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I. INTRODUCTION

II. EXPERIMENTAL

The recent discovery of oxide supercondutors with transition temperatures in excess of 90 K 1 has for the first time offered the possibility of operating a superconductor at liquid nitrogen temperatures. Many of the potential applications for such a superconductor will be in the area of electrical devices and detectors and will require the production of superconducting thin films. Within a very short time of the announcement of the discovery of the high-temperature oxide superconductor, research groups at both IBM and Stanford University reported the successful fabrication of thin-film oxide superconductors.2'3 Since that time several other research groups have also reported the successful fabrication of thin-film superconductors. In all published reports to date, all of the thin-film processing techniques discussed have utilized either the coevaporation of the three metallic components by electron-beam deposition,4""6 alloy sputtering from a multicomponent target or multiple sources,7"1' or laser-assisted deposition from the bulk.12 In these techniques an alloy film is produced by the simultaneous deposition of the alloying constituents onto the substrate. In the present work we report for the first time the fabrication of a thin-film oxide superconductor from an oxygen-annealed multilayered metallic film. We will discuss the importance of thermochemistry on this process as well as the possible role of nonsuperconducting second phases on the superconducting transition width.

The fabrication of thin-film high-temperature oxide superconductors was accomplished by the sequential electron-beam deposition of the metallic constituents onto a heated substrate in a base vacuum better than 1X 10~ 7 Torr. Ten sets of a metallic trilayer of M/Ba/ Cu, where M = Y or Gd, were deposited onto a heated substrate of SiO2 or A12O3 that was held at approximately 675 K. The deposited thickness of each layer in the trilayer was approximately 100 A for Y or Gd, 395 A for Ba, and 107 A for Cu, producing a sample with an atomic ratio of 1/2/3 and a total thickness of 6000 A. After allowing the as-deposited samples to cool down to 300 K in vacuum, they were thermally reacted in a tube furnace under flowing oxygen. All annealing was carried out in a quartz tube with temperature measurement made between the tube and the furnace. Preliminary annealing experiments were carried out isothermally at temperatures ranging from 573-1273 K. In addition, two other thermal annealing treatments were also examined, the first of which employed a slow heat up from 8 7 3 t o l l 2 3 K followed by a furnace cooldown, similar to the annealing treatment used by the Stanford group,5 and the second of which placed the sample quickly into the furnace held at 1223 K, held it there for 15 min, and then furnace cooled, similar to the treatment specified by IBM.4 Samples were examined both before and after oxygen furnace annealing using Rutherford backscattering spectroscopy (RBS) with 3 MeV a particles, Auger sputter depth profil