Pulsed laser deposition and surface chemistry of device quality YBa2Cu3O7-δ Thin Films

Abstract

In view of the material requirements for high Tc Josephson tunnel junctions, we have defined the device quality YBa2Cu3O7−δ (YBCO) thin films and investigated their fabrication technology. High quality c-axis-oriented YBCO films can be fabricated using the laser ablation method. The atomically smooth and chemically stable surface was demonstrated by cryogenic STM/STS. However, high density of precipitates was observed on the surface. Scanning Auger electron spectroscopy identified these precipitates to be BaCuO2 and CuO. The small compositional deviation from Y:Ba:Cu=1:2:3, although undetectable by ICP, caused the outgrowth of the precipitates. The precipitate density could be decreased either by using off-axis substrates or by growing the film under the conditions which resulted in the lower crystallinity of the matrix film. The film thickness dependences of the density and the size of the precipitates revealed that the nucleation of the precipitates took place at the initial stage of the film growth.