Combinatorial Atmospheric Pressure CVD of a Composite TiO2/SnO2 Thin Film†

Combinatorial atmospheric pressure (cAP)CVD is used to deposit a film of graded composition from mainly TiO₂ to TiO₂/SnO₂ to mainly SnO₂. This is the first cAPCVD study of a TiO₂/SnO₂ system. The thin film is characterized using a range of techniques such as X-ray diffraction (XRD), wavelength dispersive X-ray (WDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and ultra violet-visible (UV-vis) spectroscopy. It is found that, at various positions on the film, there are intimate compositions of TiO₂ and SnO₂. The photocatalytic activity is examined via the degradation of a Resazurin-based ‘intelligent ink’ under 365 nm wavelength irradiation. The change in the concentration of the dye can be monitored by digital imaging alone. The results show how TiO₂-rich regions are photocatalytically active, producing a maximum formal quantum yield of 3.32 × 10⁻⁴ molecules per absorbed photon. The sheet resistance is determined using a four-point probe via the van der Pauw method. The conductivity is highest in the SnO₂-rich and thicker regions of the film, however some of the intimate composite regions of TiO₂/SnO₂ show both conductivity and photocatalytic activity.