Effect of Oxygen Pressure on the Surface Roughness and Intergranular Behavior of YBCO Thin Films

YBa₂Cu₃ O _7?δ (YBCO) thin films were deposited by pulsed laser deposition on single-crystal LaAlO₃ (100) substrates in O₂ partial pressure (P _O2) from 400 to 500 mTorr. The XRD data shows the presence of a-axis-oriented grains in the YBCO films deposited at P _O2 = 500 mTorr. The a-axis grains lead to increase of strain. Atomic force microscopy images show as oxygen pressure has increased, average surface roughness of the films and size of droplets were increased. The grain misorientaion could be the reason for high average roughness. However, surface analysis by statistical methods reveals that three surfaces have multi-affine structure irrespective of oxygen pressure. Analysis of the temperature dependence of the AC susceptibility near the transition temperature indicates that with increasing oxygen pressure, intergranular critical current density has decreased. It is also suggested that the nature of weak links in the samples is of superconductor-normal-superconductor (SNS) type irrespective of the oxygen pressure.