ORIENTATION RELATIONSHIPS IN HETEROEPITAXIAL ALUMINUM FILMS ON SAPPHIRE

We investigate the microstructure and orientation relationships observ ed in aluminum thin films deposited epitaxially on sapphire (0001). Th e films consist of grains with three distinct types of orientation rel ative to the substrate. The primary orientation is such that (0001)(Al 2O3)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 symmetr ically equivalent orientation variants resulting in a film composed of interlocking regions of these two domains. Unexpectedly, two addition al orientation types are identified in the films. As in the primary va riant, 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 parall el to directions near either [<(1)over bar 2>(1) over bar](Al) (30 deg rees rotation) or [<5(41)over bar>](Al) (similar to 11 degrees rotatio n). (C) 1997 Elsevier Science S.A.