Properties of aluminum overlayers on chemically modified TiO2(110) surfaces

Abstract

The chemical interactions of ultra-thin aluminum films with clean and chemically modified stoichiometric TiO2 (110) surfaces have been studied by several electron spectroscopies (ultraviolet photoelectron, x-ray photoelectron, and Auger electron) and low-energy electron diffraction. The chemical properties of the Al overlayers on clean TiO2 surfaces were compared to those on surfaces pre-dosed with submonolayer amounts of carbon or potassium. The thermal stability of each system was also examined. On the clean surface, the first monolayer of aluminum completely wets the surface and becomes oxidized, while the Ti 4+ cations in the near surface region are reduced. Submonolayer amounts of potassium interact with the stoichiometric TiO2 surface in a similar manner and form a potassium oxide overlayer. Aluminum deposited onto a potassium-dosed TiO2 (110) surface competes with K for oxygen and reduces more Ti 4+ cations in the interface region. Carbon species adsorbed on the TiO2 (110) surface by electron beam decomposition of ethylene prior to the aluminum deposition interact only weakly with the oxide surface, but retard the oxidation rate of aluminum and decrease the temperature stability of the aluminum oxide overlayer.