Evidence for the Predominance of Subsurface Defects on Reduced AnataseTiO2(101)

Scanning tunneling microscopy (STM) images taken on a freshly cleaved anatase TiO2(101) sample show an almost perfect surface with very few subsurface impurities and adsorbates. Surface oxygen vacancies are not typically present but can be induced by electron bombardment. In contrast, a reduced anatase (101) crystal shows isolated as well as ordered intrinsic subsurface defects in STM, consistent with density functional theory (DFT) calculations which predict that O vacancies (V_{O}'s) at subsurface and bulk sites are significantly more stable than on the surface.