STUDIES OF LAALO3(100) SURFACES USING RHEED AND REM .1. TWINS, STEPS AND DISLOCATIONS

Lanthanum-aluminate (LaAlO3) is one of the optimum substrates for epit axial growth of YBa2Cu3O7-x thin films. In this paper, the structures of the {100} surfaces of annealed LaAlO3 are studied using reflection electron microscopy (REM). The importance of substrate steps on the gr owth of defects in the film is shown. It has been found that a {010} t win boundary is normally terminated with a [001] step at the surface. Dislocations are not observed in the flat surface areas but occur at t he twin boundaries that intersects the {100} surface. The observed dis location is screw-type with Burgers vector a[100]. Numerous [010] and [001] ''sawtooth'' steps have been observed, and they are believed to be the lowest surface energy steps. It is suggested that the {100} sur faces are terminated entirely with either the La-O layer or the Al-O l ayer, but not a mixture of both. The miscut angle and the heights of s urface steps are measured using the mirror imaging technique. Finally, the effect of surface contaminants on the growth of surface steps is shown, and a growth mechanism is proposed.