TiO2(110) single crystals, doped with nitrogen via an NH3 treatment at 870 K, have been found to exhibit photoactivity at photon energies down to 2.4 eV, which is 0.6 eV below the band-gap energy for rutile TiO2. The active dopant state of the interstitial nitrogen that is responsible for this effect exhibits an N (1s) binding energy of 399.6 eV and is due to a form of nitrogen that is probably bound to hydrogen, which differs from the substitutional nitride state with an N (1s) binding energy of 396.7 eV. Optical absorption measurements also show enhanced absorption down to 2.4 eV for the NH3-treated TiO2(110). A co-doping effect between nitrogen and hydrogen is postulated to be responsible for the enhanced photoactivity of nitrogen-doped TiO2 materials in the range of visible light.

The effect of impurity doping on the photoactivity of TiO 2 rutile single crystals was subjected to a combined surface-science and bulk-analysis study. The incorporation of nitrogen ions, N -, into TiO 2 single crystals was achieved by sputtering with N 2 + /Ar + mixtures and subsequent annealing to 900 K under ultrahigh vacuum conditions. This procedure leads to a 90 Å thick structurally modified near-surface region, which, by the use of cross sectional transmission electron microscopy, can be described as rutile grains imbedded within a monocrystalline strained rutile matrix. The presence of Nions distributed in the first 200 Å below the surface was revealed by X-ray photoelectron spectroscopy, in agreement with sputter depth profiles obtained by secondary ion mass spectroscopy. The concentration of Ndoping is about 10 20 cm -3 in the first 200 Å of the near-surface region. The photodesorption of O 2 was employed to study the changes in the photochemical properties of nitrogen-implanted crystals. The action curves for O 2 photodesorption exhibit an unexpected blueshift compared to undoped crystals. The effect is attributed to the deposition of electronic charge in the lower levels of the conduction band (band-filling mechanism), causing allowed indirect photoexcitation processes to shift to energies higher than the band gap.

Photochemical Activity of Nitrogen-Doped Rutile TiO 2 (110) in Visible Light. -TiO 2 single crystals, doped with nitrogen via NH 3 treatment at 870 K exhibit photoactivity at photon energies down to 2.4 eV, which is 0.6 eV below the band-gap energy for rutile TiO 2 . A co-doping effect between nitrogen and hydrogen is postulated to be responsible for the enhanced photoactivity of nitrogen-doped TiO 2 materials in the range of visible light. -(DIWALD, O.; THOMPSON, T. L.; ZUBKOV, T.; GORALSKI, E. G.; WALCK, S. D.; YATES*, J. T.