Surface characterization of sputtered N:TiO2 thin films within a wide range of dopant concentration

Nitrogen-doped titanium dioxide thin films were deposited using a new approach, which involves the sputtering of a sintered TiN target in a reactive DC magnetron discharge running in O2/Ar mixtures. Based on the higher chemical affinity of titanium for oxygen compared to nitrogen, samples with N concentrations ranging between 1.1 and 9.3 at% were conveniently prepared by adjusting the gas composition in the deposition chamber. Surface characterization of the prepared thin films was done by using X-ray photoelectron spectroscopy, atomic force microscopy and contact angle measurements, while film crystallinity was checked with an X-ray diffraction. The current results show how the dopant content can be controlled by adjusting the oxygen intake in the films during reactive discharge deposition. The XPS spectra clearly show that nitrogen–titanium bonds are formed. Nitrogen doping induces broadening of the valence band, and, consequently, narrowing of TiO2 band gap. Additionally, doping affects the surface morphology, as demonstrated by atomic force microscopy and contact angle data. The effect of carbon contaminant removal under UV irradiation on the hydrophilic conversion process is discussed.