in-plane and out-of-plane resistivities of vicinal hg-1212 thin films
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In-plane and out-of-plane resistivities of vicinal Hg-1212 thin filmsS. H. Yun, J. D. Pedarnig, R. Rössler, D. Bäuerle, and X. Obradors Citation: Applied Physics Letters 77, 1369 (2000); doi: 10.1063/1.1289489 View online: http://dx.doi.org/10.1063/1.1289489 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/77/9?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Structural and anisotropic transport properties of ( Hg , Re ) Ba 2 Ca Cu 2 O y vicinal films J. Appl. Phys. 97, 013903 (2005); 10.1063/1.1825631 Resistive substrate heater for film processing by spray pyrolysis Rev. Sci. Instrum. 75, 2884 (2004); 10.1063/1.1781364 Microwave surface resistance of HgBa 2 CaCu 2 O 6+δ thin films Appl. Phys. Lett. 76, 1606 (2000); 10.1063/1.126110 High-performance (Hg,Re)Ba 2 CaCu 2 O y grain-boundary Josephson junctions and dc superconductingquantum interference devices Appl. Phys. Lett. 73, 990 (1998); 10.1063/1.122062 Orientation control of ex situ ( Hg 1−x Re x ) Ba 2 CaCu 2 O y (x≈0.1) thin films on LaAlO 3 Appl. Phys. Lett. 72, 972 (1998); 10.1063/1.120613
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In-plane and out-of-plane resistivities of vicinal Hg-1212 thin filmsS. H. Yun, J. D. Pedarnig, R. Rossler, and D. Bauerlea)
Angewandte Physik, Johannes-Kepler-Universita¨t Linz, A-4040 Linz, Austria
X. ObradorsInstitut de Ciencia de Materials (CSIC), Campus de la U.A.B., E-08193 Bellaterra, Spain
~Received 18 May 2000; accepted for publication 27 June 2000!
Vicinal Hg12x Rex Ba2CaCu2O61d films have been grown on tilted (001)SrTiO3 substrates. Thecaxis of films is oriented in parallel to thec axis of the substrate for tilt angles up to 12°. The vicinalfilms show a step-like surface morphology with smooth terraces that are tilted with respect to thesubstrate surface. The in-plane and out-of-plane resistivitiesrab and rc reveal metallic behaviorwith a slight upturn nearTc for the latter. The resistivity anisotropy derived from thesemeasurements isrc /rab;6506150 at 300 K. This value is between that found for YBa2Cu3O72d
and the Bi-based cuprates, and it increases with decreasing temperature. ©2000 AmericanInstitute of Physics.@S0003-6951~00!01734-4#
The physical properties of high-temperature supercon-ductors~HTSs! are strongly anisotropic due to their quasi-two-dimensional structure. Transport measurements per-formed within theab plane and along thec axis reveal thisanisotropy and essentially contribute to a better understand-ing of the normal-state and superconducting-state properties.For instance, in-plane and out-of-plane resistivities ofYBa2Cu3Ox~YBCO! and the Bi-based cuprates have quitedifferent values and temperature dependences. The resistivityanisotropy is rc /rab(YBCO,T5300 K);10– 102 andrc /rab(Bi-2212,T5300 K);103– 104. For Hg-based cu-prates much less is known due to the difficulties in growingsingle crystals. The influence of Re doping on the anisotropyof Hg-based superconductors has raised strong controversyafter it was suggested that~Hg, Re!–O layers have a metal-like behavior.1,2 High-quality a-axis oriented Hg-cupratefilms have been grown epitaxially, but they are not suitablefor c-axis transport and anisotropy measurements due to theirheavily twinned structure.3 In this situation, it has been founduseful to grow vicinal Hg-cuprate films on off-c-axis ori-ented substrates. The anisotropic electrical properties of theHTS material can then be derived from measurements per-formed along two orthogonal directions on the vicinalfilm.4–6
In this letter, we report on the growth of vicinalHg12x Rex Ba2CaCu2O61d (Hg, Re-1212) thin films and onmeasurements of the in-plane and out-of-plane resistivitiesrab(T) and rc(T). Off-c-axis oriented (001)SrTiO3 wasused as the substrate. The tilt angleus between the surfacenormal n and the~001! direction of the substrate was variedwithin the range 0°<us<12°. The orientation, morphology,and stoichiometry of films were investigated by x-ray dif-fraction ~XRD!, atomic-force microscopy~AFM!, scanningelectron microscopy~SEM!, and energy-dispersive x-rayanalysis. XRD investigations were performed using a three-circle goniometer with a two-dimensional detection system.The electrical resistivities were derived from four-point mea-surements on patterned films.
