Paper TF-ThP12
The Influence of N-dopping for Titanium Dioxide Thin Films on Photo-functional Properties

Thursday, October 23, 2008, 6:00 pm, Room Hall D

TiO₂ is anticipated as one of materials which are alternative for existing solar cell technology based on silicon. TiO₂ shows relatively high reactivity and chemical stability under UV light whose energy exceeds the band gap of 3.2 eV in the anatase crystalline phase. The sun can provide an abundant source of photons. however, UV light accounts for the only small fraction (～5 %) of the sun’s energy compared to the visible region (45 %). Many techniques have been examined to achieve this purpose, including the doping of TiO₂ with transition metals (such as Cr, Fe, Ni, V), but these doped materials suffer from thermal instability and an increased number of carrier recombination centers. Many research groups proposed to replace Oxygen by another anionic species (such as C, P, S, N, F) rather than incorporating transition metals into TiO₂. Especially, Nitrogen-doped TiO₂ is often used to improve the photocatalytic properties of TiO₂ in order to achieve visible light response.¹ In this study, the Nitrogen-doped TiO₂ film has been prepared by reactive magnetron sputtering using a Ti target in an Ar/N₂+O₂ gas mixture. Composition and microstructure of these films were investigated by X-ray photoelectron spectroscopy and X-ray diffraction, respectively. Chromatic change of a methylene blue solution was applied to a photocatalytic property. Light irradiation to the TiO₂ film in a methylene blue solution was carried out using a commercial sterilizing lamp as ultraviolet light and a commercial fluorescent lamp as visible light. Transmittance of a methylene blue solution was measured by a spectro photometer. Furthermore, photocurrent between the TiO₂ film and a platinum electrode was measured by a volt-ampere characteristic using an unresisted ammeter in a KCl solution of 0.5 mol/ℓ. In the case of the Nitrogen-doped TiO₂ film, the higher photocatalytic property and photocurrent under a sterilization lamp were obtained at N₂ gas flow rate of 0.6 sccm and 0.4-0.5 sccm, respectively. In the case of a fluorescent lamp, the photocatalytic property showed lower transmittance and photocurrent as compared with that of a sterilization lamp. But transmittance and photo current showed the maximum value at N₂ gas flow rate around 0.5 sccm, so Nitrogen-dope effect was confirmed under a fluorescent lamp.

¹ R.Asahi, et al.; Science, 293(2001)269.