Excimer Laser Induced Deposition of BiSrCaCuO HTSC Thin Films and Buffer Layers - Depth Profiling by SNMS
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EXCIMER LASER INDUCED DEPOSITION OF BiSrCaCuO HTSC THIN FILMS AND BUFFER LAYERS - DEPTH PROFILING BY SNMS
M.LQRENZ, H.HOCHMUTH, H.BORNER AND K.UNGER Universitht Leipzig, AG Diinnschichttechnik am Fachbereich Physik, Linn~str. 5, 0-7010 Leipzig, Germany.
ABSTRACT Secondary Neutrals Mass Spectrometry SNMS was used to investigate interdiffusion processes in laser deposited BiSrCaCuO HTSC thin films on various substrate materials. The in-situ deposition of epitaxial Bi2Sr2CalCu2Os+x films requires a substrate temperature just below the decomposition temperature of the 2212 - phase of BiSrCaCuO. This high substrate temperature of about 850'C seems to be the reason for interdiffusion processes of BiSrCaCuO films and MgO(100), YSZ(100) and Si(100) with YSZ or SrTiO 3 buffer layers as substrate materials. Therefore, Tc(R=0) of BiSrCaCuO films on silicon with buffer layer is not higher than 70 K at present. SNMS depth profiling gives a more detailed insight into interdiffusion phenomena than other analytical techniques. INTRODUCTION Epitaxial Bi 2 Sr2 CalCu2 O 8 +x (2212) HTSC thin films with Tc(R--0) above 80 K and critical current densities higher than 106 A/cm 2 at 4.2 K have been deposited up to now only on substrate materials as SrTiO 3 and NdGaO 3 [1-3]. Sputtering [1] , pulsed laser deposition [2], liquid phase epitaxy [3] and molecular beam epitaxy [4] have proved to produce high quality BiSrCaCuO films on this substrate materials. Several attempts have been published [5-12] on the deposition of BiSrCaCuO films on technologically more important substrate materials. Table I. summarizes results of deposition of BiSrCaCuO films on silicon, saphire and polycrystalline substrate materials with and without buffer layers. BiSrCaCuO films on this reactive substrate materials show Tc(R=0) to be not higher than 73 K. The structural and electrical properties of the BiSrCaCuO films seem to react very sensitivly upon structure of substrate material and interdiffusion of film and substrate. Secondary Neutrals Mass Spectrometry SNMS [13] is used to investigate the elemental composition of laser deposited BiSrCaCuO films and buffer layers in dependence on depth. SNMS has a depth resolution up to some nm and an accuracy of elemental concentrations up to 10 % if standard samples of known composition are available. So more detailed results on interdiffusion processes in multilayer systems can be expected by SNMS in comparison to SIMS, AES depth profiling and RBS. In SNMS the sputtered neutrals are analyzed which reflect the true composition of the sputtered sample (in sputter equilibrium). Mat. Res. Soc. Symp. Proc. Vol. 285. @1993 Materials Research Society
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Table I. Representative results of deposition of BiSrCaCuO HTSC thin films technological important substrate materials. Substrate
Buffer layer
Tc(R=O)
Deposition by
Reference
Si(100) Si(100) Si(100) Si/Si02 Sapphire Sapphire Ni-alloy CuO polycr. YSZ polycr.
YSZ NiSi 2 , CeO 2 Si3 N4 , SiO 2 ZrO 2 /ZrSiO ZrO2 no YSZ no no
70 K no no 69 K 70 K 72 K 62 K 72 K 73 K
Ex
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