TiO2-SiO2 Thin Films Research Articles

Formation of Anatase Nanocrystals in Sol-Gel Derived TiO2-SiO2 Thin Films with Hot Water Treatment

We have successfully prepared transparent and porous anatase nanocrystals-dispersed films by treating the sol-gel derived TiO2-SiO2 films containing poly(ethylene glycol), PEG, with hot water. This process was done at temperatures lower than 100°C under atmospheric pressure, and thus anatase nanocrystals-dispersed films can be formed on various kinds of substrates including organic polymers with poor heat resistance. The changes in structure and composition of the TiO2-SiO2 gel films with hot water treatment were related to the formation process of anatase nanocrystals in the TiO2-SiO2 gel films with hot water treatment. The formation of anatase nanocrystals was found to proceed to hydrolysis of Si–O–Ti bonds and dissolution of SiO2 component. In addition, porous film structure formed by leaching of PEG with hot water treatment led to homogenous dispersion of anatase nonocrystals in the films.

Sol-Gel preparation and optical nonlinearity of CdS microcrystallite-doped SiO2-TiO2 thin films

Sol-gel technique was used to prepare thin films of CdS microcrystallite-doped SiO2-TiO2 glass onto soda-lime glass substrates. The presence of the CdS microcrystallites in the films was verified by using Raman spectroscopy. The evidence of size effects was evident from the absorption spectrum of the thin films. The nonlinear refraction and nonlinear absorption of the thin films were tested by Z-scan technique.

Sol–gel preparation and optical non-linearity of CdS microcrystallite-doped SiO2–TiO2 thin films

Abstract Sol-gel technique was used to prepare thin films of CdS microcrystallite-doped SiO2-TiO2 glass onto soda-lime glass substrates. The presence of the CdS microcrystallites in the films was verified by using Raman spectroscopy. The evidence of size effects was evident from the absorption spectrum of the thin films. The nonlinear refraction and nonlinear absorption of the thin films were tested by Z-scan technique.

Preparation and properties of SiO2-TiO2 thin films from silicic acid and titanium tetrachloride

The preparation of SiO2-TiO2 thin films by the sol-gel method using silicic acid and titanium tetrachloride as starting materials was studied. The homogeneous sols were obtained by the condensation reaction of silicic acid with titanium tetrachloride in methanol-tetrahydrofuran. The dipcoating of slide glasses and silicon wafers followed by heat treatment gave oxide thin films of 88–93% transmittance, 3000–4500 A thickness, and 1.45–1.80 refractive index, depending on heat-treatment temperature and TiO2 content. FT-IR measurement showed that the Si-O-Ti bond is formed even in the sol and films. The variations of film thickness and refractive index on transformation from the gels into the oxides were found to be quite low.

Phase modulated ellipsometry from the ultraviolet to the infrared: In situ application to the growth of semiconductors

Nanocomposite TiO2–SiO2 thin films with different compositions (from 0 to 100 mol% TiO2) 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% TiO2 with a grain size in 6–10 nm range. Whereas, the inclusion of SiO2 enlarges the optical band gap and suppresses the grain growth up to 4 nm in size. High TiO2 dispersion in SiO2 matrix was observed for all mixed materials. The refractive index (at λ = 600 nm) increases linearly with composition from 1.48 (in 100% SiO2) to 2.22 (in 100% TiO2) 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 E0 and Ed, the average oscillators, strength S0 and wavelength λ0 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).

Sorbed water and intrinsic stress in composite TiO2-SiO2 films

Water sorption and stress properties of mixed composition TiO2-SiO2 thin films, formed by reactive evaporative codeposition, were studied. These properties were observed to depend on the composition, and also on the reactive gas pressure and annealing conditions. Process conditions to produce water-free films were established. Detailed stress studies in vacuum and in ambient indicated that intrisic stress also depends on ambient conditions, with irreversible changes occurring during the initial exposure of the films to ambient. This induced opposite types of stress on TiO2- and SiO2-rich films. These observations can be explained in terms of the structural and compositional properties of the films.