Yoji Yasuda

New oxygen radical source using selective sputtering of oxygen atoms for high rate deposition of TiO2 films

We have developed a new oxygen radical source based on the reactive sputtering phenomena of a titanium target for high rate deposition of TiO2 films. In this oxygen radical source, oxygen radicals are mainly produced by two mechanisms: selective sputter-emission of oxygen atoms from the target surface covered with a titanium oxide layer, and production of high-density oxygen plasma in the space near the magnetron-sputtering cathode. Compared with molecular oxygen ions, the amount of atomic oxygen radicals increased significantly with an increase in discharge current so that atomic oxygen radicals were mainly produced by this radical source. It should be noted that oxygen atoms were selectively sputtered from the target surface, and titanium atoms sputter-emitted from the target cathode were negligibly small. The amount of oxygen radicals supplied from this radical source increased linearly with increasing discharge current, and oxygen radicals of 1 × 1015 atoms/s/cm2 were supplied to the substrate surface...

Control of Nano-Structure of Photocatalytic TiO2 Films by Oxygen Ion Assisted Glancing Angle Deposition

Control of the nano-structure of TiO2 photocatalytic films by a glancing angle deposition was investigated using an oxygen ion assisted reactive evaporation (OARE) system. The porosity of the film was increased as the incidence angle of Ti vapor increased, and films with clearly separated columnar grains were obtained at an incident angle above 60°. The increase in the porosity led to a significant decrease in UV reflectance and the film deposited at 60° had a large UV absorptance above 80% at 300 nm. The photocatalytic performance of the film, however, did not improve remarkably, since the crystallinity of the film was degraded by the deposition at a high incidence angle above 60°. To improve the crystallinity of the film, control of energy of the incident oxygen ions was attempted. However, only a slight improvement of photocatalytic properties was observed.