UV-ray photoelectron and ab initio band calculation studies on electronic structures of Cr- or Nb-ion implanted titanium dioxide

The electronic structure of TiO2 doped with Cr or Nb by ion implantation is investigated by UPS and ab initio band calculations. Rutile TiO2 was implanted with 150 keV Cr or Nb ions and subsequently annealed in an air, and the recovery of radiation damage and substitution of implanted metals for Ti atoms was confirmed. UPS spectra for both of these oxides revealed a signal corresponding to the electron-occupied level in the band gap. For Cr-doped TiO2, this signal appeared close to the edge of the valence band (VB), while Nb-doped TiO2 exhibited a small signal far from the VB edge. According to band calculations, the midgap levels of Cr- and Nb-doped TiO2 consist of the electronic states localized in the Cr t(2g) orbital and delocalized over the Ti t(2g) and Nb t(2g) orbitals, respectively. Consequently, the electronic character of both of these oxides is determined by the energy of the t(2g) states of Ti and the dopant. (C) 2003 Elsevier Science B.V. All rights reserved.