Triethylene glycol–titanium oxide hydrate hybrid films with high refractive index and surface evenness

Abstract

We have evaluated high refractive index organic–inorganic hybrid films fabricated from a solution prepared from triethylene glycol and titanium(IV) butoxide in N,N-dimethyl acetamide (DMAc). The organic–inorganic hybrid solution in DMAc is homogeneous and stable. The solution was spin-coated on a silicon wafer and a glass plate and dried under nitrogen to give a transparent film. The refractive index (n), transparency, and thickness of the hybrid films fabricated from the solution varied as the film drying conditions and feeding mole ratios between the organic and inorganic compounds were varied. The film drying condition was observed to have a strong influence on the surface evenness of the films. The refractive indices of the films were between 1.62 and 2.16 at a wavelength of ca. 600 nm. Scanning electron microscope (SEM) and atomic force microscope (AFM) results showed that the films were very smooth and that the root-mean-square values (R_a) of the surface roughness of the films were between 0.25 and 2.37 nm depending on the film drying conditions. Values for n and R_a of the hybrid film were 2.06 and 0.25 nm, respectively, when it was annealed at 250 °C. The film transparency and thickness increased with decreasing the annealing temperature. We identify our organic–inorganic hybrid solutions as possible good candidate materials for films with high refractive index and surface evenness.