Scanning tunneling microscopy studies on thin film oxide surfaces

Many oxide surfaces are unsuitable for detailed studies due to their insulating nature, the lack of large, single-phase crystals, and/or difficulties associated with surface preparation. These problems can be obviated by using ultrathin films grown epitaxially on single crystalline, conducting substrates. As a real space probe, the STM can directly determine the microscopic surface structure of these films, especially defects. Two examples will be presented: MgO grown on Mo(001) and TiO{sub x{approximately}1} grown on W(110). MgO is an insulator in the bulk, however, ultrathin films of MgO (up to 30{Angstrom} thick) can be imaged. The microscopic structures of these films are strongly dependent on the growth conditions with defect densities ranging from 40% down to less than 5%. Macroscopic single crystals of the rocksalt oxide, TiO{sub x{approximately}1}, are not available. Long range, periodic structures of ultrathin film TiO, however, can be grown on the surface of W(110) substrates.