Preparation And Optical Properties Of Mg/N Co-doping TiO₂ Thin Films

Titanium dioxide（TiO₂）is widely used in the field of photoelectricity,solar cells,water decomposition and water purification due to its non-toxic,high chemical stability,good photostability and strong oxidation ability.However,TiO₂has large band gap energy（about3.2e V for anatase type TiO₂）and fast electron hole recombination,which limits the application of TiO₂in more fields.Therefore,the photocatalytic performance of TiO₂can be improved by controlling the exposed crystal surface,increasing the specific surface area and increasing the light absorption capacity.Doping metal or nonmetallic elements can reduce the band gap energy of materials by creating intermediate gap states,changing the minimum conduction band of materials,or changing the maximum valence band of materials.In this thesis,the structural characteristics,preparation and characterization methods of titanium dioxide thin films are described.TiO₂films,Mg-doped TiO₂films and Mg-N co-doped TiO₂films with different concentrations were prepared on glass and silicon substrates by sol-gel method.The structure,elements,two-dimensional morphology,three-dimensional morphology and optical properties of the samples were analyzed by X-ray diffractometer（XRD）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscope（SEM）,atomic force microscope（AFM）,ultraviolet-visible spectrophotometer（UV-Vis）and Raman spectroscopy.The experimental results are as follows:（1）The prepared titanium dioxide is Anatase,and（101）crystal surface is selected for growth.When the sol concentration is 0.52 mol/L,the crystallinity is the highest and the film’s dense crystal quality is the best.The sample has the best absorption effect on visible light,and its band gap is 3.279 e V.（2）Doping Mg does not change the crystal phase of TiO₂,and the sample is still anatase.The crystal size is uniform,the absorption edge is redshifted,and Mg doping can effectively improve the optical properties of TiO₂.When the Mg doping amount is 2.00 at%,the photoabsorptivity of TiO₂is the highest,and the band gap decreases to 3.127 e V.（3）The crystal type of Mg-N co-doped TiO₂film sample is still anatase phase.The addition of N decreases the（101）diffraction peak of TiO₂,decreases the grain size,and increases the absorbance generally.Ti2p detected the spin-orbit coupling peaks Ti2p_3/2and Ti2p_1/2,and the spin-splitting peak splitting distance was 5.788 e V,which was consistent with the characteristics of TiO₂.When the N doping amount was 7.50 at%,the absorbance of Mg-N co-doped TiO₂film was the highest,and the band gap of TiO₂was reduced from 3.127eV to 2.694 eV.