The photoinduced hydrophilicity of TiO2/WO3 double layer films was fabricated by using a conventional rf-magnetron sputtering method. The photoinduced hydrophilic reaction of the TiO2 surface was enhanced by the presence of WO3 under the TiO2 layer by irradiation of a 10 W cylindrical fluorescent light bulb. However, when the TiO2 and WO3 layers were separated by an insulating layer, the surface did not appeared high hydrophilic,under the same light bulb. The enhanced photoinduced hydrophilic reaction can be explained by the charge transfer between TiO2 and WO3 layers. It was also demonstrated that visible light passing through the TiO2 layer could excite WO3. Thus, visible light can be used for the hydrophilic reaction in the present TiO2/WO3 system.

Thin films of cubic Na0.6WO3, which is one of the sodium tungsten bronze, were fabricated byrf sputtering for the electrode applications in integrated sensors and actuators. A single-phase cubicNa0.6WO3 sputtering target of power type was prepared by conventional solid-state reaction. Thin filmswere deposited from the powder target, and the as-deposited films were amorphous, thus they annealedby tube furnace or RTP for crystallization. Thin films having cubic phase NaxWO3 were fabricated by theoptimization of sputtering and post-annealing conditions, but single-phase cubic Na0.6WO3 thin films werenot obtained. Although the films were not in single phase, they had good electrical conduction propertiesshowing electrical resistivities of 10-4 Ω·cm order.

The powders for the NaxWO3 (x= 1 and 0.75) sputtering targets were synthesized by the calcination in reductive atmosphere. Near single-phase NaWO3 and single-phase Na0.75WO3 powder targets were prepared. By using the targets, thin films of each composition were deposited by rf magnetron sputtering on the SiO2 (100 nm)/Si substrates and annealed by RTP (rapid thermal processing) for crystallization. In the case of the NaWO3 composition, single-phase NaxWO3 thin films, where x was believed to be slightly less than 1, were fabricated accompanying the Na-diffusion into the substrates during RTP. However, in the case of the Na0.75WO3 thin film preparation, it was unable to make single-phase thin films. From the phase formation behaviors of both powders and thin films, it was revealed that NaxWO3 with nonstoichiometric composition of x, which was slightly less than 1, was favorable. The good electrical conduction properties were obtained from the single-phase NaxWO3 thin films. Their electrical resistivities were as low as 7.5 × 10-4 Ω·cm.

CuO doped WO3-SnO2 thick film gas sensors were fabricated by screen printing method on alumina substrates and heat-treated at 350℃ in air. The effects of mixing ratio of WO3 with SnO2 on the structural and morphological properties of WO3-SnO2 were investigated X-ray diffraction and Scanning Electron Microscope. The structural properties of the WO3-SnO2:CuO thick film by XRD showed that the monoclinic of WO3 and the tetragonal of SnO2 phase were mixed. Nano CuO was coated on the WO3-SnO2 surface and then the surface of WO3 was coated with SnO2 particles with 1~1.5 μm in diameters, as confirmed form the SEM image. The sensitivity of the WO3-SnO2:CuO sensor to 2000 ppm CO2 gas and 50 ppm H2S gas for the various ratio of WO3 and SnO2 was investigated. The 4 wt% CuO doped WO3-SnO2(75:25) tkick films showed the highest sensitivity to CO2 gas and H2S gas.