Studies On Preparation And Optical Characterization Of Modified TiO₂ Thin Films

As a low-cost, non-toxic and chemically stable semiconductor, TiO₂ has been regarded as one of the most extensively investigated materials in the filed of solar cells. However, the inactivity in the visible light region limits the practical applications of TiO₂. Therefore, different elements were doped into TiO₂ to improve the inherently low efficiency of TiO₂ in harvesting sun light by shifting its spectral response into visible light range.In this thesis, pristine TiO₂ thin films were synthesized by sol-gel method and magnetron sputtering systems. Modification of the films was performed by sol-gel and ion implantation methods respectively. Ge was doped into films of TiO₂ by sol-gel method. Fe, Cr ions were implanted into the films by sol-gel method. Fe, Cr were implanted separately and then co-implanted. Ge, Si implantation were carried out on the films deposited by middle frequency magnetron sputtering system. The effect of the doping methods and different ions were investigated on the surface morphology, crystallization, surface chemical states and optical characterization.According to XRD and XPS, TiO₂ films obtained by sol-gel method and magnetron sputtering systems were anatase, and the different optical properties resulted from the difference of surface chemical states and bonds of these two kinds of films. The proportion of sol materials affected the quality of films.Certain optical property improvement was achieved by Ge doped TiO₂ films synthesized by sol-gel method and deoxidization. In comparison to the pristine TiO₂ films, the absorption edge of the doped films (Ge: Ti = 3: 7) had distinct red shife, and the same result appeared on account of polyethyleneglycol joined. The doped films had high crystallinity at atmosphere temperature of 22℃, and the majority of Ge was element based on XPS spectra. In contrast the doped films had low crystallinity at atmosphere temperature of 18℃, and Ge existed mostly in the form of oxides based on XPS spectra.Fe/Cr co-implanted films showed lower crystallinity than the pure TiO₂ films, and in the co-doped films Fe and Cr existed in the form of element and oxides based on XPS spectra. After the implantation of Fe and Cr, optical property of the film was worse than when Fe was doped. The interaction between these two kinds of ions decreased the efficient implanted ions, which made the absorption of the co-implanted films worse than when Fe doped because of the existence of Cr.Unlike the Fe/Cr co-implanted films, optical property of the Ge/Si co-implanted films was improved significantly. Ge and Si ions could promote the optical behavior of the films. However, crystallinity of the flims was destroyed because of the implantation. Si existed in the form of oxides, and Ge existed in the form of element and oxides based on XPS spectra. The interaction between Ge and Si was beneficial to improve the optical property of TiO₂ films.These results provide a valuable reference for the further investigation of visible light sensitive TiO₂ thin films.