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Heat treatment and substrate dependant properties of titania thin films with high copper loading


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Copper-doped titania thin films have been prepared on SiO2/Si(100), fused-silica and soda-lime glass substrates by using sol–gel deposition and subsequent annealing in air atmosphere at 200–900 °C. Several experimental techniques [X-ray photoelectron spectroscopy (XPS), wavelength dispersive X-ray fluorescence (WDXRF), Raman spectroscopy, atomic force microscopy (AFM), UV–Vis spectroscopy, energy dispersive X-ray analysis (EDX), photocatalytic activity measurements and hydrophilicity measurements] have been applied to characterize these films. The results demonstrate that the films prepared on SiO2/Si(100) and fused-silica substrates start to crystallize after annealing above 300 °C, then anatase phase is formed. At 700 °C anatase content starts to decrease and from 800 °C the films consist of rutile. Annealing causes a formation of regions with increased Cu concentration, in case of titania films prepared on SiO2/Si(100) substrates. On the other hand films prepared on soda-lime glass substrates show large sodium diffusion into the films, the crystalline nature of the films decreases during annealing and outward segregation of copper compounds does not occur. However, the surface of copper-doped titania films on soda-lime glass appear to be naturally hydrophilic (i.e. surface is hydrophilic without UV irradiation), water droplet contact angles as low as 4.2° were achieved. Influence of annealing time and copper-doping to the photocatalytic activity of thin titania films was also studied by using two organic dyes as model contaminants.