notiziario neutroni e luce di sincrotrone - issue 3 n.2, 1998

NOTIZIARIONeutroni e Luce di Sincrotrone

Vol. 3 n. 2 Dicembre 1998

Cover photo: Molecular model of three molecules of the protein annexin IV arranged around the three-fold axis in the trigonalcrystals (Zanotti et. al., Biochem. J., 329, 101-106, 1998). Annexins are a family of proteins able to bind to phospholipidmembranes and consequently promote the formation of Ca2+ ion channels. Despite the fact the the protein is present insolution as a monomer, several experimental evidences suggest that the formation of the trimer shown in figure is relevant forthe interaction with the membrane.

Editoriale ............................................................................................................................................................................................................ 2F.P. Ricci

RASSEGNA SCIENTIFICA

The Use of Synchrotron Radiation in Protein Crystallography:Old Considerations and New Developments ...................................................................................................... 4G. Zanotti

Development of Microfocus X-Ray Zone Plates .......................................................................................... 12M. Gentili and E. Di Fabrizio

Orientational Correlations and Hydrogen Bondingin Liquid Hydrogen Chloride .................................................................................................................................................. 17C. Andreani et Al.

DOVE LUCE DI SINCROTRONE

Infrared Synchrotron Radiation, a New Tool for the ItalianScientific Community ........................................................................................................................................................................... 20P. Calvani

SCUOLE E CONVEGNI .............................................................................................................................................. 28

CALENDARIO ................................................................................................................................................................................. 31

SCADENZE ........................................................................................................................................................... 32

FACILITIES ............................................................................................................................................................. 33

2 NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE • Vol. 3 n. 2 Dicembre 1998

EDITORIALE

I n questo ultimo mese vi sono stati due eventi di notevoleimportanza per lo sviluppo della nostra comunità neutroni-ca. Alla fine di ottobre il professor Fontanesi, a nome del

CNR, ha firmato a Madrid il “Memorandum of Understan-ding”. In questo modo il CNR è entrato ufficialmente a far par-te dell’European Spallation Source R&D Council, l’organismointernazionale che ha come obiettivo la costruzione di una nuo-va sorgente di neutroni impulsati europea (ESS), che è bene ri-cordare, costituirà la sorgente di neutroni più intensa nell’im-mediato futuro (Vedi Notiziario Neutroni e Luce di Sincrotro-ne Vol. 3 n. 1 - 1998). Per la nostra comunità scientifica questorappresenta uno stimolo per le attività di sviluppo di strumen-tazione nel campo, e una occasione per incrementare lo staff digiovani ricercatori operanti in spettroscopia neutronica. Inoltrequesto impegno del CNR sarà per i ricercatori italiani occasio-ne di scambio scientifico a carattere internazionale.Il secondo evento è relativo alla visita del Presidente del CNR,prof. Lucio Bianco, recatosi al Rutherford Appleton Labora-tory, presso la sorgente neutronica pulsata ISIS, per l’inaugu-razione dello Spettrometro TOSCA (Vedi Notiziario Neutronie Luce di Sincrotrone Vol. 3 n. 1 - 1998), l’1-2 dicembre. Oltreal Presidente, facevano parte della delegazione italiana, il prof.Marcello Fontanesi, Presidente del Comitato Scienze Fisiche,la prof.ssa Carla Andreani, segretario scientifico del Comitato,il dott. Alberto Conti dell’ufficio rapporti internazionali delCNR ed il dott. Daniele Colognesi, il prof. Francesco PaoloRicci e il dott. Marco Zoppi, in rappresentanza del gruppo cheha progettato e realizzato lo spettrometro TOSCA. Era presen-te anche l’ing. Checchi, in rappresentanza dell’industria fio-rentina che ha costruito lo spettrometro. È rilevante che sottola spinta del CNR un’industria italiana abbia realizzato que-sto strumento avviandosi quindi in un campo di elevata tecno-logia il che permetterà al nostro Paese di concorrere con suc-cesso a ulteriori gare europee nel campo.Il Presidente del CNR ha anche incontrato i ricercatori italia-ni, presenti ad ISIS in quei giorni per esperimenti, ed i compo-nenti italiani nei panels di valutazione, il prof. Roberto De-renzi, la prof.ssa Maria Antonietta Ricci, ed il prof. RomanoRinaldi, i quali hanno sia illustrato le modalità di selezionedelle proposte di esperimenti per ISIS sia sottolineato il buonvalore scientifico delle proposte italiane.Va sottolineata la lungimiranza scientifica del CNR nella scel-ta, che risale all’anno 1985, di partecipare alla sorgente neu-tronica pulsata ISIS. Infatti attualmente la comunità scientifi-ca operante nel campo della spettroscopia neutronica nel mon-do è orientata verso questo tipo di sorgenti, sia per le ampiepossibilità scientifiche offerte sia per le garanzie ambientali.Infatti al momento la costruzione di nuove sorgenti staziona-rie incontra delle difficoltà. Basti ricordare il recente caso delprogetto di costruzione del reattore di Monaco di Baviera che,

benché ormai quasi ultimato, ha subito un rallentamento.Dal punto di vista della organizzazione della ricerca in lucedi sincrotrone, durante i mesi scorsi vi sono state alcune im-portanti novità. Vi è stata l’assunzione di personale a tempoindeterminato (tecnico, tecnologo e ricercatore) presso i labo-ratori ELETTRA ed ESRF. Presso ESRF, l’INFM ha creatoun gruppo che costituisce il primo nucleo stabile di supportoai progetti ed agli utenti italiani di ESRF e della linea italia-na GILDA. Nello stesso ambito opera personale a tempo de-terminato, parte del quale segue l’attività del CRG italianoad ILL. Presso ELETTRA, l’INFM ha assunto personale cheseguirà la progettazione e la costruzione di progetti INFM.Per quanto riguarda la situazione a Trieste è significativa epositiva la recente approvazione di quattro nuove beamline,tutte con finanziamento della Sincrotrone Trieste; sono lebeamline dedicate a cristallografia di proteine (seconda li-nea), alla microfrabricazione, alla nanospectroscopia ed unlaser ad elettroni liberi. Questi nuovi sviluppi consolidano inmodo significativo l’attività italiana di luce di sincrotrone.Formuliamo l’auspicio che la attuale cooperazione fra gli entiimpegnati nella ricerca con luce di sincrotrone in Italia(CNR, INFM, INFN e Sincrotrone Trieste) possa non solocontinuare nel futuro ma rafforzarsi. La vitalità del campo è stata recentemente dimostrata dall’ap-pena svolto Users’ Meeting di ELETTRA. Sono stati illustratirisultati in campi che vanno dalla spectromicroscopia delle in-terfacce, alle correlazioni angolari nella fotoemissione con tec-niche di coincidenza, alla mammografia digitale. Durante loUsers’ Meeting il prof. Giorgio Margaritondo, al termine delsuo mandato di Direttore Scientifico, ha eseguito una stimo-lante rassegna dei risultati scientifici più significativi ottenutie degli obiettivi raggiunti per le linee e la macchina. Cogliamol’occasione per fare gli auguri di buon lavoro al prof MassimoAltarelli, che dal 1° gennaio avrà la responsabilità di coordina-re le attività scientifiche e complessive di ELETTRA.Ricordiamo che lo Users’ Meeting di ESRF viene svolto nelfebbraio 1999; oltre alla giornata plenaria con quattro relazio-ni su invito, la relazione dei direttori e la premiazione del“Young Scientist” vi sono tre workshop, dedicati a dicroismomagnetico, scienza dei materiali e scattering a basso angolo diraggi X e neutroni. Gli argomenti delle relazioni ad invito del-lo Users’ Meeting di ESRF (rilevazione dell’ordine orbitale inossidi, covalenza del legame idrogeno, nuove possibilità di ra-dioterapia anti-tumorale e cristallografia di proteine) illustra-no in modo chiaro l’importanza della luce di sincrotrone innumerosi campi della ricerca scientifica.Infine, ricordiamo che a fine estate verrà svolta una nuova edi-zione della scuola di luce di sincrotone organizzata dal prof.Settimio Mobilio e dal prof. Gilberto Vlaic presso S. Margheri-ta di Pula (Cagliari). È auspicabile che si ripeta una numerosa

è pubblicato a cura del Gruppo Nazionale di Struttura della Materiadel C.N.R. in collaborazione con il Dipartimento di Fisicadell’Università degli Studi di Roma “Tor Vergata”.

Vol. 3 n. 2 Dicembre 1998

Autorizzazione del Tribunale di Roman. 124/96 del 22-03-96

Vol. 3 n. 2 Dicembre 1998 • NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE 3

EDITORIALE

partecipazione di giovani a questo importante appuntamentoper la comunità della luce di sincrotrone.

F.P. Ricci

V ery recently there have been two important events forthe Italian neutron community. At the end of Octoberprof. Fontanesi, representing CNR, signed in Madrid

a Memorandum of Understanding which will allow CNR toparticipate in the European Spallation Source R&D Council,the international group whose objective it is to build the neweuropean pulsed neutron source (ESS); this source will be themost intense neutron source in the near future (as described inNotiziario Neutroni e Luce di Sincrotrone Vol. 3 n. 1 - 1998).For our community this represents an opportunity for the de-velopment of neutron spectroscopy instrumentation and alsoto increase the number of young researchers working withneutrons. Moreover, this commitment of CNR increase inter-national scientific exchange for Italian researchers.The second event is the visit on 1st and 2nd of December of thePresident of CNR, prof. Lucio Bianco, to the ISIS pulsed neu-tron source (Rutherford Appleton Laboratory) for the inaugu-ration of the TOSCA spectrometer (Notiziario Neutroni e Lu-ce di Sincrotrone Vol. 3 n. 1 - 1998). With the President ofCNR were prof. Marcello Fontanesi, President of the PhysicsCommittee, prof. Carla Andreani, scientific secretary of the sa-me committee, dr. Alberto Conti of the international relationsoffice of CNR and dr. Daniele Colognesi, prof. Francesco PaoloRicci and dr. Marco Zoppi, representing the group which desi-gned and built TOSCA. Ing. Checchi, representing the floren-tine company which built the spectrometer was also present. Itis important that thanks to the effort of CNR an Italian com-pany has built this instrument, thus acquiring the know-howwhich will allow Italy to compete successfully in Europeantenders in this field.The President of CNR also met Italian researchers involved inexperiments at the time and the Italian members of the reviewpanels: prof. Roberto Derenzi, prof. Maria Antonietta Ricciand prof. Romano Rinaldi, who explained the selection processfor proposals at ISIS and stressed the good scientific level ofItalian proposals.We would like to stress the far-sighted policy of CNR in choo-sing, in 1985, to participate in the ISIS pulsed neutron source.In fact, the international neutron community now prefers thiskind of source because of the numerous scientific applicationsand also because of environmental concerns. Indeed, construc-tion of new continuous sources is encountering problems, asdemonstrated by the recent difficulties of the Munich reactor.In the past few months there have been some important new

events concerning the organization of Italian synchrotron ra-diation research. Permanent contract staff (technicians, deve-lopment scientists and research scientists) has been hired inTrieste and Grenoble. At ESRF, INFM has established agroup whose function it is to provide support to projects andItalian users of public beamlines and of the Italian CRG GIL-DA. Fixed term personnel is also involved in the Italian CRGat ILL. At ELETTRA, INFM has hired staff to work on the de-sign and construction of projects and beamlines. ConcerningELETTRA, a significant and positive development is the re-cent approval of four new beamlines, all with SincrotroneTrieste funding; they are dedicated to protein crystallography(second beamline), microfabrication, nanospectroscopy and anFEL. These new developments consolidate Italian activity insynchrotron radiation research. We hope that the cooperationwhich is presently taking place between the various institutesinvolved in synchrotron radiation research in Italy (CNR,INFM, INFN and Sincrotrone Trieste) will not only continuebut will be further strengthened.The vitality of the field was demonstrated by the recently heldUsers’ Meeting of ELETTRA. Results in fields ranging fromspectromicroscopy of interfaces to angular correlations in pho-tomemission with coincidence techniques to digital mammo-graphy were illustrated. During the Users’ Meeting prof.Giorgio Margaritondo, at the end of his successful term asScientific Director, reviewed the most significant scientific re-sults obtained and the performance of the accelerators and ofthe beamlines. We take this opportunity to wish prof. MassimoAltarelli , who from January 1st takes global responsibility foractivities at ELETTRA, every success in his new role.The ESRF Users’ Meeting takes place in February 1999; alongwith the plenary session with four invited talks, the directors’report and the Young Scientist Award, there are three work-shops dedicated to magnetic scattering, materials science andneutron and x-ray small angle scattering. The topics of the in-vited talks clearly illustrate the importance of synchrotron ra-diation research in diverse areas of science; they deal with thedetection of orbital ordering in oxides, of covalency in the hy-drogen bond, of new possibilities of micro-beam radiation the-rapy and with protein crystallography.Lastly, we remind readers that in the early fall a new edition ofthe synchrotron radiation school organized by prof. GilbertoVlaic and prof. Settimio Mobilio will take place in S. Marghe-rita di Pula (Sardinia). We hope that, as for previous editions,many researchers will participate to this important event forour community.

F.P. Ricci

DIRETTORE RESPONSABILE: F.P. Ricci

COMITATO DI REDAZIONE: C. Andreani, F. Boscherini,R. Caciuffo, R. Camilloni

SEGRETERIA DI REDAZIONE: D. Catena

HANNO COLLABORATO

A QUESTO NUMERO: C. Mariani, F. Boscherini, M. Catti

GRAFICA E STAMPA: omgrafica, via Fabrizio Luscino 73, RomaFinito di stampare nel mese di Dicembre 1998

Per numeri arretrati: Grazia Ianni, GNSM-C.N.R., vialedell’Università 11, 00185 Roma. Per informazioni editoriali: DesyCatena, Università degli Studi di Roma “Tor Vergata”, Dip. diFisica, via della Ricerca Scientifica 1, 00133 Roma. Tel: +39 672594364 Fax: +39 6 2023507. E-mail: [email protected]


SummaryThe latest developments in the use of synchrotron radiation inmacromolecular crystallography are briefly reviewed. In parti-cular, the advantages in terms of increase of resolution and thepossibility of measuring data on very small or poorly diffrac-ting crystals are described. The advances in Multiple Anoma-lous Dispersion (MAD), direct methods and dynamic measu-rements are discussed, along with some possible future deve-lopments.

IntroductionThe determination of the three-dimensional structure ofbiological macromolecules by means of X-ray diffractiontechniques has shown, since its birth in the ’50th, anearly-exponential growth: from about twenty-thirty

structures solved per year during the period 1974-80, tonearly 2000 structures which have been deposited at theBrookhaven Protein Data Bank1 in 1997 alone (Fig. 1).Several different reasons are at the basis of this ’explo-sion’ of structural data, among them:a. the technological advancements in the field of com-

puters and measuring devices (area detectors arecommercially available since about fifteen years,graphic workstations for the display of electron den-sity maps and model manipulation since the begin-ning of the ’80s);

b. the improvement of the methodologies for structuresolution, along with the parallel increase of thenumber of laboratories involved in protein crystal-lography;

c. the progresses in molecular biology, that nowadays

THE USE OF SYNCHROTRON RADIATIONIN PROTEIN CRYSTALLOGRAPHY:OLD CONSIDERATIONS AND NEW DEVELOPMENTSG. ZanottiDip. Chimica Organica dell’Università e Centro Studi suiBiopolimeri del CNR, via Marzolo 1, 35131 Padova, Italy

Articolo ricevuto in redazione nel mese di Settembre 1998

Fig. 1. Number of macromolecular structures deposited at the Brookhaven Protein Data Bank (PDB) since 1974. PDB is the organization that takes careof the collection and free distribution of all macromolecular structures, solved either by X-ray diffraction or NMR. Of the total 8174 structures present inthe data bank at the 1st of September, 1998, 6693 have been determined by X-ray diffraction, 1289 by NMR in solution and 192 are theoretical models.The data for the graph were taken directly from PDB statistics.



make available to the crystallographer relatively largeamounts of proteins that are present in nature inquantity insufficient for crystallization trials;

d. and finally, but not last for relevance, the availabilityof second and third generation synchrotrons: theyhave strongly contributed to accelerate the processof structure determination and made possible sometypes of measurements unattainable with conventio-nal sources.

