C.N.R., Via Panciatichi 56/30,1-50127 Firenze (Italy)

2 - Dip. di Fisica - Universita di Firenze, 1-50125 Firenze (Italy)

3 - Dip. di Fisica - Universita di Trento, 1-38050 Povo, Trento (Italy)

Computer simulation of Na, K, Rb and Cs have been performed by making use of

the potential model implemented by Price et al. The aim of the work is to ascertain

whether the alkali metals can be thought of as a class of physical systems whose

properties scale in terms of the relevant parameters of the potential e and <r, at least in

the neighbourhoud of the melting point. We have evaluated both static and dynamical

quantities; e.g. the structure factor S(k) and diffusion coefficient D. A good agreement

with the scaling hypothesis is found for K, Rb and Cs, whereas some deviations are

found for liquid Na.

165

7P:a50CONFORMATIONS OF ETHOXYLATED SURFACTANTS IN AQUEOUS SOLUTIONS

T.O. HUSHCHA AND G.S. POPInstitute of Bioorganio Chemistry and Oil Chemistry,Ukrainian Academy of Soiences, Kharkivsky Highway 50,253160 Kiev, Ukraine

The ultrasonic absorbtion speotra of ethoxylated dinonyl-phenols in aqueous solutions have been measured in the fre-quency range from 5 Mils to 120C MHz. The temperature inter-val was from 280 to 330 K.

The process of oonfcrmational changes of surfactant moleculeswith the characteristic time of about 10 ns was found tocontribute to the excess absorbtion in studied systems.

The observed conformational changes have been attributed tothe rotational isomerism of ethylene oxide chains. Theenthalpy difference between the conformers was found to be36,8 - 40,2 kJ/mcl. Some other kinetic characteristicsincluding the activation enthalpy and entropy werecalculated.

7P:a51APPLICATION OF THE COLLECTIVE VARIABLES METHOD IN DESCRIBING CF THELIQUHM3AS PHASE TRANSITION

YUKHNOVSKII I.R., IDZSK I.M., KDLOMIETS V.O.Institute for Physics of Condensed Systems, 14/16 Dragonanova str.,290005 Lviv, Ukraine.

Two main problem arise at the description of the liquid-gas phase tran-sition. The short- and long-range interparticle interaction has to be takeninto account simultaneously. The second problem is connected with the natureof the phase transition on its own and reduces to the compulsory considera-tion of nongaussian fluctuations. The collective variables method provides Ithe solution of both these problems. Starting from the microscopic hamil- jtcnian, the functional of the ccnfigurational integral with the coefficients >given explicitly is constructed. The critical point coordinates, the criti- Jcal exponents and thermodynamical functions are determined both below and |above the critical point (Tc, tfc) for the case of o^model. X

166

7P:a52[L> TRANSITIONS: THEORY AND EXPERIMENT.

V. V. BRA1IHKIN

Institute of High Pressure Physics. 1U2092. Trolck Moscow

Region. USSh

Recently we have discovered ths transitions in melts of

some elements. These transformations have all features of

first-order phase transitions, in this work the model of this

Phenomenon is presented. The model explains the possibility of

the existence of long-lived crystal-like clusters in a liquid.

The nature of tne melt-melt transition is connected with the

changes of the cluster's structure. The model is in a good

agreement with the experiment: the values of widths of the

transitions and positions of critical regions are correctly

predicted.

7P:a53;P-T> PHASE DIAGRAM OF SOLID AND LIQUID Te UNDER PRESSURE

UP TO 10 GPa.

V. V. BRAZHKIN. R. N. VOLOSHIN, S. V. POPOVA. A. G. UMNOV

Institute of High Pressure Physics. 112092 Troick. Moscow

Region. USSR.

The iP.T)-diagram of Tellurium was investigated by means of

the measurements of electro-resistance and of volume Jumps under

high pressure. The melting curve was established up to 10 GP&.

In the melt of Te the transition L-L1 was discovered,

accompanied by sharp changes of electro-resistivity and volume.

For crystalline Te the boundary of the transition Te - T*»v

was found and the location of the triple points 'reIii~L' "T*iv

and L-Te -L' were established.

167

7P:a54THE INFLUENCE OF THE NONMETAL- METAL TRANSITION IN SELENIUM

MELT ON THE SOLIDIFICATION PROCESS

V. V. BRAZHKIN. R. N. VOLOSHIN. S. V. POPOVA

Institute of High Pressure Physics. 1U2092. Troick Moscow

Region. USSR

Under pressures between 1.75 and & CjPa the supercooling

of Se melt and the average grain size of" the samples quenched

under pressure with constant cooling rate 100 K/s were

measured. The experimental results were analysed in the

frames of the classic theory of nueleation and grain growth.

The comparison of properties of supercooled Se melt to that

of Pb and In reveals anomalies on the pressure dependences of

Se melt properties. This is discussed in connection with the

nonmetal-metal transition in selenium melt.

7P:a55

a- RELAXATION STRETCHING IN SUPERCOOLED LIQUIDS

M. Fuchs and A. Latz

Physik-Department, Technische Universitat Munchen

D-8046 Garching, Federal Republic of Germany

Ab initio calculations of the primary or a— relaxation of supercooled simple

liquids are presented. Relaxation amplitudes, times and stretching parameters

characterizing the non- exponential decay, e.g. Kohlrausch- /9' s, are calculated

within the Mode Coupling Theory. The relaxation times and stretching parame-

ters are found to be different in different relaxation functions. The wave vector

dependence is rather pronounced in coherent and incoherent dynamical structure

factors, whereas the corresponding moduli show smaller variation with wave vec-

tor. The calculated parameters are experimentally accessible in colloidal systems.

168

'•{

7P:a56FREE-ENERGY DENSITY FUNCTIONAL FOR THE MELTING OF SIMPLE LIQUIDS.

L.MEDEROS, G.NAVASCUES, P.TARAZONA and E.CHACON.Departamento de Fisica de la Materia Condensada (UAM) andInstituto de Ciencia de Materiales (CSIC). Universidad Aut6nomade Madrid. E-28049 Madrid, Spain.

A theory for the Helmholtz free-energy functional F of aninhomogeneous sinple liquid is presented. We make a perturbativeanalysis taking the hard sphere fluid as reference system. Adensity functional model, based on the coarse grained densitydistribution1, is used for this reference tern. The role of theperturbative attractive interaction is modelled with a theorybased on the Weighted Density Approximation. With this newfunctional we get the full solid-liquid-vapour phase diagram ofa system with Lennard-Jones interactions.

1. P.Tarazona. Phys.Rev.A 31 (1985) 2672.

7P:a57

INSTABILITIES IN FLUID MIXTURES

X. S. CHEN, F. FORSTMANNInst. f. Theor. Physik, Freie Universitat Berlin, Amimaltoe 14, D-1000 Berlin 33

We describe a method for analyzing the stability of fluid mixtures. A density functionalapproach allows the discussion of simultaneous fluctuations of concentration and total densityas well as a clear characterization of the instability.For several mixtures of particles with dipolar, Coulomb- or Yukawa interactions we calculatethe correlation functions from integral equations and discuss the instabilities.

References: X. S. Chen, M. Kasch, F. Forstmann, Phys. Rev. Letters 6JZ, 2674 (1991)X. S. Chen, F. Forstmann, Mol. Phys. in print

169

7P:a58

DIELECTRIC RELAXATION OF AQUEOUS SOLUTIONS OFMONOALCOHOLS

D.Fioretto, A.Marini, G.Onori, L.Palmieri, A.Santucci, G.Socino, L. Verdini.Dipartimento di Fisica, Universita' di Perugia

1-06100 Perugia, Italia

Dielectric relaxations of aqueous mixtures of monoalcohols have been studied as a function ofconcentration and temperature. In this kind of mixtures of associating polar liquids, two moreor less distinct relaxations can be expected, related to the strongly correlated motions ofneighbouring molecules. Measurements of the complex dielectric constants have been done inthe frequency range 10MHz-3GHz by means of a coaxial technique, employing a semi-rigidprobe dipped into the liquid under test. The values of dielectric constants have been obtainedmeasuring the reflection coefficient of the system by means of a HP8753A Network Analyzer.The behaviour of the real and imaginary parts of measured dielectric constants in the water-rich region (mole fraction of cosolvent X2<0.1) can be represented by a single relaxation timeTJ that increases with xj- At higher alcohol concentration the dielectric data can berepresented by a sum of two Debye relaxation functions: a slower "principal" relaxation,characterized by TJ , still increasing with X£ aRd a second relaxation characterized by a time t-ythat is almost independent of alcohol concentration. The experimental results are comparedwith other physico-chemical measurements available for these mixtures and discussed interms of structure changes in the aqueous alcohol solutions.

7P:a59

COTTON-MOUTON AND KERR EFFECTS IN BINARY 0ILU1ED SYSUMii t)r

•^-PICOLINE IN BENZENE AND P-XYLENE

M.Kaczmarek, Z.Wofniak

Optics Laboratory, Institute of Physics, A.Mickiewicz

University, Grunwaldzka 6, 60-780 Poznari, Poland

Electrooptical Kerr constant and magnetooptical Cotton-Mnuton

constant in o^-picoline solutions in benzene and p-xylciu;

were determined. The results permitted the calculation (if

the molar Kerr constant K^ for the four different mndrrl'i nf

local field. The molar Cotton-Mouton constant, H* , nf thn

studied solutions was calculated. Analysis of the results

provided the grounds to propose a model of molecular

interactions in the studied solutions.

170

7P:a60MAGNETOOPTICAL FARADAY EFFECT IN BINARY SOLUTIONS OF DIPOLARLIQUID DISSOLVED IN BENZENE AND p-XYLENE

M.SurmaInstitute of Physics, A.Mickiewicz University,Grunwaldzka 6, 60-780 Poznari, POLAND

Faraday effect have been measured in binary diluted solutions ofdipolar liquids o-Anisidine, o-Bromoanisole,Toluene,°£-Picolineand P-Picoline dissolved in nondipolar Benzene and p-Xylene.The pulse high magnetic field technique was used to detect theFaraday rotation. For a very low molar concentrations, f4, ofa dipolar liquid in Benzene or p-Xylene the local extreme valuesof the Faraday rotation with respect to the molar concentrationof the solution are observed. The results are consistent withmagnetooptical Cotton-Mouton effect in diluted solutions ofdipolar liquids in Benzene and p-Xylene 11,21.

1. M.Surma, Acta Phys.Polon. £67., 885 (1985).2. M.Surma, P.Tepper, T.Porwich, A.Mickiewicz University Press,

Seria Fizyka Nr 65, J_, 43 (1991).

7P:a61P-T PHASE DIAGRAM OF 1,3-CYCLOHEXANEDIONE

M. SZAFRAtfSKI, P. CZARNECKI, A. KATRUSIAK*, S. HABRYLOInstitute of Physics, "Faculty of Chemistry, Adam Hickiewicz

University, Grunwaldzka 6, 60-780 Poznaii, Poland.

DTA and dielectric constant measurements have been applied to

study the pressure and temperature dependence of the phase

transitions of 1,3-cyclohexanedione crystals. The Measurements

were performed up to 180 MPa and in the temperature range 270

to 400 K. The investigated area of the P-T diagram contains

transformation between two crystalline phases of I

1,3-cyclohexanedione, both have the same space group symmetry |

PZ^c, and its melting point. A strong positive and linear .

pressure dependence of the transformation temperature of 0.33 *

K/MPa has been observed. The obtained phase diagram confirms j

the role played in this phase transition by the disorder of the ~*

methylene C(5)H2 group.

171

7P:a63TEM STUDY OF 25 GRAIN BOUNDARIES IN COPPER

Zuzana Vicherkova. Institute of Phvsics, Czech.Acad.Sci.Na Slovance a, 180 40 Praha 8, Czechoslovakia

The structure of high angle grain boundaries has beenstudied using transmission electron microscopy. Secondarygrain-boundary dislocations (SGBDs) have been found in near 25boundaries in copper bicrystals. Experimental samples havediffered in the deviation A* from exact 25 orientation< 0°-3°>. The dependence of the SGBDs arrangement on thedeviation A* has been discussed in connection with thediffusion experiments carried out by other authors.

7P:a64MOSSBAUER PHASE ANALYSIS OF THE NANOCRYSTALLINE ALLOYS

TOMAS ZEMfilKInstitute of Physical Metallurgy, Czechoslovak Academyof Sciences, Zizkova 22, CS-616 62 BRNO, Czechoslovakia

FeCuNbSiB alloys with the nanocrystalline structure produced bythe controlled crystallization of the amorphous state representa new extremely soft magnetic material. While a general consenthas been reached on their principal phase compositionconsisting of the a-Fe3Si-like nanocrystals immersed in thehighly disordered amorphous-like intergranular matter remainingafter the crystallization, the exact data on the individualphases are still missing or contradictory. By using the FeMossbauer spectrosccpy as a special magnetic and phase analysismethod we succeeded in the qualitative identification,quantitative determination and in gaining some additionalinformation on the iron phases and sites as follows. Fourcrystalline sites of the a-Fe-Si phase were distinguishedindicating its depletion in Si (in comparison with thestoichiometric Fe^Si), three distinct boride-like iron sitesresembling these of the tetragonal Fe-jB (the spectral componentof one of them overlapping with that of the Fe-Sinanocrystals), and a considerably broadened contribution of theamorphous-like intergranular remainder characterized by a broadhyperfine field distribution and distinguished by its Curietemperature near the initial amorphous material.

172

7P:a65DETERMINATION OF ELECTROMECHANICAL NONLINEARITIES IN CRYSTALS

CARL K. HRUSKAPiezoelectricity Research Laboratory, York University, Ont M3J 1P3, Canada

The electromechanical nonlinerities in crystals are nonlinear elasticity,electroelasticity, electrostriction and nonlinear permittivity. Theyrepresent the changes in the elastic and dielectric properties of crystalsoccurring under the effect of a mechanical strain and electric field. Theirfull spectrum is present in piezoelectric crystals (in 20 out of 32 crystalclasses). The strongest representatives of these phenomena are the third-order nonlinear material constants. Their knowledge is most advanced in thecase of quartz which is thus used as a testing ground for the currentnonlinear theory of the electroeiastic continuum.

This paper briefly describes experiments employed to determine the third-order nonlinear constants and their computation. Its main mission is towarn about errors (illustrated by real life examples) which are made in theinterpretation of the computed values of the nonlinear constants (as wellas in their standard errors, including factors overlooked hitherto) and topoint out the instances of their false verification. State-of-the-artresults are given for quartz showing the corrected values of nonlinearconstants and the agreement reached among various methods.

The interest in the third-order nonlinearities is stimulated by practicalindustrial needs. The first international standard on piezo-electricnonlinearities is under preparation by the IEEE.

7P:a66THE DISLOCATION MOBILITY UNDER MAGNETIC FIELDS IN NON-MAGNETIC CRYSTALS

V.I.ALSHITS, E.V.DARINSKAYA AND E.A.PETRZHIKInstitute of Crystallography, Leninsky pr.59, 117333, Moscow, USSRA new physical phenomenon - the displacement of dislocations as a result ofexposing of the specimens to a static magnetic field (B = 0.1 + 2 T) in theabsence of the mechanical loading - is found out and investigated for NaCl,Csl, LiF, Zn and Al single crystals. This effect is characterised by follow-ing properties: Dthe field direction reversal jJoea not change the disloca-tion displacement; 2)the mean dislocation path I linearly increases with thetime t of the magnetic treatment; 3)the mean dislocation velocity v is pro-portional to square magnetic induction and inversely proportional to squareroot of concentration of paramagnetic impurities; 4)there is no influence ofthe magnetic field on dislocation mobility in crystals with diamagnetic im-purities; 5)the effect is temperature independent in the range T = 4.2 + 77Kand it grows only by~20X with further increase of temperature up to a roomvalue; 6)the saturation of -C(t) and £(B) dependencies takes place at largevalues of t and B on the level corresponding to an average distance betweenthe "forest" dislocations; 7)abrupt decreasing of the effect when the frequ-ency v of alternative magnetic field exceeds some critical value Wccsa a2;8)an anisotropy of the phenomenon with respect to mutual orientation of mag-netic field, dislocation line and Burgers vector is investigated. The pheno-menon is interpreted as a result of unlocking of dislocations from paramag-netic centers because of spin-dependent electron transitions in a dislocati-on-impurity system under the action of external magnetic field with furthermotion of dislocations in the long-range internal stress field.

173

7P:a67X-RAY POWDER DIFFRACTION ANALYSIS OF PbMDgSg BETWEEN 25 K AND 295 K

M. FRANCOIS(1>, K. YVCN(1), D. CAnMJI ( 2 ), M. DECROUK*2*, R. CHEVREL<3),M. S E R G Q J T ' 3 ) , S. BOUDOADA'3', OH. WRCBLEWSKP4'(1) Laboratoire de Cristallographie and (2) Departement de Hiysique de laMatiere Condensee, 24 quai E. Ansermet, University de Geneve, CH-1211 Geneve,Switzerland(3) Laboratoire de diimie ttLnerale B, University de Rennes, Rennes, France(4) HASYUB at DESY, Notkestrasse 85, D-2O0O Hairburg, 52.

Following an X-ray Guinier powder diffraction work1 the anisotropicline broadening in EbHogSg was studied by synchrotron ponder diffractionanalysis in the temperature interval between 25 K and 295 K. The resultsare interpreted in terms of anisotropic changes of the crystal mosaicity.

1H. Francois, K. Yvcn, D. Cattani and M. Decroux: International Workshop enChevrel Hiase Superconductors, September 1991, Hotel de Chavannes-de-Bogis,Switzerland.

7P:a68ON THE POSSIBILITY OF THE COEXISTAHCE OF SUPERIOHIC ANDFERROELECTRIC SUBSYSTEMS IN CRYSTAL

RAKITIN A. S.Institute of New Physical and Applied ProblemsAcadamy of Sciences of UKraineUritzKogo 11-47, 253035 Kiev. UKraine

The problem under consideration: is the situation possiblewhere electron-electron correlations result simultaneouslyin ferroelectric (FE) ordering of one subsystem and super-ionic (SI) disordering of another one?The "FE interband model" is utilized for analysis. The Dy-son equation for anomalous Green function is solved in FEphase outside the mean field approximation frameworK. it'sshown that along with purely FE potential minima additionalvacant sites can exist for another branch of exitations. Inthe vicinity of phase transition SI conductivity will taKeplace, but at the same time another ionic sybsystem willremain to be ordered.

174

7P:a69EFFECT OF LAYER FLEXURAL RIGIDITY UPON DYNAMIC CHARACTERISTICS

OF LAYERED CRYSTALS WITH COMPLEX LATTICE

E.S.SYRKIN, S.B.FEODOSYEV, AND O.YA.SHAMFAROVA

B.I.Verkin Institute for Low Temperature Physics &

Ingeneering Ukr. Academy of Sciences, Kharkov, 310164, USSR

The evolution of dispersion laws and phonon densities of

layered crystals with a complex lattice are analysed at the

microscopic level along with the localized "gap-type"

ocillations <iue to the ixpurity atoms in such system*. Th»

evolution is observed to be accompanied by changes in the tlm-

xural rigidity of the layers (noncentral interaction between

the atoms of the same layer).

; 7P:a70?• POLARIZATION BY NONUKIFOBM DISTOBTION (PND)#:| Dir.V.V.Gafyichuk, Dr.I.A.LubashevskiiI (Inst.Appl.Problems of Mechanics and Mathem. of Ukrainian,1 Academy of Sci.,290601, str.Naukova, 3"b", Lviv, Ukraine)

i We develop a theory of strongly nonunifoxm elastic defor-| mation of crystals, i.e. such dsfoxmation which spatial scaleI may achieve a lattice spacing* In this case even tor cubic' crystals deformation can give rise to polarization due to ap-

preciable asymmetry in the nearest neighbour arrangement.First, we consider a linear chain of atoms which interac-

tion is detennined by H • Z.*(*i -*L-<)* + 6(Xi+4 +Xt-, -2Xi)x,

where a b are o t n t and / is ^ o o d i n t of tomy H Z.(i L<) 6(Xi+4 t, i ,

where a, b are constants, and /i i s ^ n e coordinate of atomResults obtained in this model enable us to develop phenomeno-logical description of PND for a three-dimensional isotropiccontinuum, where the polarization pt- , and the defoxnationtensor /y are related as pt=oc\£Utj: *jS VtUjj. (^tfl are con-stants), and correspondently both electrostatic and elasticinteraction are taken into account. In particular, we proposea new phenomenological model for the known effect called multylayer relaxation. Good agreement whith available numericalresults is obtained.

175

7P:a71DIELECTRIC DISPERSION IN THE COMMENSURATE PHASE OF Rb2ZnCl4

V.Novotna.H.Kabelka* ,J.Fousek,M.Havrankova and H.Warhanek*

Institute of Physics, Czech.Acad.Sci.,Na Slovance 2,

180 40 Praha 8, Czechoslovakia

• Institut fur Experimentalphysik.Universitat Wien,l090 Wien,

Austria

Rb2ZnCl4 crystals have a wide incommensurately modulated phasewhich at TL*=193K locks into ferroelectric state. Dielectricbehaviour in the latter is determined by domain walls whicharise from phase solitons in the former. We have studiedtemperature and frequency dependencies of complexpermittivity. Dispersion behaviour in the measured rangelOOHz-lOMHz strongly depends on temperature and revealsa superposition of two polarization mechanisms. The onedominating at low temperatures has a strongly non-Debyecharacter and can be suppressed by applied electric bias. Thedata surprisingly suggest that in a highly purified crystal anequilibrium domain structure exists which is a well definedfunction of temperature.

7P:a72SOME STUDIES GRAIN-BOUNDARY MICROSTRUOTURES OF HOT-PiffiSSED

BN-AlH-SiO2 ELECTROCERAMICS

Ya.I.BUIBIKtU,V.VASILEMO,A.G.KOZLOVI n s t i t u t e of Space Technology,Krasnoyarsk,PO Box 486,Russia

The present paper concerns the e f fec t of grain-boundary p ro -per t ies - fo r hot -pressed BN-A1N-Si02electroceramics. In p a r t i -cular we studied for this materials transient current responseat pulse electric field and at temperature range from 300 K to850 K.The resulting current response almost obeys" "universal"power low that account two components,a current due dynamicpolarization of grain-boundary microstructures and a "eondu-ction" current due to charge hopping.The electrical propertiesof this materials are consistent also with the presence ofglassy phase in electroceramies.The analysis of experimentaldata is carried out with account dipolar interactions on fra-ctal microctructures of hot-pressed electroceramics.

176

7P:a73NEW ASPECTS IN DIAMCND SYNTHESIS

E. PAVEL, GH. BftUJia,Dacla Synthetic Diamond, P.O.Box 58-52, Bucharest, Romania, andD. BARB, V. SANDU, M. POPESCU,Institute of Atonic Physics, P.O.Box 52-06, Bucharest, Romania.

He have studied the structural properties of new carbonic phases Involvedin diamond synthesis at high-pressure and also at low pressure.

X-ray diffraction analysis of graphite after a high-pressure high-tem-perature treatment (5.5 GPa; 1800 K; FeNi catalyst) showed the presence ofa new carbonic phase which plays a key role in the growth of diamond crys- -.tals. j

Experimental examination of the metallic surface layer on CVD diamondsuggest the existance of a new carbon phase. H.A. 'tenor and K.C. Hass1 pro-posed a new structure for carbon, called H-6. We introduce also a hypothet-ical new carbon phase H-8, with hexagonal symmetry, which we suggest facili-tates diamond growth: a=b=2.543 A; c=8.82 A; A(0;0;0); B(O;1/2;1/12); C{0;1/2;1/4); D (1/2; 1/2? 1/3); E(1/2;1/2;1/2); F(1/2;0;7/12); G(1/2;O;3/4);H(O;O;5/6). this structure H-8 can be continuously deformed to diamond with-out breaking any bonds.

1. 'Earner M.A. and Hass K.C., Hypothetical superhard carbon metal,J. Mater. Res., Tfol. 5, 2273, 1990.

7P:a74STRUCTURE OF THE POTASSIUM SALT OF HEXAMERIC MALONDIALDEHYDE

A. LOPEZ-CASTRO, M.J. DIANEZ, M.D. ESTRADA 8. S. PEREZ-GARRIDO

Institute* de Clencias de Materiales, CSIC, and Departamento de Ffslcade la Materla Condensada, Universidad de Sevilla, Apartado de CorreosNo. 1065, E-41080, Seville, Spain.

Crystals of C18H19K010 (Mr 434.45), aonoclinlc, space group P2i/n witha= 13.255U), b= 6.794(1), c= 1Q.862(1)A, p- 96.96(1)*, V»=968,77(18)A , 2= 2, Dc« 1,49 g.cm . The structure consists ofcentrosymmetric KH(C9H905)2 Molecules lying on a centre of symmetry.Reflections were scanned up to e= 20* using Mo-Ku radiation. Of the ,'2786 reflections Measured, 1682 having K3o-(I) were used for the ,structure deternination and refinements. The structure was solved by JPatterson and Fourier techniques. Potassium and one hydrogen atoms are '••in special positions (0,0,0) and (0,1/2,0), respectively. An empirical j'absorption correction following the OIFABS procedure was applied to the 'Isotropically refined data. The structure was then refined by 5full-matrix least squares with anisotropic temperature factors fornon-hydrogen atoms and lsotropic ones for hydrogen atoms to R factor of0.04, ratio of maximum least-square shifts to e. s.d.» 0.22 and maximumpeak height in the final difference Fourier maps 0.2S eA~ . The K -Ionis hexacoordinate to six oxygens.

177

7P:a75

QUANTITATIVE STRUCTURAL ANALYSIS OF SUPERLATTICES FROM X-RAYPROFILE REFINEMENT

Y. BRUYNSERAEDE, H. VANDERSTRAETEN, K. TEMSTLaboratorium voor Vaste Stof-Fysika en Magnétisme, Katholieke Universiteit Leuven, B-3001 Leuven, BelgiumE.E. FULLERTON, I.K. SCHULLERPhysics Department 0319, University of California-San Diego, La Jolla, CA 92093, USA

A generally valid refinement procedure for fitting the X-ray diffraction spectra of a wide •»variety of multilayered structures was developed. This kinematical diffraction formulainvolves continuous, discrete, and random deviations from the average structure. Thestructure factor of only one single layer of each of the constituent materials needs to beaveraged over the variables. The non-linear Marquardt algorithm was used to optimizethe fitted values of peak positions, relative intensities and line profiles. The SUPREXprogram (available from the authors) thus yields the average superlattice structure anddeviations from that average structure. These refinements are in excellent agreementwith independently obtained results of artificially introduced roughness, crystal latticeparameters, and relative thicknesses of the layers.

Work supported by the Belgian IUAP and Concerted Action Programs at KUL and DOEgrant # DE-FG03-87ER45332 at UCSD. International travel support was provided bythe Belgian NSF and by NATO.

7P:a76HETEROGENEOUS MICROSTRUCTURE OF TITANIUM NITRIDE FILMS STUDIED

BY X-RAY DIFFRACTION.

R.KU2EL Jr., R.CERNY, V.VALVODA, M.BLOMBERG*. M.MERISALO*

Faculty of Mathematics and Physics, Charles University, Prague

+ Department of Physics, University of Helsinki, Finland 1

Microstructural heterogeneity Means that both crystallographlc ;

and grain orientations are of Importance. For the characteriza- '\

tlon of differently oriented crystallite groups (grain size and I

shape, defect content) four-circle and Seemann-BohlIn ;j

goniometers were used in addition to the conventional powder |

dlffractometer. Porous and compact films deposited at different $

energy of incoming particles were studied. The former consist

of large number of well-developed grains oriented with the

(111) plane parallel to the surface, others are smaller and

more defective. Results are compared with various models

considering elastic anlsotropy and different lattice defects.

178 ;

7P:a77USE OF THE X-RAY PENETRATION POWER FOR STRESS ANALYSIS

I.Kraus and N.tianevCzech Technical University, 115 19 Prague 1, Brehova 7.

AMong considerations about technical application of «o-lids, much attention is paid to residual stresses in surfacelayers affected by Mechanical, thermic or therao-chemicaltreatment. The most reliable way of meac.urement of th«eestresses is the non-destructive X-ray diffraction Method. Untilrecently X-ray diffraction Measurements of stress in poly-crystalline materials had been based on the conception of auniform state of stress in the whole volume irradiated byX-rays. In practice, however, we meet quite often a field ofstress very much non-uniform, both vertically to the surfaceand in the surface. It is shown, how the penetration depth ofX-rays can affect the results of stress measurement. Amongothers this problem is illustrated by solution of the followingtopics:

• X-ray analysis of residual state of stress with variablecomponents of stress tenzor,

• X-ray measurement of residual stresses on the surfaceof polished steel specimens,

• X-ray analysis of non-uniform stresses in Al-alloysf iK diti

yby means of TiK , CrK^ and CuKa radiations.

7P:a78

THE X-RAY DIFFRACTION IN REAL PERIODICAL SUPERLATTICES

V. Holy, 1. KubenaDepartment of Solid State Physics, Faculty of Science, The Masaryk University, Kotlarska 2, 611 37Brno, Czechoslovakia.

The X-ray diffraction in real periodical superlattices has been described using a four-dimensional for-malism on the basis of the Taiagi diffraction theory and an optical coherence approach. This methodenabled us to study the diffraction properties of real superlattices containing rough interfaces and otherstructural defects (precipitates etc.). The interfaces have been described by a statistical model, whichtakes into account lateral correlations in a rough interface. The theoretical conclusions have been veri-fied by X-ray diffraction measurements on a GaAs/AIAs superlattice using a double crystal and a triplecrystal diffractometers. From the reflection curve of the O-th diffraction satellite and from the integra-ted reflectivities of non-z«ro satellites the averaged parameters of the lattice have been determined, thestatistical parameters of the interfaces could be estimated from the shapes of non-zero diffraction peaks.

179

7P:a79DOUBLE-CRYSTAL NEUTRON SMALL-ANGLE SCATTERING CAMERA WITH

POSITION SENSITIVE DETECTOR (PSD)

J.SAROUN*, B.ALEFELD", P.LUKAS*, P.MIKULA*. V.WAGNER*

+ Nuclear Physics Institute,25068 Re4, Czechoslovakia

o Instltut fur FestkOrperforschung, W-5170 JUllch, Germany

• Phys. Techn. Bundesanstalt, 3300 Braunschweig, Germany

Two perfect crystals in non-dispersive arrangement are commonly

used for high resolution small-angle scattering measurements.

Till this time, an elastic bending of crystals has been applied

in NPI Re4 to increase the luminousity of this device. The rate

of data aquisition can be substantially improved using fully

assymetric diffraction geometry on analyser and PSD. We present

first experimental results obtained by this method in

comparison with other SANS techniques.

7P:a80

SIODI or He-inni einrra II urn snn IT suu-ueu nonoi scmniK

6. 1UUTIII1, I. CUSOCil1'3, I. COFNU2, I. II5TIU1CB3, G. IIICOHO4, F. 1DSTICIIUI1, D. SCHIU3,

I. DLUUII13

1) OiWeriita i i Ucoia, M131 iicoia, Italy

2) llU-Cuiccia, C.P. 2400, 00100 lou, Italy

3) Intit i t fir Festkoiptrforiciiif, VI, Jilick, Genaiy

4) I.l.C. Iipta oi 0 U fiait, IUlj

Tkii coitribitioi preuiti reeeit renlti of a Saall lifle Introi Scatteriej (SUS) itidy of modified •

urteititic iteel DII 1.4)14 (IUH}, iibject to iiplaiUtioi vitk a-jarticlei aid to nbieqieit '

iiockroial mei l i ig i at 7)1, Ml, 10)1 aid 12411. f

Tkt aialyiii of tke SUS iiclear ctoit section related to tke preieice of Be babbles gives qiaitititiTe ;

•icroitnctaral paraieteri of tke bebble popalatioa for tke differeit tuptiatatei aid piovidei alto <

iifonutioi oi tke i n premie vitkii tke bibilei.

180

7P:a81USIDOU stun n i rosiM luctoi FIIST i iu cooann SDUICTID TO m u u HTICDI

c. uimiii1, e.irar2, ijunu3, J.IIIU3, i.mou', I.MUII2, MKTICIIIII5

1} Diputimto dl Sclent dti Iittrlili t l i l l t Ttrri, OilnniU, (1131 lieou (Italy)2) Utontolrt U M Irilloiii, Utltj (Fruct)3) Iititito per 1 Uteriili I m u t i , CCI HIM, 21121 t i tn |T») (Italy)4) IU CCI Itpn ud lolittcilco di UllK, CBBP, 11133 U l i u (Italy)5) Iititito dl Fiiiet Mlci , hinri l t t , (1131 IKOM (IUIT)

ne reiidul i tn i i i i i sock-ip of first Mil for ucltir fnioi metori kit tea imitiMttd.U 1ISI 31(L i tu l coipoitit m nsjtctt* to 27IH tkirul cyclts tiailitiH tit ktit f l u nrlttloiidiriif ructor optntiois, l i u izptriintil ititioi btilt for tilt pirpon it tit JC1 Iipri.Tie riiidul itrili up MI obtiiiid tteorttieillf kj n i i f fiiiti t l m i t i n i l j i i i . l i t imrlei ln n l t i ire coipind viti tit strait n l i t i Minrtd iloif tw l i m , kj nitf ititroi diffrutioi.UtkHfk tti tktorttinl coipititioi dott wt eoiiidtr tkt ictnl itott of tit wapoint, iielidln titeffecti of udeiiribli tkiml Tiriitiou coutcttd to prtpintioi nd kiidliif, i jood i frmtit n iobtilud betvtti tkeortticil pttiictiim ud Mmrtd nliei , iidieitiif tut i n t r n dlffnetloi l i irefiied tool for itidjiij rtiidiil strain.

7P:a82STRUCTURAL AND TRANSPCHIT PRCM"ERTIES OF ReSii.75.

B. Lambert-Andron*. M. Kuhn0*, U. Gottlieb**, R. Madar°* C.N.R.S., Ciistallograpbie, 166X, 38402 Grenoble Cedex** C.N.R.S., CRTBT, 166X, 38402 Grenoble Cedex01.N.P.G., E.N.S.P.G., (URA 1109), BP46, 38402 St Martin dUeres* Universitat Kalsruhc

Structural and transport properties are strongly correlated particularly with the occurenceof order-disorder vacancies in the ReSi2-x compounds. The ReSi2 compound isorthorombic with the space group Immm.The X-Ray diffraction was performed on a single crystal of ReSii.75 ; an ordering, ofvacancies was observed with a selective repartition on two silicium sites leading to asymmetry reduction.Resistivity of oriented single crystals was measured in the temperature range between4.2 K and 300 K. Between 110K and 140 K the resistivity shows thermalhysteresis, wich is probably due to a structural transformation. The resistivity is quitehigh and anisotropic ; for I in the (a, b) plane p is about 5 mflcm and rather constantwith temperature, along the C axis it is larger and it seems to be very sensitive tostoichiometry and annealing. This is probably related to the distribution of vacancies.

181

7P:a83INFLUENCE OF MELT STATE ON PROPERTIES OF RAPIDLY QUENCHED

METALLIC MATERIALS

O. SCHNEEWEISS, N. PIZUROVA, T. 2AK

Institute of Physical Metallurgy, Czechoslovak Academy of

Sciences, CS-6166Z Brno, Czechoslovakia

Structure of materials prepared by means of melt quenching is

usually studied in dependence on quenching rate. However, very j

important role could play the state of the melt from which

cooling starts (i.e. its temperature and heating time). This

contribution examines structure and phase composition of some

iron alloys upon conditions of specimen preparation, e.g.

quenching rate and melt state. Specimen prepared by spark

erosion and double roller melt spun methods are investigated.

It is shown that besides quenching rate the state of the melt

influences the structure and namely the phase composition

importantly.

7P:a84

HELIUM IN METALS

H. ULLMAIERInstitut fur Festkdrperfbischung des Forschungszentrums, Postfach 1913, D-5170 Julichand Association KFA-EURATOM

The extremely high heat of solution of helium (and the other inert gases) in solidsprevents the making of any metal-helium "alloy" by conventional methods.Investigations of helium atoms as defects in metals were therefore neither interesting norfeasible. This situation changed with the introduction of nuclear technology (fission and •fusion reactors) and ion beam methods (sputter and plasma deposition, ion beam mixing) iand helium in metals is presently an active field of research1. .•This contribution summarizes the basic properties of helium atoms in metals (solubility, >diffusivity, nucleation and growth of bubbles) and briefly describes the experimental and itheoretical methods applied. Finally the influence of helium on macroscopic properties of zmetals (embrittlement under static (=creep) and cyclic (=fatigue) loads) is discussed. *

iProc. NATO Advanced Research Workshop, Bonas, France, 16-22 Sept. 1990 (S.E. -Donnelly and J.H. Evans, eds.), London, Plenum Publ. Comp. (to appear in Jan. 1992)

182

7P:a85ON STRUCTURAL PHASE TRANSITIONS IN C20

F42'

V. DVORAK and J. HOLAKOVSK*Institute cf Physics, Czech. Acad. Sci.Na Slovance 2, 180 40 Praha 8, Czechoslovakia

Structure of the perfluoroalcane C 2 QF 4 2 consists of parallel

layers? in each layer the molecules are arranged in a two-dimen-

sional hexagonal lattice. The long axes (around which molecules

may perform rotations) are perpendicular to the layer. The mole-

cules form right- and/or left-handed helices. At sufficiently

high temperatures the helix-handedness may change. Three diffe-

rent phase transitions in C 2 0F- 2 have been identified so far.

We propose the following mechanism of these transitions being

successively effective when lowering temperature:

1) ordering of layers leading to their regular stacking of the

type ABCA ..,

2) ordering in helicity,

3) freezing of molecular hindered rotation and orientational

ordering of molecules.

7P:a86WATER VAPOUR INDUCED TRANSFORMATION OF Cs2CdBr4

P. VANEK, J. HORVATH and M. HAVRANKOVAInstitute of Physics, Czech. Acad. Sci.,

Na Slovance 2, 180 40 Praha 8, Czechoslovakia

Cs2CdBr4 has been widely studied because of series of structuralphase transitions. We have observed that in the atmosphere satu-rated with water vapour, a clear single crystal changes into anopaque, white, polycrystalline material in a few hours. Its massincreases by 0.01%. The summary chemical composition and themelting point (733 K) of the white phase remain the same as ofthe clear one. The lock-in transition detectable in the clearphase by DSC at 237 K was not observed in the white phase. Onthe other hand, an irreversible endothermic phase transition (atthe first heating only) and a reversible one were detected byDSC at about 500 K and 710 K in the white phase, respectively.These phase transtions were not observed in the clear phase. Inthe originally white phase melted and solidified in a Au pan du-ring DSC measurements, the transitions at 237 K and 710 K wereobserved.

Phase transformations and instabilities induced by watervapour are known only at compounds containing hydrogen. To ex-plain above described phenomena, rentgenographic studies of theclear and white phases are in progress.

183

7P:a87

NOSE-HOOVER MOLECULAR DYNAMICS STUDY ON SELF-DIFFUSION ALONGTHE DISSOCIATED [112] EDGE DISLOCATION OF GOLD

J. VON BOEHM and R. M. NEEMINENHelsinki University of Technology, 02150 Espoo, Finland

The self-diffusions of interstitials (i) and vacancies (v) along the dissociated [112] edgedislocation of gold are studied with Nosd-Hoover molecular dynamics using the many-atomATVF1 and glue2 models. We find the following formation energies for the ATVF (glue) model:Ej(v)= 1.4 (0.8)eV; Ej(i)= 2.7 (1.5)eV. The vacancy migrates in the whole stacking fault region in-dicating that diffusion in the stacking fault ribbon3'4 and not the decrease of the Burgers vector5 isresponsible for the slowing down of pipe-diffusion in dissociated dislocations. The correspondingmigration energy Em(v) = 0.2 (0.3) eV is estimated from the jump frequency relationf ~ e x p ^ E ^ g T ) . The interstitial is not found to migrate. The activation energy for vacancy self-diffusion E^vJ+E^v) is about 1.6 (1.1) eV that is significantly less than Ej(i) alone. This resultagrees with the traditional view favouring vacancy mechanism but differs from the recent studyfor Cu3 where vacancies and interstitials were found to contribute comparably.

1. G.J. Ackland, G. Tichy, V. Vitek and M.W. Finnis, Phil.Mag. A56,735 (1987).2. F. Ercolessi, M. Parrinello and E. Tosatti, Phil.Mag. AS8,213 (1988).3. J. Huang, M. Meyer and V. Pontikis, Phys.Rev.Lett. 63,628 (1989).4. M. Wuttig and K.H. Birnbaum, Phys. Rev. 147,495 (1966).5. R.W. Balluffi, Phys. Stat. Solidi 42,11 (1970).

7P:a88INFLUENCE OF ELECTRIC, MAGNETIC FIELDS AND IRRADIATION ON THE PROPERTIESOF INCOWENSURATE STRUCTURES

I.I. FOUOVINKO, S.A. SVELEBA, V.S. ZHMJRRO, V.B. KAPUSTIANIKLviv University, 290005, Lcmonosova st. 8, Lviv, Ukraine.

On the basis of optical and dielectric properties of (N(CH3)4)2MeCl4(Me=Zn,Cu,Mi,Fe,Co) crystals investigations in the region of incoimensurate(IC) phase existence the localization of modulation wave vector on the com-mensurate values of higher order k=(m/l)c was found. The conmensurateregions were induced by X-ray defects, external electric and magnetic fields.It mist be noted that concrete values k=(m/l)c were obtained using exter-nal fields of certain symmetry. The influence of defects concentrationgradient, temperature, mechanical stress and electric field on the dynamicsof investigated crystals IC structure was also studied. The value of ICstructure pinning force on the defects was determined.

184

7P:a89NON-STOECHIOMETRY AND PHASE TRANSITION IN SPUTTERED NbTe THIN FILMS

Y.MATHEY,M.KASSEM,D.PAILHAREY,G.RICHARD;URA CNRS 783-Faculte des Sciencesde Luminy.Departement de Physique-13288 MARSEILLE Cedex 9-FRANCEet S.FAYEULLE;Lab.M6tallurgie,Ecole Centrale de LYON-BP63-69131ECULLY .

The feasibility of preparing films of low-dimensional materials by sput-tering is now well demonstrated.Non-stoechiometry phenomena,however,arefrequently observed.In the case of niobium tellurides,for example,the gradient of cell parame-ters detected by glancing angle XRD.as well as the regular decrease ofthe Te content achieved upon annealing,strongly suggest the existence ofTe and Nb atoms intercalated within the parent NbTe2 or NbJTe4 structures.A transition mechanism,based upon the orientational relationship existingbetween films of these two phases,will be proposed.

We will also discussed the role of extra-atoms on the performances of ourfilms as solid lubricants.

7P:a90ON THE NUCLEATION PROCESS IN THE NMTENSITIC TRANSF0MKT10N OF A Cu-Zn-AlSINBLE CRYSTAL.

Y. ANAZIT., A. 2ARENBOWITCH.Mpartement de Recherches Physiques (C.N.R.S. UA 071).University P. & M. CURIE, 4. Place Jussieu 75252 Paris Cedex 05. FRANCE.

Cu-Zn-Al alloys are known to exhibit shape memory properties when thetemperature Is varied. This behaviour 1s directly connected to themartensitic transformation that such materials undergo. If the generalcaracteristics of this transformation are well understood, the nucleationmecanism of the transformation is not completly clear. However it seemsthat the residual stresses play a major role in the process of nucieation.As a consequence, the measurement of the nonlinear elastic constant \parameters as a function of temperature for shape memory single crystals :may clarify the process of nucieation. Such data are reported In this 1paper, a model is proposed for the intrepretation of the experimental \results. \

185

7P:bl01ON THE WIDTH OF IMPURITY BANDS IN DOPED SEMICONDUCTORS

J. Monecke , w. Cordts and J. KortusDept. of Physics, Mining Academy of Freiberg,0-9200 Freiberg, Germany

Calculations of the widths of impurity bands have been per-formed in the past using multiple scattering theories (e.g.Klauder V) , two-particle Green function methods and bandstructure calculations of hypothetical impurity superlatti-ces with essentially different results. Whereas the Klauderapproximation results in extremely broad impurity bands,two-particle Green function techniques give a vanishing bandwidth at zero temperature and the calculations of hypotheti-cal superlattice bands yield intermediate results. The rea-sons of these differences are discussed and the width ofimpurity bands in doped semiconductors is calculated withina theory which is correct in the first order in the impurityconcentration. The resulting band width is approximately20 % of that obtained in the Klauder V approximation.

7P:blO2

Study of the output properties of nondegenerateparametric amplifiers with Unear losses by meansof symmetrically ordered two-mode operators

P. Garcia-Fernindes

Institute de Estructura de la Materia, CSIC,

Serrano 119-123, 28006 Madrid, Spain

A theory baaed on aymmetricaUy ordered two-mode operator! it uaed to

•tudy the nondegenerate parametric amplifier with linear loam in free apace. *•

The squeezing properties and the degreee of coherence of the output, which •>

depend on the modulation frequency, have been analysed aa well aa the '}

effects of correlations between the light beams. 1;

186

7P:blO3OPTICAL RESPONSE OF INTERFACES H U H ARBITRARY DETERMINISTIC ROUGHNESS

SHU WANG and P. HALEVI*Centre de Investigacidn en Ffsica, Uiiversidad de Sonora, Mexico.

A perturbative formalism has been developed to study the electromagneticfields near a rough interface and a rough film with arbitrary deterministicprofiles. We apply the Rayleigh-Fano approximation to calculate the amplitudefunctions analytically up to arbitrary order on the roughness height. Westudy the sensitivity of the optical response by changing the profile shapes.Numerical calculations have been carried out for different profile functions.

"Permanent address: Institute de Flsica de la Uiiversidad Autohcnade Puebla.

