Types of nitrogen incorporation in reactively sputtered titania thin films: Influence on UV-visible, photocatalytic and photoconduction properties

Undoped and nitrogen-doped titania thin films were deposited by reactive DC sputtering technique at various oxygen partial pressures. Three types of nitrogen incorporation, namely chemisorbed, interstitial and substitutional, were identified in the doped films by X-ray photoelectron spectroscopy technique. Chemisorbed and interstitial nitrogen existed in the doped film with 1.2 at.% of nitrogen whereas, a significant fraction of substitutional nitrogen additionally emerged when the nitrogen concentration increased to 2.4 at.%. UV-visible absorbance, UV and direct sun light activated photocatalysis and photoconductive properties of the undoped and nitrogen-doped films were compared. Nitrogen doping did not significantly influence the UV-induced photocatalytic activity. However, the properties such as visible light absorption, photocurrent generation under visible light and solar activated photocatalysis were found to be perceptibly enhanced in the doped film containing substitutional nitrogen. Possible reasons to explain the variations in the film properties are discussed.