STUDY OF DEFECTS AND INTERFACES ON THE ATOMIC SCALE IN EPITAXIAL TIO2 THIN-FILMS ON SAPPHIRE

TiO2 thin films grown on (1120BAR) sapphire (alpha-Al2O3) at 800-degrees-C by the metallo-organic chemical vapour deposition technique have been characterized by transmission electron microscopy. The TiO2 thin films are single-crystal rutile. The epitaxial orientation relationship between the rutile thin films (R) and the sapphire substrates (S) is (101)[001]R parallel-to (1120BAR)[0001]S. Growth twins are commonly observed in the films with (101) twin planes and <101> twinning directions. The atomic structure of twin boundaries and TiO2-alpha-Al2O3 interfaces have been investigated by high-resolution electron microscopy. When the interfaces are viewed in the direction of [010]R-[0001]S, the interfaces appear structurally coherent along the direction of [101BAR]R-[1100BAR]S. The small misfit (0.5%) is accommodated at interface steps. In contrast, in the direction of [101BAR]R-[1100BAR]S, the interfaces are semicoherent. Growth mechanisms are discussed, based on information about the atomic structure of the interfaces.