The role of interstitial sites in the Ti3d defect state in the band gap of Titania

Titanium dioxide ( TiO2) has a number of uses in catalysis, photochemistry, and sensing that are linked to the reducibility of the oxide. Usually, bridging oxygen ( O-br) vacancies are assumed to cause the Ti3d defect state in the band gap of rutile TiO2( 110). From high- resolution scanning tunneling microscopy and photoelectron spectroscopy measurements, we propose that Ti interstitials in the near- surface region may be largely responsible for the defect state in the band gap. We argue that these donor- specific sites play a key role in and may dictate the ensuing surface chemistry, such as providing the electronic charge required for O-2 adsorption and dissociation. Specifically, we identified a second O-2 dissociation channel that occurs within the Ti troughs in addition to the O-2 dissociation channel in O-br vacancies. Comprehensive density functional theory calculations support these experimental observations.