THE EFFECTS OF SUBSTRATE SURFACE STEPS ON THE MICROSTRUCTURE OF EPITAXIAL BA2YCU3O7-X THIN-FILMS ON (001) LAALO3

The effects of steps in the (001) surface of LaAlO3 substrates on the microstructural evolution of heteroepitaxial Ba2YCu3O7-x (BYC) thin fi lms were characterized by high resolution transmission electron micros copy (TEM) and atomic force microscopy (AFM). Native substrate surface steps acted as nucleation sites for both the c-ads normal and c-axis in-plane (a-axis normal) orientations in BYC films prepared by post-de position annealing of a precursor film. The density of c-axis in-plane BYC grains varied dramatically across the surface of the substrates. In several samples, the spatial pattern of c-axis in-plane regions pre sent in the BYC films was similar to the twin structure present in the LaAlO3 substrates. Surface grooves present near twin boundaries in th e substrates and lattice rotation of the LaAlO3 during its rhombohedra l-cubic phase transition at similar to 450 degrees C may produce the l arge surface steps that act as preferred sites for BYC nucleation.