Effect of surface microstructures on photo-induced hydrophilicity of NaNbO3 thin films by sol–gel process

The photo-induced hydrophilicity of sodium niobate (NaNbO3) films prepared by the sol–gel method was investigated. Although the films annealed at by 700 and 900 °C exhibited a more heterogeneous microstructure (average grain size: 30–40 nm, 50–80 nm, respectively) than that for films annealed at 500 °C (15–20 nm), the crystallinity and the band gaps of the films were all approximately the same. The films exhibited photo-induced hydrophilicity under UV-B light irradiation. The photo-induced hydrophilic response of the film annealed at 500 °C was higher than those of the films annealed at 700 and 900 °C. It is proposed that the photo-induced hydrophilicity of NaNbO3 films is affected by the surface microstructure.