Structural and optical properties of thermally annealed TiO2-SiO2 binary thin films synthesized by sol-gel method

Thermal annealing effects on structural and optical properties of TiO2-SiO2 binary thin films deposited on glass substrate were studied. X-ray diffraction was used to investigate the crystal structure of as-deposited and annealed films at different temperatures (300, 500, 600) A degrees C. The XRD pattern of annealed film at 600 A degrees C showed a growth of anatase TiO2 structure at 24.95. The surface of binary thin films were scanned by the optical microscope and revealed the crack reduction with increasing annealing temperature up to 600 A degrees C. The thickness of binary thin films were derived from spectroscopic ellipsometry data and it was found that the thickness increased linearly with increasing the annealing temperature from room temperature to 600 A degrees C. From the UV-Vis spectrophotometer the optical constants were studied and the optical band gap energies (E-g) were estimated. The results indicated that the annealing leads to an increase in the absorbance and decrease the transmittance. This can be ascribed to the slight increase in crystallite size of the films with increasing temperature. The optical energy gaps of binary thin films were direct and indirect, and both were decreased with increasing the annealing temperature which can be attributed to the homogeneous and regular dispersion of Ti and Si atoms in the mixed films and the formation of Ti-O-Si bond.