There are various reasons which stimulate the crystallo-grapher to use the synchrotron radiation: the crystals aretoo small or do not diffract under conventional X-raysources; the need for wavelengths different from theclassical Cu Kα or Mo Kα; the need of a white-beam ra-diation for time-resolved studies; the presence of verylarge unit cells, as in the case of virus crystals, that requi-res a well collimated beam and the possibility of selec-ting the wavelength to separate the reflections; the possi-bility of attaining a definitely higher resolution with re-spect to a conventional source, either for a better defini-tion of the molecular model or even to allow to solve thephase problem. All of these points will be briefly re-viewed and their relative relevance and the theoreticallyobtainable results discussed.It should be pointed out that the use of synchrotron ra-diation for a crystallographer consists very often in aroutine measurement: data are collected with the sametypes of detectors as used on conventional sources andprocessed with the same kind of programs. The impor-tance of the experiment can eventually reside in the bio-logical or medical relevance of the results obtained.

Crystal size and diffracting powerThis point is apparently not worth a long discussion: ifthe crystal is too small or it diffracts only to low resolu-tion under a rotating-anode X-ray source, the use of syn-chrotron radiation, well collimated and of high brillian-ce, often solves the problem. It is in fact true that this isfor a protein crystallographer one of the main reasonsfor going to a synchrotron facility. Having only smallcrystals, in the past the crystallographer had no otherchoice than testing conditions for growing bigger andbetter crystals. Nowadays, the availability of a synchro-tron source often allows the measurement from smallcrystals of diffraction data good enough for solving thestructure. It must be pointed out that this behavior is nota result of laziness: the growth of crystals of appropriatesize for X-ray analysis represents, in the generally longprocedure of structural determination, the step that hasobtained less improvements from the technical progres-ses of the last twenty years. Protein crystallization stillrepresents a “trial and error” process, which requiresmonths (or eventually years) of experiments, often un-successful. It has to be considered as one of the main rea-sons why only a few thousands of three-dimensional

structures have been determined, compared to the morethan 200,000 protein sequences availablea,2.One could ask what is the lower limit of the size of aprotein crystal that could be utilized for the structuraldetermination. Taking into account that the total energyof the diffracted beam from a family of planes (hkl) foran ideal crystal is inversely related to the cell volume:

E(hkl) ∝ |F(hkl)|2 Vcryst/Vcell (1)

where Vcryst and Vcell are the total volume of the crystaland of the unit cell, respectively, it appears evident howthe diffracting power is dependent on the number of cel-ls present in the crystal and, finally, on the size of thecell itself. In practice, for crystals with very small cells,like those of minerals, structural determinations havebeen successfully undertaken with samples of few mi-crons of linear size: for a cell with a volume of 1000 Å3,in a crystal with edges of 10 µm there are 1012 cells, stilla quite high number. In the case of a macromolecule,whose crystal cells range usually from 100,000 to somemillions of Å3, a crystal of the same size as the previousone contains a number of cells that ranges from 1010 to109. That corresponds to a mean decrease of the diffrac-ted intensities of at least two-three orders of magnitude.Besides, protein crystals are essentially composed of li-ght atoms and they also contain a lot of solvent, whichdecreases the order of the crystal lattice and consequen-tly the diffracting power. It is not possible to state whatis exactly the minimum size useful for a data collectionof a protein crystal, since it depends on many differentconditions, but we could cautiously state that crystalswith a total volume of 105 ÷ 106 µm3 (i.e. 50-100 µm of li-near size in all directions) can be measured on a synch-rotron source. Much smaller volumes are neverthelesspossible, depending on the crystal quality and the beammicrofocusing: diffraction patterns that extend to about2.5 Å resolution have been obtained3 for bacteriorhodo-psin crystals with a total volume of about 5·103 µm3.All the previous considerations have a relevant practicalaspect. It is in fact relatively easy to obtain very smallcrystals of a globular protein. What is often consideredan “amorphous” precipitate is composed, if observedwith the appropriate microscope, of crystals of verysmall size. It is much more difficult to grow these smallcrystals to a size suitable for a diffraction experiment.Lowering the threshold to which crystals are suitable forX-ray diffraction experiments shortens, in practice, theprocess of crystal growth and, finally, of the structuraldetermination.

ResolutionCrystals of globular proteins present a very high solventcontent, generally from 40 % to 60 %, but cases areknown where the estimated solvent is much larger. This



fact, coupled with the size and the intrinsic flexibility ofthe macromolecule itself, strongly reduces the order ofits crystal lattice. It is not comparable with that of a ioniccrystal and not even with that of a molecular one. Underconventional sources, a ‘normal’ protein crystal diffractsat about 2 Å resolution, whilst quite good crystals canreach 1.5 Å. But often, particularly for very large macro-molecules, the crystallographer is happy enough in ob-taining a spectrum at 2.5 Å or 3 Å resolution. Owing to its high brightness and brillianceb, synchro-tron radiation generally gives rise to a significant increa-se in resolution: it is impossible to quantify a priori thisimprovement, but I will illustrate this point with a fewexamples from my personal experience. In the cases de-scribed, data were measured at the ELETTRA facility inTrieste, a third generation synchrotron, with a MAR Re-search imaging plate as a detector. The laboratory sourcewas a M18XHF-SRA rotating anode, and the detector amultiwire proportional counter HIGH STAR (Brücker).It must also be taken into account that rotating anodedata were collected at room temperature and synchro-tron data at 100°K (there was no special reason for that,but simply the lack of the cooling device in our labora-tory. On the other hand, data at ELETTRA cannot bemeasured without freezing the crystal, since the very hi-gh intensity of the beam drastically reduces the crystallife-time). The first example is represented by the enzyme rhodane-se, whose crystals diffract to a maximum of 1.8-1.9 Å re-solution on a rotating anode source4. Data could be col-lected at a resolution of 1.36 Å with synchrotron radia-tion, with an increase of the number of independent re-

flections from 21000 to 56000 5. This has allowed a muchbetter definition of the molecular structure and the posi-tioning of 407 ordered solvent molecules (Fig. 2).Crystals of annexin IV, despite their reasonable size (Fig.3), are very unstable and they last for only few minutesunder a rotating anode source. Frozen crystals at ELET-TRA show a diffraction pattern that extends to at least 3Å. The measurement of a native data set has allowed tosolve the structure using the molecular replacement te-chnique6.As a final example, the diffraction spectrum of crystalsof a mutated B-subunit of heat-labile toxin from E. colican be hardly observed at 6-7 Å on a rotating anode,owing to the exceptionally high solvent content of thecrystal, more than 75% of the total volume (Fig. 4). Datacould be measured in Trieste at 3 Å and the crystal struc-ture solved and refined7. It must be stressed that, whilst in the first example de-scribed the synchrotron radiation simply allowed to ex-tend significantly the resolution and to have a better de-fined model, in the other two cases it was absolutely es-sential, since without its use data could not have beenmeasured at all. Since two other similar situations hap-pened to the author in the last two years, it is easy to ex-trapolate that the use of synchrotron can often be deter-minant in structural biology.

The phase problem and the multiple anomalousscattering (MAD)MAD represents the technique where synchrotron radia-tion has given the more crucial contribution to the reso-lution of the phase problem in biocrystallography: abouthundred structures has been solved up to the 1997 usingit, 80 of which only in the years 1995-19978.The so called “anomalous scattering” is based on the fol-lowing principle: when the energy of the X-ray radiationthat interacts with the matter is close to the value of theelectronic transition from a bonding atomic orbital, a re-sonance condition takes place and the classical Thomsonscattering is perturbed9. At the wavelengths used for thenormal diffraction experiments on single crystal thiscomponent is totally negligible for light atoms, like H, C,N, O and S. It becomes on the contrary significant forheavy atoms, i.e. for atoms with many electrons. For thelatter, the atomic scattering factor, f, can be separated intwo components, one, f0, purely real and totally inde-pendent from the wavelength and a second, f∆ , complexand dependent on λ. We can consequently write:

f = f0+ f∆ = f0+ f’(λ) + if”(λ) (2) c

An example of the trend of the two components of f∆,real and imaginary, with the wavelength is illustrated inFig. 5 for selenium. It must be remembered that both f’and f” depend on the bonding situation of the heavy-

Fig. 2. Cartoon showing the structure of enzyme rhodanese. Arrows re-present β-strands, helical ribbons α-helices, the two black spheres thesulfur atoms of the catalytic cystein 247, small crosses the ordered sol-vent molecules surrounding the protein in the crystal (ref. 5).



atom itself in the macromolecule: this makes necessarytheir experimental determination from fluorescencemeasurements of atomic absorption of the sample understudy. However, as a consequence of this resonance effect, the-re is a wavelength (λ1 in Fig. 5) for which f” is maximumand one (λ2) for which f’ is minimum: in both cases thevalue of the structure factor will be different from thatmeasured at a wavelength (λ3) where both effects are ne-gligible. When the imaginary component f” is not negli-gible, the Friedel law, that states that

| F(hkl) | = | F(-h-k-l) | (3)

does not hold: the two reflections, formerly equivalent,are now called a “Bijvoet pair” and their difference is so-mehow related to the position of the anomalous scatte-rer, i.e. the heavy-atom. Moreover, the value of | F(hkl)| measured at λ1 will be different from that at λ2. Conse-quently, the measurement of each structure factor at thethree different wavelengths will be virtually equivalentto that of diffraction data of a native data set and twoheavy-atom derivatives. The processing of MAD datacan consequently be turned into that of the multiple iso-morphous replacement (MIR), well known and docu-mented in protein crystallography10. The disadvantagearising from the fact that the anomalous effect is relati-vely small, particularly if compared to that of iso-morphous replacement, is largely compensated by thetotal absence of the problems deriving from the lack ofisomorphism, largely present in the latter.Anomalous scattering measurements are anyhow not so

simple: despite of being routinely performed at manysynchrotron facilities, great care must be taken to mini-mize systematic and statistical errors (counting errors,crystal absorption and decay). The Bijvoet pairs shouldbe measured on the same frame or eventually in quiteclose time intervals.Despite the practical problems during data collection,the need of a synchrotron for performing the measure-ments and of a heavy-atom in the macromolecule, theMAD technique has become a nearly routine approachto the solution of the phase problem. This is due to thefact that nowadays, thanks to the developments of mole-cular biology, within recombinant proteins it is possibleto substitute the methionine, an amino acid containingsulfur, with seleno-methionine or, less frequently, tellu-ro-methionine, i.e. methionines where the S atom hasbeen substituted by Se or Te11. The protein so modifiedbehaves, from the conformational point of view, as thenative protein and can generally be crystallized iso-morphously to it. In this way one or more anomalousscatterers have been introduced inside the macromole-cule without perturbing its three-dimensional structureand a MAD experiment can be easily performed.

The phase problem and direct methods ‘Direct methods’ in crystallography refers to the techni-que that allows the determination of the phases of struc-ture factors only from the knowledge of their moduli.They are based on probabilistic relationships, that takeinto account the fact that relationships among intensitiesmake some phase values for a single structure factor mo-re or less likely. Their physical validity stands on thequite obvious assumptions of the positivity of the elec-tron density and of the ‘atomicity’ of it. But whilst theformer is always necessary true, the latter is unfortuna-tely valid only for diffraction data at atomic resolution.The probabilistic formulas derived from them allowanyhow the solution of the phase problem in a nearlyautomatic way, for the so called ‘small molecules’ cry-stals, which includes those with a maximum of aboutone hundred non-hydrogen atoms in the asymmetricunitd.One of the fundamental formulas of direct methods gi-ves the probability that the phase of the triplet φ-h+φk+φh-k assumes the value Φhk and can be writtenas:

P(Φhk) = (1/L)exp [(2/√N) |EhEkEh-k| cos(Φhk)] (4)

In (4) E are normalized structure factors, L is a normali-zation term and N the number of atoms in the unit celle.Relationship (4) estimates the probability distribution ofthe phase Φ based on the values of the moduli of threereflections. A more general relationship, called “tangentformula”, estimates the phase from the moduli of all the

Fig. 3. Trigonal crystals of bovine annexin IV, obtained in the absence ofCalcium ion (ref. 6). Crystals are approximately 0.1 mm on all sides.



reflections (for a general description, see, for example,ref. 12). But the important point, evident from (4), is thatthe probability depends on 1/√N and, since N can bevery large for a macromolecule, the probability distribu-tion becomes very flat. It is also true that for a macromo-lecule, at a given resolution, there are many more reflec-tions with respect to a small molecule crystal and thisshould compensate the reduced relevance of each rela-tionship. Unfortunately, the diffracting power of macro-molecular crystals only exceptionally reaches atomic re-

solution. If this condition is not fulfilled, the classical re-lationships of direct methods do not work, and other te-chniques (MIR, MAD etc.) have to be used to solve thephase problem. The use of synchrotron radiation in thisrespect can be fundamental: the increase of diffractingpower, for example, from 1.5 Å to about 1.2 Å, can allowthe use of direct methods. Unfortunately this representsfor the moment an exception rather than the rule and ithas been successfully applied only in a very limitednumber of test cases13,14. Nevertheless, it is likely that the use of more powerfulphase relationships and the improvements of themathematical tools can decrease the limit of resolutionnecessary to reach the structure solution. In this respect,

the combination of them with the high resolution datameasured at a synchrotron could lead to the determina-tion of macromolecular structures without the need toresort to the cumbersome experimental methods used inthese days.

Time-resolved measurements: The Laue methodAs described previously, protein crystals contain a lot ofsolvent. A large portion of it is disordered or, in any ca-se, is in equilibrium with the external solution where thecrystal is kept. This fact allows the soaking of the crystalin a solution that contains ‘small’ molecules, which candiffuse in the channels formed by macromoleculespacked in the crystal. This is in fact the basis of the iso-morphous replacement technique, which historically hasrepresented the first method of determination of a pro-tein structure and it is still used to solve new structures.It consists in diffusing compounds containing ‘heavy’atoms, i.e. atoms with many electrons if compared to N,C, O and S, inside the crystal. From their positions it ispossible to calculate the phases of the structure factors ofthe native crystal. Moreover, the presence of the solvent can allow the dif-fusion in the crystal of molecules that bind to the macro-molecule, like substrates or inhibitors in the case ofenzymes. Enzymes very often maintain their activity inthe solid state and ‘static’ studies, that is the comparisonbetween the structure of the enzyme with and withoutligands (inhibitors, partial substrates or activators) cangive indirect information about the mechanism of actionof the enzyme itself. It is obvious that these kind ofinformation can, in principle, be obtained also from dy-namic measurements, i.e. measurements taken duringthe enzymatic reaction. This can be done with themethodology known as ‘Laue’. It originates from Maxvon Laue, that used it at the dawning of crystallography(1912) to demonstrate the diffraction of X-rays from acrystal of copper sulfate. The method was very rapidlyousted by monochromatic measurements, much simplerto carry out. Besides, polychromatic techniques are veryhard to perform when X-rays are produced from a con-ventional source, whose spectrum is characterized by afew sharp peaks and a low, continuos background. On the contrary, synchrotron radiation is very well sui-ted for this kind of measurements and Laue techniqueswere consequently rediscovered in recent years, alongwith the diffusion of synchrotron facilities. After the de-termination of a small molecule structure in 198315, thefirst electron density map of a protein was obtained forthe enzyme glycogen phosphorylase b16. In this modern version of Laue technique, an entire dif-fraction data set can be measured in a very short time,from few ms to some ps: with a stationary crystal andwhite radiation, a lot of lattice planes satisfy the Braggcondition and so most of the spectrum can be measured

Fig. 4 Schematic drawing of the crystal packing of the subunit B mutantof heat-labile enterotoxin from E. coli. In the drawing, the cell is seenprojected along the c axis and only Cα atoms are represented. Each pro-tein molecule is an omo-pentamer, made by five polypeptide chains of111 amino acids each. The space group is P41212 and there is only onepentameric molecule in the asymmetric unit, which accounts for a totalof 76% of the crystal volume being approximately occupied by solventand only 24% by protein atoms. The macromolecules, packed in the cry-stal around the four-fold axes in super-helical structures, form the largesolvent channels that can be observed in the drawing. (The figure wasproduced by Dr Dubravka Matkovic-Calogovic with coordinates takenfrom ref. 7).



without rotating the specimen. The larger the interval ofwavelengths used, the more are the spots accessible tothis geometry17. But, of course, with increasing ∆λ, thebigger is the probability that spots can overlap. Best sui-ted crystals for this kind of measurements are those withvery high symmetry, that allow the collection of nearlythe entire set of data with the stationary crystal. The very brilliant beam of the third generation synchro-trons, coupled with the advent of fast detectors, allowsin principle the examination of very fast reactions. The

basis of the method is the following: the crystal is posi-tioned in a flow-cell, which allows the exchange of themother liquid inside the crystal with a solution from theoutside. When the substrate is injected, data sets aremeasured at given intervals. If the time necessary for ameasurement of a set of data is sensibly shorter than thereaction time, in principle we can take pictures of thecourse of the chemical reaction. Time intervals obviouslydepend from the reaction rate: fortunately, the speed ofbiochemical reactions can be often controlled by the pHand the solvent medium and so reactions can be madenot too fast. Time-resolved studies present, as can be easily imagi-ned, some very serious difficulties, either practical ortheoretical. One of the former is represented by thespeed of substrate diffusion inside the crystal: since dif-fusion is a relatively slow process, only chemical reac-tions much slower than it could be studied. To overcomethis problem, it is possible to introduce the substrate, inan inactive form, in advance inside the crystal: the sub-strate is suddenly activated, through a photochemicalreaction, generally with a pulse of a laser light18. Thissolves the diffusion problem and allows a precise controlof the reaction initiation. Unfortunately, photochemical

reactions are not always available for all kinds of possi-ble substrates of enzymes and this partially limits theuse of the technique.Nevertheless, the major hindrance to the method is atheoretical one. What we observe in a diffraction experi-ment is the mean, over time and space, of all the molecu-les in the crystal. It is therefore necessary that a stable in-termediate accumulates during the reaction, and it has todo so in a large fraction of molecules of the crystal at thesame time. It represents possibly the reason for which,despite the many promises and some very brilliant re-sults, it has not yet given very outstanding contributionsto the understanding of biological mechanisms.

