Paper TF-ThP8
Influence of Microstructure and Surface Morphology on Photofunctional Properties of Titanium Dioxide Film Prepared by Reactive Magnetron Sputtering

Thursday, November 12, 2009, 6:00 pm, Room Hall 3

Since the photoinduced decomposition of water on TiO₂ electrodes was discovered, semiconductor based on photocatalyst has attracted extensive interest. 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 as an energy source can provide an abundant photons, however, UV energy in the sunlight accounts for only a small fraction (～5%) compared to the visible region (45%). Many techniques have been examined to achieve the purpose, i.e. harness of the visible light. Improvement of TiO₂ has been performed by doping transition metals or anionic species, but these doped materials induce thermal instability and an increased number of carrier recombination centers. On the other hand, the relationship between structure and photofunctional properties of TiO₂ has some unclear points. Different TiO₂ structures can be obtained in the reactive magnetron sputtering method by control of O₂ gas flow rate and formation temperature.

In this study, TiO₂ was prepared by reactive magnetron sputtering using Ti target in an Ar/O₂ gas mixture. Composition and microstructure of these TiO₂ films were investigated by XPS and XRD, respectively. The surface morphology of TiO₂ was observed by AFM. Chromatic change of a methylene blue solution was applied as photofunctional property. Light irradiation to TiO₂ in a methylene blue solution was carried out using a commercial sterilizing lamp as UV light and an artificial sunlight lamp (with UV filter) as visible light. Transmittance of a methylene blue solution was measured by a spectrophotometer.

As results of XRD, the crystal structure of TiO₂ turned from a ruttile type into an anatase type by each increase of O₂ gas flow rate and formation temperature (100~300℃). In addition formation temperature had a large effect on TiO₂ surface morphology and roughness. The TiO₂ film prepared with high formation temperature showed a smooth surface. In the case of 300℃ in formation temperature, the higher photofunctional property under irradiation of UV light was obtained at an anatase type (O₂ gas flow rate of 2.5 sccm). In the case of visible light, lower photofunctional property was shown as compared with the case of UV light. However, photofunctional property showed the maximum value at a ruttile type (O₂ gas flow rate of 1.0 sccm) in visible light. The mutual relationship between the photofunctional property and the formation condition was dependent on not only the film structure but also the surface morphology.