Optical characterizations and refractive index dispersion parameters of annealed TiO2 thin films synthesized by RF-sputtering technique at different flow rates of the reactive oxygen gas

Optical Characterizations of annealed TiO2 thin films have been discussed. Samples have prepared by sputtering technique at different reactive oxygen gas rates, R (1.00% <= R <= 30.00%). The pressure within the sputtering room was fixed at 7.5. 10(-7) Pa by controlling the rate of introducing pure Ar and O-2 gases. All film-samples were annealed in vacuum at 500 degrees C for 2 h. X-ray diffractograms revealed that annealed samples have polycrystalline nature of tetragonal anatase phase. Optical transmission and reflection were employed to study optical properties. Optical energy-gap values decrease from 3.38 eV to 2.91 eV for direct transition and from 3.12 eV to 2.10 eV for indirect transition, respectively. While, Urbach's energy values increase from 686 meV to 884 meV as R-value increased. Wemplee Di-Domenico model and Sellemeier postulate were utilized to study the refractive index dispersion and oscillator parameters. All estimated optical parameters are strongly dependent upon the flow rate of oxygen.