Only advantages?It is reasonable to ask if no drawbacks are present whenusing synchrotron radiation. In fact, at least one physicaland some practical disadvantages can be listed. The for-mer is particularly true for very brilliant sources, wherethe crystal has to be frozen in order to limit the drasticcrystal decay due to the very high photon flux. Crystalsfrozen in the liquid nitrogen stream, usually at 100°K, la-st for several hours (or eventually forever, if kept coo-led), generally enough for at least an entire data collec-tion. The freezing process is anyhow not a simple task,since protein crystals contain mother liquid which ismainly composed of water, that can crystallize by itselfwhen cooled, cracking the crystal and giving rise to apowder diffraction spectrum of ice (along with that ofother salts, if present in the crystallization medium). Themother liquid must be therefore substituted by an ap-propriate solution, called cryo-protectant, containingsubstances with a low freezing-point, like glycerol.Unfortunately, the cryo-protectant solution often increa-ses the mosaicity of the protein crystal, in some cases si-gnificantly and so diminish the gains obtained by the in-tense, collimated source.Practical problems in the use of synchrotrons arise in-stead from the need of moving to a distant place toperform the measurements: the transport of unstablesamples is not so easy, particularly by plane, and, whenpossible, crystallographers tend to take their measure-ments at home. Synchrotron measurements have to be areal necessity.

Future developmentsIt is always risky to foretell the future developments inscience, particularly in a field of rapid growth. In the ca-se of synchrotron radiation, it is quite easy to predictthat its use by the crystallographic community willgrow: at present, despite the large number of beamlinesin the world which are dedicated to single-crystal dif-fraction, the demand largely exceeds the total time avai-lable to usersf. Moreover, the continuos increase of the

Fig. 5. f’ and f” components of the scattering of Se as a function of the X-ray energy. Continuos lines represent the theoretical values calculatedaccording to the Cromer/Liberman theory, dashed lines are “simulated”experimental ones for Se in a macromolecule. The shift of the absorptionedge is significant.



number of research groups in the world engaged in pro-tein crystallography, along with the reasons listed in theprevious paragraphs, all drive towards a massive use ofsynchrotron radiation. But here I want to discuss aboutanother development that is at the moment far frombeing utilizable in the field (and perhaps will never be),but that could eventually change, if successful, our expe-rimental approach to structure determination: X-ray ho-lography.Holographic methods offer a mean of extracting both in-tensity and phase information from a spectrum, lettingthe scattered waves interfere with a single wave, takenas reference19. Holographic images using visible lightare very common, but their resolution is limited by thewavelength. To be useful for structural applications, ho-lography must be performed with a wavelength suffi-ciently small to resolve atomic details, i. e. X-rays, orelectrons with the appropriate energy. The latter is infact used, but, owing to the limited penetration of elec-trons, only for imaging of surfaces20. X-rays presenthowever an apparently insuperable problem: what canbe used as the reference wavelength? Two years ago ithas been demonstrated21 that atomic resolution is attai-nable in special cases: in a single crystal of SrTiO3, fluo-rescent X-rays emitted from the strontium atoms wereused as the reference wave and interference with diffrac-ted beams used for reconstructing the three-dimensionalimage. The Sr atoms in the crystal lattice can consequen-tly be directly visualized. Despite the limited informa-tion (only the Sr atoms, heavier than Ti and O, can beseen), the importance of the experiment stands in thefact that a molecular structure has been visualized direc-tly, without deriving the phase information from someother sourceg. Can this be used for direct imaging of ma-cromolecules? For the moment the answer is no: even-tually, some heavy atoms in the macromolecule could beseenh. But we cannot exclude that further advances inthe technique will allow the direct visualization of ma-cromolecules in the future.

AcknowledgmentsI would like to thank Dubravka Matkovic-Calogovic,Roberto Battistutta and Anna Bassetto for reading themanuscript and for the helpful comments.

References1. Bernstein, F. C., Koetzle, T. F., Williams, G. J. B., Meyer, Jr., E. F., Bri-

ce, M. D., Rodgers, J. R., Kennard, O., Shimanouchi, T. and Tasumi,M. “The Protein Data Bank: a Computer-based Archival File for Ma-cromolecular Structures” J. Mol. Biol. 112, 535-542 (1977)

2. Bairoch A. and Apweiler R. “The SWISS-PROT protein sequence databank and its supplement TrEMBL in 1998” Nucleic Acids Res. 26, 38-42(1998)

3. Pebay-Peyroula, E., Rummel, G., Rosenbusch, J.P. and Landau, E.M.“X-ray structure of Bacteriorhodospin at 2.5 Å from microcrystals

grown in lipid cubic phases” Science 277, 676-681 (1977)4. Gliubich, F., Gazerro, M.L., Zanotti, G., Delbono, S., Bombieri G. and

Berni, R. “Active site structural features for chemically modifiedforms of rhodanese” J. Biol. Chem. 271, 21054-21061 (1996)

5. Gliubich, F., Berni, R., Colapietro, M., Barba, L. and Zanotti, G.“Structure of sulfur-substituted rhodanese at 1.36 Å resolution” ActaCryst. D54, 481-486 (1998)

6. Zanotti, G. Malpeli, F., Gliubich, F., Folli, C., Stoppini, M., Olivi, L.,Savoia A. and Berni, R. “Structure of the trigonal crystal form of bovi-ne annexin IV” Biochem. J. 329, 101-106 (1998)

7. Matkovic-Calogovic, D., Loreggian, A., D’Acunto, M.R., Battistutta,R., Palù, G. and Zanotti, G. “Structures of two mutants of B subunitof heat-labile enterotoxin from E. coli”, in preparation

8. Hogata, C.M. “MAD phasing grows up” Nature Struct. Biol., 5, 638-643 (1998)

9. Hendrickson, W.A. and Hogata, C.M. “Phase determination frommultiwavelength anomalous diffraction measurements” in Methods inEnzymology, Vol. 276, Part A, Academic Press, N.Y., pp.494-523 (1997)

10. Terwilliger, T.C. “MAD Phasing: treatment of dispersive differences asisomorphous replacement information” Acta Cryst. D50, 17-23 (1994)

11. Doublié, S. “Preparation of selenomethionyl proteins for phase deter-mination” in Methods in Enzymology, Vol. 276, Part A, AcademicPress, N.Y., pp. 523-530 (1997)

12. Giacovazzo, C., Monaco, H.L., Viterbo, D., Scordari, F., Gilli, G., Za-notti, G. and Catti, M. “Fundamentals of Crystallography” Oxford Uni-versity Press, Oxford, (1992)

13. Smith, G.D., Blessing, R.H., Ealick, S.E., Fontecilla-Camps, J.C.,Hauptman, H.A., Housset, D., Langs, D.A. and Miller, R. “Ab initiostructure determination and refinement of a scorpion protein toxin”Acta Cryst. D53, 551-557 (1997)

14. Frazão, C., Carrondo, M.A. and Sheldrick, G.M. “Ab initio determina-tion of the crystal structure of cytochrome C6. Comparison with pla-stocyanin” Structure 3, 1159-1169 (1995)

15. Wood, I.G., Thompson, P. and Matthewman, J.C. “Crystal structurerefinement from Laue photographs taken with synchrotron radia-tion” Acta Cryst. B39, 543-547 (1983)

16. Hajdu, J., Machin, P., Campbell, J.W., Greenhough, T.J., Clifton, I.,Zurek, S., Gover, S. Johnson, L.N., and Elder, M. “Millisecond X-raydiffraction and the first electron density map from Laue photographsof a protein crystal” Nature 329, 178-181 (1987)

17. Helliwell, J.R. “Macromolecular crystallography with synchrotron ra-diation” Cambridge University Press, Cambridge (1992)

18. Moffat, K., Bilderback, D. and Schildkamp, W. “Laue photographyfrom protein crystals” in Synchrotron Radiation in Structural Biology,Sweet, R.M. and Woodhead, A.D. eds, Plenum Press, N.Y., pp. 325-330 (1989)

19.Gabor, D. Nature, 161, 777-778 (1948)20. Harp, G.R., Saldin, D.K. and Tonner, B.P., Phys. Rev. Lett. 65, 1012-

1015 (1990)21. Tzege, M. and Faigel, G. “X-ray holography with atomic resolution”

Nature, 380, 49-51 (1996)22. Szöke, A. “Holographic methods in X-ray crystallography. II. Detai-

led theory and connections to other methods of crystallography” ActaCryst. A49, 853-866 (1993)

23. Xu, G. “Solving the phase problem of X-ray diffraction using atomicresolution X-ray holograms” Acta Cryst. A53, 236-241 (1997)

Notesa. Protein sequences are available through specialized data bank, like

SWISS PROT (ref. 2)b. Brightness and brilliance are defined as:

brightness = photons/sec/0.1%δλ/λ/mrad2

brilliance = photons/sec/0.1%δλ/λ/mrad2/mm2



the former defines a well collimated source, the latter a source of smallsize and well collimated.

c. Decreasing the wavelength, for example around 5-6 Å, anomalous di-spersion can be observed for S and P atoms. Experiments made by thegroup of Prof. Sthurman in Hamburg have shown that these kind ofmeasurements are possible. The operating experimental conditionsare nevertheless quite hard to manage: at these wavelengths, forexample, the absorption of X-rays by the air is determinant and it isnecessary to operate in the vacuum. At present the approach is stillunder development.

d. This number is definitely underestimated, since most of the direct-methods programs are at present able to solve structures with a biggernumber of atoms, not necessarily in a fully automatic way. As a mat-ter of fact, crystals with more than about 100 atoms in the asymmetricunit are not common, since medium-size molecules are difficult tocrystallize.

e. Relathionship (4) is valid for N equal atoms in the unit cell. If theatoms are different, as normally happens, (4) takes a slightly morecomplicated form, but our considerations are not affected.

f. The previous statement is true for ESRF (Grenoble) and ELETTRA(Trieste) and it is reasonable to assume that the situation cannot be toodifferent in other facilities around the world.

g. As pointed out by Szöke (ref. 22), the crystallographic technique canbe considered a sort of holography, for example making the assump-tion that, if a portion of the electron density in the cell is known, thecomplex amplitude of the diffracted wave can be considered as the re-ference wave and used to reconstruct the hologram. This is in factwhat happens in real diffraction experiments. Otherwise, in a holo-graphic experiment it is assumed that phases are recovered directlyfrom the experiment itself.

h. An holographic approach for the visualization of the entire moleculehas been recently proposed, but not yet applied in practice (ref. 23).


Conventional electron microscopes cannot be used to investi-gate biological samples under their natural conditions, due tothe need for a vacuum environment. X-ray microscopy, in-stead, provide a different way of studying biological specimensgiving in principle the possibility of observing living cells orsimilar materials at atmospheric pressure. On the other hand,x-ray focusing is a formidable challenge, since the refractiveindexes of all materials is close to unit at the used wavelength.A different way to focus x-rays is to use a Zone Plate, which isessentially a circular diffraction grating made of alternate con-centric rings of absorbing material and transparent ones. ZonePlates combined to high brightness X-ray sources, such as tho-se provided by third generation synchrotrons, open a new pathfor the investigation of samples by means of micro-focused x-rays. This paper describes the Zone Plate development activitycarried out at the Solid State Electronics Institute of the CNRin Rome, Italy. It will be demonstrated that by making use ofElectron Beam Lithography it is possible to design and fabrica-te soft X-ray zone Plates whose minimum feature size is wellbelow 100 nm.

IntroductionX-ray microscopy is living a period of fast development,which is having strong impact on many domains ofscience and technology. Thanks to the new possibilitiesoffered by microfocusing techniques, X-rays are findingapplication in new fields, and are opening new avenuesin disciplines that have been using them for a long time.This rapid progress was triggered by two combined fac-tors: on one hand the recent technological developmentsin the fabrication of microfocusing optical elements forX-rays, which have pushed their resolution limit to thenanometer scale; on the other, the advent of third gene-ration synchrotron radiation sources, which provideenough brightness to make efficient use of this high spa-tial resolution. In this report the main aspects involvedin manufacturing of high resolution Zone Plates (ZPs)for soft X-ray focusing are described. In particular, weshow how direct patterning by means of electron beamlithography is used to draw on thin membranes ZPswith critical dimensions down to 70 nm. These featuresof nanometer size are successfully transferred into goldor nickel by plating, producing efficient absorbing mediafor the desired wavelength. The precision reached in the

control of feature size and aspect ratio, line-to-space ra-tio and external diameter makes this patterning approa-ch particularly suitable to cover a wide range of microfo-cusing applications and illumination wavelengths. Thedeveloped process allows reproducible results with sub-100 nm resolution absorbers made of gold or nickel.

Fresnel ZPsIt is well known that focusing of X-rays is a very difficulttask. The refractive index of most of the materials at su-ch a wavelength is close to unity so that X-rays are inhe-rently difficult to bend by means of conventional opticssuch as refractive lens [1]. A conventional refractive X-ray lens would have an impractical focal length whendesigned to operate with a refractive index close to theunity, as well as its depth of focus would be extremelylimited [2]. On the other hand, reflection focusing with arefractive index close to unity implies that conventionalmirrors would be operated at a very small X-ray beamangle of incidence [3]. Normal reflection focus can beachieved by exploiting Bragg reflection from crystal pla-nes or by making use of ultra-precise and ultra-smoothmultilevel X-ray mirrors; however this choice is particu-larly challenging due to the difficult in manufacturingthem [4,5,6]. Diffraction can, however, be used to focusefficiently X-rays. A Zone Plate (ZP) is essentially a cir-cular diffraction grating made of alternating concentricrings of absorbing and transmitting materials, where thespatial modulation of the single ring follows a preciselaw:

r2n= nfλ+(nλ)2/4 (1)

where r2n is the radius of the nth zone, f is the focallength and λ is the wavelength with which the ZP is tobe illuminated [7]. Figure 1 shows a typical ZP layoutwhere the black zones represents the absorbing regionand the white zones the transmitting one.ZPs are not ideal optical elements; in fact they sufferfrom chromatic aberration and, since they are essentiallydiffraction gratings, also produce several diffractive fo-cusing orders, which result in many coaxial foci to form.In addition, ZPs working in amplitude mode, where al-ternate zones are blocking completely the destructive in-

DEVELOPMENT OF MICROFOCUSX-RAY ZONE PLATES

M. Gentili, E. Di FabrizioIstituto di Elettronica dello Stato Solido - CNR, Via Cineto Romano 42, I-00156 Roma, Italy

Articolo ricevuto in redazione nel mese di Ottobre 1998




terference can produce focusing efficiency not higherthan 10%. High resolution ZPs can be fabricated usingdifferent pattering techniques including, electron and X-ray lithography [8,9], holography [10], and slicing tech-nique [11]. Other fabrication methods, such as those re-laying on scanning probes have still to prove effective-ness and reliability for ZP patterning. So far the best re-sults in terms of efficiency and resolution are achievedby electron beam lithography patterning followed by asuitable absorber manufacturing technique. This reportdescribes the fabrication process for soft X-ray ZPs deve-loped at the Solid State Electronics Institute of the Natio-nal Research Council in Rome (Italy).

