Reaction of O 2 with Subsurface Oxygen Vacancies on TiO 2 Anatase (101)

Oxide Chemistry Below the Surface Although metal oxides, such as titanium dioxide (TiO 2 ), are used for catalytic oxidation reactions and photocatalysis, the O 2 does not react directly with substrates. Vacancies in the surface region of the TiO 2 rutile phase can transfer a negative charge to adsorbed O 2 to create more reactive species. By contrast, in anatase—the phase associated with nanoscale TiO 2 particles—subsurface vacancies form. Setvin et al. (p. 988 ) used a scanning tunneling microscopy tip to pull these vacancies to the surface in a niobiumdoped anatase crystal and followed the transformation of adsorbed O 2 − into a peroxo species and a bridging O 2 dimer.