Thin films of SiO2–TiO2 composite oxides with various SiO2:TiO2 compositions were prepared by the sol-gel method, using tetraethylorthosilicate (TEOS) and titanium tetraisopropoxide (TTIP) as precursors. The composition, crystal structure, and chemical bonding configuration of the as-deposited and annealed SiO2–TiO2 thin films were analyzed using Rutherford backscattering spectrometry (RBS), glancing incident angle x-ray diffraction (GIAXRD) and Fourier transform infrared spectroscopy (FTIR), respectively. Optical properties of the films were characterized by spectroscopic ellipsometry and ultraviolet-visible spectrophotometry. The Si/Ti ratios in the SiO2–TiO2 films agree with the TEOS/TTIP molar ratio in the sol-gel precursor. When the TEOS/(TEOS + TTIP) ratio is greater than 40%, the SiO2–TiO2 thin films remain amorphous (without formation of TiO2 crystalline phase) after annealing at temperatures as high as 700 °C. FTIR spectra indicate that the quantity of Si–O–Ti bonding can be maximized when the TEOS:TTIP in the precursor is 80%:20%. The refractive index of the SiO2–TiO2 films increases approximately linearly to the mixing ratio of TTIP/(TEOS + TTIP). However, SiO2-rich films possess higher ultraviolet-visible transmittance than the TiO2-rich films. The modification of microstructure and chemical bonding configuration in the SiO2–TiO2 films by the composition and its influence on the optical properties are discussed.
Influence of annealing on structural and optical properties of n-TiO2 thin films grown by sol-gel spin coating