Description of the fabrication process

• Substrate Preparation and Patterning by Electron BeamLithographyThe standard substrate used are silicon nitride (SN)membranes 100 nm thick, made by means of standardwet etching on silicon wafers with chemically vapor de-posited layers of SN. The dimension of membrane win-dows depends on the desired ZP diameter, and in ourcase ranged from 100 to 500 micron. Substrates were firstcovered with a double layer of chromium (7 nm) andgold (7nm) which was evaporated directly onto the sur-face making it electrically conductive as required by thesubsequent absorber formation electroplating process.Figure 2 shows schematically the various fabrication ste-ps involved in ZP manufacturing. The recording mediaused for the e-beam exposure (resist) was Poly-Methil-Methacrylate (PMMA) having molecular weight of 950K, which was spun on the substrate for a thickness of200-300 nm. After exposure, the samples were develo-

ped at room temperature in a mixture of one part ofMethil-Isobutil-Ketone (MIBK) and three part of Iso-Pro-pil-Alcohol (IPA) for two minutes.The following relation relates the resolution of any ZP tothe outermost zone width:

R=1.22 drn (2)

where R is the focusing resolution and drn is the outer-most zone width. Therefore, any nanofabrication proce-dure must comply with the requirements of having ade-quate resolution whilst maintaining flexibility for the ge-neration and the placement of the many circular ringscomposing the ZP itself. The electron beam lithographymachine used for ZP exposure is a Leica MicrosystemsLithography EBMF 10 working at accelerating voltageup to 50 kV, and equipped with an exaboride lanthanumelectron emitter. Since most of commercial e-beam sy-stems do not have a specific polar pattern generator, asoftware capable to approximate the circular feature re-quested in ZP patterning, with the available set of featu-re primitives which include rectangles and polygons,had to be developed [12]. This software also compensa-tes for both forward and backward scattering effects inresist and substrate. This correction, which in most ofthe high resolution application is mandatory, is calledproximity effect compensation [13]. The developed algo-rithm assigns the single zone exposure dose as a resultof all neighbored zone-zone interactions and thus avera-

Fig. 1 Typical Zone Plate layout.

Fig. 2 Fabrication steps involved in Zone Plate manufacturing.


ging locally the resist absorbed dose. Otherwise, whenpassing from the center of the ZP to its outermost partthe electron scattering effects would result very diffe-rent, leading to a non-uniform absorbed dose. The effec-tiveness of the correction is shown in Figure 3. Figure 3shows for a 40 kV exposure and an e-beam spot size of50 nm the assigned dose as a function of the single expo-sure pixel (upper curve) and the resulting convolutionon the actual 150 micron diameter ZP (lower curve). Asit can be seen, after the correction the dose is correctlyequalized to the unit (resist threshold or clearing dose).This guarantees, in principle, that the ZP feature sizewould result all correctly exposed.

• MetallizationAfter the development, the substrate was electricallycontacted by selectively removing a small PMMA re-gion; this was performed with the aid of oxygen reactiveplasma and by protecting the ZP pattern with a metallicmask. Plating was carried out by a commercial appara-tus; a typical growth rate of 100 nm/min ensured a de-posited metallic film which exhibits a nanometer grainsize.

• Inspection and Zone ControlPatterning of ZP with outermost zone widths below 100nm and external diameter exceeding 100 µm introducesa great challenge in e-beam exposure. First, resolutionrequirements are demanded for external zones where, e-beam in-field distortions are the highest; secondly, largediameter ZPs force the use of adequately large field si-zes, which in turn, always result in a less dense e-beamaddressing grid. This latter fact is of paramount impor-tance in ZP patterning; the approximation of circularfeatures with rectangular primitive shapes, always de-mands a dense beam addressing grid, which gets lessdense when the deflection field size is progressively in-creased. As general rule, the greater the field size, thelarger the distortion errors. In order to minimize e-beamscale errors, which could be introduced if the writing

plane is put higher than the calibration one, special cali-bration routines were used by making use of a geometri-cally regular (square) high contrast (200 nm thick gold)marker fabricated on the substrate itself. Under theseconditions, and for the used writing fields ( less than 500µm), it is expected that our e-beam machine has a pat-tern placement accuracy which is a small fraction of theminimum line-width and close to the laser interferome-ter intrinsic precision (4.6 nm). However, the exposureand the resist development influence the trade-offbetween resolution and ZP diameter. Errors in the ZPpattern can be introduced during the fabrication process;non-circular zone pattern or misplacement of zones areaccountable errors in manufacturing, and introduceaberrations. For amplitude ZPs, partial transmission ofthe absorbing media, irregularities in line-width of zonesand in line-to-space ratio as well as deviation from a per-fectly rectangular zone profile, also affect the efficiency.

• Resolution, line-to-space ratio and resist profileResolution in electron beam lithography is a strong func-tion of both forward and backward scattering effects inthe resist and the substrate [14]. Due to the very thinsubstrate (100 nm silicon nitride), most of the incomingelectrons pass through the membrane, and therefore aweak effect of electron backscattering from the substrateis expected. Monte Carlo electron scattering simulationwas carried out to evaluate quantitatively this amount[15]; only 2 % of electrons are reflected back and theircontribute is negligible in terms of a proximity effect[16]. More important is the spreading of the electronbeam passing through the resist; i.e. forward scatteringeffect (FS). At 40 kV, Monte Carlo simulation indicatesthat beam spreading caused by FS is about 50 nm for a250 nm thick resist. Figure 4 shows the Monte Carlo cal-culated point spread function (proximity function) alongwith its analytical approximation by means of a linearcombination of gaussian functions. The point spreadfunction represents the behavior of the normalized expo-


Fig. 4 Monte Carlo proximity function and multi-gaussian fit.

Fig. 3 Monte Carlo calculated absorbed dose after proximity effect compensation.



sure dose for an infinitely small beam spot size incomingon a particular experimental system (substrate and resi-st). The most intense and collimated peak accountsmainly for the electron forward scattering effect into theresist, whereas the broader distribution is related to theelectron backscattering arising from the substrate. It isnoticeable the “noisily” character of the backscatteringdistribution; this is caused by the relatively low amountof electrons coming from the substrate. This distributionextends for only 1.3-1.4 µm and is several orders of ma-gnitude less intense than the collimated part accountingthe forward scattering Therefore, it can be concludedthat the attainable ultimate resolution in this experimen-tal system is related to the e-beam spot size, FS effectand degree of approximation of the circular features. Fi-gure 5 shows the effect of e-beam spot size variation onthe modulation of the absorbed dose for an high resolu-tion ZP. A 30 nm beam spot size increase results in achange of about 40 % of the absorbed dose modulation(peak-to-valley distance). In addition to the above men-

tioned effects, also the resist development time, the ex-posure dose or a very aggressive developers can alter si-gnificantly the targeted line-to-space ratio, and thereforethe diffraction ZP efficiencies. Nominal line-width va-lues have to be normally smaller than the final pattern,because FS and spot size are finite; this procedure, whichconsists in altering (reducing) the dimension of the pat-terns to be written, is called “biasing”. The typicalamount of bias introduced in our process is in the rangeof 30-50 nm.

• Aspect ratioAspect ratio is the ratio between height and width of agiven feature. It is known that high aspect ratio featurecan collapse due to the lack of mechanical strength [17].In the case of soft X-ray ZPs, in order to have in half con-trast and hence good efficiency too, gold plated structu-res should be 120-300 nm thick. This introduces a practi-

cal limit in the resist thickness, which in turn has to be asthick as 350 nm. Under these conditions a 70 nm resolu-tion feature exhibits an aspect ratio that can exceedsfour. In addition, we have observed more pronouncedmechanical instability in case of ZPs rather than in fabri-cated conventional one-dimensional grating. The resistmechanical stability problem at sub-100 nm level is stillan unknown process and more investigations are nee-ded to clarify its behavior. We observed that best resultscan be achieved by making use of fresh developer andby stirring the sample during its development.

Examples of fabricated Zone PlatesIn this section a few examples of fabricated ZPs will bepresented. They are all made of gold on silicon nitrideand most of them are in use or have been used for spec-tro-microscopy applications at several synchrotron ra-diation facilities world-wide, including ELETTRA inFig. 6 SEM micrograph showing a 150 micron diameter gold Zone Plate.

Fig. 5 Effect of e-beam spot size variation on Monte Carlo calculated absorbed dose.

Fig. 7 SEM micrograph showing a 70 micron diameter gold Zone Plate.



Trieste, Italy and the Advance Light Source in Berkley,CA, USA. Figure 6 shows a scanning electron micro-graph taken at low magnification on a finished 150 mi-cron gold ZP made on silicon nitride. The central brightspot is the so-called apodization region, that is a thickergold pad (about 1 micron thick) necessary to stop theunwanted zero diffraction order. The dark square in thecenter is the thin silicon nitride membrane supportingthe ZP itself. The three small bright features visible atthe corner of the pattern are the calibration marker usedto locate and align the exposure field to the pattering

area. Figure 7 is a close-up showing a 70 micron diame-ter ZP, the interference patterns visible on the picture arethe so-called Moiré figures resulting from the superposi-tion of the scanning grid of the electron microscopeused to take the image and the circular gratings compo-sing the ZP. Figure 8 is a close up of a group of outermo-st zones, whereas Figure 9 shows a high-resolution ima-

ge on the 70 nm resolution outermost zone. Microscopytest carried out on some of the fabricated ZP have confir-med the excellent quality of these devices that haveperformed high resolution focusing with efficiency veryclose to 10% (theoretical limit) [18].

ConclusionsA fabrication process for sub-100 nm resolution, largediameter, amplitude soft x-ray ZP has been developed. Itmakes use of electron beam nanolithography and goldplating. In particular the issues of data preparation andoptimization, resolution, control of line-to-mark ratio,have been addressed in detail by means of Monte Carloelectron scattering modeling, proximity effect correctionand experiments. Under optimized conditions, 70 nm re-solution. Measured efficiency for amplitude ZP was 9.5% very close to the theoretical limit of 10%.

AcknowledgmentsThe authors wish to thank colleagues who contributedduring the past years to the development of this techno-logy, in particular we wish to acknowledge Dr MarcoBaciocchi, Dr Luca Grella, Mr Luigi Mastrogiacomo andMr Romano Maggiora.

References1. E. Spiller, in Handbook of Synchrotron Radiation, Vol. 1, E.E. Koch

Ed., North Holland Amsterdam 1983.2. J.H. Underwood and D.T. Attwood, Phys. Today, 37 (4), 44, (1984)3. A. Franks, “X-ray Optics”, Sci. Prog. 64, 371, (1977)4. T. W. Barbee, in X-ray Microscopy, 114, ( Springer, Berlin 1984),5. J. Kirz and H. Rarback, Rev. Sci. Instruments, 56 (1), 1, (January 1985)6. H. A. Padmore, G. Ackerman, R. Celestre, C-H Chang, K. Franck, M.

Howells, Z. Hussain, S. Irick, S. Locklin, A.A. McDowell, J.R. Patel,S.Y. Rah, T.R. Renner and R. Sandler, Synchrotron Radiation News,Vol. 10, No. 6, (1997).

7. J. Soret, Arch. Sci. Phys. Nat. 52, 320, (1875)8. Y. Vladimirski, D. Kern, T.H.P. Chang, D. Attwood, H. Ade, J. Kirz, I.

McNutty, H. Rarback amd D. Shu, J. Vac. Scie. Technol., B 6 (1),(Jan/Feb 1988)

9. D. C. Shaver, D.C. Flanders, N.M. Ceglio, H.I. Smith, J. Vac. Scie. Te-chnol. 16 (6), 1626, (Nov/Dec 1979)

10. C. David, in Springer Series in Optical Science, Vol. 67, X-ray Micro-scopy III, eds.: A. Michette, G. Morrison and C. Buckely, SpringerVerlag, Berlin Heidelberg, 87, (1992)

11. D. Rudholp, S. Niemann and G. Schmahl, High Resolution X-ray Op-tics, Proc. SPIE 316,103, (1981)

12. E. Di Fabrizio, L. Grella, M. Baciocchi, M. Gentili, D. Peschiaroli, L. Ma-strogiacomo and R. Maggiora, Jpn. J. App. Phys. Vol. 35, 2855, (1996)

13. T.H.P. Chang, J. Vac. Scie. Technol. 12, 1271, (1975).J.S. Greenich, Electron Beam Processes, in Electron Beam Technologyin Microelectronic Fabrication, Edited by G.R. Brewer, AcademicPress, 1980D.F. Kyser and R. Pyle, IBM J. Res. Develop. Vol. 24, No.4, (July 1980).M. Gentili , A. Lucchesini , P. Lugli , G. Messina , A. Paoletti , S. San-tangelo, A. Tucciarone and G. Petrocco, J. Vac. Scie. Techol. B 7(6),1586, (1989)Tanaka, M. Morigami and N. Atoda, Jpn. J. App. Phys., 32 , 6059,(1993)Morris, M. Gentili, M. Baciocchi, S. Contarini, P. De Gasperis, C. Ga-riazzo, M. Kiskinova, R. Maggiora, P. Melpignano, N. Minnaja, M.Musicanti, P. Nataletti and R. Rosei, Proceedings of the XIII Interna-tional Congress on X-ray Optics and Microanalysis, 539-542, August1992 Manchester U.K.

Fig. 9 Detail of 70 nm resolution gold absorbers.

Fig. 8 Close up of the outermost zones of a sub-100 nm resolution ZonePlate.



ORIENTATIONAL CORRELATIONS AND HYDROGENBONDING IN LIQUID HYDROGEN CHLORIDE

C. AndreaniDip. Fisica, Università degli Studi di Roma Tor Vergata,Istituto Naz. per la Fisica della Materia, Unità di Roma TorVergata, Via della Ricerca Scientifica 1, 00133 Roma, Italy

M.A. Ricci, M. Nardone, F.P. RicciDip. Fisica “E. Amaldi”, Università degli Studi di Roma Tre,Istituto Naz. per la Fisica della Materia, Unità di Roma Tre.Via della Vasca Navale 84, 00146 Roma, Italy.

A.K. SoperISIS Facility, Rutherford Appleton Laboratory, Chilton, Did-cot, OX11 0QX, U.K, and Dept. of Physics and Astronomy,University College London, Gower Street. London WC1E6BT, U.K.

Neutron diffraction studies aimed to look at orientatio-nal correlations among molecules in a liquid havealways been limited by the intrinsic difficulty that theresponse of the system to the probe is a weighted sumof all the independent site-site correlation functions.1 Itis nevertheless now well established that for hydrogencontaining liquids one can exploit the large change inthe coherent neutron scattering length existing betweenH and D isotopes by performing neutron diffraction ex-periments with Isotopic H/D Substitution (NDIS)2 andthus extract three independent site-site correlationfunctions. In simple molecular fluids, such as the hy-drogen halides, this technique allows the extraction ofthe whole set of independent functions.3,4 In these mo-lecular liquids the availability of the whole set of site-site correlation functions is ‘’per se’’ of great help inunderstanding the orientational correlations, althougha detailed knowledge of the entire angular pair correla-tion function cannot be achieved. As a matter of factthe angular pair correlation function contains moreinformation than contained in the set of site-site corre-lation functions, since the latter are averages of the an-gular pair correlation function over the molecularorientations, keeping the site-site distance fixed.5 Dee-per insight into the orientational correlations can be ob-tained only by interpreting the experimental data alongwith appropriate computer simulations, such as Rever-se Monte Carlo6, Molecular Dynamics7 (MD) or the re-cently developed Empirical Potential Structural Refine-ment8 (EPSR).Molecular liquids composed of hydrogen halides havetwo features in common, which can be of help in under-standing the orientational correlations. First the centre ofmass is approximately coincident with the halide atom,which means that the halide-halide correlation functionextracted from the diffraction experiment coincides withthe centres of mass radial distribution function to a goodapproximation. Secondly the hard core part of the inter-molecular potential is almost spherically symmetric: the-refore the orientational correlations can be interpreted in

terms of electrostatic multipolar interactions and hydro-gen bond formation. In particular the anisotropy of theintermolecular potential is strongly varying within thehalide series, since the dipolar contribution decreaseswhen going from hydrogen fluoride to hydrogen iodide,while the quadrupole contribution increases.5,9