Precursor films were prepared by pulsed-laser deposition~PLD! using 248 nm KrF-laser radiation (f'1.3 J/cm2,t l '25 ns, v r510 Hz! and a stoichiometricRe0.15Ba2Ca2Cu3Ox target.7 Rhenium-doped targets wereused to profit from the improved chemical stability and phaseformation of the~Hg, Re!-cuprates.8 After deposition, theprecursor films were annealed at 800 °C for 30 min in Hg-vapor atmosphere using a modified encapsulating method.3,9
The film thicknesses after annealing were around 1mm. Pat-terning of the annealed films was performed by photolithog-raphy and wet-chemical etching in 1% – 10%HNO3. Filmbridges (200mm31000mm) were oriented parallel and or-thogonal to the100& direction of the substrate.
The XRD patterns of Hg,Re-1212 films reveal thec-axisorientation parallel to the001& substrate direction forus
50° – 12°. The texture and the vicinal structure of the filmsare determined from rocking curves~v andw scans!. Figure1 showsv scans of the (002)SrTiO3 and ~005! Hg,Re-1212reflections performed for different in-plane sample orienta-tionsw. The scan anglev5u2uBragg is measured relative tothe Bragg anglesuBragg523.26° anduBragg517.82° of thesubstrate and Hg,Re-1212, respectively. Forw50°, the(100)SrTiO3 direction is parallel to the plane of incidenceand the reflections of film and substrate occur atv50° andx510° ~inset in Fig. 1!. For w5690°, the substrate peakintensities are observed atv56us and x50° due to thesubstrate tilt. The peak intensities of the film are measured atv56(us1du) and x50°. The deviation from an idealc-axis alignment (du50°) is in the range 0°<du<1.5° fordifferent samples and is comparable to results obtained onvicinal Bi2Sr2CaCu2O81d films.10 The rocking-curve widthof the vicinal Hg,Re-1212 films,DvFWHM'2°, is largerthan for epitaxial films11 and in situ grown vicinalYBa2Cu3O7 ~Ref. 6! and vicinal Bi2Sr2CaCu2O81d ~Ref. 12!films. The Hg,Re-1212 films also show good in-plane align-ment to the substrate.w scans reveal widths of the in-planetexture DwFWHM>8° and DwFWHM>3° for vicinal (us
510°) and epitaxial films, respectively.The surface morphology of the films was investigated by
scanning electron microscopy and atomic-force microscopy.a!Electronic mail: [email protected]
APPLIED PHYSICS LETTERS VOLUME 77, NUMBER 9 28 AUGUST 2000
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The SEM image in Fig. 2 shows the step-like surface profileof a 10° vicinal film. The surface structure reveals smoothterraces with straight or irregularly shaped boundaries andsharp steps between adjacent layers. AFM measurements in-dicate terrace widths of 0.5–2mm and step heights of 0.01–0.4 mm. The surface roughness of individual terraces iswithin 5–10 nm. The terrace surfaces are tilted by 10°–13.5°with respect to the substrate surface. From the XRD, SEM,and AFM results we conclude that moderately tilted sub-strates initiate oriented crystallization of films during the Hgannealing. The platelet-like growth of Hg-cuprate ceramics8
and films13 may favor this crystallization mode and cause asurface topology similar toin situ step-flow grown vicinalYBCO ~Ref. 6! and Bi-2212~Ref. 12! films.
