Preparation of low-density porous silica thin films by ambient pressure drying

Low-density silica thin films having densities ρ of 0.574-0.957(g/cm3 )and refractive indices n of 1.12-1.20 and porosities ∏ of 61%-77% as well as dielectric constants k of 1.92-2.54 were prepared by a two-step sol-gel process at ambient pressure, with a simple dip-coating procedure, which take the wet gel through solvent exchange and reaction with trimethylchlorosilane(TMCS) without any supercritical drying. The process was optimized by varying the dilution, aging, organic substitution, organic modification, heat treatment and dip-coating conditions. Ellipsometer was used to determine refractive index and thickness of films. Atomic force microscopy (AFM) used to observe the microstructure and surface of thin films. Infrared spectroscopy and anti-reflectance measurement was carried out too. Abrasion-resistant properties were tested by the methods suggested by Floch et.al .