Previous neutron diffraction studies10-12 and MD simu-lations13-15 suggest that hydrogen chloride is likely toform weak hydrogen bonds. To better investigate thispoint and to complete our study on the orientational cor-relations in hydrogen halides3-4,9 we have performed adetailed NDIS study on liquid hydrogen chloride at twothermodynamic states (in the vicinity of the meltingpoint and of the critical point respectively) and appliedthe EPSR method to produce three-dimensional configu-rations of HCl molecules compatible with the experi-mental site-site radial distribution functions. From theseconfigurations selected angular pair correlation func-tions have been calculated.Figure 1 shows the probability, g(r,θL), that, given a mo-lecule in the origin, oriented along the z axis, anothermolecule, however oriented, is found at a distance r inthe direction θL at the lowest temperature state. Twoshells of neighbors are identified in Figure 1: the first atr= 35nm and the second at r= 65nm. Similar mapsalthough with broader peaks are obtained at the otherstate point. The function g(r,θL) shows a strong depen-dence on θL at r values close to the first neighboringshell, indicating, contrary to what would be expected foran uncorrelated model liquid, a clear preferred orienta-tion of the intermolecular axis within a cone of halfwidth θL =50°. In other words, while the preferred di-stance of the first neighboring molecules around anoriented molecule is the same in all θL directions, theyare not isotropically distributed, since they prefer to liein the axial direction. It is worthwhile noticing that, sincethe Cl site is close enough to the molecular center ofmass, deviations from the uncorrelated model results,and in particular the existence of a hydrogen bond peakin the Cl-H radial distribution function, depend on the

Articolo ricevuto in redazione nel mese di Novembre 1998



strong directionality observed in the first neighbors di-stributions.From the EPSR simulation we have also calculated theprobability that, given a central HCl molecule in the ori-gin, oriented along the z axis, another molecule lies at adistance r, with orientation defined by the polar axis θM,, at nine selected θL values, g(r, θM,θ L=costant). Thisanalysis shows that at both state points the majority ofthe first neighboring molecules, which lie in a regionwhere 0< θL <20° or 160°< θL <180°, have their dipoles al-most aligned. Very few L-shaped configurations arefound at θL =90°, where however a preferred relativeorientation of molecules is hardly detectable. This analy-sis suggest the existence of strong correlations betweenthe intermolecular vector and the molecular axis. A clo-ser look at the preferred orientations at θL =0°, is givenin Figure 2, where the function g(r, θM,θ L=0) at bothstate points is reported. In the vicinity of the meltingpoint, although first neighboring molecules seen alongthe positive z direction strongly prefer to align their di-pole parallel to the dipole of the molecule at the origin,

significant density of molecules is also found at θM=70°,while no antiparallel dipole orientations are found. Theangular distribution sharpens on going towards the criti-cal point, indicating a better alignment of the dipole mo-ments at the lower density state, while the intensity ofthe shoulder at θM=70° decreases, and only a few antipa-rallel configurations appear.The EPSR analysis of the HCl data gives strongly diffe-rent results in comparison with those found by the sphe-rical harmonics analysis of the HI16 and HBr4 data. Inthose liquids the correlation between θL and the molecu-lar orientation was found to be very low, with the majo-rity of the molecules forming an angle θM=45° with the zdirection and almost the same number of parallel andantiparallel dipoles. These differences may be due to thedifferent dipole and quadrupole moments associatedwith the three molecules or to the presence in liquid HClof hydrogen bonds, which implies stronger directiona-lity in the local coordinations.Because the Cl-H bond direction coincides with the HCldipole moment direction, a suitable geometric definition


Fig. 1 Map of the of the probability, g(r,θL), that, given a central HCl molecule in the origin, oriented along the z axis, another molecule, however oriented, is found at a distance r in the direction θL, at T=194 K.



of the H-bond in this system is not available at the pre-sent time, unlike the case of liquid water where the O-Hbond direction is distinct from the water molecule’s di-pole moment direction. What is clear already however isthat there appear to be competing dipolar and hydrogenbonding interactions in HCl, and as the temperature israised and the density is lowered the dipolar interac-tions tend to dominate the structure.In summary this study has shown that although strongorientational correlations between HCl molecules arepresent at both states investigated, the radial distribu-tion function of molecular centres is similar to thatfound in so-called ‘’simple liquids’’; thus implying thatthe short range electronic overlap forces in liquid HClare spherically isotropic.Electrostatic and hydrogen bonding forces must therefo-re be primarily responsible for the observed orientatio-nal correlations. These correlations are characterized bya strongly anisotropic angular distribution of first neigh-boring molecules, which is markedly peaked aroundθL=0°. First neighboring molecules along this directionprefer to align their dipoles parallel to the molecule atthe origin, although, at the lowest temperature also a re-levant fraction of molecules forming an angle θM=70°with the molecule at the origin is found. We believe thatthese molecules are those engaged in hydrogen bonds.Going towards the critical point the number of these mo-lecules decreases in favor of those with parallel orienta-tion. This assignment is supported by the evidence forzig-zag structures with θM=87° in the crystalline formsof HCl17 and by its dependence on the thermodynamicstate. The presence of hydrogen bonds is traditionallyassociated with the presence of a peak at r=24nm in theCl-H radial distribution function: this peak is indeedpresent in our data. The behavior of its intensity is consi-stent with that of the number of first neighboring mole-

cules around θL=0° forming an angle θM=70°.We stress that liquid HCl looks different from the otherhydrogen halides studied so far, because in the othertwo systems no evidence was found for the presence ofhydrogen bonds and the correlations between the inter-molecular vector and the molecular orientations were al-so very weak.3,4,16

References1. S. W. Lovesey, “Theory of Neutron Scattering from Condensed Mat-

ter”, vol.1 (Clarendon Press, Oxford, 1984).2. A. K. Soper, in “Methods in the Determination of Partial Structure

Factors”, edited by J.B.Suck, D. Raoux, P.Chieux and C. Riekel,(World Scientific Publishing, London, 1993), p.58.

3. C. Andreani, M. Nardone, F. P. Ricci, and A. K. Soper, Phys.Rev.A 46,4709 (1992).

4. C. Andreani, F. Menzinger, M. A. Ricci, A. K. Soper, and J. Dreyer,Phys.Rev.B 49, 3811 (1994).

5. C. G. Gray and K. E. Gubbins, “Fundamentals, Theory of MolecularLiquids”, vol.1 (Oxford University Press, New York, 1984).

6. R. L. McGreevy, and M. A. Howe, Annual Review of Material Science22, 217 (1992).

7. M. P. Allen, and D. J. Tildesley, “Computer Simulation of Liquids”,(Oxford University Press, Oxford, 1987).

8. A. K. Soper, Chem. Phys. 202, 295 (1996).9. C. Andreani, F. Menzinger, M. Nardone, F. P. Ricci, M. A. Ricci, and

A. K. Soper, in “Hydrogen Bond Networks”, edited by M. C. Bellis-sent-Funel and J. Dore, NATO ASI Series, Series C, 435, 113, (KluwerAcademic Plublishers, Dordrecht, 1993).

10. J. G. Powles, E. K. Osae, J. C. Dore, and P. Chieux, Mol. Phys. 43, 1051(1981).

11. A. K. Soper, and P. A. Egelstaff, Mol. Phys. 42, 399 (1981).12. T. Bausenwein, H. Bertagnolli, K. Todheide, and P. Chieux, Ber. Bun-

senges. Phys. Chem. 95, 577 (1991).13. J. G. Powles, W. A. B. Evans, E. McGrath, K. E. Gubbins, and S. Mu-

rad, Mol. Phys. 38, 893 (1979).14. M. L. Klein, and I. R. McDonald, Mol. Phys. 42, 243 (1981).15. D. Gutwerk, T. Bausenwein, and H. Bertagnolli, Ber. Bunsenges.

Phys. Chem. 98, 920 (1994).16. A. K. Soper, C. Andreani, and M. Nardone, Phys.Rev.E 47, 2598

(1993).17. “Comprehensive Inorganic Chemistry”, edited by J.C. Bailar,

H.J.Emeleus, Sir Ronald Nyholm, and A. F. Trotman-Dickenson (Per-gamon Press, Oxford, 1974).

Fig. 2 Map of the probability, g(r, θM,θ L=0°), that, given a central HCl molecule in the origin, oriented along the z axis, another molecule lies at a distance r, in the direction θL=0°, with orientation defined by θM : a) T=193 K; b) T=313 K.


After a couple of decades of attempts, the aim of extending theunique performances of the synchrotron source to the infrareddomain is achieved by about ten dedicated beamlines in diffe-rent countries. With their high-brilliance, broad-band radia-tion one may perform experiments that are out of the range ofconventional black-body sources. The first Italian infraredbeamline, SINBAD, is presently under construction on thenew double-ring DAΦNE of Laboratori Nazionali INFN diFrascati.

IntroductionInfrared spectroscopy probes the rotations and the vi-brations of molecules (their “finger-print” spectral re-gion), the low-energy excitations of solids (phonons, ex-citons, polarons, etc.), the forces between a surface andan adsorbate, and many other low-energy phenomena ofbasic importance for condensed matter physics, chemi-stry, biophysics, and materials science. A giant step in the detection of infrared spectra was ma-de in the Sixties with the introduction of Michelson in-terferometers coupled to Fourier-transforming compu-ters. On the other hand, until mid-eighties the onlybroad-band radiation sources available for this techni-que were those of the early experiments, namely globarsor mercury lamps. The emittivity of a globar, which canbe roughly approximated by that of a black body heatedat 1500 or 2000 K, is peaked at λ≈5 µm, and decreasesrapidly for λ>20 µm, the crucial region of the far infra-red. A mercury lamp has slightly better performances atlarge λ’s. Moreover, just a small fraction of the poweremitted by these sources on a 4π solid angle can be focu-sed on the sample.The spectra collected with conventional sources are thenaffected by a poor signal-to-noise ratio whenever the ex-periment is made under non- standard conditions. Mo-dern spectroscopy may demand a high source stability,like in differential spectroscopy, or a large angle of inci-dence, as in surface science, or a small spot, as in infra-red microspectroscopy and in experiments at high-pres-sure. As, moreover, Fourier-transform spectroscopy re-quires a broad-band source, the answer to these require-ments is the extension to the infrared of the use of synch-rotron radiation, with its high brilliance over a “white”spectrum and its absence of thermal fluctuations.

A short historyThe development of InfraRed Synchrotron Radiation(IRSR) has been less rapid than one may expect on thebasis of its present success. This has been partly due totechnical reasons, partly to the spectacular developmentof SR in the UV and X-ray domain, that has heavily en-gaged the scientific and budgetary effort of the researchinstitutions in the last three decades.The first attempts aimed at extending the use of thesynchrotron source to the infrared date back to the Se-venties, when pioneering observations were made inStoughton (USA) by Stevenson and coworkers1 and inOrsay (France) by Lagarde and coworkers.2 At the be-ginning of the 80’s, a port dedicated to the extractionof IRSR was built on the ring of Daresbury (GB) byYarwood.3 This project was interrupted for a few yearsbut a member of the Daresbury group, Takao Nanba,

built in Japan on UVSOR, in 1985, the first IRSR beam-line routinely open to users.4 In 1987 Gwyn Williamsinaugurated the first American infrared beamline atBrookhaven,5 which triggered the rapid developmentof the IRSR in the USA. The first efficient Europeanbeamlines were realized in the early 90’s at Lund(Sweden) by Bengt Nelander,6 at Orsay by Pascale Roy

Articolo ricevuto in redazione nel mese di Settembre 1998

INFRARED SYNCHROTRON RADIATION,A NEW TOOL FOR THE ITALIAN SCIENTIFIC COMMUNITY

P. CalvaniIstituto Nazionale di Fisica della Materia and Dipartimentodi Fisica, Università La Sapienza, P.le A. Moro, 2, 00185Roma, Italy

Fig. 1 The ultra-high-vacuum section of SINBAD under test in summer1998. The 3m-long front-end which connects the beamline to DAΦNE th-rough a series of rapidly-swithcing valves can be seen on the left. Thetwo chambers in the middle contain the extraction mirror and the focu-sing ellipsoid, together with their motors.



and coworkers,7 at Daresbury by the group of MichaelChesters.8The realization in Frascati of an IRSR beamline for theItalian spectroscopic community was first proposed byA. Marcelli and P.C. in 1993.9 The old ring ADONE wasabout to be dismanteled, for leaving place to the “Φ-factory” collider DAΦNE, at that time already designedand funded. The high current (2A) and the low energy(0.51 GeV) foreseen for DAΦNE made this double-ringan ideal source of infrared radiation. The optical layoutof SINBAD (Synchrotron INfrared Beamline At DAΦ−NE) was calculated by Augusto Marcelli of INFN andAlessandro Nucara of INFM, who first applied ray-tra-cing simulation techniques to the infrared domain.10

The project was presented in 1996 by Emilio Burattinito Istituto Nazionale di Fisica Nucleare, together withthat for two beamlines in the soft X-ray domain, and ra-pidly approved. INFN started the construction of SIN-BAD and of its laboratory in 1997 under the directionof Burattini and Marcelli. The measuring apparatus,which includes a Michelson interferometer suitablymodified for high-vacuum operation, an infrared mi-croscope, high-pressure cells, and several detectors, hasbeen instead prepared at the Dept. of Physics of Uni-versity La Sapienza. Other groups of users already in-volved in the project come from the Dept. of EarthSciences of Università di Roma III (A. Mottana), theDept. of Earth Sciences of La Sapienza (A. Maras), theDept. of Physics of Università dell’Aquila (U. Buontem-

po). After a series of successful tests on the vacuumchambers (Fig. 1), presently the beamline SINBAD isbeing assembled in the DAΦNE hall (Fig. 2) .Nowadays there are fifteen IRSR beamlines in theworld (see Fig. 3), if one includes SINBAD and theothers under construction. Most of them have been in-stalled in the USA (up to six at Brookhaven, in addi-tion to those of Berkeley and Stoughton), in a context of

growing interest of industrial users for infrared micro-scopy. In Europe, as already mentioned, the develop-ment of IRSR has proceeded at a slower rate, in spite ofthe pioneering experiments made in France, Britain andGermany in the Seventies. In order to fill the gap withUSA and Japan in this field, in 1995 the EuropeanUnion has funded a network that has been coordinatedby the Department of Physics of University La Sapien-za. The network was aimed at providing a forum forthe European groups involved in the realization andthe exploitation of IRSR sources. It has greatly helpedto realize the beamline of Frascati and to better exploitthose of Orsay and Daresbury. Moreover, the networkhas organized the first international meetings in thisfield (University of Rome III, 1995; LNF-INFN Frascati,1996, LURE-Orsay, 1997) and has published the firstbook entirely devoted to IRSR.[11]

Characteristics of synchrotron radiation in the infrared

• BrillianceThe gain in brilliance of infrared synchrotron radiationwith respect to a conventional source may attain two or-ders of magnitude or more. This quantity is calculatedin Fig. 4 for the radiation emitted by a bending magnetof DAΦNE as a function of the wavelength λ and fordifferent angles of acceptance. The angle of acceptanceis defined by the dimension of the port placed in frontof the magnet. In turn, this selects the arc of electrontrajectory which contributes to the emission. At longwavelengths the brilliance gain is of 103 or even more, aperformance which can be surpassed only by a monoch-

Fig. 2 The DAΦNE double-ring assembled in the experimental hall, end1997.

Fig. 3 Evoultion with time of the number of infrared beamlines in theworld. The extrapolation is made by considering the beamlines underconstruction.



romatic source like a free-electron laser. The reflectivityof the diamond window, the absorption from the resi-dual gas, and other effects which limit the optical tran-smittance of the beamline may reduce the gain on theblack body, once measured at the sample position.However one easily obtains for this latter, in the far in-frared, values which range from 10 to 100 for samplessmaller than ≈0.5x0.5 mm.

• DivergenceThe complicated behavior of the brilliance in Fig. 4 isdue to the combined effect of the port size and of the na-tural divergence θnat of the synchrotron radiation. In theinfrared domain this latter is much larger than in the UVor X region and depends on the photon wavelength λ th-rough:12

θnat = 1.66 (λ/ρ)1/3 (1)

where ρ is the radius of curvature of the electron trajec-tory. As it will be described below, the large divergencepredicted by Eq. (1) implies the use of focusing optics oflarge size for transfering the infrared beam to the detec-tion apparatus.

