Enhanced visible light photoactivity and charge separation in TiO2/TiN bilayer thin films

Abstract

Multi-layered thin films of TiO2 and TiN were created by RF reactive magnetron sputtering and were compared with homogeneous thin films of N doped TiO2 having the same thickness. The crystalline, chemical, optical and photoactive properties were measured and discussed in detail. The number of bilayers was kept constant either 9 or 18 bilayers, but the overall composition (TiN to TiO2 ratio) was varied. The TiN and TiO2 layer thicknesses were controlled systematically in order to produce films with TiN to TiO2 ratio ranging from 5% to 28%. The TiN/TiO2 ratio was controlled for both bilayers in order to get the best synergic effect of light absorption/reflection and charge separation based on the generation of the photo-electrochemical current and the photocatalytic activity under UV and visible light. A maximum photocurrent generation was found for thin films having a TiN/TiO2 ratio of 21% and 28% for the 9 bilayer and the 18 bilayer films, respectively. The superiority of the configuration of the 18 bilayer has been confirmed by studying the photocatalytic activity. The photoactive improvement of the bilayered thin films as compared to non-doped TiO2 is the result of the enhanced charge separation at the heterogeneous junction, interfacial effects between TiN and TiO2, which is found to depend on the thickness of the TiN layers. Electronic as well as optical approaches have been presented to explain the superiority of the bilayers strategy. This study has shown that a bilayered morphology of TiN and TiO2 can significantly enhance the photocatalytic and photoelectrochemical behavior of TiO2 under visible light illumination conditions which is applicable to numerous fields.