EVIDENCE FOR THE TUNNELING SITE ON TRANSITION-METAL OXIDES - TIO2(110)

We present atomically resolved scanning tunneling microscopy (STM) ima ges from TiO2(110) surfaces. After annealing nearly perfect stoichiome tric 1 X 1 surfaces to elevated temperatures in ultrahigh vacuum, rand omly distributed oxygen vacancies are observed. The apparent shape of these defects provides strong evidence that the STM is imaging underco ordinated Ti atoms, as do first; principles pseudopotential calculatio ns of the electronic states accessible to tunneling. We thus resolve a controversy as to whether STM imaging on this surface is dominated by geometric-structure or electronic effects.