7P:blO4

THE DYNAMIC CROSSOVER IN THE •< MODEL (d= l ) • AN EXAMPLE FOR AN^-SCENARIO OF MODE COUPLING THEORY?

S. FLACH, J. SIEWERT(Imtitut far Theoretische Phytik, Technische Universit&t Dresden)

I The dynamic crossover of the Id $4-model was numerically investigated by S. FLACH et. al.,f J. Phys. CM 3, 7061 (1991). The result* show a drwtical slowing down of relaxation time* at| finite temperature*. The temperature dependence of these relaxation times look* similar toi that of freezing processes near the glass transition, which can be described by an ^j-scenario] of the mode coupling theory (MCT). On the other hand, the increasing correlation length*• and the existence of nonanalyticities in the local susceptibility are feature* of a 2nd order, phase transition.• In order to study the applicability of MCT predictions near the glass transition the time

dependence of the displacement-displacement correlation function On(t) is calculated by useof molecular dynamics. The scaling properties of <7«(t) and GII(UI) are analysed in thecrossover region.

187

7P:blO5Bow CoMdeacAtioB for tke Wa-Autim Huntltoaiaa withoat pampiag

H. Boltenmer ami L. Lndwig

Institut fur Theoretische Physik, Justus-Liebig-Univenit&t Giessen, D-6300 Giessen, FUG

There seem to be general agreement that the Hamiltonian defined by Wu-Auatin1 de-scribe a microscopic model for the biological theory invented by Frohlich3. We considerthe eigenstates of the Wu-Austin Hamiltonian without coupling to the pumping system.We are able to show that for a high quantum number N the energy of the system mustbe proportional to —N3. This has dramatic effects for the system at a certain tem-perature. The thermaliaed Wu-Austin system shows Bose Condensation even withoutpumping. It is well known that the rate equations defined by Frohlich describe a totallydifferent behaviour. We therefore conclude that these rate equations cannot be foundedfrom Wu-Austins Hamiltonian.

1. T. M. Wu and S. Austin, Phys. Lett. 64A.151 (1977)

2. H. Frohlich, Phya. Lett. 36A, 402 (1968)

7P:blO6THE FUNCTIONAL FORMULATION OF THE STATISTICAL MECHANICS.

L.F.BLAZHIEVSKY, G.B.OILL, S.S.SEMAKState University, 12 Drahomanov Str., Lviv, Ukraine-290005

The functional formulation of the statistical meohanios that isbased on the modification of Feynmann path integration methodis suggested. The new representation of the matrix elements ofthe evolution operator and of the operators of physical quanti-ties by regularized path integrals in configuration spaoe havebeen found. The analogous representation have been found forthe Liouville equation Green function. The generalization ofobtained expressions to the case of imaginary time leads to theinitial relations of equilibrium quantum statistical meohaniosand permits one to get the path integrals for the equilibriumdensity matrix, the partition function and the partial distri-bution functions. In the suggested approach all relations areexpressed over the Lagrangian of the system that is essentialfor the constructing of postNewtonian statistical meohanios.

188

7P:blO7

FLUCTUATIONS IN A LEVY FLIGHT GAS

H.C. FOGEDBYt, T. BOHR*, and H.J. JENSEN*Institute of Physics', University of Aarhus8000 Aarhus C, DenmarkandNiels Bohr Institute* and NORDITA*Blegdamsvej 17, 2100 Copenhagen 0 , Denmark

ABSTRACT. We consider the density fluctuations of an ideal Brownian gas ofparticles performing Levy flights characterized by the index / . We find that thefluctuations scale as AN(t) ~ tB, where the Hurst exponent H locks onto the uni-versal value j for Levy flights with a finite root mean square range ( / > 2). For Levyflights with a finite mean range but infinite root mean square range (1 < / < 2) theHurst exponent H = £?. For infinite range Levy flights (/ < 1) the Hurst exponentlocks onto the value j . The corresponding power spectrum scales with an exponent1 + 227, independent of dimension.

7P:blO8

THE LONGITUDINAL RELAXATION FUNCTION OB' THE 1D IZING MODELIN TRANSVERSE FIELD

R.R.LEVTTSKII, S.I.SOROKOVInst.Cond.Matt.Phys.,14/16 Dragomanova Str., Lviv-5, Ukraine

For the 1D Izing model in transverse field

the longitudinal relaxation function^. {^A.) is approximatedby expressions that use two exaot moments ( )exact expansions of - (tf t ) wlth accuracy up to^f/fc)2 and^VC/r)2" . In the high-temperature case (T~*°°) numericalresults for suggested expression are closed to exact ones forall values of parameters f", l< in contrast to continiousfraction approximation method. This approach have been usedfor the description the quasi-one-dimensional ferroelectrics

189

7P:blO9THE INVESTIGATION OP CLUSTER EXPANSION'S CONVERGENCE FORTHE IZING MODEL

R.R.LEVITSKII, S.I.SOROKOV, O.R.BARANInst.Cond.Matt.Phys.,14/16 Dragomanova Str., Lviv-5, Ukraine

In the frames of previously proposed approach the effectof higher orders in cluster expansion for the free energy,the order parameter, the susceptibility and the correlationfunction is investigated in the case of the Izing model on Jthe gipercubic lattice (Z = 2,**,6) and two-site cluster.The convergence of the obtained results to well-known resultsof numerical method in wide interval of temperature is demon-strated. In the first cluster approximation model with S > V 2is studied also.

7P:bllOON THE KINETICS OP THE SYSTEM OP PARTICLES

WITH THE ELECTROMAGNETIC INTERACTION

L.F.BLAZHIEVSKY, G.B.GILLState University, 12 Drahomanov Str., Lviv, Ukraine-290005

The influence of many-particle electromagnetic interactions onthe dynamics and kinetics of charged particles systems is in- /vestigated. On the basis of field approach and BBGKI chain the '•Vlasov equation are derived for the case of weakly relativisticcharges as well as the generalization of Balesou-Lenard equa- ):tion which takes into account the contributions from Coulombic iand electromagnetic interactions both to dissipative and ncn- *dissipative characteristics. It is shown, that '.he long-range rigelectromagnetic interactions can lead to the screening of ex- -|ternal fields as well as pair and three-partiole interactions $which corresponds to the extension of Breit-Darwin model to thecase of medium presence.

190

7P:blll

Pseudohamiltonians for Quantum MontecarloAndrea Bosin (1.2) , Andrea Lastri (1) , Vincenzo Fiorentini (2,3) ,

Alessandra Continenza (4) and Giovanni B. Bachelet (1,5)

(I) University di Trento, Italy; 2) Universita' di Cagliari, Italy, (3) Universita' diTrieste, Italy; (4) Universita' dell'Aquila, Italy; (5) I Universita' di Roma, Italy.

Quantum Montecarlo simulations of condensed matter systems for atomic numbersZ > 20 can become feasible using pseudoatoms (valence-only). As conventionalnorm-conserving pseudopotentials (NCPP) are unsuitable due to non-locality,which is in conflict with key aspects of Green's function Montecarlo, a localpseudohamiltonian (PH) has been recently proposed as a substitute (Phys. Rev.Lett. 62, 2160 (1989)). We generated PH's within DFT for a number of atoms by asimulated annealing technique; they do perform very well in DFT calculations inatoms, molecules, and solids. In the latter case the results are quite accurate, butpartially at variance with those obtained by NCPP (confirmed by all-electronFLAPW). This is in contrast with the comparable or better performance of PH's ascompared to NCPP in a number of transferability tests; the puzzle is partiallyresolved by a Wigner sphere test which shows a slight superiority of NCPP on PHs.

7P:bll2CHARGE FLUCTUATIONS IN DOPED MOTT INSULATOR

CYROT Michel

Laboratoire de Magneusme Louis Nfel, CNRS, BP166,38042 Grenoble Cedex 9, Fiance

Following Mott's original idea, we show that with neither Hubbafd's approach nor Gutzwiller's can on describe

in a satisfactory way the doped Mou insulator. This stems form the fact chat one need a finite critical doping in

order to delocalize the bound electrons of a Mott insulator. As a consequence excitonic lilce and itineiant

excitations coexist in a certain range of doping. We show that this could be the situation needed for the excitonic

mechanism for superconductivity. We discuss possible signature of such an effect.

191

7P:bll3LIGHT SCATTERING NEAR PHASE TRANSITIONS IN BCCD : A PERTURBATIVE APPROACH

H. Poulet and R.M. Pick, Departement de Recherches Physiques, URA 0071.University Pierre et Marie Curie, 4 Place Jussieu. 75252 PARIS CEDEX 05,France

BCCD, which cristallizes at high temperature in the Pnma structureundergoes, between T. = 163 K and T_ z 43 X, a series of phase transitionscharacterized by a wave vector q = S(T)c* and an order parameter having thesane symmetry in all phases. 6(T) decreases monotonously with temperature,BCCD exhibiting an incomplete harmless staircase behaviour, with a seriesof incommensurate and partial lock-in phases. The lock-in phases are

"idescribed by &y « —, and have different symmetries depending on the parity

of n1 and P,. It has been suggested that the change of size and symmetry ofthe lock-in cells explains the reported jump in frequencies measured byRaman Scattering at the various transitions. On the basis of a perturbativeapproach, we shall argue that the detection of an important evolution ofthe Raman spectra at such a lock-in transitions is very unlikely, the "new"modes which could appear at these transitions being presumably too weak tobe detected.

7P:bll4

Two-Arid relathrfctk msdel for mpercoBdactan.

I.B.Boaljrj«rimr

Moscow Pkfrinl Society, Lenitukf pro$. S3, FIAN. SU-H79H JMMOPV, Runt

192

7P:bll5TUNNELING TIME MEASUREMENTS BY MICROWAVE MODEL

P. FABENI, D. MUGNAI, G.P. PAZZI, A. RANFAGNIIstituto di Ricerca sulle Onde Elettromagnetiche del CNR, Firenze, Italy.

The problem of evaluating the tunneling time, that is the time spent bya system to tunnel through classically forbidden region, is still an openquestion and at least three theoretical models have been proposed.

In spite of the differences in the predictions, there are considerabledifficulties to do a direct experimental test because of the very short timeinvolved in this kind of processes.

Tunneling occurs also in optics in the visible region the magnitude ofthe tunneling time is of the order of picoseconds but a decisive increase ofthis time can be obtained by increasing the wavelength up to microwaves, aswe have done.

Delay time measurements and beat amplitude detection with a microwaveset-up, where a step-narrowing in the wavequide simulates a quantum mechan-ical potential barrier, have been performed even beyond the cut-off. Thisallows to do experimental measurement in the very accesible temporal rangeof the order of nanoseconds. The results, interpreted as tunneling times,are compared with the existing quantum mechanical models, translated intoelectromagnetic framework.

7P:bll6THERMODYNAMICS AND CORRELATION FUNCTIONS OF THEQUANTUM TODA LATTICE.

Alessandro Cuccoli, Mauro Spied, Volerio TognettiDipartimento di Fisica, Universita di Firenze. 1-50125 Firenze, Italy.

Ruggero VaiaIstituto di Elettronica Quantistica C.N.R., 1-50127 Firenze, Italy.

The Toda lattice is a ^ne-dimensional lattice with neaiest neighbour exponential inter-action. The model is exactly integrable both in the classical and quantum case, and ithas been widely investigated in the last years. We present here the results given by theapplication to this model of a method which allows to reduce the evaluation of quantumstatistical averages to the calculation of classical configurational integrals1'2. Such goalis obtained by defining suitable renormalization parameters which describes the effectsof the quantum fluctuations, and by means of which an effective potential, having thesame form of the original one, can be written. At the last stage of our calculation apowerful method to evaluate classical statistical averages for a chain of nearest neighborinteracting atoms has been applied, so that significative results have been obtained veryeasily. The quantum specific heat in all range of temperature has been evaluated, re-producing the results of the much more cumbersome Bethe-Ansatz approach. Moreoverwe have been able to evaluate also the quantum correlation function, and the relativecorrelation length, of the interparticle distance fluctuations,1 R. Giachetti, V. Tognetti, Phys. Rev. Lett. 55, 912 (19S5) and Phys. Rev. B 33,7647(1986)2 A. Cuccoli, V. Tognetti and R. Vaia, Phys. Rev. A 44, 2734 (1991)

193

7P:bll7

BROWNIAN MOTION IN PERIODIC SYSTEMS

R. FERRANDO, R.SPADACINI and G.E.TOMMEIDipartimento it Fisica and CFSBT/CNR, via Dodecaneso SS, 16146 Genova, Italy

The classical diffusion in periodic systems is studied solving the position and velocitydependent Fokker-Planck equation (FPE)in an external field offeree. The dynamic structurefactor and all the relevant correlation functions are calculated by the matrix continued fractionmethod. The dynamics is characterized by three different time scales: the velocity relaxationtime, the oscillation period in the potential well and the time of flight between nearestneighbour sites. The relationship between these time scales is determined by the frictionand the potential amplitude. While, at high friction liquid-like and single-jump diffusionare obtained, at low friction also multiple jumps are possible. Moreover, in both cases, theFPE describes an intermediate behaviour between liquid-like and jump diffusion. In thehopping regime the distribution of the jumps and the escape rate from the potential wellare calculated, solving exactly the Kramers problem in a periodic system. Applications tohigh-temperature atom diffusion at crystal surfaces are discussed.

7P:bll8FREE RELAXATION INDUCED BY COLORED NOISE: ANALYTICAL.NON PERTURBATIVE RESULTS FOR MULTILEVEL SYSTEMS

L.Andreozzi,C.Donati,M.Giordano,D.LeporiniDipartimento di Fisica, Piazza Torricelli 2. 1-56100 PISA ITALY

In the last few years the relaxation of quantum systems induced bystochastic external perturbations attracted renewed attention. For thecase of a particle with S = 1/2 in a static magnetic field Ho the long-time behaviour is often described in terms of a single exponential. Thistwo-level system ( TLS ) has been extensively investigated in the case ofcolored noises acting trasversely with respect to the direction of Ho. Byresorting to the memory-function formalism, we extend the analysisfirst by generalizing the TLS model and then facing the case ofmultilevel systems. The relaxation of relevant observables induced bycolored noise is expressed analytically in terms of continued fractionsand their asymptotic behaviour studied. In the case of well-spacedmultiplets and noises of small amplitude ( with respect to multipletspacing ) it turns out that the long-time behaviour of the populations isexponential with single decay-time. We derive simple, analyticalexpressions of the decay time In terms of the spectral densities of thenoise.

194

7P:bll9DEVELOPMENT OF BASINS OF DUFFINGS OSCILLATOR

R. K. RATYHelsinki University of Technology, 02150 Espoo, Finland

The motion of Duffings oscillator x + QAx + x- 4x* = 0.115cos(<0t) is studied. When COis decreased the oscillator exhibits symmetry breaking, bifurcations, chaos, periodic win-dows and symmetry returning crisis. The development of the basin structure of the attrac-tors in these phases is studied. The role of the homoclinic tangle1 in the Poincare' map isconsidered.

1. F.C. Moon and G.-X. Li, Phys. Rev. Lett 55 (1985) 1439.

7P:bl20RENORMALIZATION GROUP APPROACH AT GENERAL DIMENSIONS.

THREE LOOP APPROXIMATION.

i Yu.HOLOVATCH-• v

^ Institute for Condensed Matter Physics, 14/16 Drahomanov St.,'\\ LVIY-5, 290005, UKRAINE

In order to investigate the critical behaviour of different mc-dels at general space dimensionality d we use the standard, pro-cedux-e of renormalization of one-particle irreducible vertexfunctions at zero external momenta and nonzero mass. The appro-priate Callan-Symanzik equation is treated directly for arbit-rary nonlnteger .fixed & . Corresponding loop integrals are ob-tainert numerically1". The values of critical exponents are esti-mated with the use of Pade-Borel resummation method.1 .Holovatch Yu. .Shpot M., .T.Stat.Phys.66(1932)8472.Hoio7atch Yu. .Krolthmalskii T., Preprint. IOMP-92 (in press)

* *i

195

7P:bl21

OPTICAL PROPERTIES OF SOLIDS AND SPATIALLY NON-LOCALPOTENTIALS

E. PIPARO, R. GIRLANDAIstituto di Struttura della Materia, Facolta di Scienze m.f.n.Universita di Messina, salita Sperone 31, C.P. 571-98166 Sant'Agata - Messina, Italy

The theory of the RPA optical response of a crystalline solid is generalized toconsider the spatial non-locality in the potential. New expressions for first andsecond order susceptibilities are given. Since the "usual" theory gives wrongresults for the second harmonic generation fn a two-band semiconductor onemust use the general theory when the space of basis function is truncated. Thetheory is extended to surfaces and interfaces exploiting the supercellapproximation. Using a generalization of the dipole approximation, first andsecond order in the external field z-dependent densities of polarization areexpressed in terms of "effective" z-dependent susceptibilities.

7P:bl22

MONTE CARLO CALCULATION OF THE GREEN'S FUNCTION OFHETEROGENEOUS MATERIALS.

J.P. Bouchaud. P.G. Zerah

Commissariat a l'dneigie atomique. B.P. 27, 94190 VHleneuve S'Georges. France

We use the Green's function Monte Carlo (GFMC) introduced by Kalos in the contextof the solution of the Schrodinger equation, to devise a method of calculation ofeffective properties of heterogenous materials (as e.g. electrical or thermal conductivityetc.). In essence, we can construct the Green's function as the superposition of localGreen's functions, which, due to the heterogeneous nature of the material can becomputed on large parts of the material. It therefore allows for large steps in therandom walk, and is then very efficient. (See the broken line for a typical path)

The link with the more usual first passagetime technique is established, and resultsrelative to various configurations are given.

196

7P:bl23X-RAY DIFFRACTION SPECTRA OF DETERMINISTIC NON-PERIODIC

STRUCTURES: DYNAMICAL VS KINEMATICAL THEORY

G. C. LA ROCCA • * , L. TAPFER «••>, R. CINGOLANI «»*, K. PLOOG •»a) Scuola Noimale Superiore, 56100 Pisa, Italy b) Max-Planck-Institutfuer Festkoerperforschung, 7000 Stuttgart 80, Germany c) CentraNazionale Ricerca e Sviluppo Material!, 72023 Mesagne (Br), Italyd) Dip. Scienza dei Material!, University' di Lecce, 73100 Lecce, Italy

Layered systems, e.g. semiconductor superlattices, with a deterministicnon-periodic structure exhibit characteristic lenghts at all scales,therefore their properties are especially interesting in the infinite limit.X-ray diffraction spectra of such systems are usually analysed in termsof their Fourier transforms, i.e. within the kinematical theory ofscattering. The diffraction pattern of an infinite lattice, though, isrigorously described only by the dynamical theory of scattering which,in particular, takes multiple reflections and extinction into account. Asan example, the diffraction pattern of the Thue-Morse lattice is studiedtheoretically in the infinite limit. The results of high resolution X-raydiffraction measurements on a GaAs-AlAs Thue-Morse superlattice arepresented and analysed. Photoluminescence and photoluminescenceexcitation spectra of the same structure are also discussed.

7P:bl24CORREL - A PROGRAM FOR REPRESENTATION CORRELATIONS OFGR0UP-SUB6R0UP RELATED SPACE GROUPS

N.DJOURELOV, M.AROYOCondensed-Matter Phys.Dept., Faculty of Physic*,University of Sofia, bul. A.Ivanov S, 1126-Sofia, Bulgaria

A computer program CORREL, for the calculation of correlationsbetween irreducible representations of a space group A andthose of its arbitrary maximal subgroup B is developed. CORRELcomputes the correlations into two steps! (i) determination ofk-vector correlations for the group-subgroup chain A > B; (ii)calculation of the corresponding subduction coefficents and ;subduction matrices. The program KAREP1 for calculation of 'space group representations is used as a building unit. CORREL 'is written on Pascal version S.O. The program is running under |MS-DOS 3.10 and higher on a number of PC's which should be at ,least AT-compatible with RAM 640KB. The program needs at jexecution time an ASCII data file containing the matrices of >the space group generators for the group, its maximal subgroupand the k-vector coefficients under consideration.

1. E. Hovestreydt et. al. Z. Kristallogr.,vol. 140, p.137(1989)

197

7P:bl25

SPECTRAL SHAPE OF QUANTUM CHAINS.A. Cuecoli ", A.A. Maradudin *>', A.R. Me Gum e>d, V. Togneiti ' and R. Vaia *

* Dipartimento di Fisica, Universita di Firenze, 1-50125 Firenze, Italy.* Department of Physics, University of California, Irvine, CA 92717 U.S.A.c Department of Physics, Western Michigan University, Kalamazoo, MI 49008 U.S.A.d Project on Condensed Matter Theory "Forum" of Consorzio INFM - Italy.e Istituto di Elettronica Quantistica C.N.R., 1-50127 Firenze, Italy.

The first four even moments of the displacement quantum correlation function for achain of atoms interacting through a Lennard-Jones po;ential are presented. They havebeen obtained both by a Quantum Monte Carlo simulation and by using an effectivepotential derived by a variational approach to the path integral formulation of thestatistical mechanics. The last method allows to reduce the computation of quantumaverages of time-independent functions to classical-likc phase space integrals, to whichall the took developed for classical calculations can be applied. The effective potentialreveals to be especially suitable to describe at best the behaviour at any temperatureof non-linear system, like quantum solids, whose low energy excitations have a quasi-harmonic character, but whose thermodynamic properties, at the same time, show cleareffects of non-linearities. The agreement between the results of the two independentcalculations is excellent. Moreover, the strong simplification in the evaluation of quan-tum averages introduced by the variational method opens the possibility to reconstructthe dynamical behavior of the system from the knowledge of a sufficient number ofmoments, and some examples are given for the spectral shape of the Lennard-Joneschain.

7P:bl26

MAPPING OF CRYSTAL GROWTH ONTO THE 6-VERTEXMODEL: GROWTH MODE AND SURFACE ROUGHNESS

MIROSLAV KOTRLA and ANDREA C. LEVI

Dipartimento di Fitica dett'Univenita, 16146 Qenova, Italy

Crystal growth is mapped onto the 6-vertex model of statistical me-chanics. Master equations are written for finite-size versions of themodel, and solved either analytically (for extremely small sizes), or byMonte Carlo simulation, using Glauber's rules for the probabilities ofthe various processes relevant for growth, evaporation and diffusion.The model depends explicitly on temperature T and supersaturationA/z: as a function of these parameters, both the growth mode and thesurface structure change. The surface is rough at all temperatures.At high temperatures, however, the roughness is logarithmic if A/z issmall, but a cross over takes'place to a power-law behaviour when A/zincreases.

198

7P:bl27

DISORDERED PEIERLS CHAINS

J. MERTSCHINGMax-Planck-Arbeitsgruppe Humboldt-Universitat BerlinHausvogteiplatz 5-7, O-1086 Berlin, PRG

The electron density of states of weakly disordered tight-binding Peierls chains is cal-culated. For diagonal disorder, the Peierls gap edges are smeared, and the gap disap-pears. For off-diagonal disorder, a pseudogap occurs for large gap parameters, whereasthe gap vanishes, and the density of states diverges for small gap parameters. Theseresults are similar to those obtained from the continuum approximation which, however,is not strictly justified for short-ranged disorder potentials.

7P:bl28ELECTRONIC STATES OF ALMOST PERIODIC DISCRETESCHRODINGER EQUATIONS.

R.Farchioni**, G.Grosso* and G.Pastori Parravicini**(•) Dipartimento di Fisica, GNSM-INFM, Piazza Torricelli 2, S6100Pisa, Italy(•*) Dipartimento di Fisica, GNSM-INFM, via Bassi 6, 27100 Pavia,Italy

We present a careful study of the electronic states of onedimensional incommensurate systems by an implementation ofthe renormalization procedure.The general expression for theevaluation of the Lyapunov exponent here proposed, is a usefultool for the characterization of the electronic spectrum. Inparticular we focus on the role of self dual symmetry of thealmost periodic tight binding hamiltonian, for the determination ofthe Lyapunov exponent, also when this symmetry is reached inthermodynamic limit.

199

7P:bl29

SQUEEZING TRANSFORMATION FOR POLARITONS

Z. HRADIL a A. QUATTROPANIb and P. SCHWENDIMANN c

a. Laboratory of Quantum Optics, Palacky University, 77146 Olomonc,Czechoslovakiab. Institut de Physique Theorique, Ecole Polytechnique Fed6rale, PHB Ecublens,1015 Lausanne, Switzerlandc Defense Technology and Procurement Group, System Analysis Division,3000 Bern 25, Switzerland

The unitary transformation1 relating free exdton and photon states to polaritonsis constructed. This transformation allows to calculate the exciton and photoncomponents of any polariton states. The statistical properties of polariton statesare derived in this framework and are shown to be non-classical. Suggestions foran experimental observation of these properties are given. In order to describethe absorption process the time evolution of coherent photon states is discussed.

1. A. Quattropani, L. C. Andreani and F. Bassani, Nuovo Cimento D 7,55 (1986)

7P:bl30ELECTRONIC PROPERTIES OF KINKS AT THE ORDER-DISORDER-LIKEPEIERLS INSTABILITY

E. V. KholopovInstitute of Inorganic Chemistry, 630090 Novosibirsk, USSR

Domain walls are typical for one-dimensional systems sufferingdoubling of the period. Different unusual properties can beassociated with domain walls. Here we discuss a conductingsystem with the order-disorder-like Peierls instability, wherethe consideration based on exact solutions is accomplished.The tight-binding approximation is used. The situation orig-inated by a single domain wall is relevant to the limit of lowtemperatures. The additional electron states of differentnature are predicted there. The state at the Fermi level in-side the Peierls gap merely corresponds to the fact that theelectron states on both the sides of the kink are not co-herent. Furthermore, there are two other states connected withthe domain wall itself and localized outside the regular spec-trum. The density of states and the electron contribution tothe domain wall energy are obtained. The total number ofstates is naturally conserved. The case of two touching domainwalls is also instructive. In this event each Peierls subbandis surrounded by a pair of additional states separated on theenergy scale. The" appropriate density of states and the entireenergy of this configuration are derived and discussed too.

200

7P:bl31^NORMALIZATION OF LAUGHLIN'S INCOMPRESSIBLE QUANTUM LIQUID

U. BROCKSTIEGER and G. MEISSNERTheoretische Physik, Universitat Saarbriicken, Germany

The ground-state energy and the collective excitations arecalculated for interacting electrons fully polarized ina perpendicular magnetic field with partial filling of thelowest Landau level. The projected density-response insingle-mode approximation evaluated with Laughlin'svariationai ground-state wave function is renormalized viaan approximate effective interaction of magnetorotons beingdetermined by static four-point correlations. Results forthe renormalized ground-state energy and the magneto-rotondispersion are compared with previous calculations atrational filling factors v = 1/k for k = 3,5,7.

201

7P:c201

THE PHYSICS OF SiGe HETEROJUNCTION BIPOLAR TRANSISTORS:A MONTE CARLO STUDY OF THE QUEST FOR ENHANCED SPEED

D T Hughes, R A Abram and R W Kelsall,Department of Physics, University of Durham, Durham, DH1 3LE, UK

Heterojunction bipolar transistors with a Si emitter and collector and a SiGe base have beendemonstrated to be fast as well as compatible with silicon technology. An important factorin enhancing the speed of the device is the use of band structure engineering in the base. Thetransit time of electrons across the thin (< 0.05 fun) base is reduced by the effects of strainand can be reduced further by grading the alloy composition. The transport of elecrons in thecollector can also be influenced by a region of p-type doping or by the mobile space chargecreated at high current levels as well as hot carrier effects.

In this paper we study the dynamics of carriers in the base-collector region of the transistorusing Monte Carlo simulation, and show that the technique is capable of providing aquantitative description of all the phenomena introduced above. In particular it is shown thatin a device with an ungraded base the base transit time decreases significantly as the Gecontent is increased from 0 to 13% but remains essentially unchanged after a further increaseto 30%. The decrease in base transit time resulting from alloy composition grading isillustrated for a typical device by deducing the optimum grading profile and showing that itprovides a fivefold reduction in transit time relative to the ungraded case.

7P:c202DIPOLE EFFECTS AT SEMICONDUCTOR INTERFACES. TOWARDS ABAND-OFFSET ENGINEERING

A. MUJICA.P. RODRIGUEZ-HERNANDEZ and A. MUNOZDepartamento de Fisica Fundamental y Experimental, Vniversidad de La Laguna, E-38204La Laguna (Tenerife) - Spain.

It is known that band-offsets can be modified at semiconductor heterojunctions andhomojunctions by deposition of thin intralayers of any group IV or III-V atoms*1'2'. Wepresent a theoretical analysis of different semiconductor heteroj unctions in polar and nonpolar directions. We use state of the art Ab Initio Selfconsistent Pseudopotencial studiesand Selfconsistent Tight-Binding calculations. Our results show that the band offset issensitive to the intralayer size. Comparison with recent experimental results supports ourideas about the role of the interface dipole. We also present a study from the thin to thethick limit coverage, showing that essentially at 3 monolayer the band offset modificationsaturate.

We acknowledge to the Consejeria de Education del Gobierno Autonomo de Canariasfor partial finantial support.

1 A. Munoz, N. Chetty and R.M. Martin, Phys. Rev. B 41,2976 (1989); P. Rodriguez-Hernandez and A. Munoz, Phys. Rev. B, in press.

2 L. Sorba et al, Phys. Rev B 43, 2450 (1991).

202

7P:c203

STRONG CHANGES OF THE ABSORPTION AND REFRACTIVEINDEX IN N-I-P-I HETERO STRUCTURES BY BANDFILLING

S. Malzer. P. Kit-scl. M. Kneissl. and ( i .H. Doliler

Inslilnl fi'ir T'rlinisrlii Pliiisit: I'mi t isitiit Frlaiijim Siinib'iy. Km in Riwuntl Sir. I. 11' 83.20 Erluti-

.' !;. (it i lluintj

i\.EI. (Iiilden. S. Smith. X.X. Wu. and J. Whimieiy

I'limmtjl nf Cuhfnrnia til Buhlii/. C'A 947 JO. f'.S'.-l

Wo report on haudfilling effects in Typ-I-Ilctoro - ii-i-p-i structures, (i.e. UaAs quantum wells in-lerspersed in the u doped region of a periodically n and p-doped Alott'OmAs crystal). The spatialseparation ofthe elections and holes in this kind of structures is responsible for a reduced recombinationrate and strongly iiirrvratil carrier lifetimes. As a consequence, charge carrier induced changes of theabsorption coefficient and refractive index occur at very low optical power.

To achieve a wide I lining range for the 2D sheet concentration, the sample was grown by the shadowmask liclmiqiii'. which allows the simple in situ fabrication of selective contacts for the application ofan external volla^< . The 2U shed concentration in the u channels is dominated by electrons, as theoptically ^inflated holes escape into the p layers. Depending on the applied voltage, the optical powerand the ..adjustable lifetime", we are able 1o tune the election concentration and shift the Fermi leveln\ei a wide range uf energies. The large baudfilliug induced changes of the absorption coefficient andrefractive index as deduced from transmission and reflection measurements are in good agreement withour theoielical predictions.

7P:c204

NARROW -BANDGAP TYPE I I MISALIGNED HEPEROJUNCTIONS

BASED ON InGaAsSb SOLID SOLUTIONS

M.P.Mikhailova, A.N.Baranov, V.V.SherstnevA.F.Ioffe Physico-Technical Ins t i tu te ,194021 St Petersburg

We present f i r s t r e s u l t s i n geowing and studying narrow-bandgap hcterojunct ions based on Injia,, Jis Sb^ .V GaSb s o l i d s o -l u t i o n s with, a composition near^to ^ J r A s ^(x 0.80,y 0 .70,E = 0.26 eV at T=300 K).Unusual asymmetrical e l e c t r i c a l and

^ h c t c e l e c t r i c a l p roper t i e s of the heterojjunctions as well asenergy band diagrams are discussed.The Ohmic behaviour of P -GaSb-n-InGaAsSb s t ruc tu re and diode- l ike c h a r a c t e r i s t i c s ofN-p, N-n and P-p junctions have been observed i n the tempera- )ture region from 4.2 K up to 300 K.The quasiclassical approxi- Imation was used for evaluation of the quantum well parameters |and double layer ones in the vicinity of N-n heteroboundary. 4I t was foundthat InGaAsSb heterojunctions are type II ,,misaligned. Novel type of the photodiode based on InGaAsSb 'Istructure is proposed which can operate in the 1.6-4.7 um *spectral range. ;

203

7P:c205

INVESTIGATION OF BAND OFFSET TRANSITIVITY IN GalnAs-InP, GalnAs-AlInAs andAlInAs-InP HETEROSTRUCTURES

E. LUGAGNE-DELPON, P. VOISIN, M. VOOSLaboratoire de Physique de la Matiere Condensed de TENS, 24 rue Lhomond, F-75005 Paris

J.P. ANDRELaboratoire d'Electronique Philips, 22 Av. Descartes, F-94453 Limeil-Bre'vannes Cedex

Transitivity and commutativity of band offsets at abrupt hetero-intcrfaces are predicted by avariety of theoretical models, and have also been found empirically in ab-inMo calculations.However, there exists essentially no experimental proof up to now. We have addressed thistransitivity problem by a study of luminescence excitation spectra in GalnAs-InP, GalnAs-AlInAs and AlInAs-InP double-step quantum wells. We find that actual measurements of theconduction band offsets deviate significantly from the offset transitivity rule. In addition, thereexist large qualitative differences in the optical properties of reversed InP-AlInAs and AlInAs-InP single heterojunctions, which suggests that band offsets are not commutative either in asystem with no common anion.

7P:c206Potential fluctuations and broadening of the density of

states in doping superlattices

M. Renn, C. Metzner and 6. DoiilerInst. for Technical Physics, Uni. Erlangen-NUrnberg, Germany

A realistic discription of the luminescence from dopingsuperlattices has to take into account not only the averagedHartree-Potential of the impurity atoms, but also the fluc-tuating part of the screened coulomb-potentials. The resul-ting tails of the density of states are calculated with amodified Kane model. The luminescence spectra are calculatedfor a wide range of excitation levels and compared withexperimental results. One gets a very good qualitativeagreement, although no fitting parameter has been used. As aconsequence of this finding it is now conceivable, why it hasnot been possible to observe signature of the subband-structure in the luminescence spectra of doping superlatticeswith uniformly doped layers.

204

7P:c207EVOLUTION OF AMiriHILATIOM OF ANTIPHASE BOUNDARIES

S.I.MOLINA, G.ARAGON and R.GARCIADepartamento de Qulmica Inorganica, Universidad de Cadiz, Apdo.4011510 Puerto Real (Cadiz), Spain

Some models for explaining the evolution of the process ofannihilation of antiphase boundaries have been proposed. HighResolution Electron Microscopy (HREM) images are utilized toinvastigate the form in which the antiphase boundaries areclosed. The systems studied to elaborate our model are MBE andALMBE grown GaAs/Si heterostructures. The results obtained byHREM are correlated with another previously obtained byReflectance Difference (RD). The limit form proposed for theclosed antiphase boundaries consists in a cylindrical orprismatic form with curved corners and a square base (antiphaseboundaries running along {110} planes); the structure of closurehas an approximately semispheric form.

7P:c208

SELF-LIMITING MONOLAYER EPITAXY OF II-VIHETEROSTRUCTURES

W.Faschingerx, PJuza* and H.Sitter*"Institut fUr Halbleiterphysik, University of Linz, Austria*Inst. fUr Experimentalphysik, Univ. of Linz, Austria

Wide gap II-VI heterostructures containing S or Se are currently a topic of major inter-est for blue laser applications. In order to obtain high quality heterostructures with welldefined thickness and abrupt interfaces an UHV growth method with precise thicknesscontrol in a monolayer scale is desirable. This technological challenge motivated us todevelop a new technique, which we call Self-limiting Monolayer Epitaxy (SME). Itmakes use of a self regulating growth mechanism, as achieved in Atomic Layer Epitaxy(ALE), but avoids the occurence of fractional monolayer growth, which seems to limitthe possibilities of ALE.SME is achieved by offering the more volatile constituents S or Se permanently, whilethe group II constituents Cd or Zn are offered in a pulsed mode. In analogy to ALE wecall the growth time from one group II evaporation pulse to another a cycle. SinceX-ray diffraction of superlattices is the most accurate method to measure the growthrate per cycle, short period superlattices of ZnS/ZnSi-xTex and ZnSe/CdSe were grownat various beam fluxes and substrate temperatures. The X-ray results show that growthin discrete compound monolayer steps can be easily achieved by SME: The growth rateper cycle for all superlattices is an integer number of monolayers of the compound. It isexactly one monolayer per cycle as long as the amount of material offered within onecycle is kept between one and two monolayers, but increases to exactly n monolayers percycle (n being an integer) if the offered material within one cycle is kept between n andn+1 monolayers. We discuss a growth mechanism explaining these results.

205

7P:c209STUDY BY XTKM OF AlGaAs/GaAs MQH ON MOK-PLAMAR SUBSTRATES

G.ARAGON, S.I.MOLINA, P.S.DOMINGUEZ*, M.J.de CASTRO and R.GARCIADepartamento de Quimica Inorganica, Universidad de Cadiz, Apdo.4011510 Puerto Real (Cadiz), Spain.*Centro Nacional de Microelectronica, Serrano 144, 28006 Madrid,Spain.

We report Transmission Electron Microscopy (TEM) studies ofpatterned AlGaAs/SaAs multiguantum well heterostructure grown byMolecular Beam Epitaxy (MBE) and Atomic Layer Molecular BeamEpitaxy (ALMBE) on periodically corrugated GaAs substrates inorder to elucidate the influence of technology (type of maskused, periodicity and orientation of the groove/ridge array, etchsystem employed, and so on) and growth techniques (MBE and ALMBE)on the formation and propagation of defects along the epitaxy.

Gratings fabricated by holographic lithography on (001) GaAswafers have been used as growth substrate. Carbon contaminationfrom the resist, not comple ely removed during the cleaningprocess, could provoke the formation of planar defects in theepitaxy. This difficulty may be appropiately faced by replacing

.. the etch system. The density of planar defects is greater in thesamples grown by ALMBE, whereas the morphology of the patterned

• multiguantum well is somehow preferable.

[ 7P:c210: VELOCITY DISTRIBUTION FUNCTION AND ELECTRON FREE PATH IN

PERIODICALLY MODULATED AlGaAs/GaAs-HETEROSTRUCTURES

C.Wirner, E.Gornik, CKiener, G.Zandler, P.Vogl, G.Bohm, G.WeimannWalter-Schottky-Institut, TU Munchen, Am Coulombwall, D-8046 Garching,Germany

We have investigated the FIR radiation emitted from hot electrons in highmobility GaAs/AlGaAs heterostructures with a holographically induced weaklateral periodic potential modulation perpendicular as well as parallel to thecurrent direction. This Smith-Purcell type1 emission spectrum directly reflectsthe undrifted and the drifted part of the electron velocity distribution function.

' We present experimental results of the electric field- and electron concentrationdependent cuts of the distribution function and compare it with a drifted hot

> fermi- as well as an exact distribution function calculated using the boltzmanni transport equation. In addition the energy dependent free path of the electronsi; could be directly derived for the first time. The electric field dependence of the| free path and the drop at the LO-phonon energy are clearly observed.

| IE. Gornik et al., Solid state electronics 2L (3/4), 751,1988

f-0 206

7P:c211

INFLUENCE OF Cd AND Hg INTERDIFFUSION ON THE DISLOCATIONFORMATION IN 1SOVPE HgCdTe/CdTe EPILAYERS

C. FRIGERI, R. GLEICHMANN*. G. ATTOLJNI, C. PELOSI and C. A. GALEAZZICNR-MASPEC Institute, via Chiavari 18/A, 43100 PARMA (Italy)*Institut f. Festkoerperphysik u. Elektronmikroskopie, Weinberg 2,4010 HALLE (Germany)

The formation mechanisms of dislocations in HgxCd!_xTe layers, grown by ISOVPE(Isothermal VPE) and to be used as IR radiation detectors, has been studied by TEM. TheHgjCd^Te layers were grown on (111) CdTe substrates at temperatures of 500 and 515 °C.Either a HgCdTe or a HgTe source was used. In the latter case Cd was expected to be fed tothe growing HgCdTe layer by diffusion from the substrate. The intended x was 0.80. EDXmicroanalysis in a SEM on cleaved specimens showed that the layer Hg concentrationdecreases close to the interface by diffusion into the substrate. Cd was found to diffuse outfrom the substrate into the layer. TEM observations on plan view specimens showed theexistence of a hexagonal network of misfit dislocations. Observations on cross sectionspecimens confirmed such result and additionally showed that the dislocations are located onplanes parallel to the interface to the substrate and spaced by ~ 0.2 p.m. The dislocation densitydecreased significantly towards the top of the layers and was very small for layer thicknessexceeding - 5 - 6 |im. Dislocations with a similar layered arrangement were also detected in thesubstrate down to a distance of -1.2 |im from the interface. Such results suggest that thedislocations in the HgCdTe layers were not due to propagation/multiplication of dislocationsfrom the substrate (although this phenomenon cannot be ruled out completely) but rather tomisfit stress related to the formation of concentration gradients because of the interdiffusion ofHg and Cd across the interface. Such a diffusion also set up concentration gradients in thesubstrate which could have been the origin of the layered dislocation array observed therein.

7P:c212DISORDER EFFECTS ON OPTICAL PHONONS IN GaAIAs

FROM RAMAN SCATTERING IN BULK AND SUPERLATTICE ALLOYS

B.JUSSERAND, L.G.QUAGLIANO' and F.MOLLOT

Groupement Scientifique CNET-CNRS, Laboratoire de Bagneux,196 Avenue Henri Raver a, 92220 BAGNEUX, FRANCE

We demonstrate that including alloys in superlattices allows to greatly increase the experimentalinformation on phonons in disordered compounds, which was limited up to recently to zone centerproperties. We present Raman scattering results on GaAIAs/AIAs and GaAs/GaAIAs structures, whichgive access to finite wavevector and imaginary wavector properties respectively, and compare them withCPA predictions including mass disorder only. The overall agreement is quite good and CPA appearsto very well describe most of the optical phonon properties in this alloy: flattening of the GaAs-typedispersion curve with increasing concentration of Al, very large damping of phonons In the energy gapbetween GaAs-type and AlAs-type optical branches. We finally show that Raman spectra associated tothe minority atom (Ga in Al-rich GaAIAs) however cannot be well reproduced in the same theoreticalscheme.

* permanent adress: Istituto MAI del CNR, Roma, Italy

207

7P:c213

IMPACT IONISATION IN THE AlAaAs LAYER OFAaAs/AlAaAs HETEROJUNCTIONS

P J . van Hall and E.A.E. ZwaaiUniversity of Technology, Eindhoven, The Netherlands

In various experiments the existence of current instabilities in AaAs/AJAaAs heterojunc-tions has been demonstrated. Among these are avalanche-like phenomena. In a tentative •explanation these are attributed to the ionisation of deep donors is the AlAaAs layer. Tocorroborate this idea we have performed Monte-Carlo simulations in bulk AlAaAs icontaining deep donors. We indeed see the onset of ionisation at the same fields asobserved experimentally. Also die enhanced conductivity due to filament formation isreproduced quite well.

7P:c214

CONFINEMENT OF OPTICAL GaAs PHONONS BY THIN AlGaAs BAR-RIERS

C. Molteni, L. Colombo, L. MiglioDipartimento di Fisica, Universita di Milano, via Celoria 16, I-SOI S3 Milano, ItalyM. Bernasconi

International School for Advanced Studies, SISSA-ISAS, Strada Costiera 11, 1-34100

Trieste, Italy

In the present work we perform a thorough theoretical analysis of the confinement me-chanism of optical phonons in AlGaAs superlattices (SL's). By calculating the Ramanresponse in the framework of the bond polarizability model and the lattice dynamics bymeans of the bond charge model, we investigate the dependence upon the Al contentand the barrier thickness of the confined or extended character of GaAs optical phonons.The standard "quantization rule" for confined optical phonons and the concept itselfof confinement are then critically addressed. Moreover, we investigate if even ultrathinbarrier of AlGaAs (say, just one monolayer) can induce confinement of optical phonons .in thick GaAs slabs, once that the Al content of the alloy has been suitably fixed. The •;

results will be applied to investigate the possible tunability of the Raman response of iGaAs/AlAs SL's by inserting ultratbin intralayers. '

208

7P:c215

LATTICE PLANE TILTING IN InP/GaAs HETEROSYSTEMS: HINTSTO THE INITIAL GROWTH MECHANISM

F. RIESZ, Research Institute for Technical Physics of the HungarianAcademy of Sciences, P O Box 76, H-1325 Budapest, Hungary

K. LISCHKA, Forschungsinstitut fur Optoelektronik, University Linz, A-4040 Linz, Austria

K. RAKENNUS and T. HAKKARAINEN, Department of Physics,Tampere University of Technology, P O Box 527, SF-33101 Tampere,FinlandA. PESEK Inst. fur Experimsntalphysik, Univ. Linz, A-4040 Linz, Austria

The tilting of (400) lattice planes with respect to the (400) substratelattice planes was studied by x-ray diffraction in InP layers grown onvicinal (100) GaAs. For the growth temperature of 500°C, the relative tiltdirection was nearly coincident with the substrate lattice plane tiltingdirection. When a buffer layer was grown first at 400°C, an about 45°azimuthal rotation was found between the directions of the relative tiltand the substrate lattice plane tilting. In order to explain the results, atemperature-dependent anisotropic nucleation model is proposed: at lownucleation temperatures, the nucleation occurs at the substrate terraces,at high temperatures at the step edges, causing different misfitdislocation generation mechanisms.

7P:c216MAGNETO-TRANSPORT PROPERTIES OF AlGaAs/GaAs HETEROSTRUCTURES INPULSED FIELDS UP TO 50 TESLA.

