Microstructure and optical dispersion characterization of nanocomposite sol–gel TiO2–SiO2 thin films with different compositions

Abstract Nanocomposite TiO 2 –SiO 2 thin films with different compositions (from 0 to 100 mol% TiO 2 ) were deposited by sol–gel dip-coating method on silicon substrate. Crystal structure, chemical bonding configuration, composition and morphology evolutions with composition were followed by Raman scattering, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy and scanning electron microscopy respectively. The refractive index and the extinction coefficient were derived in a broad band wavelength (250–900 nm) from spectroscopic ellipsometry data with high accuracy and correlated with composition and microstructure. Results showed an anatase structure for 100% TiO 2 with a grain size in 6–10 nm range. Whereas, the inclusion of SiO 2 enlarges the optical band gap and suppresses the grain growth up to 4 nm in size. High TiO 2 dispersion in SiO 2 matrix was observed for all mixed materials. The refractive index (at λ  = 600 nm) increases linearly with composition from 1.48 (in 100% SiO 2 ) to 2.22 (in 100% TiO 2 ) leading to lower dense material, its dispersion being discussed in terms of the Wemple-DiDomenico single oscillator model. Hence, the optical parameters, such optical dispersion energies E 0 and E d , the average oscillators, strength S 0 and wavelength λ 0 and the ratio of the carrier concentration to the effective mass N / m ∗ have been derived. The analysis revealed a strong dependence on composition and structure. The optical response was also investigated in term of complex optical conductivity ( σ ) and both volume and surface energy loss functions ( VELF and SELF ).