Interface effects and the Auger parameter in titanium oxide thin films deposited on metals and in sandwich structures

Very thin films of TiO₂ and Ti₂O₃ were deposited by evaporation on Ag, on silver oxidized by an oxygen plasma and on Pt. Depending on the coverage, there were changes in the values of the binding energy (BE) and the Auger parameter (α′) of O and Ti. These shifts occur in the opposite direction with respect to that previously found for TiO₂ supported on insulators. Among others, reasons for these shifts are the different relaxation energy of photoholes and the occurrence of charge transfer processes at the metal oxide/metal interface. UV-visible absorption spectra of thin films of TiO₂Ag composites have shown a narrowing in the gap energy (E_g) of the oxide in respect to bulk titania. This observation shows the existence of a correlation between E_g and α′ when TiO₂ is supported on a metal surface. The Auger parameter of O and Ti is also sensitive to the intercalation of TiO₂ within a “sandwich” structure of SiO₂ and Ag, and the values found for the spectroscopic parameters are intermediate between those of TiO₂ supported on Ag and SiO₂. This result opens up the possibility of modulating the electronic properties of thin layers of TiO₂ by interaction with other materials.