| Abstract
| - A realistic model, consisting of six-layer slabs, and density-functional calculations were used to perform adetailed analysis of the structural and electronic properties of N doped TiO2(110). All the positions examinedfor adsorption of atomic N are unstable regarding the formation and further escape of N2(g). The adsorptionof atomic N could take place only when having isolated adatoms. In this case, N prefers to bond to O centerslocated either on the surface or in the interstitial channels of the oxide lattice. These N adatoms probablygive rise to the peak seen at ∼400 eV in N 1s XPS spectra. The coexistence of N with O vacancies andsurface reconstructions are explained in terms of cooperative behaviors and the special electronic structure ofthe TiNxO2-2x(110) system. Here, electrons move from the O vacancies to implanted N to fill up its electronicshell. Such electron transfer yields the normal oxidation state of nitrogen, N3-, and explains a number ofthings: the easiness to form O vacancies when implanted N is present, the easiness to implant N when Ovacancies are present, and the difficulty for the implanted N to escape. It is not likely that N-doping willimprove the photocatalytic behavior of TiO2-x(110) surfaces. For these compounds the band gap will bealways equal or larger than that of pure stoichiometric TiO2.
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