For electrical characterization, the film resistances alongthe ^100& direction, Ri , and perpendicular to it,R' , weremeasured. Rotation of the resistivity tensor byus yields theab-plane resistivity,rab5(A/ l )Ri , and thec-axis resistivity,rc5(A/ l )$R'2Ri cos2 us%/sin2 us. Here,l is the length andA
the cross section of the bridges. Figure 3 shows the resistiv-ities rab(T) andrc(T) of a 10° vicinal Hg,Re-1212 film andr(T,us50°) of an epitaxial film, for comparison. The in-plane resistivities of both samples show metallic behavior inthe normal state. The values and the temperature dependenceof rab andr(us50°) agree well with earlier measurementson epitaxial Hg-1212 films.14–16 The out-of-plane resistivityshows metallic behavior with a slight upturn close to thesuperconducting transition. This temperature dependence canbe fitted by employing linear and activation term-like contri-butions similar to slightly underdoped YBCO and moder-ately overdoped Bi-2212. Thec-axis resistivity,rc(300 K)>325 mV cm, is close to data reported for Hg-1201 andHg-1223 single crystals17,18 ~340 and 360 mV cm, respec-tively!. The measured resistivity anisotropy at room tempera-ture isrc /rab;700 and increases with decreasing tempera-ture ~inset in Fig. 3!. On different samples the anisotropy isrc /rab;6506150 at 300 K. This resistivity ratio suggeststhat the Hg,Re-1212 films have a reduced mass anisotropy ascompared to what is expected from the interlayerseparation.19 The reduction of anisotropy is possibly due toRe substitution or overdoping. Slight overdoping of all ouras-grown films is inferred from oxygen annealing experi-ments~300 °C, 12 h!, which always decrease the transitiontemperature and thec-axis resistivity. Further analysis of theanisotropy dependence on carrier concentration is, therefore,necessary to ascertain the microscopic origin of the reducedanisotropy value. The critical temperature of vicinal films(Tc0'112 K) is lower than for 1212 ceramics, probably be-cause of overdoping and film degradation during patterning.
In summary, the growth, crystallinity, surface morphol-ogy, and electrical properties of vicinal Hg,Re-1212 films isreported. Films are fabricated on tilted~001! SrTiO3 sub-strates by PLD of precursor films andex situannealing in Hgatmosphere. XRD investigations reveal an oriented filmstructure with thec axis parallel to thec axis of the substrate,and good texture. The vicinal films show relatively smoothsurfaces with a step-like profile and tilted terraces. Out-of-plane resistivitiesrc show metallic behavior with a weakactivation-term contribution. The resistivity anisotropy ofHg,Re-1212 is smaller than for Bi-2212 and increases atlower temperatures.
Financial support under the TMR project Supercurrent~ERBFMRXCT98-0189!, the Jubila¨umsfonds der Oesterre-
FIG. 1. XRD v scans of a vicinal Hg,Re-1212 film and a tilted SrTiO3
substrate (us510°). Peak intensities of the~005! Hg,Re-1212 reflection~solid symbols! and the (002)SrTiO3 reflection ~open symbols! are mea-sured at different anglesv for different in-plane sample orientationsw. Therocking curve of an epitaxial Hg,Re-1212 film (us50°) is also shown~* !.The inset shows the geometry.
FIG. 2. SEM micrograph of a vicinal Hg,Re-1212 film (us510°) displayingthe step-like surface morphology with smooth terraces and sharp steps. Ter-race surfaces are tilted with respect to the substrate surface.