I. Deckers, G. Pits! and F. HerlachLaboratoriuv voor Lage Temperaturen en Hoge-Veldenfysika, K.U.LeuvenCelestri jnenlaan 200D, 3001 Heverlee (Leuven), Belgiun

Transverse magnetoresistance and fractional quantum Hall effectmeasurements were carried out in the 400 nilliKelvin temperaturerange in magnetic fields up to 50 Tesla. For this purpose aspecially designed 3He-cryostat was developed and combined with a 21ma bore high pulsed field coil.

The measurements(x-0.3) Hall-bar

were performed as a high quality Al_Ga^.x/GaAssample (n - 3.5xl0n cm"2, n - 2x10* cm*/Vs).

Analysis of the obtained data shows a very pronounced change (2 25 X)of th« carrier concentration as a function of temperature after lowtemperature illumination by a red LED.Th« observed behavior is limited to a very narrow temperature region(- 100 «K). This is attributed to the predicted 400 mK zerofieldspin splitting.

209

7P:c217INTERFACE ELECTRON STATES IN STRAINED SEMICONDUCTORHETEROJUNCTION

V.G.KANTSER, N.M.MAUCOVAInstitute of Applied Physics, 277028, Kishinev, Moldova

The internal strains in multilayered semiconductor structuresgenerate polarization fields through the piezoelectric effect.The influence of the induced polarizations on the electronspeotrum of the strained heteroJunction is studied. Interfaceelectron states are shown to exist in suoh structures. Thesestates ocour due to the supersymmetry of two-band Hamiltonianwith the polarization effect included and exist only in adefinite energy and momentum intervals, whioh are determined bythe supersymmetry condition of the Hamiltonian. The energyspeotrum is essentially linear as a function of inplanemomentum.

7P:c218EXCITONIC TRANSITIONS IN (In,Ga)As-GaAs HETEROSTRUCTURES

UNDER IN-PLANE UNIAXIAL STRESS

J.A. BRUM*, P. HIERGEISr, G. ABSTREITER*, J.P. REITHMAIER ", AND H.RIECHERT"

• Walter Schottky Institut, TU-Munchen, D-8046 Garching, Germany** Siemens AG, Research Laboratories, Otto-Hahn-Ring 6, D-8000 Munchen

83, Germany

We study experimentally and theoretically the effects of an external in-plane-uniaxial stress (X//[100]) on the excitonic transitions in the (In,Ga)As-GaAs -system. The built-in stress split the heavy- and light-hole subbands. The light- jhole states are then nearly degenerated with the heavy-hole quantum-well *

, continuum. When we apply the external stress, three major effects are observed: ,f% the coupling among the heavy-hole and spin-orbit states induced by breaking theI quantum-well-axial symmetry, the formation of an exciton resonance at the

threshold of the heavy-hole barrier and the coupling of the fundamental light-hole exciton with the heavy-hole exciton continuum.

210

7P:c219

Subbands in Inversion Layers for Egap —> 0

B. BVeytag", U. Rossler", O. Pankratovb

a.) Inst. Theoret. Physik, Universitat Regensburg, D-8400 Regensburgb.) Fritz-Haber-Institut, D-1000 Berlin

Subband states in n-inversion layers on HgCdTe are resonances due to thecoupling to the bulk valence-band continuum. With decreasing gap energy -ihe willlli of the resonances increases. Thus the existence of subhand states atzero gap is questionable. We study the subband problem for MIS structures onnarrow-gap semiconductors starting from Kane's k-p Hamiltonian. The analy-tical approach with no specified surface potential shows, that for Egap = 0 thefree-electron term, which usually is neglected for narrow gap systems, becomescrucial, because it changes the order of the subband differential equation. Wealso solve the subband problem for an analytical surface potential and calcu-late the density of states. Our results demonstrate the existence of a subbandresonance even for vanishing energy gap provided the free electron term is notneglected.

7P:c220

SPATIO-TEMPORAL VOLTAGE OSCILLATIONS OF VERTICALTRANSPORT IN SEMICONDUCTOR HETEROSTRUCTURES

A. WACKER and E. SCHOLL(Inst. fur Theor. Physik, TU Berlin, Hardenbergstr.36, W-1000 Berlin 12, Germany) j

The heterostructure hot electron diode consists of a GaAs- and an AlGaAs-layer. Fora specific range of voltage applied across the hetrojunction, bistability between a tun- . •nelling state and a thermionic emission state associated with a S-shaped current-voltage ':characteristic is found[l]. •

Under current-controlled conditions we predict different inabilities on the middle i'branch of the characteristic. Our calculations show that besides selfsustained spatially jhomogeneous oscillations[2] and inhomogeneous stationary structures (current nlamenta- %tion) a new type of oscillations may occur where a filamentary current distribution forms I •and vanishes periodically. j! .[1] K. Hess, T.K. Higm&n, M.A. Emanuel and J.3. Coleman, J. AppJ. Phya. 60, 3775 (1986). |)[2] A. Wicker and E. SchoU, Appl. Phys. Lett. 59, 1702 (1991). ,

211

7P:c221

VALIDITY OF THE EFFECTIVE MASS APPROACH FOR GaAs/AlGaAsHETEROSTRUCTURES.

J.P. CUYPERS AND W. VAN HAERINGENEindhoven University of Technology, Department of Physics, P.O. Box 513,5600 MB, Eindhoven, The Netherlands.

With the use of the empirical pseudopotential method for the calculation ofelectronic wavefunctions in a GaAs/AlGaAs heterostructure, we haveinvestigated the validity of the effective mass approach for calculating electronicproperties of heterostructures.

The envelope function appears to be continuous at the interface. The firstderivative of the envelope function is approximately continuous (error s10%-20%), in contradiction with the often applied rule where the discontinuityof the first derivative is governed by the ratio of the effective masses. The fluxappears to be discontinuous at the interface in the effective mass approximation.This is due to inaccuracies of the effective mass approximation which maybecome as large as 20%. For a GaAs/AlAs/GaAs single barrier structure theeffective mass approach breaks down due to X-valley assisted resonanttunneling.

7P:c222

MAGNETOTRANSPORT IN DILUTE 5-LAYERS, ANGLE-TUNED METAL-INSULATOR TRANSITION.

Xiao-Mei FENG, J. J. MARES' and F. KOCH

Physik-Department E 16, TU-Munchen, 8046 Garching, Germany

* A. v. Humboldt Fellow, permanent address: Inst. of Phys., Czech. Acad. Sci., Cukrovar-

nicka 10, Prague 6.

We have investigated magnetoresistance and Hall effect of dilute 6-layers in MOVPEgrown InP in the concentration range near the metal-insulator transition. At liquid

.. helium temperatures we have observed strongly anisotropic magnetoresistance with' respect to the applied magnetic field B direction. For B parallel to the 6-layers the

magnetoresistance exhibits a variation which can be explained in terms of bopping in

f impurity band. On the other hand, for B perpendicular to the 6-layers metallic behaviour

I induced by Landau quantization was observed. This provides an interesting example ofI a metal-insulator transition tuned by the direction of the magnetic field and givesI information about the influence of magnetic field on the density of states in planar• doped structures.

I.

I 212

7P:c223

NONLINEAR (PH070-) CONDUCTIVITY EXPERIMENTS ON SINGLE PERIODPbTe NIPIs

M.Pippan, J. Oswald, B. Tranta

Institut fur Phystk, Montanuniversitat Leoben, Franz Josef Str. 18, A-8700 Leoben

PbTe has a long tradition as a basic material for the creation of nipi structures. Together

with selective In-contacts, even single period nipi's (pnp-structures) offer interesting

new properties. Due to the sensitivity of the built in potential on excess carriers, both a

feedback of photogenerated carriers on the potential modulation and an influence of

an externally forced lateral voltage drop on the carrier density occurs, which in turn

determines the voltage profile V(x) in the electron channel.

A theoretical model including both kinds of feedback mechanisms describes very well

even the experimental details of the rather complicated behaviour of the so called large

signal conductivity. It turns out that the understandig of the situation in the region near

the selective contacts plays the key rote in the presented model.

7P:c224TUNING HETEROJUNCTION BAND OFFSETS USING METAL ANDSEMICONDUCTOR INTRALAYERS

:: R. Perezt, F. Floret, A. Mujica* and A.Munoxl

'} fDepartamento de F/sica de la Materia Condensada C-XII.V\ Facul tad de Ciencias . Univers idad A u t 6 n o m a .;;: E-28049 Madr id . Spain.; { D e p a r l a m e n t o de Fi'sica Fundamenta l y Experimental .'{ Facul tad d e Fi'sicas. Universidad de La Laguna.; E-38204 La Laguna. Tenerife. Spain.

» Heterojunction band offsets can be modified by the deposition of a metal or a semiconductorf intralayer at the interface. In this contribution, we present a consistent LCAO method to-{ calculate the electronic properties of the following systems: (a) GaP/Alkali metal/Si (110) and| (b) GaAas/Ge/GaAs and GaAs/Ge/AlAs (100) interfaces. Our results show that an alkali metalF monolayer increases the GaP/Si (110) band offset by 0.4 eV., and that more electropositive:; metal atoms yield larger band offsets. As regards the semiconductor intralayer, we also find anr important increase in the heterojunction band offset with the number of Ge monolayers deposited| at the interface; this increase saturates at as 3 monolayers, for which the thick intralayer limit(< is reached.

213

7P:c225INTERFACE RELATED LUMINISCENCE FROM n-n HETEROJUNCTIONS OF THE II TYPEIN GaSb/GalnAsSb

E. HULICIUS, J. OSWALD, J. PANGR&C, T. SIMECEK, A.N. TITKOVf O.M. GUSEV*Institute of Physics CSAV, Cukrovarnicki 10, 162 00 Praha 6, CSFR

*A.F. Ioffe Physical Technical Institute, 194021 Sankt Peterburg, SNS.

2.5 - 6 um thick lattice matched n type GnlnAsSb layers Te doped to6.io!6, 3.1O*7, 4.1O17 cm"3 have been grown on 5.1O17 cm~3 Te doped GaSbsubstrates by LPE. Photoluminiscence of the interface region was measuredin the temperature range 4.2 -r 100 K. At 4.2 K we found besides the emis-sion peaks of the substrate at % = 1558, 1594 and 1656 ran and the epilayerat A - 2051 ran a peak at 1817 mr., viiich corresponr)s tn a transition from aQ.W. at the interface. This interpretation is supported by a strong temper-ature dependence of the intensity of this peak, which decreases above 15 Kand practically vanishes at 55 K while the intensity of the % = 2051 nmpeak increases in the sampe temperature interval. According our interpre-tation this phenomenon is caused by the thermal excitation of electronsfrom the interface Q.W. These electrons then contribute to the epilayerluminiscence. We have observed this extra peak only for the lowest dopingof the GalnAsSb layer. To our knowledge similar results have not been yetreported in n-n heterostructures of this type.

7P:c226

Dynamical Energy Transfer at the Interface ofZnSe/GaAs Epi layers

N.Presser, Ch.Fricke, G.Kudlek R.Heitz, A.Hoffmann, J.Gutowski*, and I.BroserInstitut fur Festkorperhysik, Technische Universitat Berlin*lnstitut fur Experimentelle Physik, Universitat Bremen

The high-density optical properties of MBE-grown ZnSe epilayers areinvestigated, comparing samples on (100) GaAs with free-standing layers. Theluminescence under high excitation densities of free-standing films shows astrong N band which has been attributed to electron-hole-plasma recombination.This band could not be recorded in epilayers still on GaAs substrate. Tounderstand this effect, ambipolar diffusion of free carriers from the layerthrough the interface into the substrate is considered. To distinguish this kind ofenergy transfer from other possibilities we studied the dynamic Dehaviour of thered near-edge luminescence of the GaAs substrate after excitation of the ZnSeepilayer by ps and ns laser pulses.

214

7P:c227

Radiative Excitonic Recombinations inStrained ZnSe Epilayers

G.Kudlek, Ch.Fricke, N.Presser, R.Heitz, A.Hoffmann, and J.Gutowski*Institut fur Festkorperphysik, Technische Universitat Berlin

*lnstitut fur Experimentelle Physik, Universitat Bremen

We investigated the electronic properties and dynamical behaviour of free andbound excitons in ZnSe/GaAs epilayers. For these investigations we used MBE-groyvn samples with different strain situations. Due to the tensile in-plane actingstrain in this heterosystem, a Ih (light hole) and hh (heavy hole) splitting of thefree- (Xjh and Xhh) and donor-bound excitons (b and h ) was observed Usingdifferent optical arrangements, like resonant photoluminescence and excitationspectroscopy, we develop a model of the excited levels in the (D°,Xih) complex interms of a three-particle system, with excited single-hole states with quantumnumbers |n,l>i.Time-resolved investigations show specific rise and decay times of the free- andbound-exciton emission in the ps time range. The observed free-exciton X|h andXhh lifetimes are correlated with the rise times of the bound excitons bOh) andI2'(hh).We compare these results with those from differently doped bulk ZnSe crystals?.' G.Kudlek. et. al. J.Crystal Growth (1992). in press2 G.Kudlek, A.Hoffmann, R.Heitz, Ch.Fricke, J.Gutowski, G.F.Neumark, and

R.N.Bhargavi), J.Lum. 48&A9 (1991), 138

7P:c228PREPARATION AND PROPERTIES OF CdS/CdTe HETEROJUNCTIONS

J. TOUSKOVA, D. KINDL, J. KOVANDA, J. TOUSEK

Fac.of Math.and Phys..Charles Univ.,Ke Karlovu 5, 12116 Prague 2

Devices of glass-SnOp-CdS-CdTe~Au were prepared. Polycrystalline

CdS layers were deposited by spray pyrolysis, CdTe layers were

electroplated. Properties of the layers were investigated by

X-ray diffraction and optical transmission. Measurements of dark

T-U ;;nd C-U chnracteristies were used to study the charge trans-

port, in n-CdS/p-CdTo heterojunctions. The results can be explai-

ned by a model consisting of the series connection of a p-n

junction and a voltage independent resistance representing seve-

ral inter^ranulcir barriers in CdTe layer. Parameters of the

junction a« the quality factor and the barrier height as well as

thfi height and the number of intergranular barriers were deter-

iTiiiiu;;. Ionized acceptor concentration in p-CdTe was established

;uvi i Lfi connection with the deposition potential was found.

215

7P:c229

RELATION BETWEEN HOMOGENEOUS LINEWIDTH AND RADIATIVELIFETIME OF EXCITONS IN QUANTUM WELLS

J. KUHL, R. ECCLESTON, B.F. FEUERBACHER, W.W. RUHLE AND K. PLOOG

Max-Planck-Institut fur FestkorperfbrschungHeisenbergstr. 1,7000 Stuttgart 80, FRG, Tel. 0049-711 6860 590

Resonant photoexcitation of the predominately homogeneously broadened heavy hole exciton

line in a 27nm GaAs quantum well (QW) at 1.8K results in a naiexponential decay of the time-

resolved exciton photoluminescence due to the decrease in the exciton-exciton scattering

contribution tc the homogeneous linewidth, Th, as the exciton population decays. This result

confirms the theoretically predicted relationship between the exciton radiative recombination

lifetime and the homogeneous linewidth of the exciton state. Comparison with the exciton

density dependence of Fh obtained from T2 measurements performed by transient degenerate-

four-wave-mixing leads to a quantitative agreement with the observed transients. Qianges in the

initial radiative recombination rate of up to a factor of 10 are observed. These results show that

time- and density-dependent carrier-scattering can significantly affect the carrier recombination

dynamics in high quality QW samples.

7P:c230

ALLOY DISORDER SCATTERING IN FINITE QUANTUM WELLS

B. PODORResearch Institute for Technical Physics of the Hungarian Academy of Sciences.1325 Budapest, P.O.Box 76, Hungary

Alloy disorder scattering is one of the dominant scattering mechanisms internary compounds. An expression for the relaxation time and mobility due toalloy scattering in a finite rectangular quantum well is derived. Sphericallysymmetric square potential well scattering centres, randomly distributed betweenthe two kinds of alloy sites are considered. The effects of the finite depth of theconfining potential well on the alloy scattering limited mobility is discussed.

216

7P:c231

A SELFCONSISTENT CALCULATION OF THE INTRINSIC BISTABILITYIN DOUBLE BARRIERS HETEROSTRUCTURES

P. L. Pernas, F. Flores and E. V. AndaDepartamento de Ffsica de la Materia Condensada C-XII.Facultad de Ciencias. Universidad Autonoma.E-28049 Madrid. Spain.

The intrinsic bistability of double barriers heterostructures has been analyzed by using thenon-equilibrium Keldysh formalism. In this approach, the induced electron charge in the well iscalculated as a function of the applied bias and the electrostatic potential induced in the hete-rostructure. Selfronsistenry is arhipvpH hy relating this induced potential to the electron charge.Different AlAs/GaAs/AJAs double barriers have been analyzed, and the bistability region hasbeen shown to depend on the semiconductor doping and the heterostructure geometry. Detailedresults for different geometries, including the electron charge, the selfconsistent potential andthe I-V characteristic, will be presented.

7P:c232THE FORMATION OF A QUANTUM WELL IN MBE GROWN Si £-DOPED GaAsLAYERS STUDIED BY FHOTOCURRENT SPECTROSCOPY

F.KAREL, J.OSW/LD, J.PASTRNAK, 0.PETRlCEK, A.SALOKATVE 1)Institute of Physics, Cukrovarnicka 10, Prague, Czechoslovakia1) University of Tampere, Tampere, Finland

The relationship between the concentration and degree ofionization of donors in 5-doped layer and parameters ofcorresponding quantum well (QW) was studied by photocurrentspectroscopy. This method proved to be very sensitive due tothe high mobility and lifetime of electrons in QW.The photo-current spectra of three MBE grown Si S-doped GaAs samples withdifferent Si concentration measured at different temperaturesand light excitation densities will be presented. Depending onthe ionization degree of donors in the sheet layer the QW isformed and in addition to the optical transitions involving thedonor impurity also transitions from valence band to discreteenergy levels in the QW were observed. The results allow toestablish the parameters of QW. At low temperatures also weakdisturbing memory effect connected with the formation of theelectric field transverse to the layer was observed.

I 217

7P:c233

Excitonic transitions in GaAs-GaAIAs Superlattices under a low electric field

J.Depeyrot , P.Tronc and E.UmdenstockLaboratoire d'Optique Physique , Ecole Superieure de Physique et Chimie Industrielles10, rue Vauquelin , 75231 Paris Cedex 05 , France

J.F.PalmierCentre National d'Etudes des Telecommunications196 , avenue Henri Ravera, 92220 Bagneux , France

B.EtienneLaboratoire de Microstructures et de MicroelectroniqueCentre National de la Recherche Scientifique196, avenue Henri Ravera , 92220 Bagneux , France

We report a study of the photoluminescence spe'ctra of GaAs-Gaol65Alo,3sAs superlatticeunder an electric field of about 10 kVcnr1 , from 9 K up to 80 K ; the ratio p = I-i/Io of theintensities of the -1 and 0 peaks varies with the temperature T.To fit these variations , weassume for both transitions a trapped exciton density of states with a gaussian distribution ofeigenenergies , and a two dimensional density of states for free excitons.We show that aboveabout 50 K there is a thermal equilibrium between direct and crossed free excitons whereas atlow temperatures , the equilibrium statistic is not respectedrthe excitons trap into the direct statein preference to the crossed one.

7P:c234

TUNNELING ESCAPE RATE OF ELECTRONS FROM QUANTUM WELL INDOUBLE-BARRIER BETEROESTRUCTURES BY THE STABILIZATIONMETHOD

Oh. PORTO and 0. SANCHEZ-DEHESAPpte Fisica <&> Is Mat&rta Corxiensarfa Vhiversidad Autoizwa deMadrid 28049 Madrid SPAINL. CURY, A. N0GARET and J. C. PORTALINSA-CMS. Departement de Physicnie, 31077 Toulouse and CMS-SW7, 38042 &#mi>le. FRANCE

We present a numerical calculation for the energy levelsand the tunneling time of electrons in double barrierstructures performed by means the Stablization Method*. Thismethod is specially feasible for the non-symmetric case: itis possible to calculate separately the tvo differenttunneling times -contributing to the total lifetime of theresonant level. Ve have used the effective-mass theory Thebehaviour with applied bias is also investigated. A comparisonwith other approximations and other calculations for thesymmetric case are presented.

1 F.Borondo and J.Sanchez-Dehesa, Phys. Rev. B33, 8758 (1986)

218

I

7P:c235COHERENT TUNNELING IN QUANTUM WELLS UNDER MAGNETIC FIELDS

P. ACEITUNO, A. HERNANDEZ-CABRERA, and H. CRUZDepartamento de Fisica Fundamental y Experimental. Universidad deLa Laguna. 38204 La Laguna. Tenerife. Spain.

In this work, we have studied the coherent tunneling oscillationsof electrons in a asymmetric double quantum well heterostructureunder an external applied electric magnetic field along the growthdirection of the structure. In this coupled quantum well system,it is found that magnetic quantization collapses the resonantcondition for coherent oscillations between the asymmetric andantisymmetric states in a discrete set of coherent tunnelingchannels. We show the possibility of a direct observation of thesetunneling processes by means of an oscillating luminescencesignal.

7P:c236SELF-CONSISTENT CALCULATIONS OF COHERENT TUNNELING OSCILLATIONS INASYMMETRIC DOUBLE QUANTUM WELLS

A. HERNANDEZ-CABRERA, P. ACEITUNO AND H. CRUZDpto. Fisica Fundamental y Experimental. Universidad de LaLaguna38204-La Laguna. Tenerife. Canary Islands.Spain

Coherent carrier tunneling in asynmetric double quantum wellheterostructures is analytically investigated through a selfconsistent method of calculation. Longitudinal electric fields areapplied,to reach the interwell resonance conditions. Exact wavefunction? in asymmetric double quantum well systems (modified Airyfunctions) are used to include the electron-hole interaction inthe coherent tunneling process. Results are in good agreement withthe available previous works.

I

1I 219

7P:c237SUPERLATTICE MINIBANDS UNDER APPLIED MAGNETIC FIELDS

p. CRUZ1, F. PIAZZA2, and L. PAVESI*

Departamento de Fisica Fundamental y Experimental. Universidadde La Laguna. E-38204 La Laguna. Tenerife. SpainDipartimento di Fisica. Universita di Trento. 1-38050 Povo(Trento). Italy

In this work, we have studied short period superlattice minibandsunder an applied magnetic field parallel and perpendicular to thegrowth direction. We have implemented a method of calculationbased on the transfer matrix approach and plane wave solutions forthe effective mass equation to compute short period superlatticeenergy levels under an applied magnetic field in both directions.The applied magnetic field effect on the superlattice density ofstates is also calculated in both cases.

7P:c238SPIN FLIP RAMAN SCATTERING IN GaAs/AlGaAs MULTIPLE QUANTUM WELLS

V.F.Sapega, M.Cardona and K.PloogMax-Planck Institute fur FestkSrperforschung, Heisenbergstrasse 1, D-7000Stuttgart 80, Germany

E.L.Ivchenko and D.N.MirlinA.F.Ioffe Physico-Technical Institute, Academy of Sciences of the USSR 194021St-Petersburg, USSR

Strong spin flip related Raman scattering (SFRS) from p-type Be-dopedGaAs/AlGaAs multiple quantum wells (MQW), as well as from an undoped sample,has been observed. In both cases the SFRS exhibits a strong dependence on thegeometry of the experiment. A theory is developed which explains SFRS in p-typeMQW as related to a spin flip of a hole bound to an acceptor via exchangeinteraction with a neighboring exciton. SFRS in the undoped MQW's is explainedas a flip of the angular momentum of an exciton localized by interface roughnessvia interaction with acoustic phonons (doubly resonant scattering by acousticphonons). The g-tensor of the hole bound to the acceptor is determined to beg =+2.3, g a<0, and that of the localized exciton ( g.-g ).. =+1.5, (g.-£ ) *0

for the narrowest wells measured (~40X).

220

7P:c239LOW TEMPERATURE ABSORPTION SPECTRA OF GaAs/AlGaAs SUPERLATTICES

V Capozzi(a), JL Staehli(b), D Martin(c), V Augelli(a),P Favia(a) T Ligonzo(a) GF Lorusso(a).

(a) Dipartiaento di Fisica, Universita' degli Studi di Bari,Via Amendola 173, 1-70126 Bari, Italy;

(b) Institut de Physique Appliquee, Ecole Polytechn. Federale,PH-Ecublens, CH-1015 Lausanne, Switzerland;

(c) Institut de Micro-Optoelectronique, Ecole PolytechniqueFederale, PH-Ecublens, CH-1015 Lausanne, Switzerland;

Transmission spectra of short-period of GaAs/ AlxGal-xAs (x=0.3)

superlattices have been measured at the temperature of 2 K. The

calculated energy ranges of the first carrier minibands are in

agreement with the experimental absorption spectra. Besides to

the heavy-hole and light-hole excitons lines associated to the Mo

point in the joint density of states, two other bumps are present

in the absorption spectra, at the upper energy edge of the

minibands. They have been attributed to saddle point excitons,

whose line-width is broadened because of the presence of a

continuum of free states.

7P:c240

MAGNETOOPTICS OF HARROW GaAs/AlGaAs QUANTUM IELLS GROINON TICIN&L SUBSTRATES

J.Sanchez-Dehesa, F.Meseguer and N.MestresInstitute de Ciencia de JfateriaJes ( CSIC ) and Departamntode Kisica. (Mv&rsidad Autonom de Madrid. 28049 Madrid. SPAIN

C.Deparis, G.Neu and J. MassiesLaboratoire de Physique du S&lide et Energy SolaireCMS 06560, FaJJbonne. FSAJNCE \

I

Magnetoluminescence measurements performed on IGaAs/AlGaAs Quantum Veils grown on a vicinal substrate shov a %blue shift of the excitonic transitions compared to those |obtained on a reference sample grown on nominal substrates. •This blue shift is interpreted in terms of the lateral •modulation induced by the steps array resulting from the useof vicinal surfaces. ..

221

7P:c241

RAMAN SCATTERING SPECTROSCOPY OF NON-EQUILIBRIUM OPTICALPHONONS IN GaAs QUANTUM WELLS.

D. Y. OBERLJ, G. BOHM AND G. WEIMANNWalter Schottky Institut, Technische Univcrsitat MUnchen, D-8046 Garching, Germany

Electron-phonon interaction in two dimensional semiconductor structures is modified fromthe bulk case due to the existence of electronic subbands and new interface and confinedoptical phonon modes. In narrow quantum well structures, the interface modes play animportant role in the relaxation of electron-hole plasma. In this paper, we present a Ramanscattering study of non-equilibrium phonons generated by the relaxation of a photocxcitedelectron-hole plasma. The emission of optical phonons is observed in the plane of the layers,thus allowing us to probe hot phonons with in-plane momenta. A comparison with a thermalphonon distribution at 200 K directly shows a redistribution in the phonon populationamong existing modes. The non-equilibrium phonon distribution is characterized by theemission of phonons with small values of in-plane momentum. Our results also indicate anincreased coupling of the photoexcited electrons with interface AlAs-like modes in wellwidths of SO A, whereas in 100 A wells the coupling occurs almost entirely with confinedoptical phonons.

7P:c242OPTICAL INVESTIGATION OF THE THERMAL STABILITY OF GalnAs/InGaAsP QUANTUM WELLS

R.W.GLEW*, H.PEYRE+, J.CAMASSEL+, F.ALSINA° and J.PASCUAL0

(*) BNR Europe Ltd, London Road, Harlow, Essex CM17 9NA, U.K.(+) G.E.S., Universite Montpellier II, 34095 Montpellier, F.(o) Dept. Flsica and ICMAB(CSIC), UAB, 08193 Bellaterra, Spain

GalnAs/InGaAsP constitute an important system for optical a-pplications in the long-wavelength range. However, for moderndevices fabrication, high temperature processes are often ne-cessary. Such treatment can modify the quantum well characte-ristics because of activated diffusion across the interfacesbetween wells and barriers. Then, to achieve predictable beha-viour of this devices it is crucial to understand the processof annealing.In this communication we report the optical characterization,by means of photoluminescence and Raman spectroscopy, of theinterdiffusion process in GalnAs/ InGaAsP single quantum wellsgrown by the OMCVD method. The structures are submitted to afurther annealing at 650°C and 750°C for various annealing ti-mes. From experiments we get the diffusion length and the ac-tivation energy of the process.

222

7P:c243OPTICAL INVESTIGATION OF THE COMPOSITIONAL GRADIENT ACROSS THEINTERFACES IN MBE GalnAs/InP SUPERLATTICES

E.MASSONE1, J.CAMASSEL1, J.PAGES2, J.PASCUAL2 and J.JIMENEZ3

(1) G.E.S., Univ. Montpellier II, 34095 Montpellier, France(2) Dept. Flsica and ICMAB(CSIC), UAB, 08195 Bellaterra, Spain(3) Dept. Flsica Mat. Cond., Facultad Ciencias, Univ. Vallado-

lid, c/ Prado de la Magdalena s/n 47002 Valladolid, Spain.

Two GalnAs/InP superlattice structures, SL1 and SL2, were grownby MBE on semiinsulating (100) InP substrates with 50 and 20 periods, respectivelly, of alternating layers with nominal thic-nesses of 25 fi (GalnAs) and 100 fi (InP). The photoluminescencespectra, at 2 K, shows two well resolved structures which oneassociates to H1-E1 and L^Ei transitions (for sample SL1),whi-le a blue shift of 30 meV is found Hi-Ei, the only one resolvedstructure in sample SL2. Complementary Raman spectra show a su-plementary shoulder on the low energy side of the InP LO phonon(in SL2) and a clear decrease of the peak intensity of foldedTA modes which are characteristic of Raman scattering on gradedinterfaces. The data are analysed getting out from the simpleabrupt square-well approximation for interfaces and working inthe framework of the transfer matrix method to give account ofchanges on the energy confinement of electrons.

223

8P:alRAMAN SCATTERING ON HIGH DENSITY 2D ELECTRON GASES

BJUSSERAND1, H.PERIC1, D.R.RICHARDS2 and B.ETIENNE1

1- Groupement scientjfique CNET-CNRS de Bagneux,

196, Avenue Henri Ravera, 92220 Bagneux, France

2- Fraunhofer InsBtut fur Angewandte FestMJrperphysik,

Tullastrasse 72,7800 Freiburg, Germany

Electronic Raman scattering is a very powerful technique to probe 2D electron gases confined in

quantum weNs [1,2]. We report on intersubband excitations in single GaAs quantum wells with electron

densitiesaround 10'Jcm2: single particle excitations (SPE), spin density waves (SDW) and charge density

waves (COW) are observed and their dispersion with the in-plane wavevector is measured. We analyse

the SPE line shape in terms of finite temperature, experimental wavevector uncertainties and the

colKsional broadening.

Raman scattering results are in excellent agreement with the luminescence properties of the same

structures. The luminescence spectra reflect the crucial role of wavevector non-conservation in the

electron-hole recombination in these highly doped systems.

1- D.Ricnards, G.Fasol and K.Ptoog, Appl.Phys.Lett.56,1649 (1990)

2- B.Jusserand, D.Richards, G.Fasol, G.Weimann and W.Schlapp, Surf.Science229,394 (1990)

8P:a2EXCITOJS AT FERMI LEVEL IN DENSE IWODIMENSICNAL ELECTR0N-H(X£MMNEFOPLASMA

L.V. BUTOV, V.D. KULAKOVSKIIS o l i d S t a t e H i y s i c s I n s t i t u t e of Academy of S c i e n c e s , Chemogolovka,142432, Russia.A. F0HCHELTechnische Fhysik, Universitat Wurzburg, Am Hubland, Wurzburg, FHG.D. GRttFZMACHERInstitut fiir Halbleitertechnik, BWIH, Aachen, FHG.

The optical spectra of a low temperature neutral dense magnetoplasnain Inp-53Ga047As/InP quantun well have been investigated. He have foundthat in this'magnetoplasma electrons and holes from the upper occupiedLandau levels bind into magnetoexcitcns. Ihe magnetoexcitons. front the sameLandau levels (Je JhN' can 1* considered as noninteracting. The inter-action of magnetoexcitons from different levels decreases their energy,for a wide range of plaana densities the experimental results agree wellwith calculations of G.E.W. Bauer which takes into account both the inter-Landau-level coupling and screening effects. For integer filling factorsthe results can be described in terras of excitons and deexcitcns in inver-ted mgnetoplaana developed by Yu.A. Bychkov and E.I. Bashba.

224

8P:a3

Theory of Macroscopic Local Single - Part ic le Charge

States and Large- .Radius Local TSxeitons in Quasi- Zero -

Dimenei o nal Structures

S.I.Fofcutnyi

Department of Physics State Pedagogical Institute

Gagarin Prospekt 54 , Krivoi fiog , SU- 324 086 , V S S R

Localization of charge carriers on a small sphere placed

into soiuo medium i s considered.Within the framework of electro-

statics a general expression has been obtained for the potenti-

al energy of a charge in the field of image forces on a spheri-

cal interface of two media with arbitrary values of their per-

mittivities

8P:a4

PERTURBATIONAL ANALYSIS OF THE PLASMON DECAY IN A

TWO - DIMENSIONAL ELECTRON GAS*

MARTINA E. BACHLECHNER

Institut fur Theoretische Physik, Johannes Kepler Universitlt, A - 4040 l ira, AUSTRIA

In the two - dimensional homogeneous election gas the contribution to plasmon damping

due to the decay of the plasmon into two electron - hole pairs is investigated within

the formalism of second-order perturbation theory. Additionally, the influences of

potential screening effects are taken into account.

Outside the particle - hole continuum the dependence of the plasmon halfwidlh on the

n»"«ifftn"" transfer q is presented for various densities.

* This woik was supported by the "Foods zur FSrderung der wissenschaftlichai Fonchung"

(FWF Projekt No. P7846 - PHY).

225

8P:a5MICROWAVE PHOTOCONDUCTIVITY OF A TWO-DIMENSIONAL ELEC-TRON GAS AT LOW FILLING FACTORSR.MEISELS1, F.KUCHAR1, J.J.HARRIS*3, C.T.FOXON3-*'Institut fur Festkorperphysik, Universitat, A-1090 Vienna, Austria, and L.Boltzmann Institutfur Festkorperphysik Kopernikusg.15, A-1060 Vienna, Austria2Philips Research Laboratories, Redhill, Surrey RH15HA, U.K.3 present address: Imperial College, Prince Consort Road, London SW72BZ, U.K.* present address: Department of Physics, University ofNottingham, Nottingham NG72RD, U.K.

In the extreme quantum limit, in a two-dimensional electron gas (2DEG) with a weak impuritydisorder potential, the electron-electron Couloumb interaction becomes dominant. Consequently,the 2DEG undergoes a transition to a correlated many-electron state. Two such states proposedare the incompressible electron liquids of the fractional quantum Hall effect (FQHE), and, formore dilute 2DEG's, the Wigner crystal. Indications of Wigner crystallization have been foundexperimentally, however, the interpretation has not remained unchallenged.

Changing the sample carrier density by illumination the filling factor v at Bmax = 11T waschanged from 1/6 to 2/7. We studied the effect of microwave radiation on the 2DEG by mea-suring its photoconductivity to examine whether the 2DEG is in different correlated states atthe two densities. The change ARXX of the longitudinal resistance RXI is a sensitive probe ofthe properties of a 2DEG.

Analyzing the dependence of ARXX on the incident microwave power PMW a distinction wasfound between the 2DEG in the state of fractional quantization (with B at the position ofat the i> = 1/3 Rxx minimum) and in the lower density state. In the FQHE case ARXX oc\EMW\ OC PMW- In the lower density case, where a rapid rise in RXX{B), attributed to Wignersolid formation by other authors, and in ARXI(B) was observed, ARXX was directly « PMW.Obviously, the lower density state is another kind of correlated or localized state fundamentallydifferent from the FQHE state.

8P:a6

CURRENT NOISE IN TUNNEL JUNCTIONS WITH MESOSCOPIC METALPARTICLES

M.A.Belogolovskil, L.G.LevinDonetsk Physico-Technical Institute:, Ukrainian Academy ofSciences, R.Luxemburg, 72, Donetsk 340114, Ultralne

We present a theoretical study of noise effects In the doublenormal-metal tunnel Junction formed by a small metal particleplaced between two bulk external electrodes. The analyticalexpressions for the correlation time, square deviation andpower spectrum of the current fluctuations connected with therandom character of the tunneling processes are given. Ourresults confirm those obtained by numerical calculations, thatthe level of the fluctuations In the double mesoscopic tunnel.junction is always lower than the value of the ordinary shotnoise. It is shown that such result Is a consequence of thecorrelation, between events of electron tunneling throughdifferent Junctions.

226

8P:a7

OPTICAL ABSORPTION OF QUASI-ONE DIMENSIONAL SEMICONDUCTORSTRUCTURES

S. GLUTSCH and F. BECHSTEDTInst. f. Festkorpertheorie u. Theor. OptikMax-Wien-Platz 1, O-6900 Jena, Germany

The optical absorption of a quantum wire is calculated in the framework of the envelope func-tion formalism. The one and two particle properties are treated using the harmonic confinementmodel.

As result we obtain a generalization of the well-known Elliot formula. The essential differ-ence, however, is the influence of the center of mass quantization on the absorption spectrum.In order to determine the exciton wavefunctions one have to talc into account the coupling of allsubbands. The results are discussed for typical wire widths 6 > t w (aae • bulk exciton radius)down to b « aexc, where qualitatively new phenomena are observed. We compare with recentexperimental results and observe quantitative agreement with excitation spectra of multi-wirestructures prepared by means of induced thermal interdifiusion.

8P:a8

SUPERCONDUCTING RESERVOIRS CONNECTED BY A QUANTUM WIRE

L. HEDIN and B. VELJCKY«University of Lund, 22362 Land, (a) on leave from Charles University 11000 Praha

This paper elaborates on a model proposed by van Wees et al.1 who consider an infinite singlechannel quantum wire which is superconducting except at a finite interval where it is in anormal state. In this model, superconducting currents with a remarkable dependence on theFermi energy are possible. In our model, the infinite quantum wire is a semiconductor. Thesuperconducting electrodes m the fonn of a semi-infinite thin film are placed above the ends ofthe wire and coupled to it across a tunneling barrier. These electrodes act as genuine *reservoirs. At the same time, they change the state of the carriers in the wire just beneath, as {can be described in terms of effective deGennes equations which can be obtained using a \projection technique. Matching between the three regions of the quantum wire using a $boundary condition of the open type allows to derive the resulting current in the wire as a j . -function of the electric bias and the parameters of the system. |1. van Wees B.J., Lennsen K.-M. H., Harmans C.J.P.M., Phys. Rev. B44 %

(1991)470

227

8P:a9AUGER-IOJIZATICN IN QUANTUM SEMICONDUCTOR STRUCTURES AND ATOMIC CLUSTERS

V.A. KHARCHENKDITAMP, Harvard Smithsonian Center, Cambridge, Mass., USATechnical University, St. Petersburg, Russia

Information about many-electron effects in quantum size objects (quan-tum wells and drops, atonic clusters) is important now both for the con-densed natter and atomic physics. Auger-ionization (A-I) probability as afunction of the structure size for high exited semiconductor quantum wellsand quantum drops is studied theoretically.

Auger-process plays an important role as a main channel of nonradla-tive recombination, which competes with optical transitions. In contrastwith bulk solids, we obtained an increasing role of non-threshold Auger-processes.

8P:alOTHE INFLUENCE OF COULOMHIC INTERACTIONS ON THE ELECTRONIC

STRUCTURE IN 1-D SYSTEMS

W. Haiisler, K. Jauregui, B. Kramer

Physikalisrh-Tcchnisdic Bundesanstalt, Braunschweig, FR(!

For a ono dimensional system of N = 2 . . . 5 electrons and length L we have solved the

eigenvalue problem numerically, including the Coulomb interaction and the spin degree

of freedom. We find that the yV-elcctron ground state energy f''N drvial.es from a ~ 1/t

law already for lengths far above the Bohr radius. The condition for the appearance of a

conductivity maximum in the experiment [2j is given by Z?/v+r — EN = EF • This neither

for short, nor for long systems turnes out to depend really linearly on the number of

charges tj—Nn on the wire. Both deviations demand for corrections to the "orthodox"

model I using solely the charging energy. The properties of the N particle spectra will be

discussed.

(1] Meirav l,\, Kastner M. A., Wind S. J., Pliys. Rev. Lett. 65, 771 (1980)

[2] Haunter W., Kramer B., Masck J., to appear in Z. Phys. H

228

8P:allLINEAR- AND NONLINEAR-OPTICAL MANIFESTATIONS OF QUANTUM CONFINE-MENT IN COPPER CHLORIDE NANOCRTSTALS

S.V.GAPONENKO, I.N.6ERMANENK0, V.P.GRIBKOVSKII, L.G.ZIMIN,V.Yu.LEBED, and I.E.MALINOVSKII

Stepanov Institute of Physics, Minsk, 220072 Republic of Belarua

Excitonic processes in CuCl nanospheres of mean radius rangingfrom 20 to 150 X embedded in glass matrix are investigated. Spe-cific features resulted from quantum confinement are analysed.Exciton-exciton interaction and k-selection rule relaxing leadto size-dependent linear and nonlinear optical properties resu-lting in light-induced blue shift of excitonic bands, slowingdown of radiative decay and drastic changes in the excitationand relaxation dynamics of excitons confined in quantum box.*

1. Gaponenko S.V. et.al., J.Lumin.46(1990)101; NATO ASI Series1992 (in press).

8P:al2BALLISTIC TRANSPORT THROUGH A Il-SHAPED ELECTRON WAVEGUIDE

ALEXANDER ONIPKO and IGOR ZOZULENKOInstitvte for Theoretical Physics, Academy of Sciences of Ukraine

J. Kiev. Ukraine

Quantum coherent electron transport in a U-shaped lateral structure is investigated.Electrous propagate in one-dimensional subbands, of which only the lowest is occupied.In the framework of a tight-binding Hamiltonian with a usage of the Green-functiontechnique analvtical expressions for the electron transmission and reflection coefficientsare obtained. It is shown that a strong interference effect can be achieved by varyingthe width of the top channel via an applied gate voltage. The transistor action of thedevice based on this effect is investigated.

229

8P:al3

ELECTRON TRANSPORT ALONG A DISORDERED CHAIN IN PRESENCE OFDISSIPATION

K. Maschke, Institut de Physique Appliquee, Ecole Polytechnique Federate,PHB-Ecublens, CH-1015 Lausanne, SwitzerlandM. Schreiber, Institut fur Physikalische Chemie,Johannes Gutenberg Universitat, Jakob-Welder-Weg 11, D-6500 Mainz, FRG

We use the Landauer-Buttiker approach to investigate the electron transportalong a disordered chain. The chain is described by a sequence of scattererswhich allow for elastic as well as for inelastic scattering processes. The inelasticscattering takes place via side branches which connect the electrons in thetransport channel to electron reservoirs which serve as a heat bath. Ourcalculations show that disorder as well as dissipation lead to an exponentialdecrease of the transmission probability. The dependence of the characteristicdecay lengths on the scattering parameters is investigated. We further study theconductivity of a disordered chain. In agreement with the well accepted pictureof localized states in one-dimensional disordered systems we find insulatingbehaviour in absence of dissipation. For finite coupling of the electrons to theheat bath the phase memory of the scattered waves is partially lost; thelocalization effects are suppressed and the chains become conducting. Forsmall coupling the conductivity increases with increasing coupling. For largercoupling it decreases again and finally becomes independent of the presenceof disorder.

8P:al4NEW NONLOCAL QUANTUM EFFECTS IN HIGH-MAGNETIC-FIELD CONDUCTANCE

A.K.Geim(Heym)* and P. C. Main, L. Eaves, P.Beton and P. Streda*^Department of Physics, University of Nottingham, Nottingham NG7 2BD, UK'institute of Microelectronics Technology, Chernogolovka 142432, USSRInstitute of Physics, Cukrovarnlchka 10, CS-16200 Prague, Czechoslovakiat

We present advanced results of our recent study ' on quantum conductanceof diffusive microstructures in high fields. The nonlocal voltage drop (farbeyond a region of classical current flow) was measured in quasi-2D heavilydoped GaAs wires in magnetic fields sufficient to cause quantum transportalong the edge states. First, we have observed a nonlocal oscillatorymagnetoresistance effect over a limited range of temperatures (10sTs50K)i.e. it is a unique case of quantum phenomenon which disappears loweringtemperature. The effect is observed when quantum ballistic transport alongthe edges coexists with diffusive and dlsslpative condition in the bulk.Using of the Landauer-Buttiker formalism falls to explain results revivinga question about location of contacts (reservoirs). Secondly, a break ofone-parameter scaling for the universal conductance fluctuations (UCF) wasfound In high magnetic fields (beyond applicability of the current theory).An amplitude of the UCF is constant over a whole range of magnetic fieldsbeing described well by the zero-field Inelastic length while anotherdiffusion length should be introduced to explain a pronounced increase ofthe Lee-Stone correlation field if WCT>1.

1. Phys.Rev.Lett. 67, 3014 (1991)2. Proceedings of EP2DS-9, Nara, Japan, 1991; submitted to °hys.Rev.Lett.

230

8P:al5DIMENSIONAL RESONANCES OF QUANTUM WIRES IN ALAS/GAASHETEROJUNCTIONS WITH NON-HARMONIC CONFINEMENT

H. DREXLER, W. H ANSEN, and J. P. KOTTHAUSSektion Physik der Universitat Munchen, 8000 Munchen 22, FR GermanyM, HOLLAND and S. P. BEAUMONTDepartment of Electronics and Electrical Engineering, University of Glasgow, GlasgowG128QQ, United Kingdom

Periodic arrays of narrow electron wires with periods down to 250nm are field-effectinduced in a novel type of heterojunctions that contain no dopands in the barrier. Weinvestigate the high frequency conductivity at low temperatures and high magneticfields with Fourier transform spectroscopy. Quantum wires in AIGaAs/GaAs hetero-junctions reported so far exhibit a single dimensional resonance in agreement with aparabolic confinement model. In contrast, in our devices we observe higher orderdimensional resonances with very strong interaction to the second harmonic of thecyclotron resonance. The observations are discussed in context of non-parabolic con-finement and inter wire interaction.

