Preparation and characterization of nanostructured titanium oxynitride films for the application in self-cleaning and photoelectrochemical water splitting.

• TiO x N y films capped with 10 nm TiO 2 layer are prepared by reactive sputtering. • TiO 2 /TiO x N y are examined for photoelectrochemical (PEC) water splitting. • The optical properties are controlled by nitrogen content in TiO 2 /TiO x N y films. • Annealing could increase the PEC performance of TiO 2 /TiO x N y bilayer films. • Wettability changed from hydrophobic to hydrophilic with ultraviolet illumination. Titanium oxynitride (TiO x N y) films capped with 10 nm titanium oxide (TiO 2) layer were prepared using reactive direct current magnetron sputtering from pure Ti target. Part of the samples was annealed. Energy dispersive analysis of X-ray revealed that all the samples contain nitrogen and the incorporation of nitrogen into the oxynitrides is not linear. Phase investigation by X-ray diffraction showed structural variation with changing oxygen and nitrogen gas flow rates as well as annealing. Anatase, brookite, rutile and titanium nitride were detected individually or mixed in the as-prepared and annealed samples. The optical properties were found to be controlled by a structure and chemical composition. Transmittance and reflectance measurements were carried out by a high performance double beam ultraviolet-visible-near infrared spectrophotometer. Based on that, the energy band gap, refractive index and extinction coefficient were derived. The obvious difference between the dark and light currents indicated the validity of the TiO 2 /TiO x N y bilayer samples to act as photoanodes. All the annealed samples have photoelectrochemical water splitting response better than the as-prepared samples. The as-prepared TiO 2 /TiO x N y bilayer films were hydrophobic (contact angels, 81° - 93°) and their contact angles were independent from the nitrogen content. The annealed samples have lower contact angles than the as-prepared samples. The wettability of the as-prepared and annealed samples was changed from hydrophobic to more hydrophilic with increasing illumination time. These results are of important interest for the self-cleaning surfaces. [ABSTRACT FROM AUTHOR]