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.