Surface studies of nitrogen implanted TiO2

M. Batzill, E. H. Morales, U. Diebold

Department of Physics, University of South Florida, Tampa, U.S.A.
Department of Physics, Tulane University, New Orleans, Louisiana 70118, U.S.A.

Chem. Phys. 339 (2007) 36-43

Rutile TiO2(110) single crystals have been doped by nitrogen-ion implantation. The change in the valence band and in the core level peak shapes are characterized by photoemission spectroscopy. Surface morphologies are characterized by scanning tunneling microscopy. N-dopants are observed to be in a 3- charge state and to substitute for O-anions in the TiO2 lattice for N-concentrations up to ~5% of the anions. The higher valency of the N-dopants compared to the host O-anions is proposed to be compensated by the formation of O-vacancies and/or Ti-interstitials. Two chemically shifted components arise in the Ti-2p core level upon N-doping. These components, shifted by 0.9 eV and 2.1 eV, are assigned to Ti-bound to N-ligands and possibly due to O-vacancies in the lattice. The Ti-3d band gap state observed in UPS is initially suppressed upon room temperature N-implantation and recovers a similar intensity as for undoped TiO2 samples upon annealing. This indicates that electrons left behind upon creation of O-vacancies are filling the N-2p level rather than Ti-3d states. The filled N-2p state is found at the top of the TiO2 valence band and is believed to be responsible for the band gap narrowing of N-doped TiO2 that shifts the photoactivity of TiO2 into the visible spectrum.

Reprints available from U. Diebold (diebold at iap_tuwien_ac_at).

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