Optical and hydrophobic nano-porous silica thin films with low refractive index

Optical and hydrophobic nano-porous silica films with low refractive index were prepared by means of a two-step acid-catalyzed method and sol-gel process using surfactant CH3 (CH2) (15) N(CH3)(3) Br (CTAB)as template, with a simple dip-coating procedure. Methyltriethoxysilane (MTES) and tetraethoxysilane (TEOS) were co-hydrolyzed in different molar ration and were used as precursors. The process was optimized by varying MTES/TEOS ration, sol aging, thermal treatment and dip-coating conditions to obtain good optical films with low refractive index. The infrared spectra of the films thus obtained indicated that they become hydrophobic with the introduction of the methyl groups. Contact angle values for optical hydrophobic films prepared are greater than120 degree supplementing the result. The refractive indices and thickness of optical films are about 1.12-1.21 and about 300-440nm according to different MTES/TEOS ration of 0.2-0.8 using CTAB(2.5 wt %)at 400 degree thermal treatment by Ellipsometry. AFM of the films provide an estimate of the root-mean-square roughness of the surface to be 312(pm). The optical transmittance spectra and mechanical intensity measurement results showed that the films have good optical and mechanical properties. As a result, the moisture-resistant ability of the films was highly improved and the mechanical intensity was improved too.