Scanning Tunneling Microscopy Investigation of Ultrathin Titanium Oxide Films Grown on Pt 3 Ti(111)

Ordered ultrathin titanium oxide films have been produced under ultrahigh vacuum (UHV) conditions by oxidation of a Pt3Ti(111) single crystal at elevated temperatures. Depending on substrate temperature, oxygen dosage, and partial pressure, four different titania phases have been observed. All phases have been investigated by low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Two commensurate phases with a rect-(6 × 3√3) and a hex-(7 × 7)R21.8° superstructure, respectively, are obtained at low oxygen pressures. Both structures form homogeneous films, which wet the complete surface and are stable against further annealing. At high oxygen partial pressures two incommensurate structures can be prepared. The first one contains several holes to release stress arising from the lattice mismatch between the oxide film and substrate. The second one shows a very rough surface morphology and is, like the other incommensurate phase, unstable against thermal treatment. The structures of the different phases are very similar to the structures found for the systems TiOx/Pt(111), VOx/Rh(111), and VOx/Pd(111), which have been described extensively in the literature