FIG. 3. Temperature-dependent resistivitiesrab and rc of a vicinal Hg,Re-1212 film (us510°). The resistivity anisotropy atT5300 K is rc /rab
;700 and increases with decreasing temperature~inset!. The resistivity ofan epitaxial Hg,Re-1212 film,r(us50°), is shown for comparison.
1370 Appl. Phys. Lett., Vol. 77, No. 9, 28 August 2000 Yun et al.
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ichischen Nationalbank, and the Austrian Bundesministe-rium fur Bildung, Wissenschaft und Kultur is gratefully ac-knowledged.
1K. Kishio, J. Shimoyama, A. Yoshikawa, K. Kitazawa, O. Chmaissen, andJ. D. Jorgensen, J. Low Temp. Phys.105, 1359~1996!.
2L. Fabrega, A. Calleja, A. Sin, S. Pin˜ol, X. Obradors, J. Fontcuberta, andP. J. C. King, Phys. Rev. B60, 7579~1999!.
3S. H. Yun, U. O. Karlsson, J. Jo¨nsson, K. V. Rao, and L. D. Madson, J.Mater. Res.14, 1 ~1999!.
4T. Zahner, R. Stiersdorfer, R. Ro¨ssler, J. D. Pedarnig, D. Ba¨uerle, and H.Lengfellner, Physica C298, 91 ~1998!.
5W. Markowitsch, C. Stockinger, W. Lang, K. Bierleutgeb, J. D. Pedarnig,and D. Bauerle, Appl. Phys. Lett.71, 1246~1997!.
6L. Mechin, P. Berghuis, and J. E. Evetts, Physica C302, 102 ~1998!.7D. Bauerle, Laser Processing and Chemistry, 3rd ed.~Springer, Berlin,2000!.
8Ch. Wolters, K. M. Amm, Y. R. Sun, and J. Schwartz, Physica C267, 164~1996!.
9S. H. Yun and J. Z. Wu, Appl. Phys. Lett.68, 862 ~1996!.
10S. T. Li, A. Ritzer, E. Arenholz, D. Ba¨uerle, W. M. Huber, H. Lengfellner,and W. Prettl, Appl. Phys. A: Mater. Sci. Process.63, 427 ~1996!.
11B. J. Jonsson, K. V. Rao, S. H. Yun, and U. O. Karlsson, Phys. Rev. B58,5862 ~1998!.
12R. Rossler, J. D. Pedarnig, D. Ba¨uerle, E. J. Connolly, and H. W. Zand-bergen, Applied Physics A~in press!.
13G. Plesch, S. Chromik, V. Strbı´k, M. Mair, G. Gritzner, S. Benacka, I.Sargankova, and A. Buckuliakova´, Physica C307, 74 ~1998!.
14S. L. Yan, Y. Y. Xie, J. Z. Wu, T. Aytug, A. A. Gapud, B. W. Kang, L.Fang, M. He, S. C. Tidrow, K. W. Kirchner, J. R. Liu, and W. K. Chu,Appl. Phys. Lett.73, 2989~1998!.
15W.-S. Kim, W. N. Kang, S. J. Oh, M.-S. Kim, Y. Bai, S.-I. Lee, C. H.Choi, and H.-C. Ri, Physica C324, 77 ~1999!.
16M. Rupp, A. Gupta, and C. C. Tsuei, Appl. Phys. Lett.67, 291 ~1995!.17G. Villard, A. Daignere, A. Maignan, and A. Ruyter, J. Appl. Phys.84,
5080 ~1998!.18A. Carrington, D. Colson, Y. Dumont, C. Ayache, A. Bertinotti, and J. F.
Marrucco, Physica C234, 1 ~1994!.19K. Kishio, in Coherence in Superconductors, edited by G. Deutscher and
A. Revcolevschi~World Scientific, Singapore, 1996!, p. 212.
1371Appl. Phys. Lett., Vol. 77, No. 9, 28 August 2000 Yun et al.
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