Structure of Sc₂O₃ Films Epitaxially Grown on α-Al₂O₃ (111)

We have characterized the structure of the epitaxial Sc2O3 films grown on a α-Al2O3 (111) substrate using molecular beam epitaxy (MBE) techniques. The Sc2O3 films grow in the bulk bixbyite phase with a very uniform thickness, and a high structural perfection. They grow with their cubic (111) axis parallel to the rhombohedral (111) axis of the sapphire substrate. The in-plane orientation of the films, however, is rotated by ±30 degrees with respect to the substrate rhombohedral axes. This is explained by the presence of two equivalent orientations of the 3-fold axis of the film on the quasi 6-fold surface of the substrate.