8P:al6EFFECT OF DISORDER ON THE CONDUCTANCE QUANTIZATION INQUASI-ONE-DIMENSIONAL WIRE

J. WR6BEL12, F. KUCHAR1, K. ISMAIL34, K. Y. LEE3, H. NICKEL8, W. SCHLAPP5

1 Institut fur Festkorperphysik, Universitat, A-1090 Wien, Austria, andL. Bolttmann Institut fur Festkorperphysik, Kopemikusg. 15, A-1060 Wien, Austria

2 Institute of Physics, Polish Academy of Sciences, Warsiawa, Poland3 IBM Thomas J. Watson Research Center, Yorktown Heights, N.Y., VSA4 Faculty of Engineering, Cairo University, Giza, Egypt6 Deutsche Bundespoet TELECOM, Forschungsinstitut beim FTZ, Darmstadt, Germany

We have measured the two-terminal conductance of a single, ungated GaAlAs/GaAs heterojunction wireof geometric length L = 20/im, width W = 0.4/im and mean free path I « 5/im. We used the time decayof the photoconductivity as a "natural" method of changing Fermi energy £>• For T = 0.35K we haveobserved fully developed universal conductance fluctuations (UCF). At higher temperatures (1.7-4.2K)UCF are thermally averaged and well resolved conductance plateaux with step height AG » 0.25x(2ea/A)are observed. At low temperatures (0.35K) we have used the voltage averaging of wave-interferencefluctuations by increasing the current through the sample. In that case we have observed the weak -"anti-resonances" in conductance, each time Ep is close to the new subband onset. We have studiedalso the transition to the perfect quantization regime through the suppression of backscattering in the 'magnetic field. Results regarding the changes of the observed features with increasing wire width will bealso presented. jj

231

8P:al7

SYMMETRY BREAKING EFFECTS OF ELECTRONS IN QUANTUM DOTS

F. Bolton and U. RofllerInstitut fur Theoretische Physik, Universitat Regensburg,8400 Regensburg, Fed. Rep. of Germany.

Experimental data for electrons in quantum dots1 have been interpreted so far mainlywithin the simplest model available: 2-dimensional electrons confined by a 2-dimensionalharmonic potential. This model is invariant under SU(2) due to dynamical symmetry.In the presence of a magnetic field the dynamical symmetry is broken, giving rise toZeeman splitting. Similarly, anharmonic contributions to the confinement potential ornonparabolicity terms from the energy band structure cause breaking of the dynamicalsymmetry of the oscillator model and level anticrossing effects of the hybrid oscillator inthe presence of a magnetic field. While the anharmonicity of the confinement potentialis uncertain, the nonparabolicity of the energy band is known and allows quantitativeevaluation of its influence on dipole transition energies. The results are compared withexisting experimental data for electrons in quantum dots on InSb.

lCh. Sikorski and U. Merkt

8P:al8MOMENTUM CONSERVATION IN 1D-2D TUNNELING PROCESSES

W. Demmerle, J. Smoliner, E. Gornik, G. Bohm, and G. WeimannWalter Schottky Institut, TU-Munchen, Am Coulombwall, D-8046 Garching,Germany

Using tunneling spectroscopy, we have investigated two independently contactedtwo dimensional electron gas systems, which are separated by a barrier of 195 A.As the electron momentum parallel to the barrier is conserved for 2D-2Dtunneling , resonances in the tunneling characteristics dl/dV are observed eachtime, a subband in one 2D channel matches a subband on the other side of thebarrier. Structuring the upper 2D-channel into quantum wires, we alsoinvestigated tunneling processes between states of different dimensionality.Momentum conservation in the direction of free motion in the quantum wiresleads to resonances in the tunneling characteristics each time ID and 2D subbandare aligned energetically. As the electron momentum in the direction of IDconfinement is not conserved any longer, we also observes situations, where the2D-Fermi level matches the ID subband energies. These two types of transitionsare directly distinguished by a different temperature behavior of thecorresponding peak amplitudes.

232

8P:al9PIEZOELECTRIC EFFECTS IN QUANTUM WIRES AND DOTS GENERATEDBY PATTERNS OF INHOMOGENEOUS STRAIN

J. M. WORLOCKSektion Physik, Ludwig-Maximilians-Universitat Munchen, andWalter-Schottky-Institut der TU-Munchen

In recent times, several groups have reported optical investigations of theproperties of quantum wires and dots formed by spatial modulation of valenceand conduction bands, using carefully designed patterns of inhomogeneousstrain. The major effect is modulation of the band-gap, and is understood as aconsequence of the dilatation operating on the hydrostatic deformationpotential, which is large. Smaller, but important, shifts arise from the strain-induced splitting and mixing of valence band states. Here I concentrate on thepatterns of shear strain - a necessary consequence of the inhomogeneity - andthe piezoelectric charges that they produce. These charge densities lead toelectrostatic fields which in turn modify the band profiles produced directly bystrain. I shall demonstrate graphically (and qualitatively) a variety of patternsof charge for (a) quantum wires with different crystallographic orientations,(b) the intersections of quantum wires, and (c) quantum dots; aii beneath the(001) surface of GaAs. By simplifying the surface boundary conditions, theelectrostatic field can be integrated, and some semi-quantitative results will bepresented for the case of a realistic buried quantum wire generated by stressimposed at the crystal surface.

8P:a20

OPTICAL PROPERTIES OF QUANTUM NETWORKS

H. KORNER, and G. MAHLERInstitut fur Theoretische Physik und Synergetik, Universitat Stuttgart,Pfaffenwaldring 57, W 7000 Stuttgart 80, Germany

Arrays of charge transfer quantum dots are promising prototype structures for a "quan-tum-network", an array of interconnected local quantum objects. The complex networkdynamics that can be controlled by an external light field is described by a general-ized master equation. Simulations of "pump and probe" experiments reveal unusualoptical properties due to cooperative phenomena. Under certain conditions this sys-tem property can be shown to perform simple image processing tasks. This is the ideaof "programmable matter", by which simulations or computer experiments would becarried out by means of actual experiments.

233

8P:a21

LATERAL TUNNELLING AND MAGNETO-TRANSPORT IN A QUANTUMTRENCH IN-PLANE DIODE

A. J. PECK, S. J. BENDING*, K. VON KLITZING and K. PLOOGMax-Planck-Institut fur Festkorperforschung, Heisenbergstr. 1, D-7000 Stuttgart 80,Germany.* School of Physics, University of Bath, Claverton Down, Bath, BA2 7AY, UK.

We report on the measurement of lateral tunnelling through thin potential barriers in-duced by shallow etching of quantum trenches on a GaAs heterostructure. Devices havebeen characterised by studying their current-voltage characteristics and thermally acti-vated conductivity. Results are compared to a theoretical model based on a numericalsolution of the two-dimensional Poisson equation. In a perpendicular magnetic field, largepeaks are observed in the device conductivity which we attribute to resonant tunnellingbetween edge states at the barrier. We propose that in-plane tunnelling devices of thistype should be capable of very high frequency operation due to their very low parasiticcapacitances and series resistances.

8P:a22

COLLECTIVE EXCITATIONS IN QUASI-ONE-DIMENSIONAL QUANTUM WELLWIRES: DEPOLARIZATION EFFECT AND PLASMON-PHONON COUPLING

L. WENDLER and R. HAUPT*Institut fur Theoretische Physik, Technische Universitat Merseburg, Geusaer Str., D/O-4200 Merseburg, Federal Republic of Germany* Institut fur Festkorpertheorie und Theoretische Optik, Friedrich-Schiller-UniversitatJena, Max-Wien-Platz 1, D/O-6900 Jena, Federal Republic of Germany

Modern integrated circuits are increasingly based on semiconductor devices in whichthe electronically active channel is an electron gas with reduced dimensionality. In aquantum well wire (QWW) we have a confinement potential in two directions. Hence,the collective and single-particle excitations of the quasi-one-dimensional electron gasare splitted into intra- and intersubband excitations. We investigate the coupled intra-and intersubband plasmon-phonon modes of a QWW within the random-phase approx-imation. In detail, we calculate the depolarization shift for square well and parabolicconfinement potential including the renormalization of the ground state by electron-electron interaction.

234

8P:a23

Single-electron tunneling and Coulomb charging effectsin asymmetric double barrier resonant tunneling diodes

M.Tewordt, L. Martin-Moreno, J. T. Nicholls, V. J. Law, M. J. Kelly,M. Pepper, D. A. Ritchie, J. E. F. Frost, and G. A. CJones.

Cavendish Laboratory, University of Cambridge, Madingley Road,Cambridge CB3 OHE, United Kingdom

Resonant tunneling is studied in an ultrasmall asymmetric GaAs-AlGaAsdouble barrier diode at low temperatures. In positive bias polarity thethreshold current-voltage characteristics exhibit well defined step-like fine-structure with varying plateau widths in bias. The step-structure is assignedto tunneling through electron-states in a quasi zero-dimensional quantumbox, subject to electron-electron interaction effects (Coulomb staircase), innegative bias polarity an additional space charge layer is formed at theemitter-barrier interface. Tunneling between the two quantum boxes leads tospike-like current-voltage fine-structure, where the structure is more closelyspaced in bias compared to the forward bias plateaux widths.

8P:a24PHONON DRAG HALL VOLTAGE IN QUANTUM HALL EFFECT DEVICES

F. Dietzel, W. Dietsche, R. Notzel and X. Ploog1

MPI fur Festkorperforschung, Heisenbergstr. 1, D-7000 Stuttgart( -1 Technische Hochschule Darmstadt, W-6100 Darmstadt )

We create acoustic phonons at helium temperatures by focusing alaser beam on a metal film evaporated on the substrate of a 0.3 mmthick GaAs/Al0 3Ga 0 7As heterostructure. The phonons can travelballistically -through the substrate to the two-dimensional elec-tron gas (2DEG) where some of them are absorbed under con-servation of energy and in plane momentum. Since the transferredmomentum points always in the same direction there is a net momen-tum transfer to the 2DEG.

This is called the phonon drag effect and can be detected inthe presence of a magnetic field by measuring the phonon inducedcurrent and the perpendicular Hall voltage. These quantities arecloseley related to the momentum transfer rate* which can bedescribed by a model, assuming quasi-elastic scattering of theextended states in the 2DEG by the phonons. In this model thephonon absorption is strongly dependent on the electronic densityof states (DOS) which is not well known in a magnetic field.Therefore this is a critical test for an assumed DOS at least inthe region of the extended states.

* A. L. Efros and Y. H. Galperin, Phys. Rev. Lett. 64, 1959 (1990)

235

8P:a25

FQHE IN THE DISK GEOMETRY: EXACT DIAGONALIZATION FOR FEW ELECTRONSWITH VARYING INTERACTIONS

M. KASNER, W. APELPhysikalisch-Technische Bundesanstalt, Bundesallee 100, D-W 3300 Braunschweig, Germany

We diagonalize exactly the Hamiltonian of electrons which move in two dimensions in a strongmagnetic field and interact via varying repulsive interactions. We work in the disk geometry.As usually the system size is defined by the area of the neutralizing background potential. Cal-culations for the Coulomb interaction and a short range potential are performed. Additionally,we regard the short range potential in a model without any background where the electrons areconfined by truncating the one-particle angular momentum basis.The multiparticle energy spectra are calculated numerically in the vicinity of filling factor 1/3.For the short range interaction the stable states can be identified, and the low lying excitationsare described with the help of quasielectrons und quasiholes. We compare our results withLaughlin's wavefunctions originally proposed for the disk geometry without background poten-tial.These results are used for the Coulomb force interacting model in order to extrapolate finitesize numerical calculations. This is done for the ground state energy and the quasielectron andquasiholes energies.We find an indication for a cusp in the extrapolated ground state energy per particle at fillingfactor 1/3.

8P:a26

TEMPERATURE DEPENDENT SCALING AND CURRENT DEPENDENT NON-OHMIC BEHAVIOUR BETWEEN INTEGER QUANTUM HALL PLATEAUX

G.Nachtwei, C.Breitlow, A.Jaeger, P.Svoboda', P.Stfeda', L.Bliek + and F.-J. Ahlers +

Humboldt Universitat zu Berlin, Institut fur Festkorperphysik, Invalidenstr. 110,D-O-1040 Berlin, FRG'Institute of Physics, Czechoslovak Academy of Sciences, Cukrovarnicka 10,CS-16200 Praha 6, Czechoslovakia+Physikali8ch-Technische Bundesanstalt, Bundesallee 100, D-W-3300 Braunschweig, FRG

We report on the temperature dependent scaling behaviour of pXI and p»y between differ-ent Quantum Hall plateaux on GaAs-GaAlAs heterojunctions. We found a characteristicdependence of the scaling behaviour on the spin quantum number indicating a longerphase coherence length for the spin-up state. A reduction of the spin-up Shubnikov-deHaas peaks at low sample currents was observed. We attribute this to a spin depen-dent equilibration between edge and bulk states based on a larger mean free path for thespin-up levels.

236

8P:a27

TRANSITIONS BETWEEN SPIN-SPLIT EDGE CHANNELSIN THE QUANTUM HALL EFFECT REGIME

A.V.Khaetskii

Max-Planck Institut fur Festkorperforschung, Heisenbergstrasse 1, D-7000 Stuttgart80, Germany; Institute of Microelectronics Technology, The Academy of Sciences of Rus-sia, Chernogolovka, Moscow District, Russia

The theory of transitions between spin-split edge channels in the quantum Hall effectregime is developed. The spin-orbital interaction is considered as a mechanism of spin flip.This mechanism is related to the absence of an inversion centre either in the elementarycell of the GaAs crystal or in the direction perpendicular to the heterojunction interface.It is shown that the mechanism is capable of accounting for the recent experimental data.

8P:a28

INVESTIGATION OF LOCALIZED STATES IN THE REGIME OF QUANTUMHALL EFFECT USING THE ACOUSTOELECTRIC EFFECT

A. ESSLINGER, A. WIXFORTH, R.W. WINKLER, S. MANUS, and J. P. KOTTHAUSSektion Physik der Universitat Munchen, 8000 Munchen 22W. NICKELForschungsinstitut der Deutschen Bundespost, 6100 DarmstadtG. WEIMANNWalter-Schottky-Institut der TU Munchen, 8046 Garching

The acoustoelectric effect caused by momentum transfer from a surface acoustic waveto a two dimensional electron system is used to investigate the properties of the electronsystem in the regime of the quantum Hall effect. The interaction between the phononfield and the electrons is sensitive to very low conductivities1 an. «s integrating innature. Thus our experiments reveal a novel approach to the bulk conductivity of QHEstates, whereas DC transport measurements are dominated by edge states. We observestrong quantum oscillations in both the acoustoelectric currents and fields, which can beexplained in part by a recent semiclassical model2. The occurence of a bipolaracoustoelectric Hall voltage, however, is not predicted in this picture. To explain thisobservation we propose a model involving the formation of electron- and holelike statesin the localized tails of Landau levels.

1. A. Wixforth, J. P. Kotthaus, and G. Weimann, Phys. Rev. Lett. 56,2104 (1986)2. A. L. Efros and Yu. M. Galperin, Phys. Rev. Lett. 64,1959 (1990)

237

8P:a33Tl Ba CuO : FROM NORMAL STATE TO SUPERCONDUCTIVITY

Z Z <5+x

J.L.JORDA, T.K.JONDO, M.T.COHEN-ADAD, C.OPAGISTE*, A.KHODER*.

M.COUACH*, F.SIBIEUDE**Univ.Lyon I, Lab. Phys. Chim Minerale 2, F-69622 VILLEL'^BANME ,* CENG, DRFMC/SPSMS/Lab.Cryophys., BPS5X, F3S041 GRENOBLE«• ISGMP, BP5, Odeillo, F-66120 FONT-ROMEU

The formation of pure orthorhombic type structureTl Ba CuO making use of a convenient progress in the

ternary T1O -BaO-CuO diagram is described. Whatever the

oxygen content is, the material remains normal to 1.2 K.It is showed that the transition from orthorhombic totetragonal symetry implies thallium oxide release and thus,the transition temperature is strongly influenced by theoxygen partial pressure. Tetragonal Tl Ba CuO with

Z-y Z <5

y ~ 0.2 becomes superconducting at critical temperaturesdependent on the oxygen stoechiometrv.

8P:a34NEUTRON DIFFRACTION STUDY OF Sr Ba Nb,O, CRYSTALS

A.M.Balagurov1, F.Prokert^, D.Sangaa1, B.N.Savenko1

Laboratory of Neutron Physics, JINR, 141980 Dubna, Russia2Zentralinstitut fur Kernforschung, Rossendorf, FRG

The mixed crystal system SrxBai_xNb2O6 with x 0.50 exhibitsa diffuse phase transition (PT). The essence of such a PT isthought to be in the formation of small polar regions withinthe parent phase. These small clusters form the dipole glass-like state without ferroelectric long-range order1.In our study2 of the dif fus••; (quasi-) elastic scattering it wasshown that the occurrence oi small polar regions in the unpolarparaelectric phase and their increase in number as well as insize at cooling are the most important characteristics of thezero-field cooling. SBN-x also exhibits an incommensurate super-structure (IC). The IC parameter S varies only weakly with in-creasing Sr-content ana the modulation is observed not to besensitive to the doping with other metals though they changesignificantly the dielectric and phase transition properties.Experiments reveal that 5" does not depend on an external pola-rizing field and, consequently, the modulation is not remarkab-ly influenced by changed ferroelectric ordering.

1. Schmidt G., Ferroelectrics. 75 (1988) 199.2. Savenko B.N. et al., F.erroelectrics 107 (1990) 207;

Balagurov A.M. et al., phys.stat.sol.(a) 103 (1987) 131.

238

8P:a35THE ANTIFERROMAGNETIC STATE INVESTIGATION OF La2Cu04+ SINGLECRYSTALS WITH DIFFERENT OXYGEN CONCENTRATIONS.

A.N.BAZHAN, V.N.BEVZ.P.L.Kapitza Institute for Physical Problems USSR Academy ofSciences, Moscow, USSR

The phase transitions to the antiferromagnetic, weak ferro-magnetic and like "diluted antiferromagnetic" states of theLagCuO^ single crystals has been investigated in as-preparedand annealing in oxygen and in vacuum samples with the vibra-ting sample magnetometer. As-prepared samples have the Neel te-mperatures T N = 280K and TN = 260K. The investigations of themagnetic susceptibility temperature dependencies and magneticphase transition to the weak ferromagnetic state in the singlecrystals of La2Cu04+ with differently (310K>TN>30K) show thatwith increasing of y from y » 0 to y » 0.1 there is decreasingnot only T^ but the middle value of Cu ions magnetic moments<n> from 0.67/*R to 0.15/jg. The linear temperature dependenciesof weak ferromagnetic moment appears in LagCuO^ with T^ < 80Kbecause of the randomly distributed regions with broken anti-ferromagnetic order, determined by random distribution of themagnetic ions interactions, [1].[I]. A.N.Bazhan, V.N.Bevz. 1991, Superconductivity, v.4, p.100.

8P:a36SUPERCONDUCTIVITY IN DOUBLE-DOPED La1+xCa Ba2_ Cu 3O ? + 6 SYSTEM

F.C.iiATACOTTA3 , P.STASTNY', C.U.SERGE\ T.MERTELJ*

IITM/ICTP HTS Laboratory, P.O.Box 586, Trieste, Italy

'Ffic.of Math.and Phys. .Charl .Univ. ,Ke Karlovu 5, 12116 Prague 2!Dept.of Physics,Illinois Inst.of Techn..Chicago,Illinois,USA

'CNH-ITM.Via Bassini 15,Milan, "iJS.Jamova 39,Ljubljana

The interval of existence of doubly-doped La1 Ca Ba_ Cu-jO-

as well as its superconducting and optical properties were stu-

died. The serie of samples without Ca were prepared under spe-

cial heat treatment in order to show the influence of Ca in this

system. Single phase samples have been found for 0< x< 0.5, de-

pending on the Ca content. Metallicity and superconductivity

were preserved throughout the single phase region. The inter-

play of direct doping due to Ca ions and usual charge transfer

mechanism seems to rule the superconducting properties in this

system.

239

8P:a37ON THE VALENCE OF PRASEODYMIUM IN

V. NEKVASIL1), E. HOLLAND-MORIT7,21, H.-D. JOSTARNDT2',

V. WALTER3), G. HILSCHER4)

1) Institute of Physics, Cukrovarnicka 10, CS-162 00 Praha 62) Universitat zu Koln, ZiHpicher str. 77, D(W)-5000 Koln 413) DLR Koln Porz, Linder Hone, D(W)-5000 Koln 904) TU Wien Wiedner Hauptstr. 8-10/131, A-1040 Wien

Praseodymium appears to be a primary cause of the suppress ionof superconductivity in PrBa2Cu3O7. Mechanisms proposed to ex-plain this phenomenon can be distinguished according to the as-sumed valence of Pr ions. It is shown that the crystal-fieldsplitting deduced from our inelastic neutron scattering dataand specific heat data in applied magnetic fields up to 11 Tcorrespond to the scheme predicted theoretically for trivalentPr '. Special.! attention is paid to the study of the nature ofthe symmetry lowering at Pr sites observed in the oxygen def f.i ••cient samples at low temperatures.1. Nekvasil V. et al., J. de Phys . 49(19881C8-955.

8 P : a 3 8

LIGHT SCATTERING FROM R 2 B A M 0 5 OXYDES WITH R = LANTHANIDEAND M = Co, Ni AND Cu.

A.de ANDRES1, S. TABOADA1, J.L. MARTINEZ1, A. SALINAS2, R. SAEZ-PUCHE2

1 Institute- de Ciencia de Materiales, C.S. I.C. . Dpt. Fisica Aplicada C-4.Universidad Aut6noma de Madrid 28049 Spain.2 Dpt. Quimica Inorganica. Universidad Complutense de Madrid 28040 Spain.

Many new families of mixed oxydes have been syntetized since the discoveryof the superconductivity in this kind of materials. Among the numeroustechniques used to characterize their properties, light scattering has beenfound to be a very useful tool because its strong relation with thecrystallographlc, electronic and magnetic structures.

Raman spectroscopy allows to observe optical phonons, magnons and alsoelectronic transitions too weak to be observed with usual luminescencetechniques. Based in these informations we present a study of the role ofthe transition metal (M) in the phonon spectra and in the charge transferprocesses. These compounds present two different structures with spacegroups Immm and Pnma, moreover several Ni and Co compounds are polymorphic,the obtained phase depends basically on the syntesis temperature. Thevibrational study as a funtion of the lanthanide ion is done for bothstructures.

240

8P:a39

FIELD-DEPENDENT THERMAL CONDUCTIVITY IN Bi2Sr2CaCu208+*:EVIDENCE FOR ANOMALOUS FLUX LINES?

A.J. Smits, J.M. van Ruitenbeek, P.H. Kes, M.J.V. Menken*, A.A. Menovsky*.L.J. de JonghKainerlingh Onnes Laboratory, Leiden University, P.O.Box 9506, 2300 RA Leiden, TheNetherlands*Natiiurkundig Laboratorium der Universiteit van Amsterdam, 1018 XE Amsterdam.The Netherlands

The high-temperature superconducting cuprates are layered superconductors with quasitwo-dimensional characteristics. This property is more outspoken for the extremelyanisotropic Bi-compounds (e.g. BiiSriCaCi^Os) than for the anisotropic YBa2Cii3O-.We havp studied this anisotropy. reflected in the vortex structure, by measurement of thethermal conductivity (K) of single crystals of Bi2Sr2CaCu2Os+/, where two parametersare varied: the magnetic field, and the angle between this field and the c-axis of the.•rvstr.!. At a temperature of 30 K the vortices parallel to the c-axis cause a reductionof K which is at least ten times larger than the reduction caused by vortices in theab-plane. This strongly suggests that vortices in the ab-plane can be described as.Tosephson vortices.

8P:a40

OBSERVATION OF VORTEX PINNING BY TWINNING PLANES IN TILTEDMAGNETIC FIELDS IN YBaCuO SINGLE CRYSTALS

I.V.GRIGORIEVA, L.A.GUREVTTCH, L.A.VINNIKOVInstitute of Solid State Physics, USSR Academy of Sciences,142432, Chernogolovka, Moscow distr., USSR

A technique of decorating a superconductor with fineferromagnetic particles has been used to study vortex pinningby twinning boundaries in YBaCuO single crystals for themagnetic fields both parallel and tilted to the c-axis andtwinning planes. The value of pinning potential at the twinningboundary was estimated from the difference of vortex densitiesalong twinning planes and in the bulk. Surprisingly, in thetilted magnetic fields this value was found almost unchangedwithin a broad interval of tilt angles from 0 to 37 andvanishing only for the angles larger than 42 while normallypinning forces are expected to drop rapidly when vortices areno more parallel to the planar defects. The results testifyunambiguosly to a pinning-induced formation of a new type ofvortex structure - zig-zag or stepwise vortices. Numericalcalculations have shown that this becomes possible due to thelayered structure of these materials. A comparison with thevortex pinning by planar defects in conventionalsuperconductors has been made.

241

8P:a41

INFLUENCE UP PREPARATION CONDITIONS ON QUALU'Y OF ÏBaCuO AND

BiSrCaCuû SINGLE CRYSTALS

M. MBHBÜI», P. DIKO1, ¥E MIN, R. DELTOUR

Université Libre Bruxelles, Service de Physique des Solides,

Boulevard du îriomphe C? 233, jj-iü^O Bruxelles, Belgium.

1/ Institute of Experimental Physics, Slovak Academy of

Sciences» Solovjevova 47» 043 53 Kosice, Czechoslovakia.

YBaCuü and BiSrCaCuü undoued and dopud single uryatals were

examined by light and electron metallography and EDX inicroaria—

lysis. Defect in the crystals as secondary phases, cruoKs and

oxygen unhoinogeuities wer« documented and diaoused v.iih the

preparation conditions and superconducting characteristics.

8P:a42LOW-TEMPERATURE CRYSTALLIZATION OP HIGH TC Y-Ba-Cu-O THIN FILMS BYRESISTIVE EVAPORATION

JACOB AZOULAYCenter for Technological Education Holon aff. with Tel-Aviv University52 Golomb Street, Holon 58102, Israel.

The post deposition heat treatment normally required for Y-Ba-Cu-0 high Tcsuperconductors preparation is notoriously known for its destructiveeffects, such as accelerating diffusions processes and creating surfaceroughness. It is therefore essential to fabricate thin film of thismaterial by insitu low temperature processes particularly when micro-electronic applications are concerned. In this study thin films ofY-Ba-Cu-0 were insitu prepared with the use of a simple conventionalinexpensive vacuum system1. No thickness monitor or control system isrequired. Pulverized mixture of Y, BaF2 and Cu constituents.weighed in theatomic proportion was evaporated from resistively heated source onto an MgOsubstrate. The substrates temperature was then raised to 700°C afterevaporation. Oxygen was injected through a nozzle placed near thesubstrate surface thus raising the pressure to about 50 mtorr. The filmwas kept at this stage for 30 min. after which it was gradually cooled toroom temperature and the pressure raised to atmospheric pressure. Theobtained films with no further heat treatment were found to besuperconductors with zero resistance at 85K detected by four probe dcmeasurements.

1. J. Azoulay, to appear in Phys. Rev. B. (September 1991).

242

8P:a43YBaCuO THIN FILM LASER DEPOSITION ON POLYCRYSTALLINE AND CRYS-TALLINE SUBSTRATES

M.Jelinek, M.Bejdova\ Z.Janfl, V.OlsanInstitute of Physics, Czech.Academy of Sciences, Na Slovance 2180 40 Prague 8V.ValvodaFaculty of Mathematics and Physics, Charles University,Ke Karlovu 5, 120 00 Prague 2

Results of the YBaCuO thin film laser deposition with io-dine, Nd:YAG, SH Nd:YAG and KrF excimer lasers are presented.As substrates alumina, polycrystalline SrTiO,, and 1102 sapphi-re were used. Problems with ZrO2 buffer layer deposition arediscussed. Superconductive layers were deposited in "ex-situ"and "in-situ" arrangements.On polycrystalline substates as alumina and polycrystallineSrTiO, zero resistance temperatures T of 65 K and 74 K werereached. On Y-cut LiNbO, and ZrO2 polpcrystalline on 1102 sa-pphire T of 83 K and 82 K were measured. Layers were characte-rized by ac-four point method, scanning electron microscopy,Rutherford backscattering, x-ray diffraction and PIXE. Atten-tion to the film surface morphology was also devoted.

8P:a44A SYSTEMATIC STUDY OF THE IN-PLANE EPITAXY OF C - AXIS ORIENTED

YBCO THIN FILMS DEPOSITED ON SrTiOg SINGLE CRYSTALS

H.-U. Habermeier, B. Leibold, R. Wegerer and H. DittrichMax-Planck-Institut fur Festkorperforschung, Heisenbergstr. 1 W 7000 Stuttgart- 80,FRG and Zentrum fur Sonnenenergie- und Wasserstoff—Forschung Stuttgart und Ulm,Hefibruhlstr. 61, W 7000 Stuttgart - 80, FRG.

Conventionally, standard in-situ YBCO thin film deposition techniques using latticematched oxide substrates result in films with the c-axis perpendicular to the film plane.The epitaxial growth which requires the alignment of the a or b axis of the YBCO withrespect to the cubic unit cell of the substrate is usually controlled by x-^ay diffractiontechniques, basically by the <j> scan of the ( 103 )— lattice plane. In our experimentsstandard YBCO thin films were prepared using the pulsed laser deposition techniqueand characterised by x— ray diffractometry and Raman scattering. All films show"epitaxial" growth in the x - ray analysis; Raman scattering, however, reveals that someof the films have the a,b orientation random. A detailled analysis of this discrepancy hasto consider the different mechanisms of the scattering process in both methods and thegrowth mechanism of the film. A set of parameters for the deposition will be derivedgiving rise to the complete alignment of the film with respect to the cubic unit cell ofthe substrate.

243

8P:a45

TEMPERATURE AND MAGNETIC FIELD DEPENDENCE OF CRITICAL CURRENTSIN YBaCuO THIN FILMS PREPARED BY LASER METHODS

C. COUTAL, M.G.MEDICIS, I. ABOUDIHAB, A. AZEMA, P. GAUCHEREL,A. GILABERT, J.C. ROUSTAN, P. SIBILLOT.Laboratoire de Physique de la Matiere condensed, URA 190, University de Nice, PareValrose, 06108 Nice Ccdcx (France)

We report on the experimental critical current density JC(T,H) versus temperature T and weakmagnetic fields H of thin films of YBa2Cu3O7.x. These films are obtained on (100) SrTiO3

substrates using the pulsed laser deposition technique ( bombardment of a YBa2Cu3O7 x

target by a beam of an pulsed ArF excimer laser). We find that near the critical temperature Tc,JC(T) is proportional to (1 - T/Tc)

2. We have found that the critical current density JC(H) doesnot depend on a weak magnetic field H perpendicular to the c axis (and to the curent) whileJC(H) decreases linearly when H is parallel to the c axis. This behaviour can be understoodwith a model of an array of SNS Josephson weak links between the superconducting grains.

8P:a46

GROWTH OF YBa2Cu307 FILMS ON SEMICONDUCTING Cu2OSINGLE CRYSTALS AND ON OXIDIZED COPPER

A. GINSBACH, G. ADRIAN, W. WILKENS, R. SCHNEIDER, G. SCHULZ,G. GRUENINGER, G. GRABEDaimler-Benz AG, Research Institute Frankfurt, Germany

We investigated YBa2Cuj07 films on Cu2O single crystals and on oxidized Cu sheets.Important for the oxidation of the Cu sheets and the deposition of YBa2Cu3O7 are thediffusion profiles of copper and oxygen within the YBa2Cu307 and copper oxide layers.Cu forms two stable oxides, CuO and Cu2O. Of these, only Cu2O forms a stable coatingof the Cu sheets. The phase diagram of these oxides shows a stable region for Cu2Oand the tetragonal phase of YBa2Cu3O7. We, therefore, deposited YBa2Cu3O7 films onCu/Cu2O, by inverted-cylindrical-magnetron sputtering. Four-point measurements showmetallic behaviour of R(T) and a resistive transition temperature of TCi0I,je( = 89 K, butwith a large transition width. The reason for this could be the diffusion of Cu out off thesheet. YBa2CusO7 films were also deposited on Cu/jO single crystals. Cu2O has a cubicionic lattice with a lattice parameter of a = 4.27 A. X-ray measurements show that theYBa2Cu307 films are chiefly polycrystalline with a small preference to c-axis orientation.This result is supported by SEM investigations of the YBa2Cii3O7 surfaces.

244

8P:a47CONTROLLED PREPARATION OF OXYGEN DEFICIENT YBa2Cu3O2: FILMS.

M. MAENHOUDT, B. WUYTS, S. LIBBRECHT, Z.X. GAO, E. OSQUIGUIL, andY. BRUYNSERAEDELaboratorium voor Vaste Stof-Fysika en Magnetisme, Katholieke Universiteit Leuven, B-3001 Leuven, Belgium

A simple method based on the Po2-T phase diagram has been used to prepare oxygendeficient YBa2Cu3Ox thin films. Systematic critical temperature and x-ray diffractionexperiments clearly show that films with different oxygen contents are obtained in a con-trolled, reproducible and reversible way1. However the typical 90 K and 60 K plateaus areabsent in the Tc(x) curve. In order to investigate the possible influence of the preparationmethod on this puzzling result, we will present a systematic study of Tc(x) as a functionof independent variations of the stabilization temperature, quenching temperature andquenching rate of the films.

1. E. Osquiguil, M. Maenhoudt, B. Wuyts and Y. Bruynseraede, submitted to Appl.Phys. Lett.

This work is supported by the High Temperature Superconductivity Impulse and Con-certed Action Programs, financed by the Belgian State.

8P:a48

MAGNETIC INVESTIGATION OF PINNING AND DIS5IPATIVE EFFECTSIN Bi(Pb)-Sr-Ca-Cu-O SUPERCONDUCTOR

D. Fiorani, A.M.Testa

ITSE, CNR, Area delta Ricerca di Roma (Rome), Italy

Pinning and dissipative effects have been investigated in Bi-Pb-Sr-Ca- CuO samples (sinteredand single crystals) by measurements of:a) hysteresis cycles;b) the time decay of the zero field cooled magnetization (Mzfc);c) the (H,T) irreversibility line measured by both DC and AC techniques.The field dependence of the reduced pinning force (Fpfl3pmax) was evaluated between 18K and50K. No scaling behaviour was found in this temperature range.For all the samples investigated logarithmic decays of the magnetization were observed forT<50 K and H = 3 kOe, with an apparent activation energy Uo increasing with temperature;

for T> 50 K, the decays follow a (Int) ~ ° (a>0) law. The behaviour of Uo and the crossoverlog- non log in the time decay of Mzfc are discussed in the framework of extensions [1] of thestandard theory of Anderson and of collective pinning [2]. The (H,T) line ( measured by DCand AC techniques) follows a power law, 1- Tin(H)/Tc a Hn , with 0.30< n <0.40.

1) C.W. Hagen et al., Phys.Rev.Lctt. 62 (1989) 2857.2) M.V. Feigelman et al., Phys.Rev.Lctt. 63 (1989) 2303.

245

8P:a49

ELASTIC AND INELASTIC NEUTRON DIFFRACTIONON ANTIFERROMAGNETIC Bi2CuOt

M. Aïn, G. Dhalennef, J. P. Ambroise, P. Molina, G. Parette, A. Menelle, A.Revcolevschif.

Laboratoire Léon Brillouin (CEA-CNRS), CEN-Saclay 91191 Gif/Yvette CedexFRANCE

^Laboratoire de chimie des solides (Bat 4U) - ^A CNRS 446 Université de Paris-Sud. - 91405 Orsay Cedex FRANCE.

is a newly studied1 copper oxide with an antiferromagnetic transition atTN — 47.5±1 K. Neutron polarization analysis will show that the magnetic momentsare in a plane perpendicular to c-axis.

Each copper of this compound is coordinated by four oxygens forming (CuOt)square plate. Two such nearest neighbors coppers interact through superexchange cou-pling Cu-0-Bi-O-Cu. An estimation of the strength of this coupling will be deducedfrom the analysis of the spin waves dispersion curves along [100] and [001].

1) J. KonstantinovicJ, G. Stanisicf, M. Aïn, G. Parette; J. Phys.: Condens. Matter.3(1991)381-384.

8P:a50

HIGH To BISMUTH CUPRATES 2223 DOPED WITH Cr Mn AND Fe

A.Grozav, V.Kantser, L.Konopko, N.Ieporda, M.Onu, G.Panaitovand G.VolodinaInstitute of Applied Physios, Kishinev, 277028, Moldova

We have investigated the high T. ceramics Bi Sr Ca (Cu M ) 0C 2 2 2 1-x x 3 y

where M=Cr, Mn, and Pe, x=0, 0.02, 0.05. The resistivity of themost doped samples showed two-step superconductive transitionat about 105 K and 95 K (XRD showed only 2223 phase). Low-fieldmagnetization data were obtained using a SQUID magnetometer. Itwas found that the samples doped with Mn exhibit lower fluxoreep rate than the samples without the dopant, and on the con-trary the samples doped with Pe exhibit higher flux creep rate.This result indioates that pinning oenters differ greatlydepending on dopant elements. Substitution of Cr and Mn for Ouwas found to be effective to stabilize 2223 phase.

246

8P:a51PHASE COMPOSITION STUDY OF Bi-Pb-Sr-Ca-Cu-O SUPERCONDUCTORS

H. SICHOVA, K. JIRMANOVA, S. BERNIK+

Fac.of Math.and Phys..Charles Univ.,Ke Karlovu 5, 12116 Prague 2

"""institute "Jozef Stefan", Jamova 39, Ljubljana, Slovenija

Samples with nominal composition Bi1_xPbxSr0 Ca^i^ ^0^

(x = 0, 0.15, 0.2, 0.25, 0.3, 0.4) were prepared by mixing,

pelletizing, grinding and heating processes. The final samples

were studied by powder X-ray diffraction technique. The

results were compared with d resistance and a susceptibility

measurements. Precise X-ray phase analysis of samples with dif-

ferent Pb concentration has shown besides the dominant high

T phase ((BiPb)oSroCa~Cu.,0 ) the evidence of other nonsupercon-

ducting and low T phases. Diffraction spectra of samples were

analyzed by Rietveld method to study texture, phase composition

and localization of Pb atoms in high Tc phase. The changes

of structure, electric and magnetic properties were detected.

8P:a52THE EFFECT OF REACTION CONDITIONS ON THE Bi, cPb n .Sr, Pr Cu0c .SYSTEM 1.6 0.4 2 x x 6+6

P.STASTNY1, N.LEYAROVSKA2, F.C.MATACOTTA%, C.U.SERGE*, S.BERNIK*1ITM/ICTP HTS Laboratory, P.O.Box 586, Trieste, Italy'Fac.of Math.and Phys..Charl.Univ.,Ke Karlovu 5, 12116 Prague 22Dcpt.of Physics,Illinois Inst.of Techn..Chicago,Illinois,USA'CNR-ITM.Via Bassini 15,Milan, "iJS,Jamova 39,Ljubljana

The final properties of Pb- and Pr-substituted 2201 superconduc-tors depend on processing parameters such as annealing tempera-ture, reaction time and atmosphere and cooling schedule. As thePr-content is reduced, their effect becomes more important andless reproducible. For samples having the compositionBij 6Pb Q 4Sr 1 5 5Pr Q 3 & C u 0 6 + 6 the TQ varies from less than 10K up

to 30 K. We have found that during the final annealing at hightemperature there is a sizable loss of lead. As the lead evapo-rates, several processes are taking place and are kinetically incompetition so that the final results depend on the detailedthermal history of a given sample. Qualitative results indicatethat the occurrence of the substitution of bismuth at theSr-site (one of the possible consequences of lead loss) is onecause of the extreme variation of the intrinsic properties ofthis compound. No positive effect of nitrogen atmosphere hasbeen detected but as the weight loss rate and decompositiontemperature depend very strongly upon atmosphere composition.

247

8P:a53REVERSIBLE 109 - 113 K AKD 85 - 80 K SHIFTS OFI K B i - S r - C a - C u - 0 SUEEECONDUG5EOES

p. BOEXSEK, J. FRACHASOVAInst. of Physics CSAS, Na Slovance 2, 180 40 Praha 8, CSER

The BiSrCaCUpO ceramic samples werecooled from 600°C»Fig. it the fall - line curves - coo-ling lQ0°C/3ec, dashed - line curves- cooling 1 - 2°C/min»Fig. 2: the T« - T dependences - eo-

ft "L

incidence with modulation structure transition at 490 C •

TI«CI 300

1. Chen Q. et al», Chinese Phys. Lett. 6 (1989) 39

8P:a54ELECTRICAL RESISTIVITY AND MAGNETIC SUSCEPTIBILITY ROUNDINGSABOVE THE SUPERCONDUCTING TRANSITION AND PAIRING STATE IN

C. Torron, O. Cabeza, J.A. Veira, J.Maza and Fdlix Vidal

Laboratorio de Ffsica de Materiales, Departamento de Ffsica de la Materia Condensada,Universidad de Santiago, 15706 SPAIN

The rounding effects above the superconducting transition of the electrical resistivity and of themagnetic susceptibility have been measured in the same Bi | 5Pb0 5Sr2Ca2Cu3Oypolycrystalline compounds. Our results confirm the absence of appreciable non-universalMaki-Thompson and structural inhomogeneity effects. The results for both observables can beexplained simultaneously and consistently in terms of two-dimensional order-parameterfluctuations in pair-breaking layered superconductors with a two real component orderparameter, but assuming also the presence, only in the paraconducti vity, of an unconventionalcontribution having a Lawrence-Doniach-like temperature dependence. These last conclusionsapply also to our previous experimental results for Y iBa2Cu3O7_6 samples, where order-parameter fluctuations in the mean-Held region are three dimensional.

248

8P:a55

POINT CONTACT SPECTROSCOPY ON Bi.., Sr , ,CaCu 2 O 8 t

B. Susla, S.C.Meepagala, E.L. WolfInstitute of Physics, Poznan Technical University

ul . Piotrowo 3, 60-965 Poznan, PolandDepartment of Physics, Polytechnic University,Brooklyn, N. Y. 11201, USA

Point contact spjctroscopy (PCS) can play an important rolein the investigation of high temperature superconductors.Measurements of dynamic resistance dV/dl versus voltage atthe point contact beetwen single crystals or BiSrCaCuO/Agsintered material and gold tips have been made. The spectraexhibit tunneling structure, which are interpreted in termsof the energy gap structure 2i = 25meV at 4.2K. We haveobserved the strong Andreev reflection of theAu-BiSrCaCuO/Ag boundary. It also shows that good metallicpoint contacts to BiSrCaCuO/Ag ceramic superconductor can bemade.

8P:a56

TEMPERATURE DEPENDENT PHASE SEPARATION IN THE EMERYMODELJ.Carstensen and K.Dichtel, Institut fur Theoretische Physik der Universitat Kiel,Germany

The variations] principle of Bogoljubov for different test Hamiltonians is applied to thehole doped two dimensional Emery model of the copper oxygen planes in the HTSC ma-terials. For an ansatz optimized for small values of the ratio hopping constant/Coulombcorrelation the curves chemical potential versus doping concentration show large regions ofthermodynamic instability. The temperature and parameter dependance of these coexistenceregions of phase separation is determined numerically. The complete phase diagram of para-,ferro-, antiferromagnetic and separated phases within this method for realistic parametervalues in the cuprates is given.

249

8P:a59THE SURFACE OPTICAL RESPONSE OF CLEAN AND OXIDIZED

Si (100) SURFACES

C.M.J. WJJERS. Twentc University of Technology, P.O. Box 2)7,

7500 AE Enschede, the Netherlands

For a solid surface, subdivided into cells, an expression has been developed, which

allows fur the direct calculation of the cellular local polarizability tensor. Using

a previously developed discrete dipole programme the macroscopic surface opical

response can be obtained from these polarizability tensors. The expression requires

ihe coefficients of the wavefunctions of the system expanded on a local basisset.

These wavefunctions were obtained from a cluster programme and hence the optical

behaviour of clean and oxidized Si (100) surfaces could be calculated and compared

with experiment.

8P:a60SURFACE STATES ON SILICON: COMPARISON OF PSEUDO-PERIODIC AND EM-BEDDED SURFACE LAYER RESULTS.

D I EASTERBROOK and P M LEESchool of Physics and Materials, Lancaster.University, Lancaster, UK, LAI 4YT.J E INGLESFIELD, Physics Department, Nijmegen University, Nijmegen, Netherlands.(E-mail: pml@uk.ac.lanes.cent 1)

Calculations have been carried out using the LMTO method on structures demonstratingsurface state features by including layers of empty spheres in an elongated tetragonal cellarrangement. Those have been applied in the case of a silicon (100) surface to demonstratechanges in the densities of states for such a free surface. Results are compared with k-resolvedsurface state calculations using an embedding method for a similar surface layer. Additionalresults are presented for simple dimer model reconstructed surface showing that in this casethere is a tendency for the energy gap to reappear.

