Scanning tunnelling microscopy and photo-emission spectroscopy were used to determine the origin of the band-gap state in rutile TiO2(110). This state had long been attributed to oxygen vacancies (Ob vac). However, a recently suggested alternative origin was sub-surface interstitial Ti species. Here, electron bombardment was used to vary the Ob vac density while monitoring the band-gap state using photo-emission spectroscopy. The results showed that Ob vac made the dominant contribution to the photo-emission peak and that its magnitude was directly proportional to the Ob vac density.

Oxygen Vacancy Origin of the Surface Band-Gap State of TiO2(110). C.M.Yim, C.L.Pang, G.Thornton: Physical Review Letters, 2010, 104[3], 036806