Air-based sputtering deposition of titanium oxynitride-based single, gradient, and multi-layer thin films for photoelectrochemical applications

Abstract

Titanium oxynitride (TiNxOy) thin films exhibiting tunable physical and chemical properties can be used in many fields. Air-based sputtering deposition of the films with diverse O/N ratios was employed to produce gradient and multilayer films. By solely altering the air/Ar flow ratio, obtained TiNxOy films could change from a crystalline to a mainly amorphous feature. Moreover, the carrier concentration, Hall mobility, and hence resistivity of the films could be modified to a large range. The optical bandgaps of the films could also be tailored to a wide extent. Based on these results, the gradient TiNxOy layer and TiNxOy/TiN(O) multilayer were also deposited on TiN(O)-coated glass substrates for the assessment of photoelectrochemical performance. Compared with the TiNxOy/TiN(O) bilayer with the best photoelectrochemical performance, the photoelectrochemical currents of gradient TiNxOy films could be improved from 99 ± 2 μA⋅cm−2 to 164 ± 2 μA⋅cm−2 by taking advantage of bandgap engineering. Additionally, the photoelectrochemical currents of TiNxOy/TiN(O) multilayer were further improved to 175 ± 6 μA⋅cm−2. This is mainly due to conductive nano TiN(O) layers providing multiple high-transport paths while allowing light transmission. The enhancement mechanisms of the gradient and multilayer films have also been elaborated.