Investigation of the evolution of YBa2Cu3O7-delta films deposited by scanning pulsed laser deposition on different substrates

Abstract

The evolution of surface morphology of YBa2Cu3O7-delta (YBCO) thin films with sequential thickness ranging from 2 to 250 nm on (110) NdGaO3, as-polished and annealed (110) SrTiO3 and (100) MgO substrates has been systematically investigated with atomic force microscopy (AFM) to elucidate the effects of lattice mismatch, pre-annealing treatment and substrate orientation on the growth mechanism of YBCO films. A scanning pulsed laser deposition system, which has been used to produce 50-mm-diameter thin films, allows us to deposit (001) or (103) YBCO films with various thicknesses on separated substrates in a single run under essentially identical deposition conditions. The AFM images show that (001) YBCO films grown on NdGaO3 follow the Stranski-Krastanov (layer then island growth) mode, while films grown on as-polished MgO and on annealed MgO follow the Volmer-Weber (island without layer growth) mode and step-flow mode, respectively. On the other hand, the evolution of (103) YBCO films grown on both as-polished and annealed (110) SrTiO3 substrates reveals the similar step-flow growth along tilt steps, i.e. the growth proceeds with the c-axis of YBCO along [100] or [010] directions of substrate. The formations of distinct elongated grains and microcracks in planar view of such films are also discussed. (C) 1997 Elsevier Science B.V.