Oxygen Vacancy Origin of the Surface Band-Gap State of TiO2(110)

Scanning tunneling microscopy and photoemission spectroscopy have been used to determine the origin of the band-gap state in rutile TiO2(110). This state has long been attributed to oxygen vacancies (O-b vac). However, recently an alternative origin has been suggested, namely, subsurface interstitial Ti species. Here, we use electron bombardment to vary the O-b vac density while monitoring the band-gap state with photoemission spectroscopy. Our results show that O-b vac make the dominant contribution to the photoemission peak and that its magnitude is directly proportional to the O-b vac density.