• StabilityAnother remarkable advantage of IRSR with respect tothermal sources, whose intensity varies at random, isthat the power delivered is intrinsically stable in time,and directly proportional to the current circulating inthe beam. After correcting for the slow variation of thislatter, that can be monitored in real time, IRSR providesthe spectroscopist with an absolute radiation source.This is of basic importance, for instance, in differentialspectroscopy. On the other hand, the IRSR spot at the sample mayfluctuate due to spatial instabilities of the electronbeam. These are amplified by the collecting optics and

may produce serious problems in several applications,as microspectroscopy. At the NSLS of Brookhaven, thisproblem has been solved by a feedback which automati-cally corrects the electron orbit by acting on the electro-magnetic fields along the ring. An economic solutionmay consist in transfering the infrared beam by a cylin-drical waveguide, instead of using complicated optics.The multiple reflections along the pipe should make theinfrared beam intrisically stable against small displace-ments of the source, while the transmittance of the wa-veguide is comparable with that of standard mirror-op-tics beamlines.13

• Pulsed structure and polarizationOther features of potential importance are the pulsedstructure of IRSR and its polarization. The former will befully exploited when fast detectors will be developed al-so for the far infrared. The typical cut-off frequency of aliquid-helium-cooled bolometer is presently 300 Hz,while the period of a radiation pulse sequence in single-bunch operation is shorter than 1 µs.The polarization properties of infrared synchrotron ra-diation are more promising for immediate applications.IRSR is linearly polarized in the plane of the electronorbit if collected on the plane itself, circularly polarizedclockwise or anticlockwise if observed above or belowthe plane. By placing a slit on the exit port one can then

Fig. 4 The calculated gain in brilliance of SINBAD with respect to anideal black body at 2000 K, in the infrared spectral region, for differentangles of acceptance.

Fig. 5 Extraction system of the infrared radiation from a bending magnetat the port U4IR at Brookhaven (from Ref. 19). A flat mirror at 45° de-flects the radiation on an aspherical mirror, often an ellipsoid, which fo-cuses the radiation on a diamond window (not shown in the Figure). He-re the selected angle is 90x90 mrad.




select the desired degree of polarization. In the case ofSINBAD, nearly 100% circularly polarized light can beobtained by a slit which selects 10% of the total fluxavailable.14 Some interesting applications have been al-ready explored successfully, like the extension to theinfrared of studies of circular dichroism in magneticmaterials.15

Sources and beamlinesThe most common sources of IRSR are bending magnets.Nonetheless one beamline, at Orsay, extracts radiationfrom a wiggler while two others, those in Stoughton andKarlsruhe, will exploit the strong emission from the ed-ge of a magnet, where the field rapidly drops. In the case of a bending magnet, the large intrinsic diver-gence of IRSR in the infrared and the considerable size ofthe source require large aspherical mirrors which maytransfer the radiation to the interferometer and focus thebeam on its entrance pupil. The standard extraction sy-stem of IRSR from the bending magnet of a storage ring isshown in Fig. 5. A flat mirror, placed in front of the portat 45° with respect to the electron orbit, deflects the radia-tion cone on a focusing mirror, often an ellipsoid. In thecase of the Figure, which refers to the port U4IR atBrookhaven, the angle of extraction is 90x90 mrad. If thebeam energy E is high, much power W from “hard” ra-diation will also hit the extraction mirror, which has thento be water-cooled. Sometimes the first mirror has even tobe partially shielded by an absorber as in Daresbury,where the beam energy is 2 GeV. The second mirror, typically an ellipsoid, focuses the ra-diation on a diamond window (DW). This isolates theultra-high-vacuum section of the beamline, directlyopen on the ring, from the remaining part. The latter iskept under a high or low vacuum (depending on itslength) for reducing the infrared absorption from air(both water vapour and carbon dioxide are strong IRabsorbers due to their permanent dipole moments). Inspite of its high cost, diamond is chosen for its excellenthardness and chemical stability, and for its “flat” tran-smittance in the whole infrared domain (except for anabsorption band at ≈5µm). Moreover, diamond can bebrazed on conflat flanges. The first beamlines were equipped with natural dia-monds, 2 cm2 or more in size and ≈0.2 mm thick. Cut-ting such windows could take several months. In a fewcases, the window was placed at a Brewster angle withrespect to the incident radiation, in order to use the pola-rization of this latter for reducing the interference effectsdue to multiple reflections. At SINBAD, a more efficientsolution at a lower cost has been obtained with a CVDdiamond film, with a wedging angle of ≈1°, realized un-der a collaboration with De Beers Industrial DiamondDivision of England.16

At SINBAD the second focus is located at the entrancepupil of the Michelson interferometer, the same detec-

tion device that one uses with conventional sources.Even if the radiation source is a 2m-long bending ma-gnet, at SINBAD its image on the pupil (Fig. 6) has a si-ze of a few mm2 even at the longest wavelengths. The

Fig.6 Intensity distribution at the last focus of SINBAD, placed at the en-trance of the interferometer, as obtained by ray-tracing simulation. Onemay remark the small size of the image of the bending-magnet source.

Fig. 8 Spatial distribution of the intensity emitted at λ = 100 µm by (a) theedge of the bending magnet A2 of the ring SuperAco at Orsay, (b) thewiggler SU3 of the same ring with K = 5.38 (from Ref. 17).


whole optical layout of SINBAD, one of the longestbeamlines due to the constraints of the DAΦNE hall, isshown in Fig. 7.As already mentioned, bending magnets are not the onlysources of infrared radiation. Fig. 8 shows the spatial di-stribution of the radiation emitted at 100 µm by two un-conventional sources: the edge of a magnet (top), wherethe field experiences rapidly drops to zero, and a wig-gler or an undulator (bottom). Unlike for a uniform di-pole (see Fig. 6), a characteristic minimum appears at thecenter of the emission pattern in both figures, due tocoherence effects. One may also notice that most radia-tion provided by the wiggler is concentrated within asmall angle.Both the edge effect and the wiggler emission contributeto the radiation collected by the SIRLOIN beamline ofLURE, at Orsay.7 Its peculiar extraction system has in-deed provided first evidence for the infrared emissionfrom the edge of a bending magnet.17 For λ>>d/γ2, whe-re d is the length required to deflect an electron throughan angle of order 1/γ, the edge radiation may be evenbrighter than that emitted from the uniform magneticfield region.18 Similar effects are found at both edges ofan undulator.19 A beamline projected by R.A. Bosch andcoworkers to exploit the edge effect is starting its opera-

ting life at the Aladdin storage ring of Stoughton (USA).A similar one is being built by Y-L. Mathis at ANKA inKarlsruhe (Germany). The edge effect is instead expec-ted to be negligible at SINBAD.

Spectroscopy with infrared synchrotron radiationThe unique features of IRSR allow the spectroscopist tocollect higher quality data in a number of experimentsusually performed with conventional sources. In a fewcases, IRSR has opened to routinely infrared spectro-scopy new fields of application, where too severe expe-rimental conditions prevented the use of black bodysources.

• Physics and chemistry of surfacesOne of the earliest applications of IRSR has been thestudy of molecular adsorbates on metallic surfaces. Theobservation of their vibrational lines and of the shiftswith respect to those of isolated molecule providesinformation on the molecule-surface interaction, on theeventual ordering of the adsorbate, on the amount ofstress on molecular bonds. Such results are also of greatinterest for applied research, for instance in electroche-mistry. As one is interested to monitor the intramole-cular vibrations of molecules which are generally ali-

Fig. 7 Optical layout of SINBAD, the infrared beamline at LaboratoriNazionali INFN di Frascati.


gned orthogonally to the surface, the electric field ofthe infrared radiation should also be perpendicular tothe surface. This implies that the angle of incidenceshould be as large as possible. Performing such experi-ments at grazing incidence with a conventional source,when moreover the adsorbate is a monolayer, is a veryhard task. By use of IRSR one has: i) the high brilliancenecessary to get a small and intense spot on the sampleeven at grazing angles; ii) the high stability needed toperform differential spectroscopy. One may thus obtainexcellent signal-to-noise levels even in such severe con-ditions, as shown in Figure 9 for the far infrared ab-sorption from a half-monolayer of CO adsorbed oncopper.

• High-pressure studies in diamond anvil cellsInfrared spectroscopy by use of the synchrotron sourceis presently considered as a powerful tool for investiga-ting the properties of matter at high pressure. The highbrilliance of IRSR is needed for obtaining appreciable re-sults in diamond anvil cells, where the size of the win-dows is a few tenths of mm or smaller. The gain in sensi-tivity with respect to conventional sources may reach th-ree orders of magnitude when using a Fourier transforminterferometer, five orders when using a grating mono-chromator.20 Pioneering measurements by Nanba where

made at Okasaki (Japan) in the Eighties, at pressures onthe order of 10 Gpa. Nowadays, infrared spectra at pres-sures even higher than 200 GPa are collected at Brookha-ven by use of infrared microscopes.21 Among the basicresults obtained by this technique one may cite the de-termination of the phase diagram of solid hydrogen upto 200 Gpa, by Hemley and collaborators. Spectra likethat of Figure 10 (where the sample is solid deuterium)have excluded any metallization of hydrogen up to tho-se pressures, imposing entirely new theoretical modelsfor this system.

• MicrospectroscopyThe gain in brilliance of IRSR with respect to black bo-dies is also remarkable at shorter wavelengths, wherean infrared microscope can work without experiencingmajor diffraction problems. The use of infrared micro-scopes coupled to synchrotron radiation sources hasstarted recently, but has rapidly met with outstandingsuccess. Figure 11 shows a spectrum taken on the innerpart of the cross-section of a polymer laminate, com-monly used as packaging material. The sheet comes outfrom the industrial process in form of a sandwich, wherethe recipe of the 10 µm-thick filling is unknown. Thespectrum of such a thin inner layer, if taken by a micro-scope using a conventional source (Fig. 10a) does nothelp to solve the problem due to its poor contrast. TheIRSR spectrum obtained by the group of M. Chesters atDaresbury (Fig. 10b) shows instead the “fingerprints” ofthe filling, which identify it as an ethylene/vinyl acetatecopolymer.22


Fig. 10 Evidence that solid deuterium persists in its insulating phase upto 170 Gpa, provided by the absorption of infrared synchrotron radiationthrough a diamond anvil cell at Brookhaven (from. Ref. 21). The solid li-ne is the observed absorption spectrum. The dashed lines are the Drudeprofiles expected for a metallic sample, for different possible values ofthe plasma frequency.

Fig. 9 The change in reflectance of a Cu(100) single-crystal surface indu-ced by the adsorption of 0.5 monolayers of CO, as measured at the U4IRbeamline of Brookhaven at grazing incidence and shown for two diffe-rent resolutions (from Ref. 20) . The negative peak (with respect to thebroad reflectivity background) monitors the carbon-metal vibrationalmode, the positive peak corresponds to the hindered rotational mode.




An example taken from geophysical research is insteadpresented in Fig. 12. The visible-light objective of the mi-croscope has selected in a rock sample an area whichcontains a small fluid inclusion. After switching the mi-croscope to the infrared, one may collect the spectrum ofthe inclusion. The spectrum displays the fingerprint ofan oil thus providing detailed information on its compo-sition and quality. The possibility of exploiting that rockas an oil source can then be evaluated on a sound basis. Another application of infrared microspectroscopy bysynchrotron radiation to geophysical research is the

study of meteoritic fragments recently performed undera collaboration between University La Sapienza and theSERC of Daresbury. These samples, collected by the Ita-lian expedition to the Antarctic, are strongly inhomoge-neous. They show insulating zones made of different si-licates, a few tens of microns in size, embedded into ametallic matrix. By use of the IRSR microscope of Dare-sbury, detailed spectra of those silicates have been col-lected, and characteristic lineshifts with respect to the la-boratory spectra of the same substances have been recor-ded. These data will provide exhaustive information onthe composition of the meteorite and on the conditionsunder which it was formed.23

AcknowledgmentsI wish to thank Alessandro Nucara and Augusto Marcel-li for useful suggestions and for providing part of the il-lustrations.

References1. J.R. Stevenson, H. Ellis, and R. Bartlett, Appl. Optics 12, 2884 (1973).2. P. Meyer and P. Lagarde, J. Phys. (Paris) 37, 1387 (1976).3. J. Yarwood, T. Shuttleworth, J.B. Hasted, and T. Nanba, Nature 317,

743 (1984).

Fig. 12 Infrared microspectroscopy of a tiny oil inclusion in a rock (from Ref. 23). The spectrum at the center displays the “fingerprint” of the oil. The spatial distributions of different chemical species, together with the visible image of the inclusion (top left), are also shown.

Fig. 11 Infrared microspectrum of the central section (10 µm thick) of apolyethilene sheet with a conventional source (a) and with the Dare-sbury synchrotron source (b) (from Ref. 22).


4. T. Nanba, Rev. Sci. Instrum. 60, 1680 (1989).5. G.P. Williams, Nucl. Instr. & Meth. A291, 8 (1990).6. B. Nelander, Vibr. Spectrosc. 9, 29 (1990).7. P. Roy, Y.L. Mathis, A. Gerschel, J.P. Marx, J. Michaut, B. Lagarde,

and P. Calvani, Nucl. Instrum. & Meth. A325, 568 (1993).8. D.A. Slater, P. Hollins, M.A. Chesters, J. Pritchard, D.H. Martin, M.

Surman, D.A. Shaw and I. Munro, Rev. Sci. Instrum. 63, 1547 (1992).9. A. Marcelli and P. Calvani, LNF-INFN report 93/027 (1993).10. A. Nucara, P. Calvani, A. Marcelli, and M. Sanchez del Rio, Rev. Sci.

Instrum. 66, 1934 (1995).11. Infrared Synchrotron Radiation, Ed. by P. Calvani and P. Roy, Ed. Com-

positori, Bologna, 1998.12. W.D. Duncan and G.P. Williams, Appl. Optics 22, 2914 (1983).13. A. Nucara, P. Dore, P. Calvani, D. Cannavò, and A. Marcelli, ibid.,

527 (1998).14. A. Marcelli, E. Burattini, A. Nucara, P. Calvani, G. Cinque, C. Men-

cuccini, S. Lupi, F. Monti, and M. Sanchez del Rio, ibid., 463 (1998).15. S. Kimura, UVSOR Activity Report 1997, BL6A1.16. P. Dore, A. Nucara, D. Cannavò, G. De Marzi, P. Calvani, A. Marcelli,

R. Sussmann, A.J. Whitehead, C.N. Dodge, A.J. Krehan, and H.H. Pe-ters, Applied Optics 37, 5731 (1998).

17. Y-L. Mathis, P. Roy, B. Tremblay, A. Nucara, S. Lupi, P. Calvani, andA. Gerschel, Phys. Rev. Lett 80, 1220 (1998).

18. R.A. Bosch, Nucl. Instr. & Meth. A386, 525 (1997); Nuovo Cimento D20, 483 (1998).

19. M. Castellano, Nucl. Instr. & Meth. A391, 375 (1997)20. L. Carr, P. Dumas, C.J. Hirschmugl, and G.P. Williams, Nuovo Ci-

mento D, 20, 375 (1998).21. R.J. Hemley, H.K. Mao, A.F. Goncharov, M. Hamfland, and V.V.

Struzhkin, Phys. Rev. Lett. 76, 1667 (1996).22. M.A. Chesters, E.C. Hargreaves, M. Earson, P. Hollins, D.A. Slater,

J.M. Chammers, B. Ruzicka, M. Surman, and M.J. Tobin, Nuovo Ci-mento D, 20, 439 (1998).

