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 films were characterized by high resolution transmission electron microscopy (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-deposition 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 present in the BYC films was similar to the twin structure present in the LaAlO3 substrates. Surface grooves present near twin boundaries in the substrates and lattice rotation of the LaAlO3 during its rhombohedral-cubic phase transition at similar to 450 degrees C may produce the large surface steps that act as preferred sites for BYC nucleation.