Photocatalysts with visible light activity have been widely studied in recent years. We have reported on WO₃ films as the high-performance visible-light active photocatalyst [1,2]. These films were deposited by dc magnetron sputtering on heated fused silica substrates at 800 ^oC. It must be preferable for the industrial application that the substrate temperature during the deposition should be lower for the window coatings for automobiles and architectures. In this study, the effect of post-annealing in air and total gas pressure during the deposition were studied. In addition, the loading effects of Pt nanoparticles on the WO₃ film surface were also studied for the improvement of the photocatalytic activity.

The WO₃ thin films were deposited on unheated fused silica glass substrates by dc magnetron reactive sputtering using a W metal target, and with Ar and O₂ as the sputtering and reactive gases, respectively. Post-annealing temperature was varied from 300 to 800 ^oC for the films sputter deposited at total gas pressure of 5.0 Pa. Furthermore, total gas pressure during the deposition was varied from 1.0 to 9.0 Pa. After the post-annealing at 400 or 600 ^oC, Pt nanoparticles were deposited on the WO₃ film surface also by sputtering for 0, 7 or 40 sec. The surface coverage of Pt on the WO₃ films were estimated by X-ray photoelectron spectroscopy. The Photocatalytic decomposition of acetaldehyde (CH₃CHO) on the Pt/WO₃ films was evaluated by the decrease in the concentration in the quartz cell. The visible light source was a Xe lamp with a 410-500 nm band pass filter (1.0 mW/cm² at the film surface).

Figure shows the photocatalytic decomposition for the WO₃ films loaded by the Pt nanoparticles under visible light irradiation. It was found that the potocatalytic activities of the films crystallized by post-annealing（400 ^oC）was superior to the films deposited on the heating substrate at 800 ^oC, which was enhanced by the Pt loadings.

[1] M. Kikuchi, Y. Shigesato, et al., Abstract of the 21st IUPAC SYMPOSIUM (2006) 496.

[2] M. Imai, N. Oka, Y. Shigesato, et al., J. Vac. Sci. Technol. A 30, 031503-1-031503-5 (2012).

[3] N. Oka, Y. Shigesato, et al., APL Materials 3, 104407-1-104407-6 (2015).

[4] N. Oka, Y. Shigesato, et al., Jpn. J. Appl. Phys. 51, 055501-1-055501-5 (2012).