Photoelectrochemical spectroscopy studies of titanium dioxide surfaces: theory and experiment

We describe experimental and theoretical studies of titanium dioxide. Photoelectrochemical data are presented for surfaces of known structure. The oxides were grown anodically on titanium metal. We report calculations of the electronic densities of states and optical conductivities of rutile TiO₂ in finite-size samples disordered by the addition of oxygen vacancies for comparison with experiments. We conclude that in less disordered surfaces the electronic structure exhibited by the photospectra is very close to that of bulk rutile TiO₂. In contrast, very thin oxides showed evidence of an electronic structure dominated by localized states near the band edge. More disordered oxides gave photospectra in which transitions associated with direct band gap transitions in bulk TiO₂ seem to have been suppressed. Taking the structural information on the oxides into account, we argue that this suppression is probably a matrix element effect.