Orientation relationships in heteroepitaxial aluminum films on sapphire

We investigate the microstructure and orientation relationships observed in aluminum thin films deposited epitaxially on sapphire (0001). The films consist of grains with three distinct types of orientation relative to the substrate. The primary orientation is such that (0001)(Al2O3)parallel to(111)(Al) and [<10(1)over bar 0>](Al2O3)parallel to[<(1)over bar 10>](Al). This configuration, which matches the close-packed planes and directions of the metal film with those of the oxygen ion sublattice in the sapphire substrate, allows for growth of two symmetrically equivalent orientation variants resulting in a film composed of interlocking regions of these two domains. Unexpectedly, two additional orientation types are identified in the films. As in the primary variant, the close-packed aluminum (111) planes remain parallel with the sapphire basal planes. However, these orientations are rotated about the aluminum [111] axis such that [<10(1)over bar 0>](Al2O3) is parallel to directions near either [<(1)over bar 2>(1) over bar](Al) (30 degrees rotation) or [<5(41)over bar>](Al) (similar to 11 degrees rotation). (C) 1997 Elsevier Science S.A.