Sol-jel daldırma yöntemi ile hazırlanan modifiye titanyum dioksit tabanlı filmlerin yapısal ve optik özellikleri

In this study, several modified titanium dioxide films were prepared via sol-gel dip-coating method and their structural and optical properties were investigated. Several forms of modified TiO2 films such as metal doped TiO2, nonmetal doped TiO2, metal-nonmetal co-doped TiO2, silver decorated TiO2 and composite TiO2 were prepared and characterized. Firstly, pure titanium dioxide sol was prepared following optimized sol recipe. Prepared sol was transparent, homogeneous and no precipitation was occurred. Pure TiO2 thin film was prepared by sol-gel dip-coating method and its structural and optical characterizations were investigated. It was seen that the crystal structure of pure TiO2 thin film was fully anatase. The XPS survey shows that position of the Ti 2p3/2 peak is close to the reported value by reference and the oxidation level of titanium is +4 as expected. The SEM image reveals that pure TiO2 sample has a homogeneous structure with a particle size between 20 nm and 30nm. The optical absorption edge of the pure TiO2 sample is around 350 nm. The band-gap value was calculated using UV transmission data by Tauc plot method. The band gap of pure TiO2 is about 3.55 eV, which is higher than the reported band gap value for crystalline anatase TiO2. We have prepared nitrogen doped TiO2 thin films via so-gel method as nonmetal doped TiO2 and the effect of nitrogen doping and dopant concentration on structural and optical characterization of TiO2 were studied. It was found that increasing the dopant concentration doesn't decrease the band-gap value and have no effect on crystal structure. Sample doped with 1.5 wt% nitrogen has lowest band-gap value. Iron doped TiO2 thin films with different dopant concentration were prepared and the effect of iron doping and dopant concentration on structural and optical properties of TiO2 were investigated. It was concluded that the band-gap value is decreasing by increasing the dopant concentration. The absorption edge of sample doped with 3 wt% iron relies on visible light region. Silver doped TiO2 thin films with different dopant concentration were prepared and the influence of silver doping and dopant concentration on structural and optical characterization of TiO2 were investigated. The optical absorbance of Ag-doped TiO2 thin films state that the wavelength of the absorption edge does not increase by increasing the dopant concentration. The absorption edge of silver doped samples rely on UV region. We studied three different 3 wt% nitrogen-iron co-doped TiO2 films with different dopants ratio and results are compared with pure TiO2 film. The resulting sols were homogeneous and transparent and no precipitation was observed in any of them. It was seen that dopants ratio changes the opacity of prepared samples and sample with medium dopants concentration was opaque in a short time after dip-coating process. It was found that the dopants ratio has effect on the crystal structure, microstructure, surface morphology and optical properties of the resulting films. Sample with medium dopants concentration has amorphous structure and bigger particle size. We also found that crystalline structure, surface morphology and its optical properties are dependent on dopants ratio of N-Fe co-doped TiO2 films. Silver decorated TiO2 films were prepared. Firstly pure TiO2 thin films were prepared as mentioned above and were dip-coated in silver nitrate aqueous solution. The idea of the preparation of Silver decorated TiO2 films was the photo-decomposition and thermal-decomposition of silver nitrate to metal silver. Several photo-decomposed and thermal-decomposed have been prepared and their optical and structural properties were studied and compared. The surface elemental analysis of photo-decomposed sample reveals the presence of titanium and oxygen element as expected and the silver amount is around 7 atomic percent. Although the surface elemental analysis of thermal decomposed sample shows the presence of titanium and oxygen element as expected but the amount of silver is too low in comparison with photo-decomposed sample. It can be concluded that the silver reduction of photo-decomposition is much higher than thermal-decomposition. The optical absorbance of silver decorated TiO2 thin films states that the optical properties of TiO2 is affected negatively by thermal decomposition of silver nitrate. The absorption edge of the photo-decomposed sample relies on visible light region. Pure ZnO thin film was prepared and the results show that the band gap of pure ZnO is around 3.6 eV which is higher than reported 3.4 eV. TiO2 @ ZnO composite films have been prepared by sol-gel dip-coating method and the effect of sol molar ratio on optical properties of the films were investigated. Three different samples with different titanium to zinc molar ratios were prepared. The absorption edge of TiO2 rich sample is close to the pure TiO2 absorption edge and the absorption edge of ZnO rich sample is close to the pure ZnO absorption edge.