Visible influence of substrate-surface defects on YBa2Cu3O7-x film nucleation and growth on polycrystalline silver

YBa2Cu3O7-x (YBCO) thin films were grown on the polycrystalline-silver subs trates by pulsed laser deposition. The influences of various substrate-surf ace defects on the film nucleation and growth have been systematically anal yzed using transmission electron microscopy (TEM). The obtained results sho w that the YBCO film usually nucleates and grows on the flat area of the su bstrate-surface with its a-b plane simply parallel to the substrate-surface plane, no matter the substrate-surface plane is a low-index or a high-inde x crystal plane. A small angle change of the substrate-surface plane will c ause the same angle change of the c-axis orientation of the grown YBCO film . On the defective surface with valleys, however, the YBCO film cannot dire ctly grow, instead, there is an intermediate layer with some other oxide ph ases previously grown on the substrate surface. Concerning the surface step s and hills. the TEM observation indicates that they can be simply covered by the lateral overgrowth of the YBCO crystals surrounding them. From the v iewpoints of energy and kinetics, a detailed discussion has been given for the forming mechanism of various film microstructures on the substrate-surf ace areas with different surface defects. (C) 2001 Elsevier Science B.V. Al l rights reserved.