Dependence of photoinduced surface friction force variation on UV intensity and atmosphere in polycrystalline TiO2 thin films

Anatase polycrystalline thin films and a plasma crystallization process were used to investigate the dependence of the photoinduced friction force variation for a TiO2 surface on the UV intensity and atmosphere. Photoinduced friction force variation for UV illumination time was divisible into two stages, decreasing and increasing, where the switching time between these two stages and the degree of variation depended on the UV intensity and atmosphere. The decreasing stage was attributable to the photocatalytic decomposition of organic compound adsorbed onto the surface, whereas the increasing stage was attributed to the capillary effect or an increase in the adsorbed water layer. Results demonstrated that UV intensity and atmosphere controlled the friction force.