THE ATOMIC-STRUCTURE OF GROWTH INTERFACES IN Y-BA-CU-O THIN-FILMS

We have examined the atomic structure of growth interfaces in thin films of Y-Ba-Cu-O grown on [001] perovskite or cubic substrates. At substrate heater temperatures in the range of 780-820-degrees-C c-axis oriented growth is observed on these substrates. On SrTiO3, the first layer appears to be either a BaO or CuO2 plane while on LaAlO3 the first layer appears to be a CuO chain layer. The mismatch on the a-b plane is accommodated by the formation of interface dislocations. Defects on the substrate surface propagate as defects in the film. These defects are primarly translational boundaries and in some cases second phases. At lower substrate heater temperatures, i.e., 650-700-degrees-C, a, b-axis growth dominates. Defects and steps on the substrate surface are more detrimental in the growth of a, b-axis oriented films, since they tend to favor the nucleation of c-axis oriented domains. This is ascribed to the ledge mechanism of c-axis film growth, for which the surface steps are good nucleation sites.