Structure and properties of low-n mesoporous silica films for optical applications

The properties and structure of the mesoporous silica films synthesized by dip-coating in evaporation-induced self-assembly are investigated. The nonionic triblock copolymer EO20PO70EO20 has been used as a template in this modified sol–gel process. A strong dependence of the formed structure on the processing conditions, especially humidity, has been revealed allowing an appreciable structure tuning. Low humidity allows the reproducible synthesis of low refractive index films, which were used as optical waveguide supports. They are crack-free, transparent, thermally stable, very smooth, and have a thickness up to 1 μm. Under higher humidity conditions a novel sustained lamellar structure was synthesized, that remains stable upon calcination.The films were characterized by angle-dependent interferometry, small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). 2D photonic crystals made of different materials, such as polymers can be deposited onto these films.