Chemical vapor deposition and characterization of nitrogen doped TiO2 thin films on glass substrates

Photocatalytically active, N-doped TiO2 thin films were prepared by low pressure metalorganic chemical vapor deposition (MOCVD) using titanium tetra-iso-propoxide (TTIP) as a precursor and NH3 as a reactive doping gas. We present the influence of the growth parameters (temperature, reactive gas phase composition) on the microstructural and physico-chemical characteristics of the films, as deduced from X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and ultra-violet and visible (UV/Vis) spectroscopy analysis. The N-doping level was controlled by the partial pressure ratio R = [NH3]/[TTIP] at the entrance of the reactor and by the substrate temperature. For R = 2200, the N-doped TiO2 layers are transparent and exhibit significant visible light photocatalytic activity (PA) in a narrow growth temperature range (375–400 °C). The optimum N-doping level is approximately 0.8 at.%. However, the PA activity of these N-doped films, under UV light radiation, is lower than that of undoped TiO2 films of comparable thickness.