Thermo-optical properties of porous silica thin films produced by sol-gel method

In this work, the spectral dispersion of optical constants of porous silica thin films have been presented. To determine the optical properties of porous SiO2 films, the ellipsometer Woolam M - 2000 working in the spectral range 190-1700 nm was applied. The thermo-optical coefficients of porous SiO2 films and thermal thickness dependence in temperature range 25-300 degrees C have been determined. The porous SiO2 layers exhibited low refractive indices. The thermo-optical coefficients of presented samples were negative due to the porous structure of SiO2 films. Moreover, it has been stated that thinness has been independent of temperature. After returning to starting conditions, the refractive indices were closer to starting values which confirmed partial reversibility of the heating and cooling process of porous. The thermal properties of porous silica films have been discussed.