250

8P:a61SURFACE ELECTRONIC STRUCTUREAND UPS SPECTRA FOR Cu/Pd SYSTEMSF. MACA and J. KOUKALInstitute of Physics, Czechoslovak Academy of Sciences, PragueNa Slovance 2, CS-18040 Praha 8, Czechoslovakia

We report results of theoretical calculations of electronic structure aswell as of angular resolved photoemission spectra for a CuPd(lOO) su-perlattice and for the centered tetragonal Cu. The layer KKR schemefor an ideal geometry is used. Both structure have recently been grownby molecular beam epitaxy. The main superlattice effects are a smallpeak experimentally observed in Ne I and He I normal photoemissionand a surface resonance on the tetragonal Cu. Both structures are wellreproduced. The results are discussed with respect to the question ofinterdiffusion in CuPd systems.

8P:a62UNOCCUPIED ELECTRONIC STATES OF RECONSTRUCTEDInP(lOO)- AND GaAs(100)-SURFACES

S. RIESE, E. MILAS and H. MERZ

Physikalisches Institut der Universit&t MQnster, W-4400 Munster

InP(100)-surfaces, prepared by sputter annealing at very low ion energies, have been

investigated with k-resolved inverse photoemission (hw = 9.9eV) along the T — ~J direc-

tion of the surface Brillouin zone. The characteristics of our halogen-free CaF2/Acetone

band pass detector will also be reported. In the normal incidence spectrum two direct

bulk transitions and a DOS peak are identified. A surface state, about 1.5eV above VBM,

shows the periodicity of a (4x2) reconstructed surface, in opposition to LEED which

shows a (4x1) symmetry. The InP(100)-results will be compared with an analogous study

of GaAs(lOO).

251

8P:a63SURFACE PLASHON COUPLING IN LAYERED METALLIC GRATINGS.

SRESELI a.H. BELYAKOV L.V. GORYACHEV D.N. RUHYANT5EV 8.L. YAR0SHET3KII I.S.A.F.Ioffe Physico-Technical Institute, 194B21, St Petersburg, USSR.

Propagation and coupling of surface plasmons (SP) in layered metal -semiconductor structures such as MQS and Schottky diodes with diffractiongratings on their surfaces as well as influence of SP on photoelectricproperties o-f these structures are considered- The electromagnetc fielddistribution has been calculated numerically. The predicted effects havebeen studied experimentally. The most interesting ones are: resonantelectroluminescence, caused by SP reradiation; interaction of two eigen-modes at outer and inner metal boundaries via grating and field resonanttunneling through the metal film; non-triviai dependence of SP node atthe inner metal - semiconductor interface an oxide thickness and others.

The Schottky diodes with corrugated surfaces exhibit resonant photore-sponse due to 5P excitation [13. This effect enhances the diode efficien-cy and enaow the riiooe a frequency, angle and polarization selectivity.These resonance properties are useti for the design of the narrow-band(a few at nanometers'? tunable photodetectors for the visible, UV and iftrange? of wavelengths, and polarization-sensitive photodetectors.1. Beiyakcv L. st al, Sov.Tech.Pnys.Lett. Sll <!9S3> 481.

8P:a64ANOMALOUS VARIATION OF THE M4 g W AUGER PROFILE OF Pd WITH

SURFACE COVERAGE ON Ti SUBSTRATE

2. BASTL AND P. MIKUS^K

J. Heyrovsky Institute of Physical Chemistry andElectrochemistry, Czechoslovak Academy of Sciences.Dolejs'kova 3. 182 83 Prague 8, Czechoslovakia

Experimental data obtained by X-ray excited photoelectronand Auger spectroscopy of Pd deposited on Ti, amorphouscarbon and some other metal substrates are presented. Incase of the Pd/Ti system C13 it is found that ratio betweenthe Auger M 4 W and ^ W signals, shift of the M_ shake-up

satellite, width of the M. _ W profile and shift of the

kinetic energy, as a function of Pd coverage, reach extremalvalues between one and two monolayers. Interpretation of thePd M4 5N 4 5N 4 g Auger profiles is given in terms of the

initial and final state effects. The present results invokean idea that screening and bonding effects culminate betweenone and two Pd monolayers on Ti.

fl] P.MikuSfk and Z. Bastl, Phys. Scripta 41C19903130.

252

8P:a65

INFLUENCE OF SURFACE SCREENING ON THE PEAK

HEIGHT IN PHOTOEMISSION SPECTRA

D. Samuelsen and W. Schattke, Institut fur Theoretische Physik, Physikzen-

trum, Universitat, D-2300 Kiel, Germany

Photoemission spectra are calculated for normal emission within the one-

step model to estimate the dependence on the surface fields. The vector poten-

tial of the photon field is determined via a realistic simulation of the dielectric

screening in the surfcace near region and as such is incorporated in the pho-

toemission calculation. The spectra show a strong influence of the screening

on the relative intensities of peaks associated with special orbital symmetries.

The variation of this effect with photon energy is very pronounced above the

plasmon frequency as well as below. The comparison with experimental data

on TiS2 shows surprisingly good agreement.

8P:a66SCANNING TUNNELING MICROSCOPY AND SPECTROSCOPY AT Ge(lll)SURFACES.P. MOLINAS-MATA. J. ZEGENHAGEN, and M. CARDONAMPI fur Festkorperforschung, Heisenbergst. 1, 7000 Stuttgart 80, F.R.G.

We have investigated the Ge(lll) surface by means of both voltage-dependent constant-current mode (CCM) and current-imaging tunneling-spectroscopy (CITS) measurements.On the defect-free Ge(Ul)-c(2x8), normalized differential conductivity (dI/dV)/(I/y),derived from CITS, yields a local density of states (LDOS; at the surface in qualitativeagreement with EELS1 and photoemission3 results.Scanning with CCM, at positive and negative bias, we analyzed point defects, some ofthem invisible at positive bias, and line defects, both appearing within large defect-freec(2x8) regions. We gained insight into the local charge transfer in the defective regionsimaging at different bias values. Thus the point defects are believed to arise from atomiclocal substitution.1 RXudeke et al., Phy. Rev. Let. 33, 653 (1974).2 T. Yokotsuka tt al., Jap. J. Appl. Phys. 23, L69 (1984).

253

8P:a67MODIFICATION OF H-PASSIVATED SILICON SURFACES STUDIED BY SCANNINGTUNNELLING MICROSCOPY AND SPECTROSCOPY.1

F.Pe"rez-Murano, N.Barniol, X. Aymerich.Dept. Ffsica-Electronica. Universitat Autonoma de Barcelona.08193-Bellaterra. SPAIN.

In this communication, the nanometer-scale modification of hydrogen-passivated n-typeSi(100) by scanning tunnelling microscopy (STM) operated in air is reported. We producethe modification of the surface while scanning (without changing the normal conditions forimaging: L=l nA, V,=1.4V). The evolution of the surface with time is studied, comparingthe results obtained from the three operation modes of the STM: topographic imaging, currentimage tunnelling spectroscopy (CITS) and local barrier height imaging. The surface showsboth: a lower local barrier height and a less rectifying behaviour in the current-voltage curveson the modified area. From these results, it is shown that not only the topography of thesurface has been modified but also the local electric properties are different. The dependenceof the modification of the surface with the cleaning method is also studied.

1 Work partially supported by CIR1T.

8P:a68T H E O R Y OF T U N N E L L I N G C U R R E N T S I N D I T E D BY LASER RADIATION IN STM

A . L E V Y YEYAT1 AND F . F L O R E S . Depar tamento de Fi'sica de la Mater ia Cor.densada.Universidad Au tonoma de Madrid. E-280-19 Madrid. Spain.

Different problems related to the interaction between tunnell ing electrons and laser ra-diat ion in the STM junction are currently being investigated by means of the Keldyshnon-equil ibrium Green 's functions formalism in a simple t ight-binding representat ion. Ourmain objective is to describe the behaviour of the induced tunnell ing cur ren t s as a functionof photon energy, t ip-sample dis tance, material propert ies , and other relevant p a r a n e t e r s .In previous works ' we have focused on the problem of the rectified signal arising due to thenon-linear characterist ic of the STM junct ion. If the tip is now placed near an absorbedm o W u l e on ' h e sample surface the rectified signal will be substant ia l ly modified due totin1 coupling between tunnelling <]i'<Uons «!.d \ ib ra i iona! modes of the ahfrorhate. In thepresent work, this situation is considered by including a local phonon propagator in theformalism. We obtain simple expressions for the photorurrent that can be compared to thecase where a direct bias is applied to the junct ion. Another problem of practical interestis the generation of difference frecuenry signals by mixing two lasers beams of differentfnTijrncif". i nc i drill on the turn.' 'Hinc junction. A5 in the cave of the rectified si en a! this isalso a second order process ami thus tin' tln'..ry proceeds in a similar way. We discuss ourre.-iilts in the light of recent <• x(i<• r i11 L'• i.t :il data .

1 - A.Levy Yeyati and F.l ' lores. I'liys Rev 1) 4 4 . 9020 (1991) and to be published inUllramycroscopv.

234

8P:a69THEORY OF SCANNNG TUNNELING MICROSCOPY.

TH. LALOYAUX. I. DERYCKE, J.-P. VIGNERON, PH. LAMBIN AND A. A. LUCAS.Facultes Universitaires Notre-Dame de la Paix, rue de Bruxelles 61, 8-5000 Namur, Belgium.

This paper is concerned with a theoretical study of the scanning tunneling microscope (STM). In the models weconsidered, both the tip and the sample are free-electron metals for which we assume various simplegeometries : hemispherical (monoatomic) or cylindrical (multiatomic) tip facing a planar surface or a surface witha gaussian boss or dip. The potential barrier between tip and sample includes the applied bias and the exchange-correlation interaction between the tunneling electron and the charges inside the tip and the sample,approximated by the classical multiple-image potential. The wavefunctions of the electrons crossing the barrierwe computed by solving the three-dimensional Schrddinger equation, without further approximation. For thispurpose, we use a numerical discretization scheme, namely the finite-element method.

For the various models we considered, we plot current density maps. From these maps, we show the width of thetunnel current beam (from which the lateral resolution of the STM depends) slightly increases with the radius ofthe hemispherical tip and admits a minimum for distance small enough for the barrier to be perfored. For acylindrical tip, this width is always slightly larger than the tip radius.

Integrating the current density on the sample surface yields the total, experimentally measured, current. Fromthe dependence of the current on the bias, the distance or the lateral position of the tip we draw the fo'lowingconclusions. The measured effective work function depends on the shape of the tip and its distance from thesample. This is interpreted to be an effect of the image potential. Due to the higher curvature of the tip than thesample, the STM rectifies the current for biases larger than 11V. For higher voltages, the I/V curve displays awide resonance in the current and in the width of the current beam. A gaussian boss and a gaussian dip on themetal surface will result in twice smaller a corrugation in the constant current image.

A comparison between the results obtained with our non-perturbative theory with those obtained by the transferhamiKonian method concludes that the latter suffers less from using a first order perturbation scheme than fromneglecting the effect of the multiple images on the potential barrier.

8P:a70EDGE MELTING IN LOW-COVERAGE NEON MONOLAYERSD.. B. Pengra* and J. G. Dash, Department of Physics FM-15, Universityof Washington, Seattle, WA 98195, USA

A calorimetrir study of low-coverage (0.13-0.36 layer) Ne films adsorbedon graphite foam explores the broadening of melting peaks in the vicinityof the two-dimensional triple point. Preliminary analysis confirms earlierindications1 that premelting is due to edge melting of long strips offilm that decorate linear defects and steps on the substrate3. A newmodel which incorporates these substrate effects and a new method ofanalysis that considers coverage-dependent trends have been developedto fit the data. The fitting indicates that additional substrate effects andexperimental difficulties may interfere with the measurements; these arediscussed, and it is concluded that substrate heterogeneity and adsorbatesize effects are relatively unimportant.

'Now at Ris0 National Laboratory, DK-4000 Roskilde, Denmark.1 Da-Ming Zhu, D. Pengra, and J. G. Dash, Phys. Rev. B 37, 5586 (1988).-E. J. Freise and A. Kelly, Proc. Roy. Soc. A 264, 269 (1961).

255

8P:a71COMPRESSION PHASES IN COPPER/OXYGEN COADSORPTION LAYERS ON ARU(OOOl) SURFACE

M.SCHMIDT, H.WOLTER and JC.WANDELTInstitut fiir Physikalische und Theoretische Chemie, UniversitatBonn, Wegelerstr. 12, 5300 Bonn, F.R.G.

Dynamic work function change (*>f) measurements for the deposi-tion of Cu on a clean and oxygen precovered Ru(0001) surface,respectively, have been performed over the wide temperaturerange 2OOK - 800K. The results provide detailed insight in thekinetics of epitaxial metal-on-metal film growth. In particu-lar, the preadsorbed oxygen causes a dramatic change in the A*fcurves which can be described by a three-stage growth mecha-nism: rjp to 6(0) - 0.25 oxygen forms a p(2x2) structure. Atlower oxygen precoverages codeposited Cu first occupies oxygen--free surface regions, then causes a compression of the oxygenp(2x2) patches to a p(2xl)-like oxygen density to occur, andfinally starts to populate oxygen covered patches. These re-sults are discussed in terms of the copper and oxygen bondenergies in the various adsorption stages, which were obtainedfrom thermal desorption spectra of pure copper, pure oxygen andcoadsorbed copper/oxygen layers on Ru(0001), respectively.

8P:a72THEORETICAL INVESTIGATIONS OF THE ELECTRONIC STRUC-TURE OF ALKALI/SEMICONDUCTOR SURFACES

B.WENZIENt, A. CHASSE, W. HERGERT, P. RENNERTDepartment of Physics , Martin-Luther-University Halle-Wittenberg,Postfach, O-4010Halle ; fFritz-Haber-Institute of the Max-Planck-Society, Faraday-Weg 4-6, W-1000 Ber-lin 33; FRG

The deposition of alkali metals on semiconductur surfaces was investigated experimentallyas well as theoretically in the last years. Especially angle resolved photoelectron spectraprovide information on the the geometrical and electronical structure of the surfaces.Angle resolved photoemission spectra are calculated for different models of the real struc-ture by means of a reduced angular momentum expansion. The TB-LMTO method anda TB-recursion technique are used for the calculation of surface states and local densitiesof states.The results of the calculations are compared with experimental results and other calcu-lations.

256

8P:a73V-U PHASE DIAGRAMME OF ALKALI-COVERED SEMICONDUCTOR SURFACES

H.C.RefoUo, vi..M.L6pez Sancho, J-Rubio and M.P.L6pez SanchoInstituto de Ciencia de Hateriales de Madrid, CSICSerrano 144, 28006-Madrid, Spain

Taking as prototypical example the K/Si<100)-(2x1) interface,a Si-K hopping (V) versus Si-K interatomic Coulomb interaction<W> phase diagramme is constructed for different values of theSi intrasite correlation energy (Hubbard U). The solutionsrange from localized to itinerant, with several spinarrangements possible on the silicon surface. The issue of theinsulating to metal transition, as well as the recentcontroversy about the ionic versus covalent nature of bondingin these interfaces, is analyzed in the light of such phasediagramme. Given the extremely small bandwith of the Sidangling-bond bands (0.5 eV or less), it appears that evensmall values of the Hubbard U may have a considerable effecton the electronic properties of these systems.

8P:a74ELECTRONIC STRUCTURE AND PROPERTIES OF LIGHT-ATOMS ADSORBED ONGRAPHITE

A. RAKOTOMAHEVITRA, C. DEMANGEAT, J. C. PARLEBAS, IPCMS, UMR46,Universite Louis Pasteur, 4 rue Blaise Pascal, 67070 Strasbourg, FranceG. MORAITIS, Departement de Physique, Universite Marien-Ngouabi,Brazzaville, CongoE. RAZAFINDRAKOTO, Laboratoire d'Energetique, BP 906, Ankatso,Antananarivo, Madagascar

We have recently discussed within Anderson's extra-orbital model, the electronicstructure of impurities (Li, Be, B, C, N) intercalated in graphite. The density ofstates of pure graphite is obtained in a tight-binding scheme. The hoppingintegrals between the light impurities and the carbon are obtained throughatomistic calculations. The intrasite perturbation on the impurity is adjusted inorder to satisfy Friedel's screening rule. This leads to the occurence of high peaksin the density of states at the Fermi level. This type of calculation is extended tothe case of light atoms adsorbed upon the surface of graphite. The exact positionof the impurity is determined through total energy calculations. The resultsobtained in the case of adsorbed atoms on graphite are discussed in terms of theirchemical natures and compared to the corresponding results of atoms intercalatedin the bulk. Extension to magnetic impurities of the transition-metal type is inprogress.

257

8P:a75OSCILLATIONS IN A REACTION ON A HETEROGENOUS SURFACE

M. L. Baacon y A. O6rdobaDepartamer.to de Fisica de la Materia Condensada, Universidad de Sevilla,Apartado 1065, 41080 Sevilla, Spain

Kinetic equations of a reaction on a heterogeneous surface with two typesof adsorbent sites are considered. The scheme of the reaction is2 A(g) + V ( s ) + V(3.) -> A(si) + A(s.) ; B(g) + V<si> -» B(si> ;

A(s.) + B<s.) -• C(g) + V(si) + V(s.) , where A, B and C denote the

chemical species, V a vacant surface site, (g) gas and (s.) surface site

of i-type (i=l,2). We assume that surface temperature may be differentfrom room temperature due to reaction heat. A system of five coupledkinetic equations result. For certain values of the parameters,oscillations in concentrations and temperature can appear. We focus ourattention on the role played by degree and distribution of heterogeneity.

8P:a76ADSORPTION ON A SQUARE LATTICE: KINETIC EQUATIONS AND SIMULATION.

M.C.LEMDS and A.CORDOBA.Dpto. de Fisica de la Materia Condensada, Universidad de Sevilla, Apdo.1065, 41080 Sevilla, Spain.

Starting from a master equation the competitive adsorption of two types ofinteracting particles on a square lattice is considered, The transitionprobabilities are chosen in the A—henius form, and the activation energyis decomposed into two terms, corresponding to the action of the substrateand to interaction between nearest neighbor adatoms.The kinetic equations have been obtained using a doublet closureapproximation (DCA) and, due to interaction, up to three stable steadystates can result. The results obtained from a simulation of the MonteCarlo type also show that multistability exists in this model. This outcomedisagrees with that of adsorption on a linear chain for the same numericalmethods (DCA and simulation) where only one stable steady state exists .Thus, this model of a far from equilibrium phase transition is some whatanalogous to the Ising model of ferromagnetism where the one-dimensionalcase never exhibits equilibritm phase transition, but the two-dimensionalcase does.

1 M.C.Lemos and A.Cordoba, J.Chem.Phys. 95, 6171 (1991).

258

8P:a77HÖHTE CARLO SIMULATION OF A SURFACE KEACTIOH MOUD. WITH LOCAL INTERACTION

J.J. LUQUE, F. JIHEMEZ-KOKALES, U.C. LEHOSDepartamento de Fisica de la Hateria Condensada. Universidad de Sevilla.P.O. Box 1065. 41080-Sevilla. Spain

Influence of the interaction between nearest-neighbor adatoas in areaction of catalyzed oxidation of carbon monoxide has been studied byHonte Carlo simulation. The transition probabilities are chosen in theArrhenius form, and the activation energy is divided into two additiv«terms, corresponding to the action of the substrate and to the interactionbetween nearest adatoas, respectively.

Hher. the interaction Bakes easier desorption or hinders adsorptionthe behaviour is similar : three steady state regimes or phases wereobserved: in the first phase, the surface is poisoned by oxygen; in thesecond phase there is a reactive steady state in which carbon dioxide iscontinuously produced and in the third phase, the surface is poisoned bycarbon aonoxide. The transition froa the O-poisoned phase to the reactivephase is continuous, or second order, and the transition froa the reactionto the CO-poisoned phase is first order. The saae occurs when theinteraction is not considered. The interaction aak.es the second zonewider, where carbon dioxide is being produced.

When the interaction makes easier adsorption or hinders desorptiononly two phases are observed: in the first phase the surface is poisonedby oxygen and in the second phase it is poisoned by carbon monoxide andthe transition from one to another is first order.

8P:a78

X-RAY PHOTOELECTRON DIFFRACTION STUDY OF CO AND NOADSORBED ON Ni(ll l)

L.S. Caputi, R.G. Agostino, A. Amoddeo, A. Rotella, A. Santaniello* and E. ColavitaIN F M and Dipartimento di Fisica, Université délia Calabria, 87036 Arcavacata di Rende,Cosenza, Italy*Sincrotrone Trieste, 34012 Trieste, Italy

The structural orientation of CO and NO adsorbed on Ni(l 11) at room temperature wasstudied by angle-resolved x-ray photoemission of the C, N and O 1 s core-level peaks, using afixed X-ray source and an hemispherical analyzer mounted on a goniometer. The C and N Isintensities versus polar angle, both obtained at saturation coverage, exhibit a peak at normalemission with a FWHM of about 23°, which indicates that molecules are vertically bound (<10° tilt). In the case of CO, this result is very different from the one obtained in a similarinvestigation performed recently on Ni(llO)1, in which it has been found that at highcoverages the repulsive interaction between adsorbed CO molecules causes a tilt of 21 ° of themolecular axis with respect to the surface normal.

I D A . Wesner, F.P. Coenen, and H.P. Bonzel, Phys. Rev. B39, 10770 (1989)

259

8P:a79CHEMISORPTION OF SIMPLE ATOMS ON AL:FROM THE MONOLAYER TO THE LOW COVERAGE LIMIT

F. J. Garcia-VidalDepartamento de Fisica de la Materia Condensada C-XII.Facultad de Ciencias. Universidad Autonoma.£-28049 Madrid. Spain.

An ab-initio LCAO method is used to analyze the electronic properties of atoms havingdifferent electronegativities chemisorbed on aluminium surfaces. Results for the chemisorptionenergies, charge transfer and local density of states for alkali atoms ( Li and Na ), Si and Clare presented at different coverages (1ML, 0.5ML, 0.33ML and 0.25ML). The alkali atoms arefound to donate electron charge to the sustrate, its value decreasing with increasing coverage;the chemisorption energy is found to be critically controlled by this charge transfer, mainlythrough the dipole-dipole interaction. For Si atoms, no charge transfer is found, however,the chemisorption energy being in this case very little dependent on the Si-coverage. For Cl,electron charge is donated by the metal to the adsorbed atoms, the charge transfer being almostindependent of the coverage; the chemisorption energy is found, however, to depend on thecoverage through the kinetic repulsion between the electron clouds of the Cl-atoms, that startsoperating for Cl-Cl distances smaller than 3.5A, still in the sub-monolayer regime.

260

8P:bl01Zui-aMt^Te EPILAYERS GROWN BY HOT WALL EPITAXY ON (Ottt)GaAs

E. Abramof», A. Pesek, P. Juza, H. Sitter, T. Fromherz, and W. JantschInstitut flir Experimentalphysik, Universität Linz, A—4040 Linz, Austria.* Permanent adress: Institute» de Pesquisas Espaciais, CP515, 12201 — S.J. Campos, SP, Brazil.

Zni-xMnxTe (0.0<x<0-7) epitaxial films were grown on 2" misoriented (001) GaAssubstrates using the hot wall epitaxy technique. The Mn content of the epilayers wasdetermined by optical reflection measurements near the fundamental energy gap and bythe lattice constant measured from x-ray diffraction. The variation between the x valuesobtained from the different methods remains within 2% for samples with a Mnconcentration x<0.2 increasing up to 7% for samples with higher Mn concentration(x=0.6). The depth profile obtained from an analysis of secondary neutral molecule massspectra showed an uniform distribution of Mn throughout- toe depth of the wholeepilayer. All the epilayers in the entire range investigated grew in the [001] direction inthe zinc-blende structure. The FWHM of the (004) reflex of the x-ray rocking curvesincreased monotonically from 100 to 2300 arcsec as the Mn concentration of the epilayersincreased from 0 to 70% These values were comparable with those published for theMBE grown Zni-xMn^Se/GaAs epitaxial films, in spite of the much larger lattice misfitin the Zni-xMnxTe/GaAs heterostructures. The x values measured by high resolutionx-ray diffraction (HRXD) along the diagonal of aZn!-xMnxTe epilayer (x=0.08) showeda maximum deviation in x of 0.2% The relative tilt between the Zni-xMnxTe epilayerand the GaAs substrate lattice planes was determined from HRXD analysis. It increasedfrom 0.1 to 0.3' as the Mn concentration increased from 2 to 60%

8P:blO2

PECULIARITIES OF THE 6AFLESS STATE IN CuFeTe2

A.A. Vaipolin, S.A. Kijaev, L.V. Kradinova, A.M. Polttbotko,Y.V. Popov, V.D. Prochukhan, Yu.V. Hud, V.E. Skoriukin

A.P. Ioffe Physioo-Teconical Institute Academy of Sciences ofthe USSR, Politekhnicheskaya 26 194021 Sankt Petersburg USSR

Investigation of temperature dependence« of the specificconductivity Ö^T) and electron concentration n(T) of singlecrystals CuFeTe» points out their power character~T. Heree£*1.15 tor 0(1) andrf«1.9 for n(T). Therefore we had conclu-ded that this compound refers to gapless semiconductor« • On»should note that these dependences differ from those cbaraoteristic for the gapless semiconductors of the first and secondtype. The electron mobility ohanges as f(T)~T with e£«0.75.This dependence is like to those of the small radius ferrcn.All these features incline us to opinion that we deal with anew type of cosapouads-the gapless magnetic aeadocttanctox withferron type of charge transfer.

261

8P:blO3VALENCE BAND OF Cd Fe Se in Fe ENHANCED RESONANT PHOTOEHISSION

B.A. ORLOWSKI1, J. FRAXEDAS2, R. DEMECKE3, B.J. KOHALSKI1, 1. LEY3

. Institute of Physics, Polish Academy of Sciences, Warsaw, PolandMax-Planck-Institut flir Festkorperphysik, Stuttgart, GermanyInstitut filr Technische Physik, Universitat Erlangen-Niirn. Germany

He have performed resonant photoemission measurements of the valence bands

of Cd. Fe Se (0 s x s 0.15) whereby the Fe 3d partial density of states is

resonantly enhanced when the photon energy coincides with the Fe 3p - 3d

absorption threshold (53.7 and 55.5 eV). The measurements were performed at

the BESSY storage ring in Berlin.

Two Fe 3d related structures were found in the valence band spectra: a

small peak at 0.3 eV above the valence band maximum (VBH) of the undoped

CdSe and a second prominent peak at about 3.0 eV below the VBH. The cross

sections of these features when measured as a function of photon energy

(Constant Initial State mode) exhibit the characteristic Fano-type

resonances at the photon energies of the double peaked absorption edge.

8P:blO4

MECHANISMS OF s-p-d-f EXCHANGE INTERACTIONS IN Mn AND Eu BASED IV-VIDILUTED MAGNETIC SEMICONDUCTORS

T. DIETL* and G. BAUERInstitut fur Halbleiterphysik, Johannes Kepler Universitat Linz,A-4040 Linz, Austria

Recent magnetooptical studies' have provided detail information on exchangeconstants characterizing coupling between carriers and localized spins in 1V-VIsemiconductors containing either Mn or Eu. This group of compounds presents aninteresting test-case for current understanding of the exchange interactions, asit involves other type of orbitals thin that in Mn-based II-VI DMS. We haveextended the tight-binding model2 of exchange interactions for IV- VI DMS,taking into account contributions from direct exchange as well as from anion-cation and cation-cation hybridization between band states (derived from spdorbitals) and d or f open magnetic shells. The obtained exchange constantscompare favorably with the experimental values. In particular, our modelexplains opposite signs of these constants in Mn- and Eu-based compounds.Furthermore, our studies have emphasized some peculiarities of IV-VI DMS, whichmay render the virtual crystal approximation invalid.

* Permanent address: Institute of Physics, Polish Academy of Sciences,Al. Lotnikow 32/46, PL-02668 Warszawa. Poland.

1. G. Bauer and H. Pasher, in: Semimagnetic Semiconductors and Diluted MagneticSemiconductors, eds. M. Averous and M. Balkanski (Plenum, London, 1991) p.209.2. see, e.g.. K. C. Hass. ibid., p. 59.

262

8P:blO5DMS WJTH 4F-STATE JOMS - A THEORETICAL FORECAST

J.BLINOWSKI AND P. KACMAN*

Institute of Theoretical Physics, Warsaw University, ul. Hoza 69, Warsaw, Poland

Institute of Physics PAS, al. Lotnikow 32/46, Warsaw, Poland

The interesting electronic properties of diluted magnetic semiconductors (DMS)

result from spin-dependent interactions between mobile carriers and localized magnetic

moments of paramagnetic impurity ions. For r f i electrons in zinc-blende type DMS the

dominant part of this interaction is due to the p-d hybridization, which for S-state

ions (Mn ) leads to a simple, antiferromagnetic FCondo Hamiftonian. fn our previous

works we have shown that in DMS with D-state ions a different interaction

Hamiltonian, leading to new physical effects, has to be used. In this work we present

the new results of a similar analysis for DMS with F-state ions.

1. Blinowski J., Kacman P., Materials Science Forum Vol.83-87 (1991) 523.

8P:blO6

INTERACTION BETWEEN BAND ELECTRONS AND TRANSITION-METAL IONS INII-VI SEMICONDUCTORS

A. K. BhattacharjeeLaboratoire de Physique des Solides

University Paris-Sud, 91405 Orsay, France

F. Hamdani, D. Coquillat and J. P. LascarayGroups d'Etudes des Semiconducteurs

University Montpellier 11,34095 Montpellier Ce*dex 05, France

We first present a theoretical study of the hole-ion interaction arising from the Andersonmixing (p-d hybridization) taken to the second order. By using the irreducible tensor method,we deduce the effective Hamiltonian in the ground-state multiplet (H, S) of the ion intetrahedral crystal field, for all 2+ ions of the 3d series. For V, Cr, Ni and Cu, in addition tothe usual spin-spin term, we obtain couplings involving the orbital degrees of freedom ; thesepredict drastic modifications of the valence band splitting in a magnetic field. On the other hand,for Mn, Fe and Co, the coupling is simply the spin-spin exchange in agreement withexperiments. Exchange parameters in different Mn-, Fe- and Co- based diluted magneticsemiconductors, determined by us and by other groups are tabulated. The systematic increaseof |NoB| from Mn to Fe to Co in a given host is explained.

263

8P:blO7PHOTOCONDUCTIVITY IN Cdi_xCoxSe ALLOYS

Jolanta StankiewiczCentro de Ffsica, Institute Venezolano de Investigaciones Cientfficas,Apartado 21827, Caracas 1020A, Venezuela.

The photoconductivity of the diluted magnetic semiconductorsCdi.xCoxSe (0.01 £ x SO.045) has been measured at temperature of 1.6Kin magnetic fields of up to 6T and in the energy range of 0.5 to 2.5eV.Near the band-gap energy two peaks in the pnotocurrent are observed.They are interpreted in terms of free-exciton (exciton A and B)dissociation which is supported by our polarized light measurements.As the magnetic field intensity increases the photocurrent peaks shifttowards lower energy. Strong exchange interactions in the systemstudied are responsible for the red shift. Its measured values as wellas results of magnetization measurements performed on the samesamples allow us to estimate the exchange integrals for theCd-|_xCoxSe alloys.

* Present address: Departamento de Ffsica Aplicada, Facultad deCiencias, Universidad de Granada, E-18071 Granada, Spain.

8P:blO8RESONANT SPIN-FLIP RAMAN SCATTERING IN CdTe-CdMnTe QUANTUM WELLS

P. PEYLA, A.WASIELA, Y. MERLE D'AUBIGNE.Laboratoire de Septrometrie Physique BP 87, 38402 Saint-MartinD'Heres CEDEX FRANCED.E. ASHENFORD AND B. LUNNUuniversity OF Hull, HULL, HU6 7RX,UK

In heterostructures incorporating a diluted magneticsemiconductor as the barrier material it is possible to tune theconduction and the valence band offsets by the application of amagnetic field. Thus the applied field can induce large changesof the carrier confinement energies, which in turn give rise tolarge Zeeman splittings of the quantum well interband opticaltransitions. These splittings, which depend on the initial (zerofield) band offsets, have been used in the past to determinethese offsets. However they depend also on the interface qualityand a gradual interface can lead to underestimation of thevalence band offset. In this paper we shall show that thecomparison of the interband Zeeman effect and of the conductionband splitting measured by spin-flip Raman scattering allows anevaluation of the interface roughness and a reliabledetermination of the band offsets.

264

8P:blO9

ROLE OF ANION VACANCIES IN SOME TRANSITION METAL PNICTIDES

J.PAPE , H. KOHNKE , J.-W. SCHUNEMANN, K. EARNER4.Phys.lnstitut Univ.G6ttingen.FB Physik, Bunsenstr.13-15,D-3400 Gottingen, FRGI.V. MEDVEDEVAInstitute for Metal Physics, Kovalevskaya Str.18,620219 Yekaterinburg, USSR

The influence of anion (As,Sb)-vacancies on the magnetic andcrystallography properties of compounds such as MnSbi-o,

CrxMni-xSbi-ft,CrxMm-xAsi-6, Mni+aAsi-2Pz, Mni+6Asi-zSbz

and MnAsi-ft is discussed for selected poly- and single crystalsand in terms of various physical quantities such as specific heatcapacity, magnetic anisotropy energy, EPR , magnetization andlattice distances. Apparently anion and cation substitution as wellas vacancy disorder can induce specific displacements relative tothe NiAs structure positions which reduces the symmetry toorthorhombic, increases the magnetic anisotropy energies andcan cause a distribution of exchange integrals which can lead toa spin-glass like behaviour in certain situations.

8P:bllOCALCULATION OF THE INCOMMENSURATE MAGNETIC

STRUCTURE OF CuO.

M. Am, A. Menelle, B. Wanklynf, and G. Parette.Laboratoire Leon Brillouin (CEA-CNRS), CEN-Saclay 91191 Gif/Yvttte Cedex

FRANCEt Clarendon Laboratory, Parks Road, Oxford 0X1 SPV, UK.

Neutron polarization analysis1'2 on a single crystal of cupric oxide CuO, has shownthat in the commensurate phase (I) {0-212.7 K; k~( 1/2,0,-1/2)}, the magnetic momentswere indeed along b"; but it was found that in the incommensurate phase (II) {212.7-232.5 K; £=(1/2,0,-1/2)} there also exist a component of the magnetic moment alongb*.

We present here, a short account of our experimental results, and a study of thestability of the magnetic structure in phase (II).

1) Brown P.J., Chattopadhyay T., Forsyth J. B., Nunez V., and Tasset F.; J. Phys.:Condens. Matter 3, 4281-4287.

2) M. A'in, A. Menelle, B. Wanklyn, G. Parette, E. F. Bertaut; to appear in J.Phys.: Condens. matter.

265

8P:blll

MAGNETIC PROPERTIES OF U(Fe,!li)2

U. ZELEN* and F. ZOUNOVA"

Faculty of Mathematics and Physics, Charles University,

Ke Karlovu 5, 12116 Praha 2, CSFR

Institute of Physics, Czechoslovak Academy of Sciences,

Cukrovarnick* 10, 16200 Praha 6, CSFR

The u(Fe1_xrIix)2 compounds with x<0.09 and C15

structure have complex magnetic properties /l/.

magnetization measurements of the sample with x-=0.06

were carried out in fields up to 3.3 T at temperatures

from 4.2 up to 270 K. In contrast to the assumptions in

/I/ it has been found that the sample is not magnetically

single-phase, h. new explanation of the magnetic

properties of the U(i)e,!ii)2 system is suggested.

/I/ L. Kavela et al, J. Less-Common Met. 114 (1985) 217

8P:bll2SURFACE AND BULK ELECTRONIC STRUCTURE OF ORDERED MTi ANDM3Ti (M = Ni,Pd,Pt) ALLOYS

P.MIKUs'lK AND S.PICK

J. Keyrovsky Institute of Physical Chemistry andElectrochemistry, Czechoslovak Academy of Sciences,Dolejs'kova 3, 182 23 Prague 8, Czechoslovakia

Core level shifts for the bulk and nonpolar surfaces of theMTi and MjTi <M = Ni,Pd,Pt) alloys are calculated within a

self-consistent tight-binding scheme. Supposing the corelevel shifts correlate with the local change of the Coulombpotential (chemical shift), considerable positive chemicalshifts Are predicted for both the constituent atoms in thebulk and at most surfaces of the alloys in agreement withavailable experimental data for both bulk and surface (cf.

application of our simple model to the PcUTi alloy and some2

other Pd-Ti systems ). Capability of the theory to calculatethe heat of formation far the alloys is discussed.

1. Pick £. and MikuZik P., Solid State Commun. 80(1991)897.2. Pick g. and Mikus'ik P., J.Phys.I France 2(1992)121.

2G6

8P:bll3

Non-collinear magnetic moments in the groundand excited states of transition metals

J. Kubler1, L.M. Sandratskii1-2, and M. Uhl1

1 Institut fur Festkorperphysik, TH D-6100 Darmstadt, Germany2 Institute of Metal Physics, 620219 Sverdlovsk, USSR

Based on symmetry arguments, band-structure calculations for spiral magnetic configura-tions with arbitrary spiral vector, q, are applied to several physical problems. Experiments andcalculations show: (a) the minimum of the total energy of 7-iron corresponds to a Rvalue incom-mensurate with the lattice, (b) in MnSi there is a tendency for the formation of a total energyminimum small Rvalues. (The physical reasons of this behaviour are discussed.) (c) The depen-dence of the optical conductivity of RE-metals on the magnetic structure is investigated and itshown to be connected with the spin-polaron concept, (d) Excited states of Fe and Ni connectedwith longitudinal as well as transverse spin fluctuations are calculated and our results are used foran investigation of thermodynamic properties of Fe and Ni.

8P:bll4ORDERING EFFECTS, MAGNETISM AND INVAR PROPERTIES IN FeiCri_x

E. G. MORONI" and T. JARLBORG6

"Universite de Lausanne and IRRMA,CH-1015 Lausanne,Switzerland.6DPMC,Universite de Geneve,CH-1211 Geneve 4,Switzerland.

Electronic structure calculations of ordered bcc Fe^Cr!., show a non-continuos variationof the Cr moment as a function of composition. We have studied the magnetic phase dia-gram at different stoichiometric compositions. At equilibrium, for x=0.5 we found a ferro-magnetic order for Cr while at other concentrations anti-ferromagnetic order is obtained.For x=0.25 total energy results show a near degenerate magnetic and non-magnetic stateswhich is characteristic of Invar systems as fee FerNU_r. Short range order is importantsince non-equivalent sites have different moments. Moreover, calculations of the local elec-tronic structure at each constituent embedded in a completely substitutionally disorderedmedium, show negligible Cr moment and stable Fe magnetisation.

267

8P:bll5STRUCTURAL AHD MAGNETIC PROPERTIES OP EroNi-,T J\lvIIJTERLIETALLIC COMPOUNDS ^ ll~xr X

I.POP, M.DIIIOIU, 1I.AHDRECUT, I.BURDA, V.CRISAN, A.VERNES"Babe§-Bolyai" University, Physics Department,M.Kog5lniceanU 1Ro - 3400 Cluj-Napoca, Romania

The Er2Hi1y_xAlx intemetallic compounds for x=O,l,3,5,7 and17 were investigated by both structural and magnetic measure-ments. It has been revealed that the investigated compoundsliave Th2Kii7 type structure.The new internist all ic compound E^Al-iy has the lattice para-meters a=8.495A and C=8.976A. It obeys a Curie law and hasan effective magnetic moment per unit formula of 13.636/fc andper Er-3"1" ion of 9.642flR. The Er2Ni17 compound is ferrimagnebicordered and it's effective magnetic moment per unit formulais of 14.95/% and respectively 1.49/% P e r ^i atom. Theeffective magnetic moment per formula unit for pseudobinarcompounds decreases monotonically as Al concentration increa-ses. Both X-ray and metallografic investigations show thatthe studied compounds form unic phases.

8P:bll6ON THE Y23?e17 ELECTRONIC STRUCTURE

V.CRISAN, I.POP, A.VERHES, V.POPESCU, D.KAPUSI, L.DULCA,M.ANDRECUT, I.BURDA"Babe^-Bolyai" University, Physics Department,M.Kogalniceanu 1Ko - 3400 Cluj-Hapoca, Romania

The YoPeiY oompound showe an anomaly in its lattice constantbelow Tc and a large pressure dependence of Tc, similar to theFe-Ni invar alloys. The electronic structure for ideal orderedstructures with Fe atoms located in 4f, 6g, 12j and 12k siteswere computed by Shimizu et al.The effects of partial disorder on electronic structure werestudied, computing the local density of states when Fe atomsmoved from 4f and 12j sites to 4e and Y atoms moved from 2b to2c positions. The DOS at Fermi energy is very sensitive evento the lesser atomic displacement similary to Y.2Ni;ijCll. TheDOS analysis was also performed for the lattice parametersvariations. The Haydock recursive method with appropiate termi-nator and one orbital per atoai was used in our calculations.

1. V.Cri§an, A.Vernes, A.Janosi, V.Popescu, D.KapusiJ. of Alloys and Compounds 1 (1992)1,

268

8P:bll7NONEQUILIBRIUM STEADY STATES IN MAGNETIC SYSTEMS

J. Marro, A.I. Lopez-Lacomba, and J.J. AlonsoFacultad de Ciencias (Fisica), Universidad de Granada, E-18071-Granada (Spain).

A class of Ising-like systems with competing dynamics which seem to model certainsituations in Nature are a convenient ground to study nonequilibrium steady statesand phase transitions12. In one of the cases, a simultaneous competition betweendifferent values of the applied magnetic field produces a nonequilibrium conditionwhich might be experimentally accessible, e.g., by subjecting a sample to a randomlyfluctuating magnetic field or to a field varying regularly with a very short period(namely, shorter than the mean time between successive modifications of the spinconfiguration)2. We shall report on some exact and mean-field results for this modelsystem. They reveal a remarkably complex variety of behaviours, including first- andsecond order phase transitions which have no equilibrium counterpart, non-equilibrium tricritical points, non-universal critical exponents,...

1. P.L. Garrido and J. Marro, Europhys. Lett. 15, 375 (1991)2. A.I. Lopez-Lacomba and J. Marro, to be published; J.J. Alonso, A.I. L6pez-

'..acomba and J. Marro, unpublished.

8P:bll8TRANSITION FROM IN-PLANE ANTIFERROMAGNETISM TO LAYEREDANTIFERROMAGNETISM IN VANADIUM ISLANDS ON Ag(001)

A. MOKRANI, Laboratoire de Physique du Solide Theorique,2 rue de la Houssiniere, 44072 Nantes, FranceS. BOUARAB, H. NAtT-LAZIZ, C. DEMANGEAT, IPCMS, UMR46, UniversiteLouis Pasteur, 4 rue Blaise Pascal, 67070 Strasbourg, FranceH. DREYSSE, Laboratoire de Physique des Soiides, BP 239,54506 Vandoeuvre-les-Nancy, France

Onset of magnetism has been recently obtained in the case of vanadiumoverlayers on Ag(001). The vanadium monolayer presents an in-planeantiferromagnetic ground state whereas a bilayer is layered antiferromagnetic.These results have been obtained through a direct-space tight-binding methodwithin Hubbard Hamiltonian. Here we discuss the onset of magnetism of islandsof vanadium on Ag(001). For an island with 1 layer thickness the in-planeantiferromagnetic solution is the ground state; ferromagnetic solution appearsonly for higher values of the exchange integral J . Atoms at the edge of the islandpresent greater magnetic moments than those at the centre. This is directly relatedto the coordination number of the considered atoms. In the case of islands withtwo layers, a layered-antiferromagnetic solution is shown to be the ground state.

269

8P:bll9PARAMAGNETIC PROPERTIES OF THE Gd(Al. Jie)_ COMPOUNDS.

G.CHELKOWSKA, A.CHELKOWSKI

Institute of Physics, Silesian University

40-007 Katowice, Uniwersytecka 4

The paramagnetic Curie temperatures and the paramagnetic

effective moments were measured for the pseudobinary

compounds Gd(Al1_xMeJ£)2(where Me=Pb,Si,Ge,Sb) in the x-range

where these compounds exsist as the Laves phases.The results

are compared with those for similar systems where

Me=Cu,Ag,Pd,In,Gd,Sn. In almost all cases the paramagnetic

effective moments were unchanged in comparison with GdAl2.

However, a dramatic decrease of the paramagnetic Curie tem-

perature was observed for all systems. This effect is

explained on the basis on band structure calculations.

8P:bl20

THE SPIN REORIENTATION TRANSITION IN FERROMAGNETIC Gd METALPROBED BY /*SR

O. HARTMANN, R. WAPPLING, E. KARLSSONInstitute of Physics, University, S-75121 Uppsala, SwedenG.M. KALVIUS, L. ASCH, A.KRATZERPhysics Department, Technical University Munich, D-8046 Garching, GermanyJ.F. LitterstInstitute for Metal Physics, Technical University, D3300 Braunschweig, Germany

Just below T c = 292.5 K the magnetization (M) in hexagonal Gd metal is orientedalong the c-axis ( 0 = 0). Around 230 K, M starts to turn reaching 0 = 60° at 200 K,then returning slowly back to 0 = 30°. We have studied this behavior by Muon SpinRotation (Relaxation) in a single crystal sphere of Gd. When 0 > 0, we observean overlay of two /xSR signals: a damped muon spin precession pattern for the spincomponent perpendicular to M and an exponential relaxation pattern for the parallelcomponent. Their relative amplitudes mirror the variation in 0 with temperature whichis found to be much steeper than previously deduced from neutron or torque data. Thedamping rate of the precession signal shows a strong increase at the onset of spin re-orientation which, however, quickly subsides even before the maximum turning angleis reached. The relaxation signal remains unaffected throughout. We interpret thesefindings as formation of strong disorder in the spin structure at the very start of re-orientation.

