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MICROSTRUCTURES OF Y123 FILMS ON SrTiO 3 , LaGaO 3 and LaAIO 3 T. ROY, I. D. RAISTRICK and T. E. MITCHELL MS K-765, Los Alamos National Laboratory, Los Alamos, NM 87545.

ABSTRACT Transmission electron microscopy(TEM) and scanning electron microscopy (SEM) have been used to study the microstructural features of YBa 2 Cu 3 O 7 (hereafter referred to as Y123) films grown on various single crystal substrates by electron beam deposition. The films are all of high quality with the best observed Jc value being 107 A.cm- 2 at 7K. Crosssectional views in TEM have shown that the morphology of the film depends on its thickness. Thinner films (2500 A) have a single layer of Y123 oriented with its c-axis perpendicular to the substrate while thicker films(8000 A) have this same c-axis perpendicular layer closest to the interface with a c-axis parallel layer above it. The interface between the film and the substrate is well defined in all cases with no amorphous region at the interface. Chemical analysis shows evidence of interdiffusion between the film and substrate. Introduction Thin films of the high Tc superconductors are more promising at the present for practical applications than bulk material due to their superior critical current densities[I]. Various thin film deposition techniques have been shown to be effective in producing good thin films with high critical current densities. A large number of substrates have been used for reasons such as lower dielectric losses or better lattice matching between the substrate and the film. In the present study Y123 films were deposited on SrTiO 3 , LaGaO 3 and LaAIO 3 (001) single crystal substrates by electron beam evaporation. Films on SrTiO 3 and LaAIO 3 have a Tc of 92K (LaGaO 3 slightly lower). The Jc values vary with film thickness and substrate. The highest value of Jc was 107 A.cm- 2 and was obtained for a film on SrTiO 3 at 7K and at zero field[2]. 2500 A films showed slightly lower Jc values than 5000 A films.

Experimental The film deposition technique has been described elsewhere[3]. In brief, Cu and Y were deposited by electron beam evaporation and barium fluoride was deposited by thermal evaporation onto various substrates at room temperature in a vacuum. The amorphous films produced by this process were annealed first in wet oxygen and then in dry oxygen at 850 °C. Cross sections for TEM observations were made by standard sandwich techniques[4]. To ensure that artifacts were not introduced due to ion thinning, the specimen was thinned using a liquid nitrogen cooling stage on a Gatan Duomill ion miller. Electron microscopy was performed on a Philips CM30 equipped with a Kevex energy dispersive x-ray microanalysis system. Results and Discussion Figure 1(a) shows a TEM bright field (BF) micrograph of a 150ooA thick film of Y123 on SrTiO 3 viewed in cross section. The layer closest to the interface has its c-axis perpendicular to the substrate and is 2000A thick. The outer layer consists of grains which have their Mat. Res. Soc. Symp. Proc. Vol. 169. ?1990 Materials Rese