EIS study of photo-induced modifications of nano-columnar TiO2 films

Long-lasting UV-induced physical and/or physico-chemical modifications of nano-structured TiO2 (anatase) films are highlighted in this work by electrochemical methods. These changes occurring in TiO2 film upon UV exposure are analysed through electrochemical impedance spectroscopy (EIS) measurements. Interfacial capacity measurements show significant and long-lasting modifications of the semiconducting and dielectric properties of TiO2 due to UV exposure. Furthermore, UV exposure significantly modifies the energetic distribution of surface states in the gap of TiO2. Based on Mott-Schottky analysis, the relative dielectric constant is found to increase (from 440 to 870) after UV exposure. An explanation for such an effect is that UV exposure enables hydrogen insertion into the nano-columnar TiO2 film and thereby increases the dielectric constant of the film. (C) 2008 Elsevier Ltd. All rights reserved.