270

8P:bl21MAGNETIC PHASE DIAGRAM OF UNiGa

V. SECHOVSKY, L. HAVELA, L. JIRMAN, M. DIVIS, P. BURLET*. H. MALETTA?E. BRUCK? F.R. de BOER?Department of Metal Physics, Charles University, CS-121 16 Prague 2, CSFR,*CENG, Grenoble, France, *Hahn-Meitner Institute, Berlin, FRG,Van der Waals-Zeeman Laboratory, University of Amsterdam, The Netherlands

We report on magnetic, neutron diffraction and resistivity studies of asingle crystal of UNiGa. This compound, possessing the hexagonal ZrNiAl-type structure, exhibits strong uniaxial magnetic anisotropy both in para-magnetic and in magnetically ordered state. UNiGa becomes antiferromag-netic at T = 38 K. Below this temperature always a collinear magneticstructure (U magnetic moments || c-axis) is observed, the magnetic phasediagram, however, is very complex. In zero magnetic field, 4 AF phasesdiffering in the propagation vector appear in 4 different temperatureintervals. The AF phases can be suppressed and ferromagnetic alignment canbe achieved by applying magnetic field up to 1 T. At temperatures above 10K, an intermediate state (uncompensate.J antiferromagnet, + + -) can bestabilized. The magnetic phase transitions cause dramatic changes inresistivity behaviour. The resistivity values are drastically reduced bythe metamagnetic transitions (Ap/p = 907. a> 2 K). The negative dp/dTobserved for t || c-axis (in zero magnetic field) in the paramagnetic rangeis a consequence of gradually arising short-range AF ordering with q || c.

8P:bl22

PRESSURE EFFECT ON THE MAGNETIC AND ELECTRICAL PROPERTIES OFTHE NEW INVAR SYSTEM La(Fe , Co , Al )/3

I.V.Medvedeva, A.A.Ganin and V.A.Sidorov*

Institute for Metal Physics, Ural Div. of Russia's Ac.Sci.18 S.Kovalevskaya St., 620219 Yekaterinburg, Russia•Institute of High Pressure Physics of Russia's Ac.Sci.142092 Troitzk, Moscow Region, Russia

The magnetization, susceptibility and resistivity ofLa{Fe,Co,Al)(3 alloys have been studied under a pressureup to 5.6 GPa. Pressure leads to a strong decrease inmagnetization and magnetic transition temperatures.The results are discussed in the context of instabilityof the ferromagnetic state in this system.

271

8P:bl23

SURFACE MAGNETIC PHASE TRANSITIONSWITH MODIFIED SURFACE-BULK COUPLING

M.VENDRUSCOLO*, A.FASOLINO" and M.ROVERE*(*) Dipartimento di Fisica Teorica, (**) SISSA Trieste

Surface magnetic phase transitions in a semi-infinite simple cubic Ising modelare investigated. Modified surface (first layer) J. and first-second layer J\couplings are assumed, eventually the latter being negative. Mean field, equa-tions are solved both analytically and numerically. Phase diagrams are de-termined and surface and bulk properties are extracted. The dependence ofthe surface-bulk multicritical point J,c on Ji is obtained. Monte Carlo sim-ulation is performed, by employing a high speed vectorized multispin codingprogram. The coupling strengths are varied to make contact with experi-mental results on surface magnetization of Gd.

8P:bl24PRESSURE EFFECT ON SPIN REORIENTATION BEHAVIOUR OF

^ B (R » Y, Gd) COMPOUNDS

Z.Arnold*, j.Kamarada, M.R. Ibarra**, P. A. Algarabel*aInstitute of Physics, Czech. Acad. Sci., Cukrovarnicki 10,162 00 Pmha 6, Czechoslovakia

Laboratorio de Hagnctismo, ICMA-DFMC, Facultad de Ciencias,Universidud de Zaragoza, 50009 - Zaragoza, Spain

In the R2Fei4B type compounds, the interplay betweendifferent nagnetocrystalline anisotropies of the magneticsublattices is manifested by the spin ceorientationtransitions. The significant decrease of the spin teorientationtransition temperature T»r under pressure (typically dTsr/dp -- 20 K/GPa) was observed for both (Eri-xRx>2Fei4 B (R « y, Gd)studied compounds (x up to 0.8) under the hydrostatic pressureup to 1 GPa, using low-field ac susceptibility method. Theindependence of dTsr/dp on the Y content is in agreement with ahypothesis based on a variation of the second order terms of ;CEF with the pressure. The slight dependence of dTsr/dp on the )composition of (En-xGdx)2Fei4B compounds and the conicalanisotropy observed on the (Ero.2Gdo.s)2Fei4B compound can be *'related to the contribution of Gd ions to the anisotropy.

272

8P:bl25

THE HYPERFINE INTERACTION OF TERBIUM IN TERBIUM HYDROXIDE

D. St. P. BUNBURY, C. CARBONI, R. G. GRAHAM, M. A. H. McCAUSLAND ANDS. M. WARNERThe Schuster Laboratory, The University, Manchester M13 9PL, UK

Terbium hydroxide, Tb(OH)3, is a uniaxial compound with highly anisotropic magneticproperties. At low temperatures it behaves as an almost ideal Ising magnet, orderingferromagnetically at 3.72 K.

We have measured the field dependence of the dipolar and quadrupolar hyperfinesplittings of 169Tb in Tb(OH)3 at liquid-helium temperatures. The measurements weremade by spin-echo spectroscopy at microwave frequencies, in fields up to 8 T. Thebehaviour of the dipolar splitting confirms that the ionic ground state is an almost pure|JC = +_6> doublet. By comparing the measured quadrupole splitting with calculationsbased on crystal-field parameters derived from optical spectroscopy we havedetermined, for the first time, the ratio of the nuclear antishielding factor yN to theelectronic antishielding factor -yE for Tb3+ in Tb(OH)3. We obtain yJyE = 171 ± 1 0 ,some 15% higher than the corresponding figure for Ho(OH)3.

1 Nuclear relaxationphenomena above and below the ferromagnetic phase transition will also be described.

1. Bunbury D. St. P., Carboni C. and McCausland M. A. H., J. Phys.: Condens. Matter 1(1989) 1309.

8P:bl26ON THE MAGNETIC STRUCTURE OF UPdSn

H. NAKOTTE8, F.R. DE BOER*, R.A. ROBINSONb, S. JOHNSON15, A.C. LARSONb,J.W. LYNNC, L. HAVELAd and V. SECHOVSKYd

a: Van der Waals-Zeeman Laboratorium, University of Amsterdam, Valckenierstraat 65, 1018 XEAmsterdam, The Netherlands; b: Los Alamos National Laboratory, Los Alamos, NM 87S4S, USA;c: Reactor Radiation Division, National Institute for Standards and Technology, Gaithersburg, MD20899, USA; d: Charles University, Ke Karlovu 5, 12116 Prague 2, Czechoslovakia.

UPdSn crystallizes in the hexagonal structure P^mc, which is an ordered ternary of the Caln2-structure type. UPdSn orders in the non-collinear antiferromagnetic structure of Cmcm symmetry (theorthorhombic form of Pfrjinc) at 40 K and undergoes a second transition at about 25 K, that isconnected with a re-arrangement of the antiferromagnetic structure. Both magnetic structures areresolved by means of neutron powder diffraction III. Here we present neutron diffraction data on asingle-crystalline UPdSn at various temperatures and in various magnetic fields, which were obtainedusing both a spallation source and a reactor. As the crystallograhic structure is hexagonal and themagnetic structure is orthorhombic, three different orthorhombic domains can occur. The results proveunambiguously, that in zero field all three domains coexist for temperatures below 25 K, but magneticfields populate preferentially one of them. For fields higher than the critical field (about 3 T) only onedomain remains. The depopulation of the other two domains is found to be irreversible, while themagnetic struture is unchanged.

/!/ R.A. Robinson et al.; J. Magn. Magn. Mater. 98 (1991) 147;

273

8P:bl27CRYSTAL AND MAGNETIC STRUCTURES OF UPtGe AND UPdSnCOMPOUNDS.

M. KOLENDA?A.SZYTULAjR. TROCfv.H.TRAN?M.BONNElfj. ROSSAT-MIGNOT?1. Institute of Physics,JagelIonian University30-059 Krakow,Poland.

2. M. Trzebiatowski Institute for Low Temperature and StructureResearch, 50-950 Wroclaw,Poland.

3.Centre d'Etudes Nucleaires, DRF/SPh-MDN,38041Grenoble Cedex,France.

The crystal and magnetic structures of UPtGe and UPdSn wererefined by the powder neutron diffraction method.The UPtGe compound crystallizes in an orthorhombic NiTiSitype structure.The magnetic structure of this compound isa cycloidal spiral with the propagation vector k=(0,0. 45,0).The value of magnetic moment of uranium Is 1.08(7)(iB.The UPdSn compound crystallizes at room temperature In ahexagonal structure.Below T =40K the orthorhombic distortionappears.At T=25K the Increase of distortion is observed.The canted magnetic structure is similar to those reportedpreviously [ll.The magnetic moment at T=2K equals 2. 16(5)JIB.

1. Robinson R.A. et al..J.Magn.Magn. Mat. 98(1991) 147.

8P:bl28WALL MAGNETIZATION REVERSAL OF COBALT FOIL INVESTIGATED BY TEM

GEMPERLE A., GEMPERLE R. and NOVOTNY P.

Institute of Physics, Czechoslovak Academy of Sciences,Na Slovance 2, CS-180 40 Praha 8, Czechoslovakia

The process of magnetization reversal of domain walls in cobalt

foils with basal plane orientation was investigated by Lorentz

electron microscopy. External field up to 300 Oe was applied

in the plane of the sample along the direction of the parallel

stripe domains. The magnetization reversal of the individual

walls was found to be a one step process corresponding probably

to the abrupt shift of vertical Bloch lines along the whole ob-

served wall lenght. In contrast to the magnetization switching

in the individual walls the reversal process of every observed

domain wall set was found to have a prominent two step character

being similar to the behaviour of garnet films .

1. NOVOTNY P. and GEMPERLE R.: J.Magn.Magn.Mat. 102 (1991) ...

274

8P:bl29NON-COLLINEAR SPIN STRUCTURES IN Fe-Zr AMORPHOUS ALLOYS

P.Kossackia,T.Stobiecki and H. Szymczak'

bInstitute of Physics, Polish Academy of Sciences, Warsaw, PolandInstitute of Electronics, Academy of Mining and Metallurgy, Cracow,Poland

Magnetization measurements have been used to study the non-collinearspin structures in Fe Zr amorphous alloys with 0.5 < x < 0.9 .The

experimental results have been analyzed in terms of spin waves as wellas Stoner excitations. Spin waves excitations seem to be important forZr-rich alloys while T Stoner-like term plays a significant role inthermal demagnetization of Fe-rich alloys. The value of high-fieldsusceptibility was found to be extremely large at high x and fallssharply with decreasing x. This suggests that the balance betweencompeting exchange interactions [1] .presumable responsible fornon-collinear structure is very sensitive to local environmenteffects.

[11 Gibbs M.R.J., J.Magn.Magn.Mater. 83 (1990) 329

8P:bl30INTRINSIC PROPERTIES AND COERCIVITY OF INTERSTITIAL MAGNETS

L. SCHULTZ, M. KATTER, C. KOHRT, K. SCHNITZKE AND J. WECKERSiemens AG, Research Laboratories, Erlangen, Germany

Starting from elemental samarium and iron powders, magneti-cally isotropic microcrystalline SiriaFeivN:* samples with coer-civities up to 24 kA/cm were prepared by mechanical alloyingin a planetary ball mill and a following crystallization andnitriding treatment. Their remanence and energy product areequivalent to similarly prepared Nd-Pe-B samples, but the pro-perties at elevated temperatures are superior because of thehigh Curie temperature of 473 °C and the large anisotropyfield of 22 T. Using Zn bonding, even higher coercivities weremeasured. Also for SmaFei^Cy and l:12-type Nd-Fe-V-N, coerci-vities of 18.5 or 6 kA/cm, respectively, were obtained.

i

275

8P:bl31THE EFFECT OF Nd PURITY ON THE MAGNETIC PROPERTIES OF SINTERED Nd-Fe-B MAGNETS

Yu.M.RABINOVICH(1), V.V.SERGEEV(1), S.SZYMURA(2> and H.BALA(3)

(1) All-Union Science-Research Institute of Electromechanics (VWIIEM), 107817Moscow; (2) Institute of Physics and (3) Institute of Chemistry, Technical

University of Czestochowa, PL 42-200 CzestochowaThe most common process of manufacturing of the Nd-Fe-B permanent magnets isthe conventional powder metallurgical method which uses pure metals as star-ting material. The effect of the technological admixture in the neodymiunproduction process on the magnetic properties of these magnets seems to be im-portant .

We report influence of Ca, Cl and C content in neodymium on the magnetic pro-perties of the sintered NdlsFeT0sSCo6AlBT>6 and NdtkPyzFe7ta6CoGB7>e magnetsproduced on its base.

The following effects of the impurities on the magnetic properties have beenfound in the paper:(i) C > O.lwti reduces the coercivity of the magnets,(ii) both Cl > 0.02 vt% and Ca > 0.1 wtt reduce the coercivity and the rema-

nence of the magnets.

8P:bl36SILICON NITRIDE FILMS PREPARED BY ION BEAM ENHANCED EVAPORATION

J.2EMEK, M.ZAVETOVA, S.KAMBA, K.KOKESOVA, P.2ICH, AND F.CERNY1'Institute of Physics, Czech. Acad. Sci. Prague 8, 180 40''state Research Inst. for Protection ox" Mater. , Prague 9, 19011

Silicon nitride films of high quality (insulation andmechanical properties) useful in microelectronics are producedby the ion beam enhanced deposition (IBED).

Our films were prepared by the electron beam evaporation of Siand simultaneous implantation of N ions (with the energies from60 to 90 keV; incident angle 45" and 80* ) . The atomic arrivalrate ratio of N to Si ranged from 0.1 to 4.4 and the filmthickness from 40 to 250 nm. The chemical composition of theIBED films was investigated using X-ray induced photoelectronspectroscopy (XPS) and Auger electron spectroscopy (AES) within-situ sputtering. Chemical bonds of Si, O and N atoms presentin the volume analyzed were determined by the line shapeanalysis of the Si LVV, O KLL and N KLL Auger spectra using thepattern recognition method. IR spectroscopy verified theexistence of the Si-N bonds (typical broad band at ~ 840 cm )in the whole concetration range studied. Results of thespectroscopic methods will be discussed in connection with thetechnological parameters.

276

8P:bl37

DEPTH DEPENDENT LATTICE PARAMETER CHANGE IN SI AFTER HIGHDOSEAS+ IMPLANTATION AND LONG TIME ANNEALING

H.METZGER # , S. RUGEL#, J. PHSL# , I. ROBINSON +andU.PIETSCH *# Sektion Physik der Universitat Munchen, D-W-8000 Munchen 22, Germany+ AT&T, Brookhaven National Laboratory, NSLS, Upton, NY, USA* FB Physik der Universitat Potsdam, D-O-1571 Potsdam, Germany

Si single crystals were implanted with 6'KT1^ As+/cm2 (lOOkeV) and annealed at tempera-tures between 200°C and 800°C for 30 minutes. The sheet resistance is increasing with tem-perature 1. We investigated the near surface structure by grazing incidence x-ray diffractionusing synchrotron radiation. Controlling simultaniously the angle of incidence and exit (bothin the order of the critical angle for total reflection) the lattice parameter variation was mea-sured as a function of depth. Two contributions were detected: a sharp, resolution limitedBragg reflection and a broad peak with 10 times the halfwidth. The lattice parameter of thebroad peak increases with annealing temperature and its intensity increases on the expenseof the sharp reflection. From the distribution of the Bragg intensity of both peaks as a func-tion of the exit angle (at various angles of incidence) we obtain information on the corespon-ding structures as a function of depth. By comparison with computer simulations variousstrucural models will be discussed.1. G. S. Cargill, J. Angilello and K. L. Kavanagh, Phs. Rev. Lett. 61 (1988) 1748

8P:bl38EPITAXIAL GROWTH AND CHARACTERIZATION OF TERNARY AND QUATERNARY Ill-V SEMICONDUCTORS

Alberto Camera3, Giovanni Attolmi6, Cesare Fngerib, Claudio PelosiD, David Ajo0, M. Luisa Favaro0

a Dipartimento di Fisica, Universita (Padova).D Istituto del Mater lali Speciali per l'Elettronica e i l Magnetismo, C.N.R. (Parma).c istituto di Chimica e Tecnologia dei Radioelementi, C.N.R. (Padova).

The properties of epitaxial layers depend on several factors, among which perfection and final

substrate treatment, growth temperature, composition, "mismatch" with respect to the substrates.

in our laboratories is in progress a comprehensive work concerning ternary and quaternary alloys of

in -v compounds (in particular, materials of interest in the field of optoelectronics, as inGaAs e

inGaAsP) grown by a quasi-equilibrium technique (HVPE) in different experimental conditions. For

characterVdtion, several techniques are used. In particular, both lateral and normal compositional

homogeneities ore assesses by Secondary ion Mass Spectroscopy (SIMS) and Rutherford

3acKcattermg(P.BS) The same techniques allow the evaluation of film thicknessand interface profiles.

277

8P:bl39CHARACTERIZATION OF SI-GaAs CRYSTALS BY PICTS

P. Hlinomaz, V. Smi'd, J. KristofikInstitute of Physics, Czechoslovak Academy of Sciences,

162 00 Prague 6, Cukrovarnicka 10, Czechoslovakia

The experimental results obtained by the Photo Induced Current Transient Spec-troscopy (PICTS) on undoped and chromium doped SI-GaAs crystals are discussed. Thecurrent components connected with the current relaxation in the bulk and at the surfaceare separated by means of three-electrode configuration prepared on the samples.

In comparison with literature the properties of real PICTS spectra (related to the bulkmeasurement configuration) are described in more detail. The deviations in the proper-ties of the measured PICTS spectra from the results developed within simple physicalassumptions have been found. The discussion of the physical models has shown that it isnecessary to use a generalized physical model for the explanation of some of these features.

The PICTS results measured in the temperature interval 250 - 450 K are interpretedas levels: EL4, EL3, HL9, EL2 and HL1. The EL4 has been observed on undoped samplesonly. The differences in parameters of found levels identified as EL2 are connected withthe possible variability in the structure of the EL2 defect. No stronger correlation betweenthe EL2 and Cr content in the samples and the observation of a certain maximum hasbeen found.

A short comparison with the results of different types of signal processing is presented.A general correspondence of the results has been found.

8P:bH0Influence of As pressure during GaAs crystal growth oncompensation

H. BOUDRIOT, W. SIEGEL, E. BUHRIG, K. DEUSBergakademie Freiberg, Fachbereich Physik and FachbereichMetallurgie und GielSereitechnikSilbermannstraBe 1, O-9200 Freiberg, BRD

In respect to the dependence of compensation on the defect

situation an influence of growth conditions on compensation

degree can be expected.

We investigated the influence of As partial pressure during

horicontal Bridgman crystal growth of GaAs on compensation

degree determined by free carrier optical absorption, Hall-

effect and local vibrational modes.

These three independent methods have results agreing quali-

tatively: For a halve As quantity the compensation is minimal.

Plausible defect reactions can explain this behaviour but un-

ambigous evidences of concret defects participating in com-

pensation are missing.

278

8P:bl41REGISTRATION ENVIRONMENT ON THE BASIS OF CHALKOGENIDE ARSENIC

J.BIRCAKP.J.Sa'fdrik University, 17.novembra 1, 08116 PreSovD.SEMAKState University of Uzhgorod, Zhovtneva 54,294000 Uzhgorod

J.JANICUniversity of Novi Sad, Veljka Vlahovica 3, 21000 Novi Sad

It was found out that in dependence from structure ofssputt-

red films via film thickness variating the increas of light-sen-

sitiveness e.g. enlargement of photoinduced change /PIC/ of op-

tical parametres can be reached. Moreover, PIC consists of re-

versible and irreversible components. In the sphere of raver -

sible PICs some dependece of character of relaxated processes

from films structure can be observed. Two components are ex -

presed here: the quasi-steady one and the component which re-

laxed immediately after switching off the light. The relation

between these components is determined by the structure of

sample, and the time of relaxation by its temperature.

8P:bl42INVESTIGATION OF Ti AND TiN DIFFUSION BARRIERLAYERS BY VOLATILE COMPONENT LOSS SPECTROSCOPY

J.KARANYI, L.LIPTAKResearch Institute for Technical Physics of theHungarian Academy of Sciences, H-1325 BudapestP.O.Box 76, Hungary

Refractory metals and their compounds *rBoften used as diffusion barrier layers to prevent"junction spiking" between semiconductor andcontact metals because of their high thermalstability, low and stable contact resistance. Inthis work magnetron—sputtered Ti and TiN layers asbarriers for Au/Ti(N)/GaAs Schottky-contacts withdifferent thickness and parameters of depositionwere investigated. The Au evaporation and heattreatment were carried out in an UHV systemequipped with a heated stage and quadrupole massspectrometer. The material iriterdiffusion takingplace during annealing is accompanied appearanceof volatile As components. This process wasmonitored by Evolved Gas Analysis method. We havedetermined a minimal thickness of barrier layersas a function of their composition and depositionparameters.

279

8P:bl43CONTACTLESS MEASUREMENT OF THE ELECTRON TUNNELINGPROBABILITY IN NATIVE OXIDES OF SILICON

F. RIESZ, Research Institute for Technical Physics of the HungarianAcademy of Sciences, P O Box 76, H-1325 Budapest, HungaryJ. MIZSEI and I. ZOLOMY, Department of Electron Devices, Technical

University of Budapest, H-1111 Budapest, Goldmann Gy. ter 3, Hungary

A novel method is proposed to measure the tunneling probability of elec-trons in native oxides on Si substrates. Illuminating the surface, theelectron concentration increases, thus giving rise to a tunnel currentcharging the traps of the external oxide surface. After switching off thelight, these trapped carriers tunnel back to the silicon until equilibrium isreached. During the process, the surface potential of the semiconductor,Vs, is changing because of the changing surface charge. Vs can be mea-sured by the contactless vibrating-capacitor (Kelvin) method. From thetime constant of the Vs-t curve, the tunneling probability of the oxide, T,can be calculated. Assuming rectangular potential barrier and ellip-sometric data for oxide thickness, the effective barrier height for theelectrons is significantly lower than the bulk value..

8P:bl44

RAMAN SPECTROSCOPY FOR ELECTRICAL CHARACTERIZATION OF IMPLANTEDGaAs LAYERS

K.KOKESOVA, I.GREGORA, V.VOR LICEKInstitute of Physics CSAV, Na Slovance 2, 18040 Praha 8

In Raman spectra of polar semiconductors so-calledplasmon-phonon modes are observed. Their frequency and halfwidthare connected with concentration and mobility of carriers.Implanted GaAs layers used in microelectronics haveconcentrations of carriers in the range well accessible by Ramanspectroscopy. Moreover the thickness of layers is comparablewith the penetration depth of visible light used to excite thespectra.

In our study we examined Si implanted GaAs layers influencedby buried N implantation. Measured spectra were compared withtheoretical model which took into account Gaussian distributionof implanted impurities, the existence of depleted layer andabsorption of light in the sample. The influence of modelparameters on the accuracy of determination of transportproperties is discussed. The values of concentration andmobility obtained in this way are compared with the results ofHall and C-V measurements.

280

8P:bl45OXYGEN PRECIPITATES IN SILICON: STOlCfflOMETRY STUDY BY INFRAREDSPECTROSCOPY

A. BORGHESr, G.GUIZZETTI", A.PIAGGI", A.SASSELLA", A.STELLA", B.PIVAC"*" Dipartimento di Fisica, Universita di Modena, Italy" Dipartimento di Fisica "A.Volta", Universita di Pavia, Italy*" Rudjer Boskovic Institute, Zagreb, Croatia

High spatial resolution Fourier transform absorption measurements are performed on oxygenprecipitates grown in silicon samples briefly annealed. The absorption spectra show a strongband at 1230 cm' 1 , not substantially influenced by the 1107 cm' 1 band of interstitial oxygen.Moreover, it is possible to avoid any average effects by using polarized light in order to studyhomogeneous aggregations of disc-shaped precipitates all lying in particular planes. The highintensity of 1230 cm"1 peak allows a detailed study of lineihape, amplitude and wavenumberposition. We demonstrate that the wavenumber position and intensity of this absorption band,directly related to the precipitate*, give information regarding itoichiometry of the oxide con-stituting such precipitates and their density. In fact, the analysis of the experimental spectra byan effective medium approach permits exclusion of detectable presence of quartz, criitobalite,B-doped or amorphous SiO2 particles, because they would give rise to IR band at 1241, 1264,1210 and 1256 cm' 1 , respectively. In particular, the precipitates in our samples are made ofamorphous suboxides, mainly SiOi.g, with 5 ppm local concentration. Moreover, our conclu-sions give evidence that disc-shaped precipitates in silicon have the same optical properties ofthermal oxide fiivns with comparable thickness grown on silicon.

8P:bl46AUGER OXYGEN KLL LINE SHAPES IN SUBOXIDES OF SILICON;

PATTERN RECOGNITION ANALYSIS

J. ZEMEK AND T. VYSTRCILInstitute of Physics, Czech. Acad. Sci., 162 00 Prague 6,

Cukrovarnickit 10

Suboxides of Si often exist on the surface of slightly oxidizedSi, in thin films of SiO deposited by evaporation, on the sur-face of air exposed Si nitride layers and at different Si in-terfaces. Leaving the technological significance aside, theSiOx provides a suited model system for studying Si-0 chemicalbonding. Here, we have studied Auger 0 KLL lineshapes takenfrom surfaces of amorphous films of SiOx (x s 2} and siNy(y s 4/3) by Auger electron spectroscopy and a pattern recogni-tion evaluating method. All films were prepared ex-situ byi room temperature air oxidation of Si(lll) wafers,ii vacuum evaporation of SiO powder onto Si(lll) wafers,iii plasma enhanced CVD using a mixture of SiH4 + 02 reactant

gases at different Si(lll) substrate temperature,iv nitrogen ion beam assisted evaporation of Si onto Si(lll).Preliminary results show significant difference in shapes ofthe 0 KLL spectra taken from SiO2 standard and from SiO or SiNyair exposed films. The changes are discussed in terms of theAuger electron transport from parent oxygen atoms into vacuum.

281

8P:bl47A NEW WAY TO THE GROWTH OP OPTOELECTBONIC SUBSTBATES

J.Venkrbec+, Z.Cefiil*, V.Hosick<£=, J.Kohout=, Jo.Sedla"cek+,

Z.KodejS a P.Paeak . +Faculty of Eleetr.Eng. CTU-Prague,

16627 Praha 6; =Inst. of Hadioelectronics; "inst. of Inorga-

nic Chent. - both Prague, Czechoslovak Acad. Scl.

This work can partially contribute to the direct growth

of bulk substrate crystals of TSS (Ternary Solid Solutions) -

(Ga.ln)Sb - with a lattice parameter "a" constant throughout

the significant part of its magnitude (length). The combina-

tion of our original methods CAM-S (A Crystallization Method

Froviding Composition Autoeontrol in Situ) and COM-S (Calcu-

lation Method of Optimal Molten-Solution Composition) with a

vibrational stirring enables to grow crystalline ingots with

"a" apriori chosen and calculated - having the deviation from

its constancy less than O,OJ3# (0,2FB) on the 75mm of a length.

Crystals possess mosaic structure, at this stage.

8P:bl48INVESTIGATIONS ON CHMIC CCMEfiCTS TO N-T5fPE GaAs

M.R. LEYS, H.A. COENEN, P.A.M. NOUWENS, J.H. WCLTERDepartment of Semiconductor Physics, Technical University of Eindhoven,box 513, 5600 *B, Eindhoven, The Netherlands.

We have investigated different kinds of ohmic contacts on n-type, MBE grownepitaxial GaAs layers using the elements tin, indium and various combinations ofgold, nickel and germanium. The changes in resistance and capacitance of themetal-semiconductor structures as a function of annealing time and — temperaturewere determined via I-V and C-V characteristics. Typically, contact resistance asfunction of annealing time could be measured from 10" fi (0 seconds) down to 10"2 fi(final value). The capacitance of the contact during a thermal treatment was found tobe from 12 to 20 pF, approximately.It was found that contacts using indium resulted in a contact resistance of 4.10'2

ft cm2 after annealing. Tin contacts were easier and more reproducible: after annealingfor 60 seconds at 440°C a contact resistance of 1.10"* ftcm* was obtained. UsingAu/Ge/Ni combinations it was noted, that these metallizations often resulted innot-smooth surfaces after annealing. Optimization of the Au/Ge/Ni contacts resultedin a metallization sequence of first Ge, followed by Ni, then Au/Ge alloy with a finallayer of Au. With this scheme smooth morphologies and the lowest pc, namely 1.10'5

Hem2, could be obtained at annealing temperatures of 370°C or less.These three types of ohmic contact (In, Sn and Au/Ge/Ni) each have a differentmetallurgical and electric mechanism of formation. A quantitative interpretation ofthe (Ge)/Ni/Au,Ge/Au metallization, based on the 1-V and C-V measurements willbegwen.

8P:bl49HELD INDUCED CHANGES OF THE DIELECTRIC FUNCTION AND OPTICAL

BISTABIUTY IN InGaAiP/InP p-i-n AND n-i-p-1 STRUCTURES

P. Kiesel, A. Hofler, M. Knelssl, B. KnUpfer, N. Under, S. Quassowski,P. Riel, and G.H. Dbhier, E. Veuhoff*; (Institute for Technical Physics,University of Erlangen, Germany; 'Siemens AG, MUnchen-Perlach, Germany)

The strong internal field of p-l-n and n-I-p-i structures Is tunable byexternal reverse bias. This leads to large field Induced changes of theabsorption coefficient near the InGaAsP bandgap. We report spectral photo-response and transmission experiments. Quantitative agreement betweentheoretical and experimental spectra is obtained, if the conventionalFranz-Keldysh theory is extented by additional consideration of excitoniceffects.For photon energies slightly above the band edge very large changes inabsorption can be observed. Within this range of wavelengths absorptiondecreases with Increasing internal field. This can be used to demonstrateoptical bistability both In transmitted light and In conductance of then-layer. In particular bistable switching between several orders of magnitutein conductance is possible, if the n-layers are sufficiently narrow.

8P:bl50ELECTRON MAGNETOTRANSPCRT IN SILICON PET-STRUCTURES

A.I.VAKSERInstitute of Radiophysics and Electronics, Academy of Scien-ces of the Ukrainian SSR, 12 Acad. Proscura str., 310085,Kharkov-85, Ukr.SSR, USSR.

It is well known that principal electric- characteristics ofmany PET-structures depend on the electron temperature T.The value of T achieves through the balance between the Joulerelease and heat removal outside the system. It is naturalthat the thermal boundary conditions are of paramount impor-tance in the formation of the value of T.

Here it is shown that both geometry form effect and field-effect allow to govern the intensity of heat removal, andconsequently the value of T.

It is demonstrated that in silicon PET-structures in the pre-sence of transverse magnetic field the both mentioned effectsinfluence highly the electric characteristics of the systems.Nonohmic and nonreciprocity coefficients for static electricfields and the volt-watt sensitivity of the structure forhigh-frequency case are investigated. A new type of high-frequency wave detector is suggef?ted(based on the form effectexamined).

283

8P:bl51ABSOLUTE NEGATIVE RESISTANCE OP SUBMICRON MIS-STRUCTURES

A.I.VAKSERI n s t i t u t e of Radiophysics and Elec t ron ics , Academy of Scien-ces of the Ukrainian SSR, 12 Acad. Proscura s t r . , 3IOO85,Kharkov-85, Ukr.SSR, USSR.

I t i s shown tha t in planar submicron metal- insulator-semicon-ductor (MIS) s t ruc tu re s due to simultaneous existence of twophysical f ac to r s : ( i ) high nonequilibrium elect ron s t a t e and( i i ) i t s abrupt s p a t i a l inhomogeneity, q u a l i t a t i v e l y neweffect occurs.

The subject is an absolute negative resistance of electronsin the partial semiconductor layer circuit of MIS-microsystem,i.e. the situation when electrons of semiconductor layermove to meet external electric field.

This phenomenon is realized at special type of boundary con-ditions provided that electric current passes along the lay-ers and transverse static magnetic field lies in MlS-structu-re plane. Hereat the whole current-voltage characteristic ofthe structure is nonlinear single-valued function.

Taking as a basis the effect predicted, a new variety of mag-netosensor is suggested.

8P:bl52DEFECTS AT THE WAFER BONDED UNIPOLAR

SILICON - SILICON JUNCTION

Stefan Bengtsson, Gen I. Andersson, Mats O. Andersson and Olof EngstromDepartment of Solid State Electronics, Chalmers University of Technology,

S-412 96 Gdteborg, Sweden

We have found ilmt defects ut wafer bonded unipolar silicon-silicon junctions strongly dominate

the electrical and electro-optical properties of these structures. We present a model in which

charged Interface stales, the origins of which we argue to be impurities and crystallographic

defects, cause a potential barrier at the bonded Interface which limits the current. Light with

photon energies larger than the silicon bandgap can increase the current across the Junction by

providing minority curriers. When Illuminating the sample with sub-bandgap light, the current

increase at low temperatures is instead caused by the change in occupancy of deep electron

traps, located In the silicon in a small volume around the bonded Interface.

2S-1

8P:bl53EARLY STAGES OF THE SCHOTTKY BARRIER FORMATIONFOR AL DEPOSITED ON GAAS(llO)

R. Rincön, J. Ortega, R. Perez, F. J. Garcia-Vidal and F.FloresDepartamento de Fisica de la Materia Condensada C-XII.Facultad de Ciencias. Universidad Autonoma.E-28049 Madrid. Spain.andC. Coluzza, F. Gozzo, Y. Hwu and G. MargaritondoInstitut de Physique Appliquée, Ecole Polytecnique Federale, CH-1015 Lausanne, Switzerland.

The low coverage limit of Al on GaAs(llO) has been analysed both experimentally and the-oretically. The syncroton radiation photoemision spectroscopy as well as internal photoemisionmeasurements of barriers have been used to study the interface density of electronic states andthe Schottky barrier as a function of the metal coverage. At the same time we have calculatedthe chemisorption properties of Al on GaAs(llO), determining the most stable geometries andthe interface electronic properties by means of a consistent free-parameter LCAO-method. Ourexperimental results show no density of states near the semiconductor charge neutrality levelfor an Al-deposition smaller or equal than a monolayer. The interface Fermi level starts beingpinned for larger coverages; our theoretical results predict that for 2 metal monolayers, the in-trinsic metal states induced in the semiconductor gap are responsible of the Fermi level pinning.Experimental data and theoretical results will be presented and discussed in the light of thecurrent models for the Schottky barrier formation.

8P:bl54ON THE TEMPERATURE DEPENDENCE OF SCHOTTKY BARRIER HEIGHT

7.S . J . HORVATHResearch Institute for Technical Physics of the HungarianAcademy of Sciences, Budapest P.O.Box 76. H-1325 Hungary

The usual experimental temperature dependence of the Schottkyharrier height for n-typp structures is the same or a little'•eaUer than that rif the band gap. On the other hand, for p-type-true tines the Schot tky hairier height does usually not depend>u ! In- temperature. This temperature dependence may be ex-pliiined h.\ tiding general equal inns derived for the equilibriumSchritt k> iiiii'ricr lieighis in n- and p-type structures by thejiireenl author. T1 may he shown that the above experimental re-'îii I t s ait- line t f: the fact that the temperature dependence ofthe band gap i s=. connected with the change of the electronaffinity of the semiconductor. The energy position of the va-lence hand edge (with respect to the vacuum level) does notchange significantly with the t emperat ure, the position of theconductance band edge changes only. In this case the recharging"•f interface states affect the barrier height of n-type struc-tures, only. The teniporature dependences of other character mayalso he explained by the above mentioned equations.This work has been supported by the (Hungarian) National^cieiMific Research Found (OTKA) through Grant N°1240.

285

8P:bl55A CONTROL OF AN INTERFACE POLARITION DISPERSIONRELATION IN SEMICONDUCTOR BARRIER STRUCTURES:

INTERFACE POLARITON OPTOELECTRONICS

N. Savostyanova, Fryazino, 141120, Moscow region, Wedensky' sSquare, 1, Inst. of Radio Engineer, and Electronics, phone 5269193

V. Sandomirsky, College of Judea and Samaria, Research Inst.,Ariel, 44804, Centre of Solid State Physics, Israel, phone 9366469

It is proposed several effective electrical and photoelectricalmethods of the control of interface polariton (IP) dispersionrelation in the barrier structures of types: metal-semiconductorSchottky-junctions, homo- and hetero.iunctions and MIS-systems.All these structures contain "dielectric" region depleted ofcarriers. One can drive the thickness of this region by electricalor/and photoelectrical ways and in result change the commondispersion law of proper 1?. This means changing of opticalproperties of whole system too. The theory of such phenomena isdeveloped. It is proposed the series of new devices: tunablespectral and spatial modulators of light intensity, the drivinglight mirror etc. Response times of discussed systems can be somepicoseconds.

A new diagnostics of interfaces is described: the scanningcontact potential difference optical microscopy.

8P:bl56NONLINEAR CONDUCTIVITY OF THE HETEROCDNTACT BASED ON PrNi5 AND CeNi5

Y.G.NAIDYUK, M.REIFFERS1, A.G.M.JANSEN2, I.K.YANSON, P.WYDER2, D.GIGNOUX3,

D.SCHMITT3

ILTP «. E, Lenin avenue 47, 310164 Kharkov, Ukraine

Inst.Exp.Phys., Solovjevova 47, CS-043 53 KoSice, Czecho-Slovakia2HML MPI, 25, avenue des Martyrs, F-38042 Grenoble, France3LMLN, CNRS, 25, avenue des Martyrs, F-38042 Grenoble, France

The authors presents anisotropic asymmetry of the conductivity of meta-

llic point-contact (PC) with respect to the current direction between single

crystals of PrNi,- or CeNi, and Cu. The first compound is well-known by crys-

talline electrical field (CEF) influence and second one as like as valence

fluctuation system. The nonlinearities in PC resistance dV/dI(V) and its de-

rivative were observed, which reflect in direct way the excitation of the

phonons and Pr + ions to higher CEF levels in PrNi, and 4f levels or para-

magnons in CeNi,- by the energized electrons. Moreover the measured pronoun-

ced asymmetry of dV/dI(V) is connected with the relaxation processes of the

above mentioned excitations in the one side of heterocontacts.

286

8P:bl57HEAT WAVES IN SUBHICRON SEMICONDUCTOR STRUCTURES

Janina Marciak-Kozlowska, Institute of Electron TechnologyAl. Lotnikdw 32/46. 02-668 Warsaw, Poland

A theory for the propagation of heat in semiconductorelectron - hole plasma in submicron structures is proposed. Itis an extension of the usual diffusion which takes into accountthe inertia of heat and predicts a finite velocity for heatpropagation ( 1/" / )

The equation: A /J*T . 4 ftf

is obtained for temperature of electron - hole plasma. Thisequation is solved for one dimensional geometry and is shownthat for 8-10 /***»<; t < o.A /*»* (l=characteristic dimen-sion of structure) the solution to equation (1) can be describedas a heat wave with phase velocity \f.m i/y t* ( o = Fermivelocity) * & r F

8P:bl58INELASTIC ELECTRONIC SCATTERING OP LIGHT IN SEMICONDUCTORMICR0STRUCTUR3S

•BAIRAMOV B.H. and TOPOROV V.V.A.P.Ioffe Physico-Technical Institute, 194021 St.Petersburg

IRMER G. and MOBBCKE J.Pachbereich Physilc. Tiergakaaeniie Preiberg, 9200 Freiberg

Quasi-elastic light scattering from non-interfering single-par-tical electron excitations and inelastic light scattering fromcoupled electron^phonon excitations are observed experimentallyand studied theoretically in GaAs- and InP-based semiconductormicrostructures v/ith non-parabolic dispersion of energy bandsRfor a wide range of electron concentrations varying from — 10(undoped semi-insulating) to —10iy cn~5 (heavily doped samples).

The results indicate that at RT scattering mechanisms associ-ated with charge-f spin-,energy-, and momentum-density fluctu-ations are represented by different light scattering line sha-pes and occur in different concentration ranges.

At LT (6K) such scattering trasforms into pure electronic scat-tering induced by transitions between ground and excited elec-tronic levels (like ell known Lyman, Calmer seTies of hydrogenatom) demonstrating chemical shifts and nature of imperfections.

287

8P:bl59NEUTRON-TRANSMUTATION-DOPED InSe INVESTIGATED BY POSITRON

ANNIHILATION SPECTROSCOPY

R. Pareja, R.M. de la Cruz, B. Marl, A. Segura and V. Mufioz

Escuela Politecnica Superior. Universidad Carlos III„ 28013 Leganes (Madrid). SpainDepartamento de Ffslca de Materiales. Universidad Complutense

28040 Madrid. Spain

Departamento de Fislca Aplicada. Universidad de Valencia46100 Burjasot (Valencia). Spain

Positron annihilation measurements have been performed on neutrontransmutation doped InSe in order to investigate the nature of thedefects Induced by this doping tecnlque. Isochronal annealingexperiments have been made in this layered semiconductor up to 775 K In50 K steps.

Recovery of the positron lifetime, T, IS found for temperaturesabove 575 K. The higher T value of (307+2) ps is attributed to positrontrapping in related defects to the In vacancies rather than the Sevacancies. The value of (294±2) ps, obtained at the recovery end, isattributed to the positron lifetime In the bulk of InSe. Comparisonswith the positron annihilation parameters previously obtained in aconventional Sn-doped InSe crystal are established.

1 de la Cruz R. M. , Pareja R., Segura A. and Chevy A., J. Phys. C: Sol.State Phys. 21 (1988) 4403

8P:bl60GaSb SINGLE CRYSTALS WITH A LOW DISLOCATION DENSITY

VERA SESTAKOVA and BEDRICH STEPANEKInstitute of Physics, Czechoslovak Academy of Sciences,

Cukrovarnicka 10, 162 00 Prague 6, Czechoslovakia

The series of undoped and doped (Te, In, N) GaSb singlecrystals were grown by means of Czochralski method [1]. Theeffects of thermal stresses in the grown crystals wereminimized because t>f the very low temperature gradientsexhibited by our apparatus. The dislocation distribution wasstudied along the growth direction. It was found that thedislocation density is very low and rapidly decreases from thebeginning to the end beeing almost the same for all growncrystals. For this reason it was not possible to lokalizeinfluence of dopants (i.e. hardening effect). The neck andcontinuing shape of the crystal beginning was thus main problemto control the low dislocation density. It follows the angle ofthe neck widening must be smaller than 38.94 [2] to assure thestarting dislocation density be kept very low.

[1] Moravec F., Sestakova V., stepanek B. and Charvat V.,Cryst.Res.Technol. 24 (1989) 275

[2] Garandet J.P., Duffar T. and Favier J.J., J.CrystalGrowth 96 (1989) 888

288

8P:bl61Single crystals of GaN and A1N.

Physical properties under pressure up to 0.5 Mbar

P. Perl in, A. Polian , H. Teisseyre, I. Gorczyca,

N.E. Christensen and T. Suski

High Pressure Research Center "Unipress"

Sokolowska 29/37, 01-142 Warszawa Poland

Physique des Milieux Condenses Universite Pierre Marie Curie

Tour 13, 4 place Jussieu, 75252 Paris France

Institute of Physics, Aarhus University, 8000 Aarhus, Denaark

In spite of the prospects of III-V nitrides for variousapplications, experimental data on their microscopic parametersare surprisingly scarce. This is mainly due to the lack of highquality - single crystals of nitrides, in this work we take theopportunity of the successful growth of GaN and A1N crystals bymeans of high temperature - high pressure synthesis.

Results of the following experiments will be presented here :- High pressure phase transitions in GaN and A1N.- Raman scattering in GaN and A1N.- Studies of dielectric constant and energy gap in GaN.The experimental results are compared with the first principlecalculations and used to verify some schemes employed forclassification of semiconductor compounds.

8P:bl62ON THE ORIGIN OF STACKING FAULTSIN SPHALERITE TYPE SEMICONDUCTOR

GALEAZZI C.A. and PELOSIC.CNR-MASPEC Institute, via Chiavari 18/A, 1-43100 Parma (Italy)

Stacking faults are the most common structural defects present inepitaxially grown layers and their presence negatively affects thesemiconductor binary material properties and consequently the III-Vapplications in the electronic field .Particularly films grown by gaseous/solid phase transitions showstacking faults presence, whose generation mechanism is not clearlyunderstood.In this communication we will try to explain the growth of stackingfaults as due to a more favourable interface energy betweenwurtzite/sphalerite than liquid/sphalerite systems.The aim of this work is to relate stacking faults concentration to the III-V compound type and to the epitaxial growth conditions.

289

8P:bl64PULSED EXCIMER LASER SYNTHESIS OF TUNGSTEN SILICIDES

S. LUBY1, E. MAJKOVA"1, E. D'ANNA2, G. LEGGIERI2, A. LUCHES2,

M. MARTINO2

Institute of Physics, Slovak Acad. Sci., 84228 Bratislava

Department of Physics, University Lecce, 73100 Lecce

Tungsten films 150 and 500 run thick were sputtered onto sili-

con wafers. Samples were irradiated by 30 ns XeCl laser pul-2

ses at fluences 0.6, 0.9 and 1.2 J/cm . Number of pulses was

N » 1 - 1000. RBS, X-ray diffraction and resistometry were

used for the study of the silicide formation. Calculations of

the time - depth profiles of temperature in the samples were

performed as well. For 150 nm tungsten film formation of WSi_

was completed at 1.2 J/cm and N= 300. Only silicon melts

under these conditions, the melt depth being 4OO nm. For 500

nm tunsten film the onset of W-Si, and WSi, synthesis was

observed.

