Metallization of TiO2(110) with Gold and Lithium

Gold and lithium have been deposited on clean, stoichiometric TiO2(110) to study the evolution of the electronic structure of the surface. For thermally deposited gold, X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) indicate that the first monolayer (ML) grows two dimensionally, while additional gold forms islands, and that the surface becomes metallic by 1 ML. Downward band bending for low coverage is confirmed by a comparison of the XPS valence and UPS spectra, which have different detection depths. Inverse photoelectron spectroscopy (IPES) shows that the deposited gold attenuates the Ti 3d states, which dominate the conduction band. In the case of lithium, XPS analysis indicates that deposited atoms penetrate into the bulk, with a gradual buildup in the near-surface region. UPS shows the formation of a Ti3+ 3d gap state 1.4 eV below the Fermi level. Band bending is not observed for low Li coverage due to pinning of the Fermi level to the gap state. Deposition of more than 10 ML is required for the work function to reach that of bulk Li. Unoccupied 3d states disappear from the IPES spectrum as they are filled by electrons injected from Li.