23. N. Guilhaumou, P. Dumas, G.L.Carr and G.P.Williams, AppliedSpectroscopy 52, 1029 (1998).

24. A. Maras, S. Lupi, P. Calvani, B. Ruzicka, M. Tobin, and M. Chesters,to be published.



SCUOLE E CONVEGNI

VI CONVEGNO NAZIONALE DELLA SILS

Il Sesto Convegno Nazionale della SILS, tenuto nella ma-gnifica sede del Palazzo Bo dell’Università di Padova ingiugno, è stato organizzato in quattro sessioni orali eduna sessione poster aperta per tutta la durata del conve-gno. Le sessioni orali sono state aperte o chiuse da sei re-latori invitati (Nordgreen, Itié, Wulff, Goulon, Sauvage eFadley). La conferenza d’apertura nel primo pomeriggio di gio-vedì 18 giugno è stata tenuta da J. Nordgren, che ha mo-strato le notevoli applicazioni della spettroscopia riso-nante di fluorescenza a raggi X molli, grazie alle nuovesorgenti di luce di sincrotrone ad alta brillanza. In parti-colare si è soffermato su alcuni esempi di studio dellastruttura elettronica di interfacce sepolte e di sistemi conadsorbati (sfruttando la selettività chimica e di simme-tria), di superconduttori ad alta temperatura critica, edell’influenza dell’intrappolamento di idrogeno nei me-talli, nonché dello studio di sistemi altamente correlatiquali i materiali magnetici. Il secondo oratore del pome-riggio, A. Martorana, ha presentato studi di caratterizza-zione strutturale di catalizzatori eterogeni supportati supomice, con tecniche EXAFS (eseguita presso la beamli-ne GILDA ad ESRF), ed XPS e XAS (eseguite in laborato-rio): con opportune tecniche di sottrazione del segnale sisono determinate le fasi strutturali dei metalli supporta-ti, sono state inoltre messe in luce le prospettive di corre-lazione fra i difetti di impilamento (stacking faults) e laattività catalitica, ottenibili con tecniche di diffusioneanomala. F. D’Acapito ha mostrato interessanti studi suagglomerati di Xe ad alta pressione impiantati in cristallidi silicio, studiandone la dinamica di crescita che mostrauna lunghezza di correlazione Xe-Xe consistente con loXe liquido, e studi di interfacce sepolte di metalli nobiliin SiO2; le tecniche utilizzate sono la diffrazione radentedi raggi X (eseguita sulla beamline ID9 di ESRF) e la fo-toemissione (presso SRRC di Taiwan). G. Piazzesi hapresentato i più recenti studi condotti su singole fibremuscolari, analizzando la diffrazione di raggi X da mole-cole di miosina (esperimenti condotti presso la beamlineID2 di ESRF); l’analisi delle strutture regolari nelle diver-se fasi di attivazione muscolare permette di approfondi-re le conoscenze in questo campo. G. Wulff ha chiuso laprima sessione orale, presentando un interessantissimostudio dell’evoluzione temporale delle molecole di mio-globina (Mb), seguendo la dissociazione del CO dal Fe

nella MbCO, utilizzando impulsi laser da 100 fs per pro-vocare la dissociazione e "fotografie" di diffrazione Xogni 3 ns, grazie alla struttura temporale del fascio diESRF. La possibilità di studiare la dinamica di azionedelle proteine apre scenari impressionanti per l’uso ditecniche di luce di sincrotrone nella biologia. La mattina di venerdì 19 giugno si apre con l’interventodi J.P. Itié, che ha presentato una panoramica sullo stu-dio strutturale di materiali sotto condizioni estreme dipressione e di temperatura, studi condotti a Grenoble,con l’uso di celle appropriate che possono raggiungere i300 GPa, pressione vicina a quella presente nel nucleoterrestre (~365 GPa); ha quindi mostrato transizioni difase di semiconduttori, di metalli e trasformazioni di fa-se magnetiche in leghe PtFe ad alte pressioni. Il secondointervento, di L. Alagna, è stato incentrato sullo studiodi strutture ordinate eteroepitassiali di InGaP/GaAs contecniche di struttura fine da diffrazione anomala, mo-strando l’influenza positiva del leggero disorientamentorispetto alle direzioni di massima simmetria per ottenerelarghi domini regolari. A. Pavese ha presentato le tecni-che di cristallografia ad altissime pressioni ed alta tem-peratura, riprendendo i temi trattati da Itié, a pressionivicine a quelle presenti nel nucleo terrestre; ha mostratoquindi alcuni risultati su fasi tipo-mica, interpretati conl’ausilio di tecniche computazionali. F. Rocca ha parlatodell’influenza dell’ordine locale nel processo di emissio-ne di luce del Si poroso, con la formazione della porositàstrettamente legata al processo elettrochimico di prepa-razione; gli studi sono stati condotti con tecniche di lu-minescenza ottica di emissione di raggi X (XEOL) edEXAFS. P. Ghigna ha presentato studi strutturali EXAFSsu campioni di Zr1-xFexZrO2, con la messa in evidenzadi legami diretti Fe-Zr, quando i campioni sono prepara-ti per sintesi di combustione. Dopo la pausa per il caffè J.Goulon ha presentato le nuove prospettive aperte adESRF per le tecniche di dicroismo di raggi X circolaremagnetico e naturale, applicato ai solidi; il dicroismo na-turale si osserva in cristalli uni- o biassiali ed in solutichirali in cristalli liquidi allineati. L’uso di nuovi ondula-tori (come Helios II) con variazione di gap e fase, per-mette di cambiare polarizzazione, conseguendo l’oppor-tunità di eseguire studi di EXAFS con polarizzazione dispin. L. Gregoratti ha presentato applicazioni avanzatedella tecnica di spettromicroscopia eseguite ad ELET-TRA, con lo studio della composizione chimica e distri-buzione spaziale laterale di strati bidimensionali (2D) e

SCUOLE E CONVEGNI


3D di fasi NiSi cresciute su Si; questa rivisitazione dei si-licuri di Ni ha mostrato come la microcaratterizzazionechimica di queste interfacce sia necessaria data la naturamorfologica complessa con coesistenza di diverse fasi. V.Carravetta, con l’uso di fotoemissione risonante con rag-gi X ad alta risoluzione (RPE), ha studiato la dipendenzaenergetica della forma di riga spettrale del CO vicinoall’eccitazione C 1s-pi*; gli esperimenti sono stati inter-pretati con l’ausilio di simulazioni numeriche e modellidi riga Fano.L’intervento successivo di A. Bravin ha riguardato la ra-diografia con luce di sincrotrone presso la linea SYRMEPdi ELETTRA, in particolare sfruttando la visualizzazionecon diffrazione e contrasto di fase, grazie alla alta coe-renza spaziale della sorgente; sono stati presentati gliaspetti tecnici ed alcuni esempi di mammografia su cam-pioni modello, discutendo le prospettive positive di talitecniche in diagnostica medica a confronto con la radio-grafia convenzionale. Il primo intervento di sabato 20 giugno è di M. Sauvage,incentrato sulla presentazione di vari esempi di allonta-namento dalle strutture a periodicità 2D ideale presentisu superfici ed interfacce di materiali cristallini. Gli espe-rimenti sono stati condotti al LURE con diffrazione diraggi X ad incidenza radente, in apparati con sistemi dicrescita epitassiale in situ; in particolare Sauvage ha pre-sentato diversi esempi su composti III-V, Si e Bi/Si, conidentificazione di domini 2D e con la identificazione diconfini in antifase fra i domini. E seguito l’intervento diS. Turchini, che ha presentato studi di dicroismo X circo-lare naturale su cristalli complessi composti con Nd, ese-guiti presso ESRF. L’effetto di asimmetria fra radiazionepolarizzata destrogira o levogira è debole in questi siste-mi naturali, ma osservabile grazie all’alta brillanza dellasorgente; i risultati sperimentali sono confrontati con cal-coli di teoria a diffusione multipla. V. Corradini ha pre-sentato uno studio di diverse fasi 2D ordinate di Bi cre-sciuto su Si(100); grazie all’alta risoluzione energeticadella linea UV di ELETTRA, l’analisi dei livelli profondidi Bi e Si è stata correlata ai siti di adsorbimento, e quin-di alla struttura 2D ordinata, nelle diverse fasi di forma-zione dell’interfaccia.La conferenza di chiusura è stata di C.S. Fadley, che hamostrato i nuovi sviluppi nella fotoemissione risonante erisolta temporalmente, possibili presso le sorgenti di ter-za generazione. Ha presentato alcuni esperimenti ese-guiti ad ALS, fra i quali lo studio degli ossidi metallici(quali MnO), evidenziando il grande effetto di risonanzain funzione dell’energia dei fotoni, dovuti ad un effettointeratomico; un altro esempio legato alla velocità di rac-colta dei dati è stato lo studio dell’ossidazione delW(110), con la possibilità di seguire temporalmente lareazione chimica. Nel tardo pomeriggio della seconda giornata si è svoltal’Assemblea annuale dei soci. In chiusura del convegnosono stati premiati i migliori poster, fra i circa 40 esposti,

presentati dai seguenti giovani: Chiara Maurizio, Ma-nuel a Panzalorto, Mauro Sambi e Massimo Tormen. (C. Mariani)

CONFERENZA XAFS-X

Nei giorni 10 - 14 agosto 1998 si è svolta la decima edi-zione della conferenza XAFS presso l’Illinois Institute ofTechnology, Chicago. Chicago è stata selezionata comesede del congresso per la vicinanza della Advanced Pho-ton Source, in linea con la scelta di svolgere le conferen-ze XAFS di questi anni presso le nuove sorgenti di terzagenerazione. La conferenza ha previsto sessioni plenarie, contributiorali e varie sessioni poster; sono stati esposti risultati re-centi nei molteplici campi di applicazione dello XAFS edelle tecniche simili e sono stati illustrati nuovi metodisperimentali, con particolare enfasi nei riguardi di quelliresi possibili dalle nuove sorgenti. Nella impossibilità didescrivere tutti gli interventi riporterò una una sceltapersonale dei risultati di maggior rilievo. Durante il primo giorno J. Goulon (ESRF) ha descritto laprima osservazione chiara del dicroismo naturale neiraggi X. Egli ha dimostrato, con l’ausilio di calcoli di dif-fusione multipla, che questo effetto è dovuto alla interfe-renza tra termine di dipolo e di quadrupolo elettrico eche esso è sensibile al grado di mescolamento di stati fi-nali di parità opposta; è prevedibile che questo impor-tante risultato apra la strada ad una nuova tecnica di in-dagine a carattere generale. Il giorno seguente A. Manceau (CNRS, Grenoble) ha illu-strato in modo particolarmente efficace come lo XAFSpossa fornire delle informazioni uniche sulla speciazionedi metalli in ambito geologico/ambientale; molti deiproblemi descritti hanno delle implicazioni importantinell’ambito dell’inquinamento e della politica del territo-rio. Questa relazione ha mostrato come si stia colmandola distanza tra studio di sistemi modello e sistemi reali;ulteriori importanti avanzamenti in questo campo sipossono ottenere con l’applicazione delle tecniche diXAFS risolto spazialmente, come illustrato da P. Bertsch(Georgia). A. DiCicco (Camerino) ha fatto una rassegnadello studio della struttura locale in solidi e liquidi conl’ausilio di codici di calcolo utilizzanti la diffusione mul-tipla (GNXAS). La mattinata del martedi si è conclusacon la relazione di H. Renevier (CNRS, Grenoble), laquale ha illustrato i principi base ed alcuni risultati re-centi ottenuti con la tecnica DAFS. Il mercoledì K. Baberscke (Berlin) ha effettuato una am-pia rassegna degli studi sul magnetismo con l’assorbi-mento di raggi X. Egli ha posto l’accento sulla possibilitàdi determinare la temperatura di Curie con sensibilitàatomica (per esempio nei multilayer), sulle applicazionidell’EXAFS magnetico e su varie tecniche complementa-ri quali il dicroismo in microscopia e lo scattering diffu-

SCUOLE E CONVEGNI


SCUOLE E CONVEGNI

so magnetico. I lavori del giovedì sono stati aperti dauna relazione a carattere storico di uno dei fondatoridell’era moderna dello XAFS, F. Lytle. Egli ha fornitouna appassionata ricostruzione dello sviluppo dellaspettroscopia di assorbimento di raggi X dal 1913 fino aiprimi anni settanta. Tra l’altro ha ricordato un importan-te finanziamento al suo gruppo da parte della Montedi-son nel periodo in cui vi era un forte interesse di taleazienda italiana allo sviluppo dello XAFS. Durante l’ultimo giorno dei lavori S. Pascarelli (ESRF) haillustrato le possibilità offerte dalla tecnica di acquisizio-ne dispersiva presso una sorgente di terza generazione,riportando esempi di studi nel campo del dicroismo ma-gnetico (utilizzando una lamina a quarto d’onda) e nelcampo dello studio delle cinetiche (XAFS risolto in tem-po). La conferenza si è conclusa con una visita alla Ad-vanced Photon Source. (F. Boscherini)

IV SCUOLA DI SPETTROSCOPIA NEUTRONICA«DIFFUSIONE DEI NEUTRONI DALLA MATERIA DURA»

Hotel Capo d’Orso, Palau (Sassari)26 settembre - 4 ottobre 1998Direttori: M. Catti (Milano) e F. Sacchetti (Perugia)Segreteria: G. Ianni (GNSM, Roma)

La Scuola si è tenuta con notevole successo, a due annidi distanza dalla III edizione, nuovamente all’Hotel Ca-po d’Orso di Cala Capra (Palau). La sede si è confermatacome ben attrezzata logisticamente e particolarmentegradevole, per cui si spera possa essere adottata ancheper la prossima Scuola. Vi sono stati 22 partecipanti, gio-vani laureati di formazione prevalentemente fisica o chi-mica di cui molti già con esperienza di attività di ricercalegata alla spettroscopia neutronica. Gli argomenti dellelezioni hanno toccato sia i fondamenti metodologici del-la spettroscopia neutronica, nei sui aspetti tanto teoriciquanto sperimentali, sia un buon numero di applicazionia problematiche scientifiche specifiche. Queste sono stateincentrate sulla cosiddetta “materia dura”, per alternan-za con i contenuti della passata edizione che era statadedicata principalmente ai materiali d’interesse biologi-co. Possiamo quindi riassumere le tematiche trattate co-me segue: generalità sullo scattering dei neutroni; sor-genti e strumentazione; diffrazione; diffusione anelasticae quasi-elastica; tecniche a basso angolo; applicazioni a:materiali superconduttori ad alta Tc, metalli e leghe,conduttori ionici, catalizzatori, materiali polimerici, mi-nerali. I docenti che hanno collaborato sono: A. Albinati(Milano), C. Andreani (Roma), V. Arrighi (Edimburgh),G. Artioli (Milano), E. Caponetti (Palermo), F. Carsughi(Ancona), C.J. Carlile (ISIS, Oxford), M. Catti (Milano),B. Dorner (ILL, Grenoble), J. Eckert (Los Alamos, USA),S. Enzo (Sassari), M. Marezio (Parma), S.V. Meille (Mila-

no), R. Rinaldi (Perugia), F. Sacchetti (Perugia). L’obietti-vo della Scuola era presentare una panoramica dellaneutronica per lo studio della materia condensata, e for-nire le metodologie per un corretto uso delle tecnichesperimentali relative, portando gli studenti ad un ade-guato livello di conoscenza per l’effettuazione di esperi-menti di base, dalla progettazione dell’esperimento allaelaborazione dei dati. Uno spazio adeguato è stato riser-vato all’illustrazione di numerosi esempi di applicazionialle tematiche di fisico-chimica dei materiali e di scienzedella terra, nella convinzione che il carattere interdisci-plinare della scuola sia di grande giovamento alla for-mazione scientifica e all’apertura culturale dei giovaniricercatori. Le conoscenze acquisite consentiranno loro,inoltre, di utilizzare le potenzialita delle sorgenti neutro-niche presso centri di ricerca europei a carattere multina-zionale, in cui l’Italia ha tra l’altro investito in tempi re-centi risorse non indifferenti.Un aspetto importante dell’organizzazione didattica, chesi è cercato di curare in modo particolare in questa edi-zione della Scuola è stato l’impegno richiesto agli stu-denti di partecipare in modo attivo 1) ad esercitazioni alcalcolatore per l’elaborazione di dati sperimentali, e 2)ad una esercitazione di “progettazione” di un esperi-mento per la risoluzione di un problema specifico asse-gnato. Gli studenti hanno quindi tenuto seminari per il-lustrare i risultati del loro lavoro, impegnandosi con en-tusiasmo in un lavoro intensivo e certamente non facile.Si può valutare in modo estremamente positivo la rispo-sta ottenuta, in termini sia di interesse dimostrato sia diprofitto conseguito nell’apprendimento.Si ringraziano il CNR e l’INFM per il sostegno finanzia-rio che ha reso possibile la realizzazione della Scuola.(M. Catti)


11-13 febbraio 1999 GRENOBLE, FRANCEESRF Users’ Meeting http://www.esrf.fr

21 febbraio-1 aprile 1999 GRENOBLE, FRANCIAHERCULES, Higher European Research Course forUsers of Large Experimental Systemshttp://www.polycnrs-gre.fr/hercules

5-9 aprile 1999 SAN FRANCISCO, USAMaterials Research Society Spring http://www.mrs.orgr

17-20 maggio 1999 UPTON, NY, USASAS-99: XIth Internat. Conf. on Small-AngleScatteringAnn Emrick, Biology 463, Brookhaven Nationallaboratory, Upton, NY 11973Tel: +1 516 344 5756; Fax: +1 516 344 6398E-mail: [email protected]://sas99.bnl.gov/sas99

22-27 maggio 1999 BUFFALO, NY, USAACA '99E-mail: [email protected]://www.hwi.buffalo.edu/ACA

14-18 giugno 1999 CATANIA, ITALYINFMeetinghttp://www.infm.it

3-7 luglio 1999 GRANADA, SPAINIV Liquid Matter ConferenceProf. Dr. Roque Hidalgo Elvarez, Depart. de FisicaAplicada, Facultad de Ciencias, Universidad deGranada, Campus de Fuentenueva, E-18071 Granada(Spagna)Tel: +34 958 243213; Fax: +34 958 243214 E- mail: [email protected]://www.ugr.es/~liquid99

4-13 agosto 1999 GLASGOW, SCOTLAND18th IUCr Gen. Assembly and InternationalCongress of Crystallographyhttp://www.chem.gla.ac.uk/iucr99