8P:bl65A PRIMARY ION BEAM SOURCE AND DIRECT ION BEAM DEPOSITION OFFILMS ON POLY AND SINGLE CRYSTALLINE SUBSTRATES

H.R. KHAN'.2) o. LOEBICH1 AND CH. J. RAUB1

1. FEM, D-7070 Schwaebisch Gmuend, Germany 2. Department ofPhysics, University of Tennessee, Knoxville, TN. U.S.A.

The quality of a thin f i lm can be improved and controlled by direction beam deposition technique ( DIBD ). A low gas pressure R.F. ionsource to produce the ions from the metallic and non-metallicmaterials and a three ion beam system for the direct ion beamdeposition of of multi component, large surface area andhomogenous thin f i lms such as superconducting YBCO w i l l bedescribed. The Cu and Y-oxide fi lms are deposited on various polyand single crystalline substrates and characterized for theparameters such as thickness, structure and microstructure andthe temperature dependent electrical conductivity is measured.

This work was supported by BMFT under the Grant No. 13N6990

290

8P:bl66

EXPERIMENTAL ANALYSIS OF THE NOISE OF STATISTICAL

ESTIMATORS USED IN CORRELATION SPECTROSCOPY

LORUSSO G.F., CAPOZZI V., MINAFRA A.

Dipartimento di Fisica, Universita di Ban and Unita di Ricerca

INFM-GNSM di Bari, Via Amendola 173,1-70126 Ban, Italy

We present an experimental analysis of the variance of photon correlation and pho-ton structure functions obtained from dynamic light scattering measurements. Theresults are compared with theoretical predictions. The noise evaluation of the statisti-cal estimators has been obtained by using a fluctuation analyser, specifically built forthis purpose 1, which uses linearly-spaced sampling time. The noise dependences onthe experimental bounds are investigated. The predicted behaviour of the estimatorvariances has been confirmed. The results 2 confirm that the stucture function hasbetter noise performance for relatively high mean count rates, strongly suggesting awider use of this statistical estimator in the case of uniform sampling.

1. Lorusso G.F., Capozzi V., Minafra A., Rev. Sci. Instrum. (1992) in press

2. Lorusso G.F., Capozzi V., Minafra A., Ph. Rev. A (1992) in press

8P:bl67SUBMILLIMETRE SPECTROSCOPY - PROMISING

TECHNIQUE OF THE SOLID STATE PHYSICS

G.V. KOZLOV, A:M. PROKHOROV, A.A. VOLKOVIr.stiture of General Physics, Russian Acad.Sci.,Vavilov str. 38, 117942 MOSCOW, USSR

S. KAMBA, J. PETZELTInstitute of Physics, Czech.Acad.Sci.,Na Slovance 2, 180 40 Praha 8, CZECHOSLOVAKIA

'Jr.ique possibilities are demonstrated of the submillimetrespectroscopy based on the use of the tunable monochromatic ge-risrctors - backward wave oscillators (BVJO) - for investigationof the anomalous physical properties of dielectrics, ionic andelectronic conductors, superconductors and antiferromagnets.

The following topics have been addressed:- Dynamical origin of the ferroelectric phase transitions- Lattice dynamics of incommensurate phases.- Cluster excitations in dipolar glasses.- Loss origin in microwave ceramics.- Origin if fast ionic conductivity in superionic conductors.- Problem of charge localization in doped binary semiconductors.- Dielectric spectra of high -T superconductors, problem of

residual losses below the gap energy.- First permeability spectra in antiferromagnets.

291

8P:bl68DISORDER INDUCED LIGHT SCATTERING IN SOLIDS:THEORY AND APPLICATIONS

P.Benassi<°>, V.Mazzacurati('), M.Montagna<+>, O.Pffla<°>, CRuocco^ andG.Signorelli<*>(o) Dipartimento di Fisica, Universita' di Trento, Povo, Trento, 1-38050,Italy.(+) Dipartimento di Fisica, Universita' di Trieste, Trieste, 1-34127, Italy.(*) Dipartimento di Fisica, Universita' di L'Aquila, Coppito, L'Aquila, I-67100, Italy.

A microscopic approach to evaluate the disorder induced light scatteringspectra in solids is presented. A quite general theory is developed and thenspecialized to some model systems that can represent an extended classof real systems. We find that the general features of the disorder inducedspectra of real systems can be predicted once the microscopic disorder andthe mechanism responsible for the induced polarizability are correctly takeninto account. Some new interesting results are derived and compared tothose predicted by Whalley and Bertie1 and Martin and Brenig2.

1 Whalley E. and Bertie J.E., J.Chem.Phys.,64 (1967) 1264.2 Martin A.J. and Brenig W., Phys.Status Solidi (b), 64 (1974) 163.

8P:bl69A CALOKIMETRIC PARTICLE UETECTOH WITH HIGH HNEHGY HESOLUTION.

M. BUHU3R, and E. UMLAUFWalther Meissner Institut fur Tieftemperalurforsohimg fier BayerischenAkademie der Wissenschaften, W-8046 Garching, Germany.

We present a highly sensitive calorimeter which is used for singleparticle detection. The compound detector consists of an absorber with120 grams of silicon and a small piece of a paramagnetic sample asthermometer. The increase of temperature on particle absorption is mea-sured with a direct coupling SQUID magnetometer of special design wor-king at millikelvin temperatures. From the signal height of 5.5 MeVoC-particles and the noise of the detector we can infer an energy reso-lution better than 60 eV. The signal rise time depends strongly ontemperature and the fastest signals are obtained at the lowest tempera-tures (25 ITIK), The signal shape is more complex when particles areabsorbed on the magnetic thermometer.

292

8P:bl70TRAPPING EFFECTS IN EXCITON MOTION IN THE FRAMEWORK OF CTRW

PAVEL HERMANPedagogical Faculty, Freedom Square 301, 501 91 Hradec KraloveIVAN BARVIKInstitute of Physics of the Charles University, Ke Karlovu 5,121 16 Prague 2, Czechoslovakia

To take into account an effect of the trap on exciton dynamics, Kenkresuggested so called "sink" nodel. In the simpler version the excitonprobability decays to the trap at constant rate /> whenever the excitonoccupies a site influenced by the trap. Kenkre suggested to append the sinkterm to the Generalized Master Equation.Our calculations of the coherent nenory functions entering GME for finitesystems (trimer, hexamer,..) display the influence of the sink. The memoryfunctions change their form appreciably, they are loosing their periodicity,the coherence tine becomes shorter. For large trapping rate r the rest ofthe system is decoupled from the sink not only in the sence, that excitonavoids the sink place. The memory functions are transformated entirely tothat for the rest. We question Kenkre's result in which no transformation ofmemory functions takes place. We have investigated also the connectionbetween the memory functions and the pausing time distribution functions andprobability densities in the Continuous Time Randon Walk in the presence ofthe sink. Only several pausing time distribution functions becomenonnegative for large trapping rate y. The usage of CTRW for Monte-Carlomodelling of the exciton transfer in quasicoherent regime is questioned.

8P:bl71OBSERVING FREE RELAXATION INDUCED BY COLORED NOISE VIA NON-LINEARMAGNETIC RESONANCE SPECTROSCOPIES

L.Andreozzl.C.Donatl.M.Glordano.D.LeporinlDipartlmento dl Flsica, Piazza Torricelli 2.1-56100 Pisa Italy

The dynamics of an observable A of a system of Interest .flcan be unravelled by preparingproper non-equilibrium states of A and then observing their free relaxation (I.e. In absenceof external disturbances). This pattern, working in the time domain. Is not always viable.In linear regime Is paralleled by simpler procedures operating In the frequency domain,since the response of A to a contlnuos disturbance and the free relaxation are related.Extending the above link to the case of non-linear response Is an Issue currently underdebate. Furthermore, one can ask if non-linearities can be controlled to disclosealternative routes to the direct observation of the free relaxation behaviour. A detailedanalysis Is presently in progress. In this communication we outline the general aspects ofthe theoretical framework and discuss some consequences. It will be shown that the non-linear response to small perturbances can be derived in terms of its free relaxation. In apurely quantum-mechanical framework the non-linear response will be factorized by twoterms, the former depending upon the degrees of freedom of the external disturbances only,the latter upon the degrees of freedom of the system *and the bath a only. In this sense theapproach extends the standard linear response theory. Applications are drawn frommagnetic resonance. They cover both the second and third order non-linear response withrespect to the amplitudes of the impinging fields for both a two-levels and a four-levelsmodel of the system X

293

8P:c201

THEORY OF ONE- AND TWO-STEP PULSED PHOTOBURNINGOF SPECTRAL HOLES

I.REBANEInstitute of Physics, 202400 Tartu, Estonia

The theory of spectral hole burning (SHB) by light pulses of arbitraryshape and duration is proposed. One- and two-step (light-gated) SHBprocesses induced by laser pulses in two-, three- and four-level systemsare theoretically considered.It is shown that at two-step SHB holes differ essentially in the casesof pulse and stationary SHB. In case of two-step SHB by two speciallychosen successive pulses the holewidth can be narrower than the oneobtainable in SHB by monochromatic light. The spectral hole can furtherbe narrowed if an additional delta-pulse is used.In case of one-step SKB the influence of the shape of a hole on the dura-tion of the burning pulse and on the steepness of its fronts is considered.Temporal responses of spectral holes as spectral filters to delta-pulse ofthe light have been found.

8P:c202THEORETICAL STUDY OF THE VERY FAST ELECTRON DYNAMICS

IN DISORDERED SOLIDS

A. Kalvova'1', B.Velicky(2)

Institute of Physics CSAV, 180 40 Praha (1), University ofLund, 223 62 Lund and Charles University 110 00 Praha (2)

In strongly disordered solids, the formation and dynamics ofelectronic excitations is dominated by the elastic scatteringchannel, and their behavior deviates essentially from theusual quasiparticle picture. For a moderate disorder, likee.g. in some semiconductor mixed crystals, the characteristictimes for the temporal evolution of the excitations arecomparable with the time of the interband photoexcitation, sothat the two processes are coherent. This leads to remarkablequantum interference effects which can be treated using thenon-equilibrium Green functions . We report the resultingelectron distribution as a function of time.1. Velicky B.,Pieczonkova A., J.Non-Cryst. Sol., 97, 455 (1987)

294

8P:c203

THE SILICON DIODE STRUCTUREFOR PICOSECOND RESOLUTION PHOTON COUNTING

B. Sopko, I. M&ha, I.Proch&ka, K.HamalCzech Technical University, Brehova 7, 115 19 Prague 1, Czechoslovakia

phone +42 2 848840, fax +42 2 847688, tlx 121254 fjfi c

We are reporting on the novel design and technology of the Silicon photodiodeoptimized for high timing resolution photon counting at a room temperature. The selfconsistent Solid State Photon Counting Module has been developed, which detects singlephotons over the wavelength range from 0.36 to 1.1 micrometers, a range and sensitivitywhich outperforms most of the photomultiplier tubes. The X ray and gamma radiation isdetected, as well. The wide spectrum of the application will be demonstrated.

8P:c204

Monte-Carlo simulation of ultrafast electron relaxation in Ag.

P J . van HallUniversity of Technology, Eindhoven, The Netherlands

R.H.M. GroeneveldUniversity of Technology, Amsterdam, The Netherlands

Recently experimental evidence has been presented on the interplay of electron-electronand electron-phonon interaction in the energy relaxation of noble metals excited with anultrafast laser pulse. We have investigated this subject using Monte-Carlo techniques. In amodelling as realistic as possible with the deformation potential of the electron-phononinteraction as the only parameter we can reproduce the features qualitatively. Detailedinvestigation of the various ingredients reveals an unexpected sensitivity to the phononenergy spectrum. Resistivity calculated with the extracted strenght of the deformation '.potential is in satisfactory agreement with the experimental value at 300 K. A

I

295

8P:c205

Time resolved exciton transfer in biased asymmetricdouble quantum wells - theoryR.Ferreira, Ph.Roussignol, P. Rolland and C. DelalandeLaboratoire de Physique de la Matiere CondenseeEcole Normale Superieure24 Rue Lhomond - 75005 - Paris

We consider theoreticaly the excitonic dependence of theinter-well (tunnel) transfer of photoexcited carriers in biasedasymmetric double quantum wells.

Our simple model accounts for the principal aspects of theoptical process: (1) initial population of photocreated carriers onone well ; (2) intra- and inter-well relaxations ; (3) radiatifrecombination of the exciton pairs ; (4) variation of the differenttimes involved with the external electric field ; (5) dependence ofthe final luminescence (PL) with the power intensity (initial densityof pairs). We discuss in detail the non-linear behaviour of the PL ;it is to be related to the appearence of an induced electricdipoie, due to the spatial separation of the electrons andholes wich form the exciton pairs (crossed excitons), after thepartial transfer of the correlated electrons into the other well,whereas the holes do not transfer.

8P:c206Time resolved exciton transfer in biased asymmetricdouble quantum wells - experimentsPh.Roussignol0*, R.Ferreira0, P. Rolland0, C. Delalande0. A. Vinattieri*.L. Carraresi*, M. Colocci*. .V. Roy", B. Sermage", J-F. Palmier". B.Etienne+.

We have measured at 4K the time evolution of thephotoluminescence (PL) of a biased asymmetric double quantumwell (ADQW). Near the first exciton resonance the time evolution ofthe PL display three different regimes, depending on the powerexcitation. A strong non-linear behaviour appears for high powers ;it is to be related to the rise of an induced electric dipoie. due to thespatial separation of the electrons and holes of the exciton pairs.

We have also measured the exponential decreasing time T ofthe PL in the weak power regime ; the variations of T with thevoltage for the two direct excitons display a resonant-like accidentat different voltages.

These results evidence the excitonic nature of the inter-well(tunnel) transfer of the carriers in a biased ADQW.

296

8P:c207

NON-RADIATIVE RELAXATION OF JAHN-TELLER SYSTEMSIN CRYSTALS BY THE PULSE MODEL

M. Dominoni and N. TerziUniversita di Milano, Dipartimento di Fisicavia Celoria 16, 20133 Milano, Italy

The pulse model [1] has been extended to evaluate the short time relaxation afterexcitation of color centers in degenerate excited states, i.e. the dynamics from unrelaxedto relaxed configuration of strong Jahn-Teller {J-T) systems in crystals.

The local J-T electron-phonon interaction is found to be in competition with thevery fast processes [1] of delocalization of elastic energy due to the surrounding crystaldynamically coupled to the center.

Tie rede of the local Anhannojiicity is also considered. Numerical estimate of xe-laxation time, for different centers and couplings, is reported.

[1] M. Dominoni and N. Tetzi, Eutophys. Lett. 15, pp 515-520 (1991)

8P:c208

ULTRAFAST ELECTRON DYNAMICS AT THE Ge(ll l) 2x1 SURFACE

M. BAEUMLER and R. HAIGHT*Fraunhofer-Institute for Applied Solid State Physics, Tullastr. 72, D-7800 Freiburg,Germany

Using angle resolved laser photoemission we have carried out investigations on thelaser excited Ge(lll) 2x1 reconstructed surface with subpicosecond time resolution.The photoemission spectrum of the Ge(lll) surface first photoexcited with 1.8 eVreveals peaks due to the occupied x as well as the transiently populated x* surfaceband. At room temperature the electron population of x* decays rapidly within the first20 ps while at 120 K the decay is significantly slower indicating the important roleplayed by phonons in mediating electron-hole recombination at the Ge(ll l) surface.The renormalization of the surface bandgap is studied as a function of electron density.

* IBM T.J. Watson Research Center, P.O. Box 218, Yorktown Heights, N.Y. 10598,U.S.A.

297

8P:c209

PHOTODARKENING EFFECT IN SEMICONDUCTOR-DOPED GLASS STUDIED

BY PICOSECOND SPECTROSCOPY

P.MALY, F.TROJANEK AND A.SVOBODA

Department of Chemical Physics

Faculty of Mathematics and Physics, Charles University

Ke Karlovu 3,121 16 Prague 2, Czechoslovakia

We study the effect of photodarkening in the CdSSe doped commercial colour

glass filter. We observed the decrease of luminiscence efficiency and cw

transmission of the filter with laser exposure in agreement with the results reported

by others. In addition, we measured the transient absorption of the sample excited by

a picosecond laser pulse (pump and probe technique with picosecond time resolution) as

a function of time and laser exposure in vis and near ir spectral regions. We compare

recent models of photodarkening and the results of our measurements.

8P:c210ULTRAFAST PROCESSES IN SEMICONDUCTORS: MONTE CARLOSIMULATION INCLUDING COHERENT PHENOMENA

TILMANN KUHN1 and FAUSTO ROSSI2

1Institut fur Theoretische Physik, Universitat Stuttgart, Pfaffenwaldring 57,7000 Stuttgart 80, Germany,2Dipartimento di Fisica, Universita di Modena, Via Campi 213/A, 41100 Modena, Italy

The Monte Carlo method has been used very successfully for the investigation of energyrelaxation processes of photoexcited carriers. The coherence effects, however, whichbecome important on ultrashort time-scales, are neglected in these simulations. Wepresent a Monte Carlo simulation which, in addition to the calculation of the carrierdistribution functions, takes into account the interband polarization responsible forcoherence phenomena. In particular, the results give insight into (i) the details of thegeneration process resulting in a time-dependent line-width related to the energy-timeuncertainty relation, (ii) the different times describing the dephasing dynamcis of thecarriers, (iii) strong excitonic effects close to the gap in absorption and emission spectra.

298

8P:c211TIME RESOLVED PHOSPHORESCENCE EMISSION IN THIANTHREN CRYSTALS.

A. ARENA, A. M. MEZZASALMA and G. SAITTAIstituto di Struttura della Materia, Universita' di Messina,

Salita Sperone 31,1-98166 Sant1 Agata - Messina, Italy.

Thianthren is an example of hetero-aromatic compound whidi, despite of the presence of an energy gap

wider than 3.5 eV exhibits an appreciable spontaneous or photostimulated electrical conductivity. The

comprehension of thianthren luminescence mechanisms allows to gain useful informations about

secondary processes such as photoemission and photoconductivity. The luminescence spectra, performed

at room temperature on a Muanthren crystal <ii the excitation wavelength of 340 ran, have shown that the

phosphorescence emission consists of two bands centred at about 460 and 530 nm respectively. The

emission curves, recorded using time delays lower than a few msec, peak at 460 nm, but the observed

maxima seem to sVvift \svifons\ty towards Vonger •waveterigttvs mtin *ie itnaeasvng oi tone tiday, Teaching

530 nm at 9.5 msec. This behaviour suggests that two energy levels are involved in the phosphorescence

emission and seems to support the experimental evidence of a double exponential decay rather than the

monoexponential one reported in literature. A model to interpiete this result may be that the triplet level

higher in energy, partially decays radiarively with a mean lifetime of a few tenth of msec, and partially

feeds the lower energy level, which in turn decays radiatively with a longer time that we have found to be

in good agreement with that reported in literature of 4 msec.

8P:c212

2HS EHSI13Y. OS1 EXCITOII EXCITATION THAT ACCOUNTS KINJffiJATIC

INTERACTION EXACTLY

O.V.DER/IHKO, R.R.LEVITSKII, A.Ph.IIOIHA

Inst .Cond. iuat t .Phys. , 14/16 Drahomanova S t r . , Lviv-5, Ukraine

Considering 1D molecular c r y s t a l of two-level p a r t i c l e s with

neares t neighbours i n t e r a c t i o n we have found tha t the energy

of exciton exc i t a t i on i s given by the formula

where t^""to is "the energy of electronic excitation of

the particle and j is the constant of interaction of

nearest particles. The peculiarity of this formula is that

it acooun-ts the kinematic interaction of excitons exactly.

The last term under the square root vanishes if one neglects

the kinematic interaction of excitons.

299

8P:c213OPTICAL PROPERTIES OF As2S3 THIN LAYERS

2. CIMPL

University of Chemical Technology; na"m. £s. legii 565,

532 10 Pardubice, Czechoslovakia

Optical transmittance and index of refraction of thin As-S,

layers were studied. The layers were prepared by vacuum eva-

poration on both thin organic films and glass substrates. The

organic films were dissolved after evaporation of ASjS,, so

that selfsupporting samples of As_S, were obtained. Differen-

ces between optical properties of the selfsupporting samples

and samples evaporated onto glass substrate were observed.

Unhomogeneity of the layers after band-gap illumination was

studied as well. The index of refraction of the both sample

surfaces was calculated.

8P:c214ANOMALOUS POSTLIMINESCENSE IN MIXED CRYSTALLS

AND NEAR-SURFACE LAYER OP SEMICONDUCTORS.

Novikov B.V., Grigoriev S.R.

Physios Institute, St.Petersburg State University, USSR 198904

Processes of postluminesoense (PL) in CdS. Se mixed orystalls

and in the nearsurface layer of treated CdS, were

investigated at low temperatures (4-80K) by time

resolved spectrosoopy methods.Secondary PL (SPL),

arising in 4|J.s (a) and 300ns correspondingly,was

discovered in the spectral region of exoitons lo-

oalized by fluctuations and bound exciton comple-

xes . The SPL decay has nonexponential shape, de-

pending on the wavelength of light irradiated,ex-

citing power and temperature.PL spectra maximum

with delay time increasing is nonmonotonous (b).

Model,connecting such SPL with the carriers,localized by fluo-

tuations of intercrystall or nearsurface field, is suggested.

300

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522 run" 0 2 4 T;.|J.Sbj

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8P:c215

OPTICAL NONLINEARITIES OF ZnCdTe

I.PELANT*, D.OHLMANN, B.HONERLAGE, R.LEVY

Institut de Physique et Chimie des Materiaux de Strasbourg, Groupe d'Optique Non-lineaire et d'Optoelectronique, 5, rue de l'Universite, 67084 Strasbourg Cedex, France

We study optical nonlinearities in high-Zn-content ternary semiconductor Zn.87Cd.13Tefor the first time. We use time-resolved pump-and-probe beam spectroscopy (hi/pump =2.106 eV) in the nanosecond time range at room temperature. Induced probe beamabsorption and deflection are measured separately and absorptive and dispersive non-linearities are determined. Unusually high nonlinearities are found (induced refractiveindex changes per e-h pair are An^i,= —4.4x10 ~ l s , A n ^ = 2.2x10 2 1). We discussthe results in terms of competition between band gap shrinkage due to an electron-holeplasma and permanent electrical dipole moments which give rise to the ferroelectricityof ZnxCdi_xTe crystals.* On leave from Charles University, Faculty of Mathematics and Physics, 121 16 Praha2, Czechoslovakia

8P:c216

EXCITONS IN STRAINED ZnTe: TWO-PHOTON ABSORPTION AND THEORY

M. Schlierkamp", F. Kubacki", M. Steckermeier6, U. R6sr\>rfc

a) Institut fur Physik, Universitat Dortmund, D-4600 Dortmundb) Institut fur Theoretische Physik, Universitat Regensburg, D-8400 Regensburg

Two-photon absorption spectra of ZnTe single crystals under uniaxial stress up to350MPa in (001) direction and for different configurations of the polarization showsrich excitonic structure. In addition to the well-known splitting of the IP states dueto the coupling between orbital angular momentum and hole spin1 this structure isdetermined also by the strain-induced heavy-light hole splitting. The symmetry of theobserved states is identified by using selection rules for the two-photon absorption pro-cess in the symmetry group Di&. We perform a variational calculation of the excitonstates for a Hamiltonian, which in addition to that of Ref. 1 contains strain-inducedterms2, of which the Bir-Pikus term turns out to be the dominating one. A fit to theexperimental data for zero-stress allows to determine the Luttinger parameters and afit to the stress-dependent exciton energies provides deformation potentials for ZnTe.

1 A. Baldereschi, N. O. Lipari, Phys. Rev. B8, 2697 (1973)2 B. Pertzich, U. Roiiler, phys. it at. 10I. (b)89, 475 (1978)

301

8P:c217

PLASMON BANDS AND FANO-RESONANCES IN SEMICONDUCTORS

K. STURMInstitut fur Feslkdrpeiforschung, Foischungszentrum Jiilich G.m.b.H.

D-5170 Jiilich, Federal Republic of Germany

W. SCHULKEInslitut fir Physik, UniversitUt Dortmund, D-4600 Dortmund SO, FRG

It is known that local field effects considerably contribute to the plasmon linewidth andshould cause plasmon bands with a plasmon band gap at the Brillouin zone boundarywhich, however, due to the strong line broadening cannot be observed directly'in EELSand normal inelastic x-ray scattering spectroscopy. Using an additional interference effectobtained from coherent inelastic x-ray scattering2 on Si the two plasmon lines at theBrillouin zone boundary can be reconstructed. Furthermore, local fields couple the smallq plasmon to the large q particle-hole excitation spectrum, leading to a plasmon antires-onance (plasmon-Fano-resonance), which is observed in normal inelastic x-ray scatteringspectroscopy3.

[1] Oliveira L. E. and Sturm K., Phys. Rev. B22 (1980) 6283[2] Schulke W. and Kaprolat A., Phys. Rev. Lett. 67 (1991) 879[3] Sturm K., Schulke W. and Schmitz J. R., Phys. Rev. Lett, to be published

8P:c218PHOTOCONDUCTIVITY DECAY IN CuInSe

M. IGALSON

Institute of Physics, Warsaw University of Technology

00-662 Warszawa, Koszykowa 75, Poland

Ternary chalcopyrite semiconductor CuInSe Is widely

investigated because of its perspective application in

photovoltaics. A role of numerous intrinsic defects in that

compound In the recombination of photocarriers is of particular

interest. We present here a study of photocurrent decay in the

thin films samples obtained by flash evaporation. A wide

spectrum of decay constants covering several orders of magnitude

has been observed and explained as a result of recombination

involving tunneling between randomly distributed donors and

acceptors.

302

8P:c219OF FERSISOTiT PHOTOCONDUCTIVriY WITHIN SEMICONDUCTOR

EPITAXIAL LAYERS BY PHOTOOONDUCTIVE GAIN

QMANUEL A. ANSGNOSTAKISHellenic Air Force Technology Research Centre, 22 Kalamakiou Avenue,GR 174 55 Aliraos, Athens, Greece.

A model is proposed for the determination of the saturation value ofPersistent Photoconductivity (PP) within illuminated semiconductor epi-taxial layers, based upon the monitoring of the optoelectronic parameter ofPhotoccnductive Gain (PG) of the respective Epitaxial layer / Substrate De-vices (ESD). The model takes into account the functionality of the macro-scopic potential energy barrier existing within the ESD interface as wellas 1-he control of ionised impurity scattering over carrier mctoility in thelow temperature regime where PP is observable.

8P:c220SPECTRAL BEHAVIOR OF THREE-PHOTON ABSORPTION COEFFICIENT INII-VI COMPOUNDS : ZnO, CdS and ZnSe.

I.H.Catalano, M.Lepore, R . T O M B S !Dipartiaento di Fisica dell'Universita* di Bari

Via G.Aaendola 173, 70126 Bari (Italy)

Three-photon absorption (3PA) process has been experimentallyinvestigated for three different centre- and noncentro-symmetric II-VI compounds: ZnO, CdS and ZnSe in a largeexcitation energy range above the energy gap in order to studythe actual role of crystal inversion symmetry. The spectralbehavior of 3PA coefficient has been demonstrated to bedescribed for both type of semiconductors by a parametricformula containing different terms, whose energy dependencebeing predicted on the grounds of 3PA selection rules. Thisresult indicates that a linear k-dependence approximation forthe optical matrix elements has to be always assumedindependently of parity of the band which are involved in thetransitions in order to correctly describe the 3PA coefficientline shape. This is further confirmed by a comparison betweenthe experimental and the theoretical line shapes.

303

8P:c221TWO-PHONON RESONANT RAMAN SCATTERING IN SEMICONDUCTORS WITH

EQUAL EFFECTIVE MASSES OF ELECTRONS AND HOLES IN MAGNETIC FIELD

V.I.Belitsky and M.Cardona

Max-Planck Institute fUr FestkSrperforschung, Helsenbergstrasse I,D-7000 Stuttgart 80, Germany

Free electron-hole pairs contribution to the two-LO-phonon scatteringis studied for compounds with approximately equal effective masses ofelectrons and holes. All kinds of processes (including both real andvirtual intermediate states) are taken Into account. The cross-section ina high magnetic field shows resonances at specific values of the laserfrequency and the field, resulting from the transitions to the Landau-bandbottoms in the real intermediate states. There are three types of singleresonances (incoming, outgoing and Intermediate) and double and tripleresonances. The reasons tor electron-hole pair mechanism to be moreimportant than excitonic mechanism are discussed.

8P:c222

DOUBLE PEAK SPECTRA IN SPONTANEOUS EDGEELECTROLUMINISCENCE

J.ZAVADIL and K.ZDANSKY

InsfcUnt.e of Radio Engineering and Electronics.Czechoslovak Academy of Sciences!,Chaherekn 57, 182 51 Pralin 8, Czechoslovakia

KxpciiiKWita) and theoretical study <>f ilie shape uf spontaneous electrolti-mnnscrnce spectra emitted from the edge of (inAsP/lnP hetorosinietureili«<k'.N is reported.The ocnirence. of double, peak spectra on some: samplesis explained in terms of selective internal absorption along the way to theeciy The spectral shape is interpreted as a manifest a! ion of the fundamental;ni'l/or the first-order mode within the liansverse mode gicdmg approach.

304

8P:c223INVESTIGATION OF BISTABLE OPTOELECTRONIC STRUCTURES ON THIN

II-VI FILMS

ZALYUBINSEAYA L. N.

Odessa University, Petra Velikogo, 2, Odessa, 270100, Ukraine

Hultielements bistable optoelectronic structures for applica-

tions in systems of the information processing were reseached.

Matrix structures were pr&duced by electro-hydrodynamic spray

and thermal evaporation in quazilimited volume of II-VI mate-

rials, such as CdS(Cu, !Te) and 2n5(Cu, Kg).

Elements of optoelectronic structures has S-form voltage-cur-

rent characteristics and were switching with light pulse.

It is showed the possibility of creating for the matrix self-

scanine optoelectronic for representation of information with

an optic coupling between the elements.

8P:c224RAMAN SCATTERING IN DIAMOND AND GRAPHITE-LIKE FILMS

AT HIGH PRESSURES

A.F.Goncharova, V.D.Andreyev'° Institute of Crystallography, USSR Academy of Sciences,

Leninsky pr. 59, Moscow, 117333, USSR6 Institute for Superhard Materials,Ukrainian Acad.of Sci.,

Avtozavodskaya, 2, Kiev, 252153, USSR

The Raman spectra of the diamond-like (a-C) and graphite-like (i-C) films weremeasured for the first time at high pressures. We determined the pressure coefficientsof the vibrational modes observed, which were found to be consistent with those ofsingle-crystalline graphite and diamond. The transformation of graphite-like film intothe amorphous phase, characterized by the Raman spectrum, which is analogous to thatof the diamond-like film, was observed.

305

8P:c225INDIRECT ENERGY GAP DEPENDENCE ON Al CONCENTRATION IN AlxGai_xAs ALLOYS

H. GUZZI, E. GRILLI and S. OGGIONIDipartimento di Fisica dell'Universita, via Celoria 16, 20133 Milano, ItalyJ.L. STAEHLIInstitut de Physique Appliquee, CH-1015 Lausanne, SwitzerlandC. BOSIODipartimento di Fisica dell'Universita, via Bassi 6, 27100 Pavia, ItalyL. PAVESIDipartimento di Fisica dell'Univesita, 38050 POVO, Trento, ItalyThe energy of the indirect X exciton in AlxGaj_xAs epitaxial layers(0.38<x<0.81) has been determined by photoluminescence measurements atsample temperature of 12 K; from these data, the dependence on the Al con-centration x of the energy of the r-X gap has been obtained: E£(x) == 1.988 + 0.207x + 0.055 x 2 (eV). This relation is characterized by a verysmall bowing. From our data we deduce also the coordinates of the r-Xcrossover point: xc = 0.385 + 0.016 and Ec = (2076 + 4) meV at T = 0 K andxc = 0.396 + 0.016 and Ec = Jl997 + 4) meV at T = 300 K.

8P:c226PHOTOCURRENT SPECTROSCOPY OF AMORPHOUS MIS-STRUCTURES

R. SCHWARZ, M. REISSNER, M. MIOSGA, and T. FISCHERTechnische Universitat Munchen, Physik-Department E16D-8046 Garching, Germany

Various techniques of photocurrent spectroscopy were used to study the interfacesbetween hydrogenated amorphous silicon (a-Si:H) and different high-band gap layers likeplasma-deposited a-SiC:H, a-SiN:H and thermal SiO2.

The first technique consists in analyzing the amplitude and phase of the ac-photocurrentunder monochromatic illumination through a semitransparent contact on the a-Si:H layer,which allows to infer the potential shape both near the heterointerface and the Schottkybarrier. In the second technique we measure the change of phase with applied voltage atdifferent wavelengths and monitor hysteresis effects. This is complementary to the firsttechnique. Finally the phase shift relaxation after applying voltage pulses of differentamplitude and polarity is used to monitor charging and discharging of interface defects.Conventional C-V measurements complete the analysis.

The results show, for example, that SiOj/a-Si:H interface charging relaxes with thelongest time constant. Lower band gap differences lead to less pronounced hysteresiseffects and to a faster phase shift relaxation in the other materials. By varying the lightwavelength we conclude that the band bending is stronger for SiO? than for a-SiN:H ora-SiC:H insulator layers.

306

8P:c227PHOTOACOUSTIC CHARACTERIZATION OF CHALCOGENIDE GLASSES:

THERMAL DIFFUSIVITY OF GexTei-x

J.C. de Lima, N.Cella, L.C.M. Miranda

Instituto Politecico do Rio de Janeiro

PO Box 97282, 28613 Nova Fribrugo, Rio de Janeiro - Brazil

Semiconducting chalcogenide glasses of Ge-Te alloys have received

considerable attention because of their Important applications as optical

memory devices. For the GexTei-x glasses, we have used the photoacoustic

technique to investigate the thermal diffusivity as a function of

composition. The results support the speculations about the glass-forming

region as the best compositional range for the technological applications.

The observed dependence on the composition is explained on the basis of

the chemically ordered network model. This Is further supported by X-ray

and electrical resistivity measurements.

8P:c228SOLID STATE AMORPHIZATION OF III-V SEMICONDUCTORS

FROM HIGH PRESSURE PHASES

V.V.BRAZHKIN *. S.V.DEMISHEV **. A.G.LYAPIN *. N.E.SLUCHANKO ••

* Institute of Hieh Pressure Physics, 142092 Trolck. USSR.

** General Physics Institute. 1179U2 Moscow. USSR

It was established recently that hitch pressure phase

transition GaSb II (ft Sn -structure type) -» GaSb I (diamond-like

structure) is accompanied by the amorphyzation of GaSb. We have

shown that as temperature treatment of GaSb II under hish

pressure as addition of third element significantly Influence on

the structural and electron characteristics of amorphous state

of GaSb. The conductivity of the samples produced at various

conditions may differ by more than 10 orders of magnitude at

U. 2 K.

It was found that metall-semiconductor transition from hish

pressure phases can lead to strong disordering of structure In

some other III-V semiconductors (InP, InAs).

307

8P:c229

OPTICAL MODULATION SPECTROSCOPY OF AMORPHOUS SILICON-CARBON ALLOYS

W. GREVENDONK and H. HERREMANSLaboratory for Sol id-State- and High-Pressure PhysicsCelestijnenlaan 200 D, B-3001 LEUVEN (Belgium)

Localised electron states in the gap of amorphous semiconductors may bestudied by their contribution to the sub band gap optical absorption,modulated by periodically irradiating the sample with strongly absorbedlaser light.Photo-induced absorption at room temperature is associated with mainlydeep-lying defect states (dangling bonds). At low temperatures the bandtails play a dominant role. The following studies will be presented:1) influence of high-temperature annealing on defect states insilicon-carbon alloys, 2) the effect of light soaking, 3) band-tail para-meters and dangling-bond distribution as a function of carbon concen-tration.

8P:c230THE SCLC TECHNIQUE AND AMORPHOUS SEMICONDUCTORS

V. CechResearch Institute for Materials and Technology,P.O.Box 547, 602 00 Brno, Czechoslovakia

The one-carrier steady-state space-charge-limitedcurrents (SCLC) technique was developed to give informationsabout discrete trap levels in the forbidden gap of lowconducting crystalline materials. However, SCLC makepossible to investigate the energy distribution of thedensity of states (DOS) in the mobility gap of amorphoussemiconductors.

This technique was extended by the assumption of thefree carrier mobility dependent on the electric field whichresults in the more precise determination of DOS and givesthe new possibilities to find the microscopic mobility, andunder the condition of the multi-trapping regime, the driftmobility as functions of the electric field. The use of theSCLC technique will be illustrated for amorphoushydrogenated silicon (a-Si:H).

308

8P:c231SUBMICRCN METALLIC INCLUSICHS IN AN AMDRPHOUS GALLIUM ANTIM3HIDE

DEMISHEV S.V., KOSICHKIN YU.V., LYAPIN A.G., SLUCHANKO N.E..SHARAMBEXAN M.S.General Physics Institute, Academy of Sciences of the USSR, 117942, Moscow,Vavilova 38.

We have studied the properties of a complex inhcnegeneous system, con-sists from amorphous gallium antimonide semiconductor's network, which con-tains some amount of crystalline GaSb and submicron metallic inclusions ofmetastable GajjSb-,^ solid solution.

An addition of sane Impurities (Cu, Ge) when synthesis of the a-GaSbtake place, investigations of LheSe (.impounds structure and superconductivityof the nonstoichiometric inclusions GaxSb.,^ and also either the inclusionsand amorphous phase heat stability experiments have allowed us to find thesize of the inclusions and sore features of their formation and destructionin the bulk amorphous A-%5-semiconductor a-GaSb, which have obtained byrapid cooling under high pressure.

8P:c232RELATIONS BfeTWKKN DEFECTS AND HYDHUGKN INUUKKKATIUN IN a-Si:H AS STUDIEDBY ttJMBINED HlUflTXXJNlXJtrflVm AND HWlOHiKKMAL, DEFLECTION SHBCTHUSCOW

f. SLADKK*, Y. BUU1ZEM, M.L. THEYK and H. KOCA*Lataoratoire d'Optique des Solides, University P. et M. Curie, 4, placeJussieu, 75252 Paris Cedex 05, france

* Ijaboratoire de Physique des Interfaces et Couches Minces, KcolePolytechnique, 91128 i^alaiseau Cedex, France

'the relations between native and light-induced defects and hydrogenincorporation are systematically investigated in device-quality nydrogenatedamorphous silicon (a-Si:H) films deposited by PKUVU under different plasmcorkiiUoriH leading to quite different deposition rates and hydrogen bonding,'ttie density and energy distribution of the defects are estimated fro* theanalysis of the sub-band gap optical absorption spectra derived fro* bothphotoconductivity (constant photocurrent Method - CPM) and phototheraaldeflection spectroscopy (PUS) experiments on the same saaples. 'Vhe hydrogenincorporation is characterized by infra-red absorption and exodiffusionexperiments. The CPM and PUS-derived results are carefully cxnpared for thedifferent types of samples in both their annealed and light-soaked states, andinterpreted in terms of film growth models and light-induced degradationprocesses.

+ permanent address : PdF Masaryk University, Brno, Czechoslovakia

309

8P:c233HIGH PRESSURE STRUCTURAL PHASE TRANSITION AND ELECTRO-NIC PROPERTIES OF IH-V NITRIDES

A. MUNOZ<°> and K. KUNC<*>

(a)Departamento de Fisica Fundamental y Experimental, Universidad de La Laguna, E-38204 La Laguna (Tenerife), Spain.(d) Laboratoire de Physique desSolides, Universite Pierre Marie Curie (associe au CNRS),Tour 13, 4 place Jussieu, Paris CEDEX 05, France.

Under normal conditions the A1N, GaN and InN crystallize in the wurzite structure. Atdifferent pressures all of them have a structural phase transition to a different structure.We present electronic and ground state properties of III-V nitrides, evaluated in thecontext of the local density theory, using nonlocal normconserving pseudopotentials. TheE(V) phase diagram set up from the calculated total energies shows that III-V nitrides,transform under pressure to a rocksalt or NiAs. The electronic band structure shows thatthese structural modifications are semiconducting. We also present static data in bothstructures, a, c and bulk modulus, etc...Finally, some information was also obtained onthe low pressure ground state B and B'.

This study was accomplished within the Franco Spanish collaboration program "ActionIntegrada". A.M. whises to thank the Consejen'a de Education del Gobierno Autonomode Canarias for partial finantial support.

8P:c234ON THE ROLE OF ELECTRON TUNNELLING IN RECOMBINATION

KINETICS IN INSULATING CRYSTALS WITH RADIATION DEFECTS

E.KOTOMIN

Institute for Solid State Physics,University of Latvia,Riga

Tunneling recombination (TR) of electron and hole centresin insulating solids is known to be one of the majorfactors determining their radiation properties. This paperaimes to give a theoretical review of recombinationkinetics for both immobile (static recombination) andmobile (diffusion-controlled process) defects. Therecombination kinetics observed during defect concentrationdecay and under irradiation is discussed. It will be shownthat TR could be responsible for the temperature dependenceof the primary Frenkel defect accumulation efficiency andprovides a unique possibility of detecting diffusion stagesof processes and of distinguishing between defect diffusionand rotation in the lattice site. The theory is illustratedby experiments on alkali halides, corundum and the Na-saltof DNA.

310

8P:c235THEORETICAL AND EXPERIMENTAL DEVELOPMENTS IN THE DETERMINATION OF THEMINORITY CARRIER PROPERTIES IN LOW MOBILITY SEMICONDUCTORS

I. BALBERGThe Racah Institute of Physics, The Hebrew University, Jerusalem 91904,Israel.

Since the photccarrier grating (PCG) technique was realized to be theonly steady state method for determining the minority Carrier mobility-lifetime (fiV) product in low mobility semiconductors, such as hydrogenatedamorphous silicon (a-Si:H), a new avenue for the understanding of these ma-terials and devices made of them, has been opened. Indeed issues such asn-type to p-type transition upon Boron doping, the value of the surface re-combination velocity and the relation between time of flight and steadystate /^values, have been resolved using the PCG technique. On the otherhand, issues such as the meaning of the results in terms of state distri-bution and the recombination mechanism have not been resolved. In thiscontribution we will address these issues in general and in a-Si:H and Cu-ternary Chalcopyrite films in particular.

8P:c236TWO-STAGE RELAXATION OF HOT ELECTRON-PHONON SYSTEM WITH

DISPERSIONLESS L0-PH0H0MS IN POLAR SEMICONDUCTORS

K. KRAL, B. HEJDA, Institute of Physics, Czechoslovak Academy

of Sciences, Na Slovance 2, 180 40 Fraha 8, Czechoslovakia

Acoustic phonon bottleneck has recently been suggested to be

the origin of the considerable slowing down of the hot electron

relaxation in polar semiconductors at about hundreds of ps

after a laser excitation. We analyze theoretically such a

nonequilibrium relaxation process taking into account the

anharmonic coupling between the dispersionless LO-phonons and

the longitudinal acoustic phonons. The corresponding kinetic

equations are solved numerically for the case of relaxation of

the electron-phonon system after the laser pulse and for a

quasi-static process of hot electron cooling in GaAs and CdSe.

A critical role of the fusion of LA-phonons into LO-phonons is

emphasized.

311

8P:c237ELECTRON SCATTERINS BY LOCALIZED OPTICAL MODES IN IONIC SEMICONDUCTORS

F.G. BASS, V.A. POGREBNYAKInstitute of Radiophysics and Electronics, Ukrainian Academy of Sciences,Kharkov, 310085, Ukraine.

In ionic semiconductors the relative displacement amplitudes of local-ized vibrations fall off at large distances from point or linear defectsby a power law. Thus, in ionic semiconductors a point defect induces macro-scopic electrical polarization. Associated with this polarization the boundcharge might essentially effect on the electron scattering and mobility.The momentum and energy relaxation tiroes for localized optical modes havebeen calculated in cur paper. The electron high field transport phenomenapeculiarities, caused by this scattering mechanism in polar semiconductors,have been investigated.

8P:c238BLOCK BOUNDARIES CONDUCTIVITY IN MOSAIC CRYSTALS

V.A. POGREBNXAK, D.D. KHALAMEIDA, V.M. YAKOVENKOInstitute of Radiophysics and Electronics, Ukrainian Academy of Sciences,Kharkov, 31OO85, Ukraine.

In this paper we present results of an experimental and theoreticalstudy of block VWL.idaries effect on electric conduction of mosaic crystals.The experiments reveal 2D electron channels at block boundaries in Hgi^CdxTe(KCT) single crystals. Thus, MET sample has a bulk, p- or n-type, conductiv-ity and two-dimensional electron conductivity along small-angle boundaries.In the given paper the surface electron density, electron masses and mobilityin 2D channels have been determined. It is shown that the conductivity along2D channels is comparable with the p-type bulk conductivity of the sampleat 77 K. On definite conditions the bulk conductivity can be essentiallydecreased, then the sample will conduct along the random network of 2D chan-nels.

312

8P:c239

A LOW TEMPERATURE HALL EFFECT AND PHOTOLITMINESCENCESTUDY OF GaSb MONOCRYSTALS

F.Meinardi and L.Tanicone

Dip.rtlm.nto dl Fiaic. . Univ.raita' dl Parma - Vial. d.U. Scl.ni* - 43100 Pa»ma-ITAIY

The energy ionbation (E.=lZmtV) and concentration (Ar.-l.B-10" cm'*) of the intriwSc acceptor dom-mat.ng the conductivity of a. grown GaSb bulk crystal, have been obtained by the bet fit («ee Fig ) of Halldensity of carrier, ver.ua temperature (7-700 K) and by a comparUon with photolumWenc. . p . * , . (j.,00 K)A n g R inversion of the Hall coefficient (RH) within the intrlutc regime (T>700 K) and a minimum at 15-20 K

followed by a conatant behaviour due to _ _CaSb n'-USO

hopping conductivity were reapeetively ob- I01*

aerved in the two extreme temperature re-

gion.. The effect of multivalley (T,L) con-

duction which gives an effective density of

carriers decreasing when the temperature

increases, was studied in Te-dopcd GaSb;

some important conduction band parame-

ters ( Ar£=«l . sme V.«*eL=0.1«) were de-

termined by fitting the experimental result*.

