The combinatorial atmospheric pressure chemical vapour deposition (cAPCVD) of a gradating N-doped mixed phase titania thin film

Abstract

Combinatorial atmospheric pressure chemical vapour deposition (cAPCVD) was used to synthesise a film with gradating nitrogen dopant and phase from anatase to anatase–rutile mixtures on a single film. This is the first time such a mixed graduating system has been reported. The film was characterised via X-ray diffraction (XRD), Raman, wavelength dispersive X-ray (WDX) and X-ray photoelectron spectroscopy (XPS) mapping. Film thicknesses were determined by Swanepoel method manipulations of UV-visible reflectance spectra and side-on scanning electron microscopy (SEM). Electrical resistivities were derived from conductivities measured on a two-point probe and the photocatalytic activity assessed using a novel high-throughput digital image colour analysis method. This allowed for the systematic investigation on the effect of phase composition and nitrogen content on the films' functional properties; indicating the effect of substitutional nitrogen doping and/or increased rutile content on the photocatalytic activity under UVA light and the benefit of substitutional nitrogen doping on the films electrical conductivity. Novel WDX, Raman and photocatalysis mapping tools are presented for derivation of a films Ti : N atomic ratio, anatase : rutile ratio and photocatalytic activity, respectively. Films synthesised by the cAPCVD route analysed in conjunction with mapping analysis tools provide a shortcut to identifying numerous phases and compositions and their functional property relationships on a single film, offering a rapid method for analysis of phase space.