TiO2 films were prepared on a silicon or soda-glass substrate using a sol suspension. The TiO2 film on the silicon substrate was composed of pure anatase phase and showed almost no contaminations. In contrast, the TiO2 film on the soda-glass substrate was composed of anatase and brookite phases. The diffusion of Na into the TiO2 film on the soda-glass substrate was observed by XPS, and Na was concentrated on the surface of the film. The yield of the brookite phase increased with decreasing distance from the surface of the film on the soda-glass substrate. Na promoted the formation of the brookite phase, although the preparative procedure was used for anatase synthesis. (C) 2008 Elsevier B.V. All rights reserved.