The Role of Interstitial Sites in the Ti3d Defect State in the Band Gap of Titania
2008
Wendt, Stefan | Sprunger, Phillip T. | Lira, Estephania | Madsen, Georg K.H. | Li, Zheshen | Hansen, Jonas Ø | Matthiesen, Jesper | Blekinge-Rasmussen, Asger | Lægsgaard, Erik | Hammer, Bjørk | Besenbacher, Flemming
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 (Obr) 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 O₂ adsorption and dissociation. Specifically, we identified a second O₂ dissociation channel that occurs within the Ti troughs in addition to the O₂ dissociation channel in Obr vacancies. Comprehensive density functional theory calculations support these experimental observations.
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