1 i • • • • i • • ~ n

Temperature 1000A *K"'

8P:c240

APPLICATION OF THE DYNAMICAL TRANSPORT THEORY TO IONIZEDIMPURITY SCATTERING IN SEMICONDUCTORS

B. P6DOR1-2,, G. GOMBOS1, J.-L. FARVACQUE2, R. MEINTRUP1 andP. MAGYAR2

1 Research Institute for Technical Physics of the Hungarian Academy ofSciences, 1325 Budapest, P.O.Box 76, Hungary1 Laboratoire de Structure et Proprietes de l'Etat Solide, University des Scienceset Techniques de Lille, 59655 Villeneuve d'Ascq, France

The dynamical transport theory proposed in1 and further discussed in2 isapplied for the calculation of the mobility and other transport coefficients forionized impurity scattering and also for various other model scattering potentials.Analytical results, where possible, are given. The implications of the energydependence of the scattering time — which energy dependence is different fromthe usual - obtained in the framework of the dynamical theory are discussed.Finally the connection between the dynamical transport theory and the virialexpansion in statistical mechanics is pointed out.

\ J.-L. Farvacque, Phys. Rev. Bj1 B. E. Sernelius and E. Soderatr

, 1682 (1989)i, J. Phys. C 3, 1493 (1991)

313

8P:c241IMPACT IONIZATION IN SEMICONDUCTOR TRANSPORT

W. QUADE, E. SCHOLLInst. f. Theoretische Physik, TU Berlin, Hardenbergstr. 36,1 Berlin 12, Germany

In modern semiconductor devices generation-recombination processes induced by impact ion-ization and its reverse, Auger recombination, play an increasing role in the description of thedevice behaviour. Impact ionization from traps is responsible for the imparity breakdown atlow temperatures inducing a non-equilibrium phase transition and sometimes leading to chaoticbehaviour. Band-band impact ionization in MOSFETs is the reason for the parasitic substratecurrent and finally limits the bias voltage that can be applied to the device without destroyingit. We present, for both types of impact ionization processes, new microscopic models whichaccount for the coulomb denominator in the matrix element. In the case of band-band impactionization the model is derived using three different spherical and parabolic bands, one for theinitial valence electron, the other two for the two final conduction electrons, and an arbitrar-ily shaped band for the impact-ionizing energetic conduction electron. From this the impactionization rate and energy relaxation rate are calculated analytically as functions of the carriertemperature. In the case of band-trap impact ionization these rates are extracted from MonteCarlo simulations and axe fitted by analytical functions. Using the models within the framework of balance equations the influence of impact ionization on carrier transport is discussed.

8P:c242

NUMBER AND MOBILITY FLUCTUATIONS: CLASSIFICATION OFNON-EQUILIBRIUM NOISE IN SEMICONDUCTORS

LUCA VARANI1, TILMANN KUHN2 and LINO REGGIANI1

1 Dipartimento di Fisica ed Istituto Nazionale di Fisica della Materia, Universita diModena, Via Campi 213/A, 41100 Modena, Italy2Institut fur Theoretische Physik, Universitat Stuttgart, Pfaffenwaldring 57, 7000Stuttgart 80, Germany

We present a unifying theory of electronic noise in semiconductor materials. Thestochastic processes due to the presence of different dynamical states for the carriers areshown to be responsible for number fluctuations, whereas those due to the presence ofdifferent states of the scatterers are shown to be responsible for mobility fluctuations.Accordingly, a classification scheme for different noise sources, which evidences the sym-metry between fluctuations of the carrier state and of the scatterer state, is developed.By using the Monte Carlo technique, which provides an exact numerical solution ofthe corresponding master equations, both cases are analyzed within a two-level model.The numerical calculations are found to be in good agreement with experiments and/oranalytical expressions.

314

8P:c243CARRIER PHONON DRAG EFFECT IN CdTe

S. VACKOVADepartment of Semiconductor Physics, Charles University, KeKarlovu 5, Praha 2

Some experimental evidence has been assembled for the presenceof carrier phonon drag effect in CdTe. In our paper [1] theSeebeck effect and the transversal Nernst - Ettingshauseneffect was measured. The paper of Rosenzweig et al. [2] hasconfirmed our results and simultaneously has pointed on thelack of theoretical explanation of that time represented byPlavitu [3]. Only just now the theoretical papers Gurevich etal. [4] and related papers offer few possible explanations,namely in the frame of intense interaction between acoustic andoptical phonons the possible role of two stage acoustoopticaldrag. In this paper we have analyzed our new experimentalresults and discussed them with the papers [3] and [4].

[1] Kubalkova (Vackova) S., phys. stat. sol.(b) 50 (1972) 111.[2] Rosezweig J. Birkholz U., phys. stat. sol. (a) 71 (1982)

K41.[3] Plavitu C. N. , phys. stat. sol.12 (1965) 265.[4] Gurevich Ju. G. , Mashevich 0. L., Physics Reports 181, No6

(1989) 327-394.

8P:c244KiSCOfc'lBINATION OP THE MINORITY CAHRIERS ON DISLOCATIONS

IN III-V SEMICONDUCTORS

PTASHCHENKO A.A., MOROZ N.V., MELKONYAN J.W.

Odessa University, P.Welikogo,2, 270057, Odessa, Ukraina

The behaviour of the capture cross section of the disloca-

tion for the minority carriers was calculated for varied tem-

peratures and generation rates. The barrier model was used.

The influence of the temperature and the generation rate on

the dislocation levels occupation was taken into account.

The electroluminescence decay was investigated on the GaP,

GaAsP and GaAlAs p-n-junctions before and after disloca-

tions introducing. The dislocations were showed to reduce the

minority carriers lifetime, especially at the higher tempera-

tures and by the lower injection rates. The obtained depen-

dences of the dislocations effective cross sections for the

minority carriers on the temperature and the injected carri-

ers concentration agree with the theoretical predictions.

315

AUTHOR INDEX

317

AAbdelmoula K.Aboudihab I.Abram R.A.Abramof E.Abstreiter G.Aceituno P.Adrian G.Aeppli G.Agostino R.G.Ahlers F.-J.Ain M.AjoD.Albertini G.Aiefeld B.Algarabel P.A.Allia P.Almeras P.Alonso J.J.Alshits V.I.Alsina F.Alvarellos J.E.Alvarez A.Amado M.M.Amazit Y.Ambroise J.P.Ammerlaan C.A.J.Amoddeo A.Anagnostakis E.A.Anda E.V.Andersson B.M.Andersson G.I.Andersson M.Andersson MO.Andre G.Andre J.P.Andrecut M.Andreev A.V.Andreoni W.Andreozzi L.Andreyev V.D.Annus J.Antognazza L.Antonioli G.Apel W.Aragon G.Arena A.Arnold Z.Aroyo M.Aryasetiawan F.Ascli L.Aslienford D.E.Atkinson R.Attenberger T.Attolini G.

246,

180,

152,

194,

205,

207,

5224420226121021924433

25923626527718118027210711826917322292

13214618524613325930321773

28475

28418120426815814329330510434

14023620629927219710

2702645337

277

Auderset H.Auffret S.Augelli V.Augustyniak B.Aupke K.Aymerich X.Ayres de Campos N.Azema A.Azoulay J.Azzoni C.B.

BBaber N.Baberschke K.Bachelet G.B.Bachlechner ME.Badaljan A.G.Baerner K.Baeuerle D.Baeumler M.Bairamov B.H.Bala H.Balagurov A.M.Balbas L.C.Balberg I.Baldini G.Ballo P.Balucani U.Baluch S.Baluta Gh.Banbury P.C.Banfi G.P.Bang Y.Baran M.Baran OR.Baranov A.N.Baranov N.V.Barb D.Barnas J.Barniol N.Baroni S.Barth K.L.Barthes-Labrousse M.G.Bartl A.Barvik I.Bascon M.L.Bass F.G.BassJ.M.Bastl Z.Batko 1.Bauer G.Bauer G. E. W.Bauer R.Bazhan A.N.Beaumont S.P.

181452215932

254146244242113

13255

19122513326574

297287

160, 27623852

311119, 120

12616510417712511484

144190203

145, 152156, 177

56254

9, 911228

10129325831260

252109262

1837

150, 23940, 231

318

Beauvillain P.Bechstedt F.Beenakker C.W.J.Beenen J.Belmia K.Bejdova M.Belien F.Belitsky V.I.Belogolovskii M.A.Belyakov L.V.Benacka S.Benassi P.Bending S.J.Bengtsson S.Bennemann K.H.Berger C.Bernasconi M.Bernhoeft N.Bernik S.Bersani D.Besson M.Beton P.Betti M.G.Bevz V.N.Bezot P.Bhattacharjee A.K.Billat S.Bimberg D.Binns C.Bircak J.Bird D.M.Blackman J.A.Blaschke H.Blazhievsky L.F.Bliek L.Blinovski J.Bloemen P.J.H.Blomberg M.Boehni J. vonBoerjesson L.Bogner U.Bohacek P.Bohm G.Bohr T.Bolterauer H.Bolton F.Bonnet M.Bonvent J.J.Bonville P.Borghesi A.Borstel G.Bosacchi A.Boscolo R.Bosin A.Bosio C.

92,

136,

112,

188,

206, 222,

116,

54227398443

2438

30422625269

2922342845296

20815724714280

230151239162263

1713228

279936066

190236263

81781847537

24823218918823227410675

281158131137191306

Botta M.Bouarab S.Bouchaud J.P.Bouchiat H.Bouda V.Boudjada S.Boudriot H.Bouizem Y.Boulyjenkov I.E.Bourges P.Boutarek N.Bowman R.M.Boyer L.L.Boyko V.H.Bragliini M.Brandt E. H.Brandt M.S.Bratsberg H.Braun J.Brazhkin V.V.Breitlow C.Brockstieger U.Broser I.Bross H.Brovetto P.Bruck E.Brueck E.Brum J.A.Brunner O.Bruynseraede Y.Brydl J.Bryknar Z.Bsiesy A.Burlier B.Buhler M.Buhrig E.Bulbik Ya.I.Buldt G.Bunbury D.St.P.Burda 1.Burlet P.Butov L.V.Buzano C.Byszewski P.

CCabeza O.Caiw P.Camagni P.Camassel J.Campbell I.A.Campos A.OannYld P.C.Cankurtaran M.Capozzi V.

6,

64,

167, 168,

127, 135,

8, 76, 178,

153,

33,

114, 116,222,

221,

119269196

613817427830919233

1452

8799

142321764

15830723620121488

12427115421034

2451401181711

29227817638

273268271224100144

248114117223315533

141291

319

Cappellini G.Caputi L.S.Carboni C.Cardona M.Carlotti G.Carmo M.C.Camera A.Carraresi L.Carsughi F.Cartensen J.Castellani C.Casula F.Catalano I.M.Cattani D.Caudano R.Cech V.Cecil Z.Celebonovic V.Cella N.Ceretti M.Cerny F.Cerny R.Cesari C.Chacon E.Chafai M.Charlier J.-C.Chasse A.Chelkowska G.Chelkowski A.Chen X.S.Cheong S.-W,Chevrel R.Chiappe G.Chiccoli C.Chirico G.Chodkiewicz W.Christensen N.E.Cimpf Z.Cingolani R.Clarke L.J.Clausen K.N.Cobden D.H.Cochran A.Coenen H.A.Cohen-Adad M.T.Colavita E.Collin G.Colocci M.Colombo L.Coluzza C.Continenza A.CookeJ.F.Coppola R.Coquilllat D.Cordoba A.

92259

153, 27317, 134, 220, 253, 304

54122277296

163, 180249849530317426308282143307163276178108

92, 169132932562702701693317481108

119, 121108289

140, 30041, 197

9331292

282238259137296

30, 91, 20836, 118, 285

94, 19160180263258

CordU W.Cortona P.Costa B.F.O.Couach M.Courtens E.Coutal C.CoxS. F. J.Coz PL.Craubner H.Crisan V.Cruz H.Cuccoli A.Cury L.Cuypers J.P.Cyrot M.Cyrot-Lackmann F.Czaja W.Czarnecki P.Czycholl G.

DD'Anna E.D'Arrigo G.Dabrowski J.Darinskaya E.V.Dash J.G.De Andres A.De Boer F.R.De Castro M.J.De Gironcoli S.De Gronckel H.A.M.De Jonge W. J. M.De Jongh L. J.De Lima J.C.De Pascale T.M.De Renzi V.De la Cruz R.M.Deckers/.Decroux M.Del Sole R.Delalande C.Delley B.Deltour R.Delunas A.Demangeat C.Demikhov E.Demishev S.V.Demmerle W.Demo P.Dencher N.A.Denecke R.Deparis C.Depeyrot J.Derycke I.Derzhko O.V.

18694

146, 15623811024416131161268

219, 220159, 193, 198

218212191

87, 9611617142

290214

173255240

154, 271, 273206988

11241,307941512882091749229618

242124

52, 61, 257, 269106

307, 309232

99, 16538262221218255299

320

Destrade Ch.Deus K.Deveaud B.Devereaux T.P.Devlen R.I.Devlin E.Dhalenne G.Di Castro C.Di Cicco A.Dianez M.J.Dichtel K.Dietl T.Dietsche W.Dietzel F.Dihoiu M.Diko P.Dittrich H.Divis M.Djourelov N.Doehler G.Doehler G.H.Doetsch H.Oominguez P.S.Dominguez-Adame F.Dominoni M.Donaldson G. B.Donati C.Dorantes-Davila J.Dorda G.Dorrer S.DozsaL.Draper R.C.J.Drchal V.Drexler H.Dreysse H.Dubiel S.M.Dulca L.Dumitru G.A.Dumitru M.Dvorak V.

EEasterbrook D.I.Eaves L.Eccleston R.Edwards D.M.Eiehler A.El-Astal A.H.Emery V. J.Endstra T.Engelhardt CM.Englich J.Engstroem O.Erhart P.Esslinger A.

1062784470

13451

24646, 81

164177249262235235268242243

152, 271197204

203, 28355

20667

2972

194, 293521656

12714182

23152, 61, 269

146, 156268162162183

250230216

7,84785347

1578057

28479

237

Estrada M.D.Etienne B.Etienne P.Euthymiou P.C.

FFabeni P.Faehnrich J.Fahnle M.Farchioni R.Farvacque J.L.Faschinger W.Fasolino A.Favia P.Fayeulle S.Fedorko P.Fehrenbach G.M.Feldberg S.FengD.Feng X.M.Feodosyev S.B.Fernandez P.Ferrando R.Ferre J.Ferreira R.Fert A.Feuerbacher B.F.Filipponi A.Finel A.Fiorani D.Fiorentini V.Fioretto D.Fischer O.Fisch«r P.Fischer T.FiskZ.Fitter J.FiachS.Flachbart K.Floret F.Ftouquet J.Flukiger R.Fogedby H.C.Fontana A.Fontana M.P.Forchel A.Ford P.J.Ford R.A.Forstmann F.Fousek J.Foxon C.T.Franchi S.Francois M.Fraxedat J.Freytag B.

1774, 218, 224, 296

51125

117, 193102, 139

59, 6019931320527222118510488

68, 7654

21265, 175

6719463

29651

21616461

245191

54, 1703462

3063338

138, 187109

28, 213, 217, 254, 28543, 72

218911216322414119

169176

19, 226131174202211

321

Frick B.Fricke Ch.Frigeri C.Frigeri P.Froehner J.Fromherz T.Frost J.E.F.Froyen S.Fruchter L.Fuchs H.D.Fuchs M.Fullerton E.E.Fuss A.

GGafyichuk V.V.GalJ .Galan J.Galatola P.Galeazzi C.A.Galeczki G.Galinetto P.Ganev N.Ganin A.A.Gao Z.X.Gaponenko S.V.Gaponov S.V.Garcia R.Garcia-Fernandez P.Garcia-Vidal F.J.Gaspard F.Gaucherel P.Gavarri J R .Geim A.K.Gemperle A.Gemperle R.Gensterblum G.Gerber R.Germanenko I.N.Ghezzi C.Giannozzi P.Gibbs M.R.J.Gignoux D.Gilabert A.GillG.B.Gillot C.Ginesu F.Ginsbach A.Giordano M.Giordano R.Girlanda R.Giulotto E.Gleichmann R.Glew R.W.Glogarova M.

13135, 214, 215

207, 277131101261235

1031

17, 134139, 168

8, 17856

17515582

107207, 289

146117179271

76, 24522973

205, 206186

28, 260, 28517

244108230274

57, 2742657

229131

9, 9124

286244

188, 19011298

244194, 293

21196114207222106

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ESPRIT BASIC RESEARCH EXHIBITION AT THE 12TH CONFERENCE OF THECONDENSED MATTER DIVISION OF EPS, PRAIIA, 1992

Basic Research in ESPRIT has two main objectives:

• to replenish the reservoir of new knowledge and expertise from which industrial researchmust draw to ensure tomorrow's innovation

• to ensure the environment for training tomorrow's researchers in the most effective waypossible, through research itself.

The first objective is achieved both by ensuring the long-term industrial relevance of theresearch undertaken and by putting in place appropriate mechanisms which ease the flowof breakthroughs and new knowledge downstream to industrial research and exploitation.

The second objective is achieved by providing young doctoral and post-doctoral studentsthe opportunity for research in priority areas within the framework of projects guided byworld-class researchers.

The dual goals of providing new technological expertise and helping to ensure the futureavailability of high-calibre scientists and engineers are key elements in the long-term abilityof Europe to compete in global markets. The Basic research (BR) Actions recognise thatfundamental research, even when it does not have immediate industrial applications, isneeded for technological developments with major industrial, economic and social impact.

(7 In the ESPRIT Basic Research exhibition several projects from the general area ofI microelectronics are showing recent results of their projects, obtained through| Europeanwide cooperation.

| In the following, exhibition factsheets are presented, which also give a contact point for

obtaining further information. The sub-areas presented are:

• NANOELECTRONICS (Actions 3042, 3043, 3133)

• ORGANICS (Actions 3121, 3200, 3314)

• OPTICS AND OPTICAL COMPUTING (Actions 3186, 3199, 3260)

• OPTOELECTRONICS (Action 3174)

• CONTROLLED SEMICONDUCTOR PROCESSING (Actions 3177,3109)

• VLSI DESIGN TRAINING (Action 3700).

ESPRIT Basic Research 2 Action3042

Performances and Physical Limits of Heterostructure Field-Effect(HEFT) Transistors (NANOFET)

Started: 2-JUNS9 Duration: 33 months

IMEC (B), University of Cambridge (UK), CNRS - Lahomtoire de Microstnictures et deMicmtUctronique (F), CNRS - Institut dElectronique Fondamentale (F), ARMJNES (F)

AIM To study the performance and physical limits of HFET transistors scaled down (oultra-subnicroN dimensions.

Background

The current trend in microelectronics points towards a further scaling-down ofsemiconductor devices to nanometre-scale dimensions. This trend is driving the continuingdevelopment of micro- and nanofabrication techniques. However, understanding is lackingabout electron-transport phenomena in these very small device structures.

The main focus of NANOFET is on horizontal electron transport in nanometre-scale field-effect transistors. The new technologies and methodologies needed to simulate, fabricateand characterise such devices are also being developed. Two main fields of investigationhave been defined:

• ultra-submicron HEMTs with gatelengths around 0.1 micron, resulting in the fabricationand characterisation of devices with record cut-off frequencies

• nanoscale HEMTs ("NANOFETs") with gatelengths between 50 and 20 nm, which has ledto the fabrication of some of the world's smallest transistors and to a systematicinvestigation of their characteristics as a function of device dimensions.

Applications

The results obtained have a direct potential for industrial use. Most of the technologiesdeveloped in this project will benefit the commercially driven process development ofHEMT devices with gatelengths around 0.25 micron. The fundamental understanding ofdevice operation will help to optimise submicron FET characteristics for analogue or digitalapplications. Substantial interest in NANOFETs results has already been expressed byEuropean industry, and formal links with ESPRIT Microelectronics projects have beenestablished to promote their exploitation.

Demonstration

Together with scanning and tunnelling electron microscope images, pictures of nanoscalestructures and devices are on display with drawings illustrating the main process steps.Panels highlight main achievements and exploitation potential.

ContactDr M. van Rossun (IMEC)<£) + 32/ 16-281-325fax + 32/ 16-229-400

E S P R I T Basic Research 3 Action3043

Lateral Microstructures: Fabrication, Low Dimensionality Effectsand Application to HIV Devices (LATMIC)

Started. l-MAY-89 Duration: .14 months

CNRS Laboratoire de Mkrostnictures el de Microflectronique (F), University of Cambridge(UK), CNET (F), University of Exeter (UK), NMRC (IRL), DRA (UK), Universitdl Stuttgart(D)

AIM To develop lateral nanosiructures at the state-of-the-art minimum scale (typically20 nm), study the bask physical properties of low-dimensional nanostructures, andfabricate entirely new devices.

BackgroundNew epitaxy methods such as M3E and MOCVD have opened up a novel field insemiconductor physics by enabling the fabrication of 2-D microstructures such as quantumwells, tunnelling barriers and superlattices. There has also been a rapid development inlithographic techniques that can define patterns with dimensions as low as a few tens ofnanometres. By combining these with state-of-the-art semiconductor epitaxial growthmethods, structures can be fabricated with 1-D or even zero-D properties. This enables thestudy of a new range of semiconductor phenomena where electron behaviour is influencedon a scale less than the mean free path between collisions, with scattering (which dominatesall electron behaviour in conventional semiconductors) eliminated.

IJ\TMIC is combining high-quality epitaxial IH-V structures with a range of fabricationtechniques capable of producing lateral microstructures on a 20 nm scale. The optimisedtechniques have been applied to the fabrication of real device structures down to 20 nm,such as a lateral superlattice with 20 nm dots and 50 nm spacing, and etched quantum dotswith regrowth with lateral dimensions of 20 nm. Breakthroughs in transport propertiesinclude the observation of ballistic transport between 1-D and 0-D structures, resonanttunnelling through the 0-D states, decrease of quantum noise under applied magnetic fields,and the first demonstration of a one-electron transistor based on Coulomb blockade effects.Optical properties of quantum wires have shown evidence of confinement effects instructures down to 20 nm, and clear polarisation effect? a:;,sigr.ed to ihe dipole moment ofthe 1-D wires.

Applications

As the tendency in semiconductor device development is to push to higher-speed operation,higher packing densities or wider bandwidths, these new effects are likely to have asignificant effect on device operation in the future. They could also be exploited to improvedevice performance and functionality.

Demonstration

The latest results on quantum dots and one-electron transistors are explained.

ContactDr II. Illinois (L2M/CNRS)© + 33/1-4529-5240fax + 33/1-4529-5378

ESPRIT Basic Research 4 Action313

Nanostructures for Semiconductor Devices (NANSDEV)Started: I-JUN-S9 Duration 33 months

Nanoeleclronics Research Centre, University of Glasgow (UK), Ludwig- Maximilians UnivenitatMunchen (D), Technuche Universiteit Delft (NL), Universiteit Genl/IMF.C (B), PhilipsResearch Laboratories (NL), Thomson CSF LCR (F), CSIC/CNM Madrid (F.)

AIM To study semiconductor structures where the confinement of electrons in more than

one direction is an important determinant of their electronic and optical properties, and

which take advantage of the very low scattering in high-nobility 2-D electron gas layers.

Background

NANSDEV is studying nanostruclures - semiconductor structures and devices with criticalfeature sizes down to 10 nm. Knowing their properties is important both for understandingthe behaviour of conventional electronic devices at the limits of miniaturisation and as thebasis for inventing new classes of device. Technologies suitable for the fabrication ofnanostructures are being optimised for this purpose. The research undertaken byNANSDEV includes studies of the confinement of electrons in devices whose sizecorresponds to the electron wavelength; development of devices in which single electronscan be controlled; investigation of the far-infrared and millimetre-wave response of periodicarrays of electron "pockets"; characterisation of the optical properties of quantum dots andquantum wires fabricated by the dry etching of quantum well layers; and fabrication ofnanometre-scale structures by direct growth.

Applications

The new physics of ultrasmal! semiconductors revealed by NANSDEV will improveunderstanding of the fundamental limitations on ullrasmall device operation, help overcomefabrication difficulties, and facilitate the exploitation of these new phenomena in usefuldevices.

Demonstration

Computer models show the direct growth of nanostructures and the operation of cellularautomata. Models of electron flow in nanoelectronic devices are also on display.

ContactProf Steven Beaumont (University of Glasgow)(£> + 44/41-3305-380Tax + 44/41-3304-907

ESPRIT Basic Research Action 3121

Conducting Organic Materials as Molecular

Components for Microelectronics (MOLCOM)

Started: l-MAY-89 Duration: 36 months

0rsted Institut (DK), Univenitd de Paris Sud (F), ADIST (P), LNETI (P)

AIM To control and understand all factors governing the flow of electrons in organicconductors and superconductors, necessary before they can be used Tor the fabricationof microelectronics components.

Background

The novel electronic conductors to be studied can He considered as a loose assembly ofunits of reduced dimensionality (ID chains or 2D planes) in which the molecules are moretightly and strongly packed than between units. Conduction in these materials proceeds viaintermolecular electron transfer. A major advantage in using molecular solids is thatapparently minor molecular changes can be used to induce important variations in theirphysical properties. The finding of superconductivity in 1980 in a family of these newmaterials by two groups belonging to the consortium, together with the improvement of thesuperconducting characteristics in other organic conductors over the last decade,constitutes a breakthrough in materials sciences.

Applications

MOLCOM is preparing a wide range of materials exhibiting varying degrees of onedimensionality and disorder in order to control all factors governing the flow of electrons incrystalline molecular conductors. This study is a prerequisite for the use of these materialsas components in microelectronics. New molecular crystals exhibiting two-dimensionalconductivity will be prepared in order to optimise conditions (critical temperature, fields,currents) for superconductivity. Physical studies will be performed using all possiblyavailable techniques, transport, magnetism, NMR, X-ray diffraction and high pressure.Computer simulation of crystal structures will be used in the design of new compounds,allowing the prediction of attainable crystal structures (starting from a given molecule) andthe interpretation of the interplay between localisation and conduction in disorderedsystems.

Demonstration

A video shows the growth of crystals of organic conductors in electrochemical cells.

Contact

Dr D. Jerome (University de Paris Sud)

Tel + 33/1-6941-5301

Fax + 33/1-6941-6086

4

ESPRIT Basic Research Action 3200

Structure and Transport Properties of Organic

Low -Dimensional Systems for Application

to Information Technology (OLDS)

Started: l-JUL-89 Duration: 33 months

Queen Mary College (UK), University of Edinburgh (UK), Universita di Genova (I). Max-Planck- Institut fur Festkorperfonchung (D), Universitat Tubingen (D), Helmut Hund (D),University of Dublin (IRL)

AIM To achieve molecular-scale information processing by (he manipulation andcontrol or charge motion or the orientation of molecular dipnles.

Background

Conventional electronics proceeds by makingconvention.il electron transporting structuressmaller by improving microfabricalion. Molecular electronics seeks to take the smallestbuilding block, the organic molecule, assemble these into designed structures. The partnersare assembling electron-transporting molecules and molecules possessing dipole moments.New organic molecules are being synthesized, designed both for their electron-transportingproperties and for their behaviour in Langmuir-Blodgett (I-B) film formation. A ScanningTunnelling Workstation developed within this project will be used in film characterisation.Patterning of the films themselves and of electrode systems will be carried out by laserablation and electron-beam lithography. The motion of photon electrons is being studiedon the picosecond timescale, and dipolar domains are being studied by optical techniques.Computer modelling is used to model the intermolecular interactions and packing of theLB film structure and to study elemental information processing steps and their collectivebehaviour.

Applications

OLDS is developing the basic science to do molecular electronics. Ideas exist within thisAction for using the charge on molecules or the orientation of a molecular dipole torepresent information. Information processing would then require manipulation andcontrol of charge motion and dipole orientation.

Demonstration

The Scanning Tunnelling Workstation is seen in operation. A pseudo-3D characterisationof a specimen surface in the nanometre region will be demonstrated. A video film of thetip-to-sample approach shows the principle of STM operation.

Contact

Or E.G. Wilson (Queen Mary College)

Tel + 44/71-975-5046

Fax + 44/81-981-9465

ESPRIT Basic Research 7 Action3314

Evaluation of Molecular Switch-Type Devices:

Theory and Experiment (MOLSWITCH)

Started: l-JUN-89 Duration: 30 months

Kobenhavns Universitel (C1SMI) (DK), Mar Planck-hutitut fur Festkorperforsdumg (MPIFF)(D), University de Strasbourg (F), Uppsala Uiwvrsitet (DOQCU) (S)

AIM To develop and lest molecular materials potentially applicable in sensor, computerand communication devices. The materials are made from organic compounds offering agreat variety of electronic properties, due to the immense number of molecularstructures possible.

Background

In the design of molecular materials today, it is only to a very limited degree possible todraw on the results of quantum chemical calculations. The reason is pronounced lack ofknowledge of the behaviour of electrons in molecular materials. Increased knowledgeregarding this fundamental problem is a prerequisite for an extensive exploration ofindustrial applications. MOLSWITCH is contributing to the elucidation of this complexproblem by working on advanced expei imenta! physics and theoretical calculations.

Applications

MO1JSWITCH focuses on the possibility of preparing molecules that can be switchedbetween two different slates and allow a signal to pass in only one of them. Such moleculescould eventually act as basic transistors. Molecular structures with delocnlised electrons,which could serve as connecting wires, are also being studied. The physical realisation ofsuch electronic building blocks could lead to the assembly of molecular-scale logic systems.

Demonstration

A model of a switching molecule is shown.

Contact

l)r K. BrunTeldi (Kobenhavns I'niversiiet)

Tel + 45/1-35.VI.V1

Tax + 45/1-350-609

ESPRIT Basic Research 8 Action 3186

Quantum Noise Reduction In Optical Systems (NOROS)

Started: 15-JUL-89 Duration: 30 months

Laboraloire de Spectroscopie Hertzienne de iENS/CNRS - University Pierre et Marie Curie(F), CNET (F), INFM (I), CNRS - IOTA (F), Universitat Komtanz (D) RSRE (UK)

AIM To Improve the noise reduction factor or squeezing systems, and explore newmaterials and systems, which would be relevant for applications for high sensitivitymeasurements and IT.

Background

Quantum noise reduction, or squeezing, can be achieved by various kinds of systemsinvolving non-linear optical processes or optical sources excited by low-noise pumpingprocesses involving different methods of producing squeezed light.• Parametric generation and second harmonic generation.• Optical bistability. Non-linear optical cavities can switch between high and low light

transmission thus modifying the Quantum noise.• In laser diodes, the flow of emitted photons can be controlled by regulating the pumping

current. In such cases intensity-squeezed light is emitted.

Main results:• Implementation of monolithic or semi-monolithic squeezing devices based on second

harmonic or parametric generation amenable for practical use.• 86% quantum noise reduction in twin beams in parametric generation (world record),

whic-h opens the way to efficient uses.• Demonstration of a quantum non demolition measurement, a model for noiseless optical

tapping.• Demonstration of the feasibility of information Iransmissiomn using sources of photon

pairs, with application to quantum cryptography.

Applications

With the rapid advances in the theoretical understanding of squeezed light and itsgeneration, and with the prospect of getting squeezing factors of over 90% within a fewyears, the application of squeezed light to practical purposes, such as high precisionmeasurements, optical communication and information technology, now lies within reach.

Demonstration

The demonstration will show a particular case of squeezed light which consists of two lightbeams (twin beams) in which the photons are highly correlated that is, distributed in thesame way. Such beams are produced by parametric generation in a crystal. The crystal isirradiated with the light of a helium-cadmium laser, and acts as a "photon splitter". Everylaser photon is equal to the energy of the laser photons; the sum of the energies of theemitted photons is equal to the energy of the laser photons. Each of the twin photons leavethe crystal in different directions. They are detected by a pair of detectors and counted.The presence of photons pairs is revealed by simultaneous detection events in the twodetectors.

Contact

Dr E. Giacobino (Laboraloire de Spectrascnpie llertzienne de 1'ENS/CNRS)Tel +33/1-44 27 43 94Fax +33/1-44 27 38 45

E S P R I T Basic Research 9 Action 3199

Workshop on Optical Information Technology (WOIT)

Started. 1-JUL-8Q Duration: 42 months

Herint-Watt University (UK), Universitat Kaiserslautem (D), Universidad Politecnica deMadrid (E), Universitat Miinster (D), Odense Universitet (DK), University de Paris Slid (F),UniversitS Louis Pasteur de Strasbourg (F), Politecnico di Milano (I), CNET (F), CNRSL2M(F), Vrije Universiteit Brussel (B), Universitat Frankfurt (D), IMEC vzw (B), UniversitatErlangen (D), King's College London (UK), IOTA (F), CERT-CNRS (F), CNRSLAAS (F),University de Toulon et du Var (F), Techinsche Universitat Braunschweig (D), InstituteNazionale di Ottica (I).

AIM To advance the enabling technologies that support 2-1) optical processing, toidentify applications uniquely suited to optical information processing technology, andto develop architectures and algorithms that efficiently exploit the technology anddemonstrate its long-term potential.

Background

There are four subgroups, covering I I -VI compounds, silicon and liquid-crystal devices, 111-FV compound electro-optic devices, free-space optical interconnect technology,architectures, systems and algorithms.Initial pioneering experiments on non-linear refraction and optical bistability in InSb andZnSe led to the first iterative synchronous circuit. The design of the O-CLIP - a

: demonstrator all-optical processor - architecture and simulations of image processing tasks. employing nearest-neighbour interconnects prompted further experimental loop circuits.\ Improved op.ical design enabled the incorporation of a programmable-logic-unit into ai loop circuit and allowed the implementation of a series of algorithms on a single-channel of

information input. Data transfer of 16 X 16 images between bistable plates, and theincorporation of fan-out/in elements, has culminated in the present O-CLIP, based on non-linear etalon active devices. Theoretical studies have spanned the microscopic physics ofthe nonlinearities, the optimisation and tolerancing op NLIF and S-SEED devices withinprocessing circuits, algorithmic code writing and simulations, and the benchmarking ofalgorithms involving non-local interconnect schemes.

Applications

The exploitation of massive parallelism and interconnect complexity offered by optics couldpermit significant advances in the computational power available for tasks such as imageprocessing and finite element analysis.

Demonstration

The demonstration is centred around the construction of a demonstrator O-CLIP. A videofilm is showing aspects of the O-CLIP operation, together with hardware components.

Contact

Prut. S. Smith (Heriol-VVatl University)

f Tel + 44/31-451-3021

Fax + 44/31-4513-088

ESPRIT Basic Research 10 Action 3260

Transverse Optical Patterns

Started: l-SEP-89

P/iysikalisch-Tecfmische Bundesamlatt (D), INFM (I).

Duration: 24 months

AIM To solve the problems or information encoding into transverse field structuresemitted by lasers and the utilisation of lasers Tor the execution of complex logicfunctions, such as pattern recognition and image processing.

Background

The research starts from noting that non-linear systems usually show coexistence ofsolutions or states between which switching is possible.

TOPP focuses on the role of defects or optical singularities and their geometricarrangements in laser fields as a method for coding information into the laser fieldsthemselves, and takes into account the similarity between the tempoial evolution and finalstates of certain cellular automata and lasers.

Theoretical studies address the laser equations, including transverse effects. The possibleand stable optical patterns are found from a varintion.il principle. The experiments use.among others, optically pumped lasers to test the predictions made.

Theoretical work shows the mathematical correspondence f lasers with compressible fluids(and of phase singularities with vortices).

The existence of free optical vortices shows that lasers are capable of extremely highnumbers of coexisting states (in age). One way of coding information into the transversestructure of laser field is to use dislocated optical vortex crystals, or the pixellisation ofimages by using arrangements of phase singularities of different orders.

Applications

Non-linear optical resonators (possibly semiconductors) could be used for parallel opticalprocessing in the same way as the " optical neural networks" but with substantially higherspeed. This would enable complex tasks like image processing and pattern recognition to beexecuted much faster than with current technology.

Demonstration

Results on experiments on optical laser systems are demonstrated showing co-existingstates which can be used for pattern recognition and associated memory

Contact

Dr C O . Weiss (Physikalisch-Technische Bundesanstalt)

Tel +49/531-592-4400

Fax + 49/531-592-4006

* • •

ESPRIT Basic Research 11 Action3174

Ultra-Thin Silicon/Germanium Superlattices (SLS)

Started: l-JUN-89 Duration: 36 months

Daimler Benz (D), University of Newcastle (UK), Teclmische Universitat Munchen (D),University of Lund (S)

AIM To study novel properties of the Si/Ge strained layer superlnltice (SLS) materialsystem and exploit its device applications (e.g. Si-based optoelectronics for opticalinterchip communication).

Background

For new optoelectronics devices, the synthesis of ultrathin SimGen SLS (m monolayers Si, nmonolayers Ge) by low temperature molecular beam epitaxy (MBE; 300°C<T_<400°C) isa crucial step. Developed SLS structures are characterized by X-ray, transmission electronmicroscopy (TEM), Rutherford backscattering, Raman and photoluminescencespectroscopy. Theoretical support is provided through calculation of bandstructure andrelated properties of the SLS leading to a theoretical understanding of the SLS.Comparison of calculated optical spectra with experimental observables are performed.

The Action fabricates p-i-n photodiodes as simple test devices and characterization ofelectrical and optical performance of these diodes are done.

Main results are:

| • Si/Ge SLS grown by MBE with monolayer sharpness down to a period length L of twoj. monolayers (L-2.8A!)

• Improvement of growth quality of the SLS (interface sharpness, growth quality) by use ofSb surfactant during growth

• Calculation of bandstructure and related properties as a function of SLS compositionand strain. Inclusion of structure imperfections (finite structure, doping, impurities anddislocations etc.)

• Strong PL signals for 10 ML Si/Ge SLS observed in the near infrared; (0.8eV)

• Observation of electroluminescence from mounted mesa and waveguide diodes fortemperatures up to T= 160K

Applications

Tailoring the optical properties of the SimGen SLS will have a dramatic impact on today'si silicon-based optoelectronics, because it makes possible the integration of opto-electronic; devices such as LEDs or photodiodes with silicon IC technology.

Demonstration

The main results are demonstrated by displays and samples.

Contact

Dr II. Presting (Daimler Benz)

Tel +49/731-505-2049

Fax +49/731-505-4102

ESPRIT Basic Research 12 Act™ 3177

Investigation of Optical Probe Techniques for InterfaceCharacterisation (EPIOPTIC)

Started: 1 MAY-S9 Duration: 36 months

Physics Department, Trinity College Dublin (IRL), Universita di Messina (I), DRA (UK),University of Liverpool (UK), University College Cardiff (UK), Technische Universitat Berlin(D), Universita di Roma II (!)

AIM To establish a new field of in situ interface characterisation, using light, with singleatomic layer resolution and accessible in all IT materials growth environments.

Background

In the foreseeable future most microelectronic semiconductor materials for IT devices willbe produced by thin-film growth techniques in environments ranging from high vacuum togaseous, liquid and solid phases. Perfecting the thin-layer interface is very important forhigher quality device performance. This Action has developed a new Held of surface andinterface characterisation, "epioptics", which uses light as both probe and signal and allowsmaterials to be characterised in situ with a resolution of less than one atomic layer.

Potential

' The results of EPIOPTICS show that following advances in understanding the underlying!' physics and improvements in instrument design, light can be used to characterise surface| and interface structure. The feasibility has been demonstrated of using optical probes to! monitor growth, under all conditions, of thin-film IT materials with submonolayer resolutionj in situ. Implementation of these new characterisation techniques should result in improvedi materials and higher yields for the fabrication of future I T semiconductor devices.

j Demonstrationi; A video shows a bolt-on attachment which allows reflected light to be used to monitor the

growth of gallium arsenide in a molecular beam epitaxy (MBE) system, one atomic layer ata time. A live experiment shows the use of the attachment to identify the crystallographicorientation of silicon wafers in air.

ContactOr J. F. McGilp (Trinity College Dublin)© + 353/1-702-1733fax + 353/1-711-759

I

E S P R I T Basic Research .13 Action3109

Programme for MOS Processing Technology (PROMPT)Started 1-JUL-89 Duration: 42 months

A EA Technology (UK), IMEC (B), University of Cambridge (UK)

AIM To gain a belter understanding of the influence of Materials processing variables onthe electrical characteristics of MOS devices, particularly when fabricated with thin(< 50 n M ) S i O 2 dielectric.

Background

PROMPT used an ultra-high-vacuum (UHV) processing facility to grow dry oxides onsilicon and to deposit clean metals and poly-Si contacts. Extensive surface and interfacecharacterisation techniques (including STM, scanning tunnelling microscopy) were applied.

The main results from PROMPT are:

• fabrication of MOS devices with high breakdown strength of I3.S M V / m

• device performance found to depend upon atomic-scale silicon roughness beforefabrication

• adhesion of metals deposited on silicon and silicon dioxide improved by several orders ofmagnitude by U H V processing

• using STM, precise atomic characterisation of initial stages of oxidation of silicon (111)and (100).

ApplicationsThe results of PROMPT will aid understanding of the effects of silicon cleaning proceduresand benefit designers of cluster tools for advanced semiconductor processing.

Demonstration

The equipment shown is similar to that used in the studies of the oxygen reaction on siliconsurfaces in UHV, and consists of a combined scanning tunnelling and atomic forcesmicroscope with associated control system (designed and constructed at CambridgeUniversity). Different samples are being imaged during the course of the Exhibition,including silicon surfaces oxidised as part of the PROMPT programme.

Please bring your own samples!

ContactDr C. Sofield (AEA Technology)© + 44/ 235-821-111 cxt 2155fax +44/235-433-02*

ESPRIT Basic Research 14 Action3700

VLSI Design Training Action (VLSI DESIGN)Stalled: I -OCT-89 Duration: 30 month!

Circuits Multiprojets (F), GMD - Schlofi Biriingltoven (D), Danmarks Tekniske Ifyjskole (DK),I MFC (B), Rutherford Appleton laboratory (UK), plus over 200 academic institutions

AIM To provide access to industrial facilities for academic institutions and training inVLSI design for an additional 3000 engineering students a year.

BackgroundStudies in several European countries have shown that the existing VlSl design trainingcapacity can only accommodate about 1500 students per year, and will have to expand by atleast another 3000 per year if Europe's needs are to be met. This shortage of traineddesigners is limiting the application of advanced microelectronics in a number of dependentindustrial sectors, including small and medium-sized enterprises.

To meet this challenge the VLSI Design Training Action has launched about fifty fabricationruns. Each run includes multi-project chips and wafers from academic institutions in severalcountries. To date 220 universities and polytechnics from member states and EFT Acountries are participating. This group includes experienced institutions already active inVLSI design training, as well as institutions proposing to enter the field for the first lime butnot yet fully equipped to do so. To enhance their training capabilities these have beenprovided with access to a range of industrial fabrication facilities and to high-quality CADsoftware. Their design hardware was supplemented, where necessary, by a dedicatedworkstation and an IC tester. If needed, they receive support for an additional lectureshipfor the Action's duration. A central service organisation, EUROCHIP, has been set up withresponsibility for all aspects of the Action.

OutcomeThe VLSI Design Training Action has already enabled about 800 courses to be held,providing a total of around 1 700 000 student course-hours and resulting in more than 1000VI.SI designs, of which 500 have been fabricated and 250 tested. More than 5000 studentshave been trained in the first full year of operation, easily exceeding the Action's originalobjective.

DemonstrationThe results of lypical integrated circuits designed by students during their academic trainingare on show, and will be demonstrated by their originators. This includes posters of theprizewinners of the exhibition at the 2nd EUROCHIP Workshop held in Grenoble earlierthis year.

ContactMr B. Courtois (Circuits Multiprojets)<© + 33/7657-4615fax + 33/7647-3814

Room C

ii—-^r«"- 7

PROGRAMME TABLE

MO

6

T U

7

WE

8

TH

g

i 10i

a l

opening

A

PLENARY

(LANDER)

11

1 12i

13

a2

APLENARY

(HENSEL) (TIMOFEEV)

A New dev. in HTc supercond.

B Semicond. multilayers

C Cond.syst. with compl.str.

D ESPRIT workshop

A Surf, atomic microscopy

B Ph.sep. in cupr.sup. (Muller,

C Dilute mag.semic. (Galazka)

D

A Application of HTc supercond.

B Defects in semicon. (Grimmtiss)

C Submicron metall. struct.

D

A Important new developments

B Correl.eff. in quantum wells

C Phys. of complex fluids

D Magnetism

APLENARY

(BEENAKKER) H P p n Z e (IBAGH)ceremony

APLENARY

(WEAIRE) (LE COMBER)closing

1430 15 16 17~ 18

A

B

C

D

A

BC

D

A

B

C

D

i i l l i

p m

Magnetic multilayers (Mathon)

Ab initio (Kunc)

El.tun. & IR spect. in HTc supercond.

Glass transition

Fullerenes

Adsorbates

Si based heterost. (Abstreiter)

Flux dynamics

Quant.wires & dots (Kotthaus)

Heavy fermions

Time resolv.spect. (Ryan)

i

EZPOSTERS

POSTERS

V

POSTERS

Names in italics: session organizers

* Monday April 6 2O00 - 2100 EVENING SESSION

ROOMB (METAKIDES)

V Tuesday 1700 HONORARY AWARDS

ROOM D (Union of Czech Mathem. t Physicists)