Superconducting Properties of HTSC Thin Films Prepared in Situ by Single Target Deposition

Abstract

Thin films of ReBaCuO (Re=Y, Gd) and of BiCaSrCuO have been deposited onto A1 2 O 3, MgO , SrTiO 3, Si and ZrO 2 substrates by planar and inverted cylindrical magnetron sputtering. The main advantage of this preparation technique is the high reproducibility allowing detailed and systematic studies of the film properties as a function of deposition parameters. Optimum deposition parameters were a high oxygen partial pressure of 2×10−1 Torr in an oxygen-argon mixture and substrate temperatures near 800°C. Except for the substrate Si the films grow highly textured on all substrates. For the 1–2–3 material zero resistance is obtained near 90 K for the case of textured growth. For Si the best film showed zero resistance near 84 K. High critical currents between 4×105 and 5.5×106 A/cm 2 were determined for films of the 1–2–3 material on the substrates MgO , ZrO 2 and SrTiO 3. On films SrTio 3 tunnel junctions with Pb and In counterelectrodes could be prepared which showed a gap-like feature in their current-voltage characteristic. These junctions could be prepared with great reproducibility and experimental arguments could be provided which show that this gap-like feature is due to a superconducting density of states effect. Finally, first results are presented on YBaCuO thin films which were deposited by a novel ablation device which uses a pulsed electron beam instead of the laser beam.

Epitaxial growth and properties of YBaCuO thin films

“…at conditions where a high degree oftexture with the c-axis inclined to the substrate surface following the substrate surface orientation was observed. Degraded properties also with respect to the normal conduction [16] again coincide with polycrystalline phase formation at lower deposi tion temperatures.…”

“…Recently an alternative approach to the laser ablation has been presented by Geerk et al [16] . That is the ablation by a pulsed beam of electrons.…”

“…These single crystals were of high quality even for the oxygen sublattice. The oxygen sublattice was studied using the resonant scattering of 3.04 MeV He-ions on 16 From the surface peak area (SPA) the number of Sr-atomslcm 2 , Nt, can be evaluated [36] by Nt=SPA·c·öEI(H·e) where c is the relative concentration of Sr-atoms, öE the energy I channel, H the height of the Sr-yield in the random spectrum at the surface, and e the backscattering energy loss factor of He ions scattered from the Sr-atoms in SrTi03. The result isthat 2.1x10 15 Sr-atomslcm 2 contribute to the surface peak shown in Fig.…”