Study of defects and interfaces on the atomic scale in epitaxial tio₂thin films on sapphire

TiO2 thin films grown on (11 0) sapphire (α-Al2O3) at 800°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)[010]R‖(110)[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-α-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 [10]R-[100]s. The small misfit (0.5%) is accommodated at interface steps. In contrast, in the direction of [10]R-[100]s, the interfaces are semicoherent. Growth mechanisms are discussed, based on information about the atomic structure of the interfaces.