ELECTRONIC AND CHEMICAL INTERACTIONS AT ALUMINUM TIO2(110) INTERFACES

The interaction between aluminum and both stoichiometric and oxygen-deficient single-crystal TiO2(110) surfaces has been studied using X-ray and ultra-violet photoelectron spectroscopies (XPS and UPS), Auger spectroscopy (AES), and low energy electron diffraction (LEED). Upon deposition of up to a monolayer of aluminum on the stoichiometric surface at room temperature, the aluminum becomes oxidized and the TiO2 is reduced. At multilayer coverages, a heterogeneous region is formed consisting of a mixture of metallic and oxidized aluminum on top of a reduced TiO2 layer. Annealing to 500-degrees-C in ultra-high vacuum completely oxidizes the remaining metallic aluminum and the titanium cations return to their fully oxidized 4 + state, due to oxygen diffusion from the bulk to the interface region. LEED shows no evidence of an ordered overlayer structure, even following annealing treatments. Oxygen-deficient TiO2 surfaces created by 500 eV Ar+ bombardment are also reactive towards aluminum; as the aluminum overlayer is oxidized, the TiO2 becomes further reduced.