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Originally published in Science Express on 5 June 2008
Science 27 June 2008:
Vol. 320. no. 5884, pp. 1755 - 1759
DOI: 10.1126/science.1159846
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Reports

The Role of Interstitial Sites in the Ti3d Defect State in the Band Gap of Titania

Stefan Wendt,1 Phillip T. Sprunger,1,2 Estephania Lira,1 Georg K. H. Madsen,1 Zheshen Li,1 Jonas Ø. Hansen,1 Jesper Matthiesen,1 Asger Blekinge-Rasmussen,1 Erik Lægsgaard,1 Bjørk Hammer,1* Flemming Besenbacher1*

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.

1 Interdisciplinary Nanoscience Center (iNANO), Department of Physics and Astronomy, and Institute for Storage Ring Facilities, University of Aarhus, DK-8000 Aarhus C, Denmark.
2 Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70808, USA.

* To whom correspondence should be addressed. E-mail: hammer{at}phys.au.dk (B.H.); fbe{at}inano.dk (F.B.)

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