23-27 agosto 1999 CHICAGO, USAX-99 18th International conference on X-ray andinner shell processeshttp://www.phy.anl.gov/X99

1-4 settembre 1999 BUDAPEST, HUNGARYSecond European Conference on Neutron Scattering(ECNS’99)Dr. Tamos Grûsz, Neutron Physics LaboratoryResearch Institute for Solid State Physics and Optics,H-1525 Budapest, P.O.B. 49, KFKI, Bldg.10, HungaryTel: +36 1 395 9220/1738; Fax: +36 1 395 9165E-mail: [email protected]://www.kfki.hu/ECNS99/

5-7 settembre 1999 SCHWAEBISCH GMUND, GERMANIAInternational Conference on Solid StateSpectroscopyhttp://cardix.mpi-stuttgart.mpg.de/icss/

20-24 settembre 1999 STUTTGART, GERMANIA7th International Conference on QuasicrystalsICQ7'99, Institut für Theoretisch und AngewandtePhysik, Universitat StuttgartTel: +49 711 685 5253/5254; Fax: +49 711 685 [email protected]

21-24 settembre 1999 VIENNA, AUSTRIAECOSS-18, 18th European Conference on SurfaceScienceInstitut für Allgemeine Physik, U Wien, WiednerHauptstr. 8-10/134E-mail: [email protected]

29 settembre-2 ottobre 1999 DUBNA, RUSSIA2nd International Seminar on Neutron Scattering atHigh Pressure (NSHP-II)D.P. Kozlenko, Frank Laboratory of Neutron Physics,Joint Institute for Nuclear Research, 141980 Dubna,Moscow Reg., RussiaTel: +7 09621 65644; Fax: +7 09621 65882E-mail: [email protected]://nfdfn.jinr.ru/~denk/NSHPII/

CALENDARIO

CALENDARIO


SCADENZE

SCADENZE PER RICHIESTE DI TEMPO MACCHINA PRESSO ALCUNI LABORATORI DI NEUTRONI

ISIS La scadenza per il prossimo ‘call for proposals’ è il 16 aprile e 16 ottobre 1999

ILL La scadenza per il prossimo ‘call for proposals’ è il 1 marzo 1999

LLB-SACLAY La scadenza per il prossimo ‘call for proposals’ è il 1 ottobre 1999

BENSC La scadenza è il 15 marzo e 15 settembre 1999

RISØ E NFL La scadenza per il prossimo ‘call for proposals’ è il 1 aprile 1999

SCADENZE PER RICHIESTE DI TEMPO MACCHINA PRESSO ALCUNI LABORATORI DI LUCE DI SINCROTRONE

ALS Le prossime scadenze sono il 1 giugno e il 1 dicembre 1999

BESSY Le prossime scadenze sono il 15 febbraio 1999 e il 15 agosto 1999

DARESBURY La prossima scadenza è il 24 novembre 1999

ELETTRA Le prossime scadenze sono il 28 febbraio 1999 e il 31 agosto 1999

ESRF Le prossime scadenze sono il 1 marzo 1999 e il 1 settembre 1999

GILDA (quota italiana) Le prossime scadenze sono il 1 maggio e il 1 novembre 1999

HASYLAB (Nuovi progetti) Le prossime scadenze sono: 1 marzo, 1 settembre e 1 dicembre 1999

LURE La prossima scadenza è il 30 ottobre 1999

MAX-LAB La scadenza è approssimativamente febbraio 1999

NSLS Le prossime scadenze sono il 31 gennaio, 31 maggio e 30 settembre 1999

SCADENZE


FACILITIES

ALS Advanced Light SourceMS46-161, 1 Cyclotron Rd Berkeley, CA 94720, USAtel:+1 510 486 4257 fax:+1 510 486 4873http://www-als.lbl.gov/Tipo: D Status: O

AmPS Amsterdam Pulse StretcherNIKEF-K, P.O. Box 41882, 1009 DB Amsterdam, NLtel: +31 20 5925000 fax: +31 20 5922165Tipo: P Status: C

APS Advanced Photon SourceBldg 360, Argonne Nat. Lab. 9700 S. Cass Avenue,Argonne, Il 60439, USAtel:+1 708 252 5089 fax: +1 708 252 3222http://epics.aps.anl.gov/welcome.htmlTipo: D Status: C

ASTRIDISA, Univ. of Aarhus, Ny Munkegade, DK-8000 Aarhus,Denmark tel: +45 61 28899 fax: +45 61 20740Tipo: PD Status: O

BESSY Berliner Elektronen-speicherring Gessell.fürSynchrotron-strahlung mbHLentzealle 100, D-1000 Berlin 33, Germanytel: +49 30 820040 fax: +49 30 82004103http://www.bessy.deTipo: D Status: O

BSRL Beijing Synchrotron Radiation Lab.Inst. of High Energy Physics, 19 Yucuan Rd.PO Box 918,Beijing 100039, PR Chinatel: +86 1 8213344 fax: +86 1 8213374http://solar.rtd.utk.edu/~china/ins/IHEP/bsrf/bsrf.htmlTipo: PD Status: O

CAMD Center Advanced Microstructures & DevicesLousiana State Univ., 3990 W Lakeshore, Baton Rouge,LA 70803, USAtel:+1 504 3888887 fax: +1 504 3888887http://www.camd/lsu.edu/Tipo: D Status: O

CHESS Cornell High Energy Synchr. Radiation SourceWilson Lab., Cornell University Ithaca, NY 14853, USAtel: +1 607 255 7163 fax: +1 607 255 9001http://www.tn.cornell.edu/Tipo: PD Status: O

DAFNEINFN Laboratori Nazionali di Frascati, P.O. Box 13,I-00044 Frascati (Rome), Italytel: +39 6 9403 1 fax: +39 6 9403304http://www.lnf.infn.it/Tipo:P Status: C

DELTAUniversität Dortmund,Emil Figge Str 74b, 44221Dortmund, Germanytel: +49 231 7555383 fax: +49 231 7555398http://prian.physik.uni-dortmund.de/Tipo: P Status: C

ELETTRASincrotrone Trieste, Padriciano 99, 34012 Trieste, Italytel: +39 40 37581 fax: +39 40 226338http://www.elettra.trieste.itTipo: D Status: O

ELSA Electron Stretcher and AcceleratorNußalle 12, D-5300 Bonn-1, Germanytel:+49 288 732796 fax: +49 288 737869http://elsar1.physik.uni-bonn.de/elsahome.htmlTipo: PD Status: O

ESRF European Synchrotron Radiation Lab.BP 220, F-38043 Grenoble, Francetel: +33 476 882000 fax: +33 476 882020http://www.esrf.fr/Tipo: D Status: O

EUTERPECyclotron Lab.,Eindhoven Univ. of Technol, P.O.Box513, 5600 MB Eindhoven, The Netherlandstel: +31 40 474048 fax: +31 40 438060Tipo: PD Status: C

HASYLABNotkestrasse 85, D-2000, Hamburg 52, Germanytel: +49 40 89982304 fax: +49 40 89982787http://www.desy.de/pub/hasylab/hasylab.htmlTipo: D Status: O

INDUS Center for Advanced Technology, Rajendra Nagar,Indore 452012, Indiatel: +91 731 64626Tipo: D Status: C

LUCE DI SINCROTRONESYNCHROTRON SOURCES WWW SERVERS IN THE WORLD(http://www.esrf.fr/navigate/synchrotrons.html)


FACILITIES

KEK Photon FactoryNat. Lab. for High Energy Physics, 1-1, Oho,Tsukuba-shi Ibaraki-ken, 305 Japantel: +81 298 641171 fax: +81 298 642801http://www.kek.jp/Tipo: D Status: O

KurchatovKurchatov Inst. of Atomic Energy, SR Center, KurchatovSquare, Moscow 123182, Russiatel: +7 95 1964546Tipo: D Status:O/C

LNLS Laboratorio Nacional Luz SincrotronCP 6192, 13081 Campinas, SP Braziltel: +55 192 542624 fax: +55 192 360202Tipo: D Status: C

LUREBât 209-D, 91405 Orsay ,Francetel: +33 1 64468014; fax: +33 1 64464148E-mail: [email protected]://www.lure.u-psud.frTipo: D Status: O

MAX-LabBox 118, University of Lund, S-22100 Lund, Swedentel: +46 46 109697 fax: +46 46 104710http://www.maxlab.lu.se/Tipo: D Status: O

NSLS National Synchrotron Light SourceBldg. 725, Brookhaven Nat. Lab., Upton, NY 11973, USAtel: +1 516 282 2297 fax: +1 516 282 4745http://www.nsls.bnl.gov/Tipo: D Status: O

NSRL National Synchrotron Radiation Lab.USTC, Hefei, Anhui 230029, PR Chinatel:+86 551 3601989 fax:+86 551 5561078Tipo: D Status: O

PohangPohang Inst. for Science & Technol., P.O. Box 125Pohang, Korea 790600tel: +82 562 792696 f +82 562 794499Tipo: D Status: C

Siberian SR CenterLavrentyev Ave 11, 630090 Novosibirsk, Russiatel: +7 383 2 356031 fax: +7 383 2 352163Tipo: D Status: O

SPring-82-28-8 Hon-komagome, Bunkyo-ku ,Tokyo 113, Japantel: +81 03 9411140 fax: +81 03 9413169Tipo: D Status: C

SOR-RING Inst. Solid State PhysicsS.R. Lab, Univ. of Tokyo, 3-2-1 Midori-cho Tanashi-shi,Tokyo 188, Japantel: +81 424614131 ext 346 fax: +81 424615401Tipo: D Status: O

SRC Synchrotron Rad. CenterUniv.of Wisconsin at Madison, 3731 SchneiderDriveStoughton, WI 53589-3097 USAtel: +1 608 8737722 fax: +1 608 8737192http://www.src.wisc.eduTipo: D Status: O

SRRC SR Research Center1, R&D Road VI, Hsinchu Science, Industrial Parc,Hsinchu 30077 Taiwan, Republic of Chinatel: +886 35 780281 fax: +886 35 781881http://www.srrc.gov.tw/Tipo: D Status: O

SSRL Stanford SR LaboratoryMS 69, PO Box 4349 Stanford, CA 94309-0210, USAtel: +1 415 926 4000 fax: +1 415 926 4100http://www-ssrl.slac.stanford.edu/welcome.htmlTipo: D Status: O

SRS Daresbury SR SourceSERC, Daresbury Lab, Warrington WA4 4AD, U.K.tel: +44 925 603000 fax: +44 925 603174E-mail: [email protected]://www.dl.ac.uk/home.htmlTipo: D Status: O

SURFB119, NIST, Gaithersburg, MD 20859, USAtel: +1 301 9753726 fax: +1 301 8697628http://physics.nist.gov/MajResFac/surf/surf.htmlTipo: D Status: O

TERAS ElectroTechnical Lab.1-1-4 Umezono, Tsukuba Ibaraki 305, Japantel: 81 298 54 5541 fax: 81 298 55 6608Tipo: D Status: O

UVSORInst. for Molecular ScienceMyodaiji, Okazaki 444, Japantel: +81 564 526101 fax: +81 564 547079Tipo: D Status: O

D = macchina dedicata; PD = parzialmente dedicata; P = in parassitaggio.

O= macchina funzionante; C=macchina in costruzione.

D = dedicated machine; PD = partially dedicated; P = parassitic.

O= operating machine; C= machine under construction.


B E N S CBerlin Neutron Scattering Center, Hahn-Meitner-Institut,Glienicker Str. 100, D- 14109 Berlin-Wannsee, GermanyRainer Michaelsen;tel: +49 30 8062 3043 fax: +49 30 8062 2523E - Mail: [email protected]://www.hmi.de

B N LBrookhaven National Laboratory, Biology Department,Upton, NY 11973, USADieter Schneider;General Information: Rae Greenberg;tel: +1 516 282 5564 fax: +1 516 282 5888http://neutron.chm.bnl.gov/HFBR/

G K S SForschungszentrum Geesthacht, P.O.1160, W-2054Geesthacht, GermanyReinhard Kampmann; tel: +49 4152 87 1316 fax: +49 4152 87 1338E-mail: PWKAMPM@DGHGKSS4Heinrich B. Stuhrmann;tel: +49 4152 87 1290 fax: +49 4152 87 2534E-mail: WSSTUHR@DGHGKSS4

I F EInstitut for Energiteknikk, P.O. Box40, N-2007 Kjeller,NorwayJon Samseth; tel: +47 6 806080 fax: +47 6 810920 telex: 74 573 energ n E-mail: Internet [email protected]

I L LInstitute Laue Langevin, BP 156, F-38042, GrenobleCedex 9,FrancePeter Timmins; tel: +33 76207263 E-mail: TIMMINS@FR ILLPeter Linder; tel: +33 76207068; E-mail: LINDER@FR ILLRoland P.May;tel:+3376207047; E-mail: MAY@FRILLfax: +33 76 48 39 06 telex: ILL 320-621http://www.ill.fr

I P N SArgonne National Laboratory, 9700 South Cass Avenue,Argonne, IL 60439-4814, USAP.Thiyagarajan,Bldg.200,RM. D125;tel :+1 708 9723593 E-mail: THIYAGA@ANLPNS

Ernest Epperson, Bldg. 212;tel: +1 708 972 5701 fax: +1 708 972 4163 or + 1 708 972 4470 (Chemistry Div.)http://pnsjph.pns.anl.gov/ipns.html

I S I SThe ISIS Facility, Rutherford Appleton Laboratory,Chilton, Didcot Oxfordshire OX11 0QX, UKRichard Heenan; tel +44 235 446744 E-mail: [email protected] King; tel: +44 235 446437 fax: +44 235 445720; Telex: 83 159 ruthlb gE-mail: [email protected]://www.nd.rl.ac.uk

J A E R IJapan Atomic Energy Research Institute, Tokai-mura, Naka-gun, Ibaraki-ken 319-11, Japan.Jun-ichi Suzuki (JAERI); Yuji Ito (ISSP, Univ. of Tokyo);fax: +81 292 82 59227 telex: JAERIJ24596http:// neutron-www.kekjpl

J I N RJoint Institute for Nuclear Research, Laboratory forNeutron Physics, Head P.O.Box 79 Moscow, 141 980Dubna, USSRA.M. Balagurov;E-mail: [email protected] M. Ostaneivich;E-mail: [email protected]: +7 095 200 22 83 telex: 911 621 DUBNA SUhttp://www.jinr.dubna.su

K F AForschungszentrum Jülich, Institut fürFestkörperforschung, Postfach 1913, W-517 Jülich,GermanyDietmar Schwahn; tel: +49 2461 61 6661; E-mail: [email protected] Maier; tel: +49 2461 61 3567;E-mail: [email protected]: +49 2461 61 2610 telex: 833556-0 kf d

NEUTRONINEUTRON SCATTERING WWW SERVERS IN THE WORLD(http://www.ISIS.RL.AC.UK/ISISpublic/neutron_sities.html)

FACILITIES

FACILITIES

L L BLaboratoire Léon Brillouin, Centre d’Etudes Nucleairesde Saclay, 91191 Gif-sur-Yvette Cédex FranceJ.P Cotton (LLB); tel: +33 1 69086460 fax: +33 1 69088261 telex: energ 690641 F LBS+E-mail: [email protected]://bali.saclay.cea.fr/bali.html

N I S TNational Institute of Standards and Technology-Gaithersburg, Maryland 20899 USAC.J. Glinka; tel: + 301 975 6242 fax: +1 301 921 9847E-mail: Bitnet: GLINKA@NBSENTHInternet: [email protected]://rrdjazz.nist.gov

O R N LOak Ridge National Laboratory Neutron ScatteringFacilities, P.O. Box 2008, Oak Ridge TN 37831-6393 USAG.D. Wignall; tel: +1 615 574 5237 fax: +1 615 576 2912E-mail: GDW@ORNLSTChttp://www.ornl.gov/hfir/hfirhome.html

PSIPaul Scherrer InstitutWurenlingen und VillingenCH-5232 Villingen PSItel: +41 56 992111 fax: +41 56 982327

R I S ØEC-Large Facility Programme, Physics Department, RisøNational Lab.P.O. Box 49, DK-4000 Roskilde, DenmarkK. Mortenses; tel: +45 4237 1212 fax: +45 42370115E-mail: [email protected] or [email protected] in SwedenE-mail: [email protected]


notiziario neutroni e luce di sincrotrone - issue 3 n.2, 1998

Documents

the trimer shown

the trigonalcrystals

notiziario neutroni

comunit neutroni

gentili and

luce di sincrotrone

protein crystallography

three molecules