Preparation of Thin Films of SnO2 Ultrafine Particles by the

Thin films composed of SnO2 ultrafine particles were prepared by RF-sputtering of a SnO2sintered target under the atmosphere of Ar, and their characteristics were examined by X-ray diffraction method and transmission electron microscopy. The pressure of Ar during the sputtering was a determining factor for the formation of the ultrafine particles. Thin films of almost spherical SnO2 fine particles with about 10 nm in diameter were obtained at the Ar pressure of 13-40 Pa, while amorphous-like films were obtained at the Ar pressure of 4Pa. The intensity of X-ray diffraction lines shows that these ultrafine particles of SnO2 are stacked on the film with orientating their C-axes or the axes inclined to the C-axes vertical to the glass substrate. The density of the sputtered films of SnO2ultrafine particles was 3.5-4.0 g/cm3, which was almost 50-60% of the theoretical density of SnO2. This value was much large than that of the films of SnO2 ultrafine particles prepared by the evaporation method of Sn under Ar and O2 atmosphere. The former had larger mechanical strength than the latter, and no breakage or peeling off from the substrates was observed in the former films when an adhesive tape stuck on the films was pulled vertically to the films. Thermal stability of the SnO2 ultrafine particles at high temperature was also examined and only 10% of increase in the particle size was observed after a heat treatment at 450°C for 6 h in air. The sputtered films of the ultrafine particles are considered to be applicable to gas sensors and catalysts, since they have rather high thermal stability and high mechanical strength.