Surface electronic structure of corundum transition-metal oxides: Ti2O3

The surface electronic structure of Ti2O3 has been studied on single-crystal samples cleaved in ultrahigh vacuum. Ultraviolet photoelectron spectroscopy, electron-energy-loss spectroscopy, etc., have been used to study nearly perfect surfaces, surfaces containing defects, and O2 chemisorption on both types of surfaces. Cleavage surfaces have a band structure essentially the same as the bulk, with a (1.40.1)-eV-wide Ti 3d a1g band separated from the (5.56)-eV-wide O 2p valence band by a (2.50.1)-eV band gap. No measurable band bending was seen on nearly perfect surfaces. Surface defects are associated with surface O vacancies and an accompanying transfer of charge to surface Ti 3d levels. The chemisorption of O2 on nearly perfect Ti2O3 surfaces removes charge from the surface Ti ions, creating a negative adsorbed species (probably O2-). The resulting surface dipole layer causes the surface O bands to shift in energy much more than either the filled or empty Ti 3d bands. Similar effects are seen for O2 chemisorption on defect surfaces. © 1982 The American Physical Society