Peparation, Characterization And Properties Of Nanotitanium Dioxide Thin Films

Nanotitanium dioxide thin films in the field of environment and energy such as photocatalytic wastewater treatment,atmospheric governance and dye-sensitized solar cells show many outstanding advantages,including super chemical stability,high biological activity and good photocatalytic performance,in recent years,it has been widely studied.However,due to the structural defects of TiO₂,it is still in the experimental exploration stage because of its low utilization rate of light energy when it is used in the photocatalytic degradation of pollutants.Therefore,the research scholars on how to improve the utilization of light energy TiO₂ launched a lot of research,It is very important to study the structural defects of TiO₂ thin films by using the surface plasticity,so as to broaden its research on the utilization of light energy.In this paper,TiO₂ thin films were synthesized by magnetron sputtering（MS）,electron beam evaporation（EBE） and atomic layer deposition（ALD） on substrates of silicon and quartz glass. As for the TiO₂ thin films of MS and EBE,the effects of annealing temperature in N2 atmosphere on phase-structure, microstuctures and optical properties were studied. For the TiO₂ synthesized by ALD,we explore the TiO₂ crystal structure,microstructures and optical properties on different annealing conditions of different cycle period.And the films were characterized by X-ray diffraction,field emission scanning electron microscopy,atomic force microscopy, Raman spectroscopy,transmission electron microscopy and ultraviolet-visible transmission spectroscopy.The results show that the deposited TiO₂ thin films prepared by MS（MS-TiO₂） and EBE（EBE-TiO₂） are continuous and smooth film with amorphous, after 400 ℃-5min annealing,MS-TiO₂ turned into anatase. When the temperature was increased to 600℃, crystal structure has not change.When the annealing conditions add up to 500℃-5min of EBE-TiO₂,phase-structure turn into anatase,Which is restricted by annealing time and the crystallization is not obvious.The optical transmittance both the deposited and annealed samples of MS-TiO₂ and EBE-TiO₂ is very high,which is related to the principle of physical vapor deposition.In addition,the band gap of TiO₂ after annealing has a blue-shift relative to the as-deposited TiO₂,and For annealed film,with the increase of annealing temperature,the band gap has red-shifted.As for atomic layer deposition of TiO₂ thin films（ALD-TiO₂）, we studied the crystal structure, morphology and optical properties of 1200 cycles, 2100 cycles and 6000 cycles of TiO₂ respectively.It found that ALD-TiO₂ showed obvious grain structure, its intensity, particle size and roughness related to the number of cycles. The XRD and TEM characterization of the samples was carried out to find the crystal form of the deposited TiO₂ with a cyclic period of 1200 cycles.In addition, due to the different cycle number of the TiO₂ surface roughness and intensive degree, resulting in optical transmittance has difference.The optical transmittance of the annealed TiO₂ varies with the change of the surface roughness of the film,the effect of oxygen vacancy concentration and O-Ti-N compound on the bandgap is also changed.Combined with MS, spin coating,reactive ion etching and annealing drying, assembled SiO2 colloidal spheres with a certain void structure on silicon and quartz glass with Ti films,and load 2100 cycles TiO₂ in the surface and voids of colloidal spheres by ALD which we named as coated TiO₂ films. The effects of annealing on the crystal structure, microstuctures and optical properties were discussed.With 10mg/L methyl orange solution as the target pollutants, compared to the same period the number of deposition（2100cycles） of the pure TiO₂ and coated TiO₂ photocatalytic properties.The results have shown that the coated TiO₂ would cover a layer of TiO₂ aggregation particles because of the cycle period. After annealing,the crystallization quality was more perfect,surface roughness has a decreasing trend and the increase of oxygen vacancy concentration also leads to blue-shift of absorption edge.Compared pure TiO₂, the Raman enhancement effect of coated TiO₂ is more obvious, but the optical transmittance will be limited by thickness. After 9h of UV irradiation,the decomposition rate of methyl orange reached 94% for coated TiO₂ with annealing conditions is 500℃-30 min TiO₂, its photocatalytic performance is better than pure TiO₂.