Electrical and hydrophilic properties of TiOx films obtained by plasma enhanced chemical vapor deposition (PECVD) were investigated in connection with OH group content of the films. A microcrystalline TiOx film prepared by rf magnetron sputtering deposition (RFMSD) was used as a reference sample in this study. Compared to the RFMSD film, the PECVD TiOx films had good hydrophilicity after ultraviolet (UV) light irradiation, low dark, and high photoexcited currents in a vacuum and high sensitivity of their dark and photoexcited currents to surface adsorbates. Low dark and high photoexcited currents measured in vacuum for the PECVD TiOx films were explained by the effect of inactivation of the defect states such as dangling bonds by the termination of OH group. Due to this effect, the PECVD TiOx films are referred to as hydro-oxygenated TiOx:OH films in this article. The sensitivity of the photoexcited currents to surface adsorbates noticed for the TiOx:OH films suggests that the surface potential is modified in response to electron affinity of the surface adsorbates during UV light irradiation. This effect contributes to generation of oxidants due to interaction between photoexcited carriers and surface adsorbates and, hence, improves the hydrophilicity of the TiOx:OH films. These results suggest that both the hydrophilicity and electrical properties of the TiOx:OH films are strongly related to the film OH groups.
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Nakamura et al. (2001) studied this question.