Interference coating by hydrophobic aerogel-likeSiO2 thin films

The present paper presents a novel method of preparation of hydrophobic aerogel-like SiO2 thin films by means of a two-step acid/base derived silica sol at an ambient pressure without any supercritical drying. Crack free aero.-el-like SiO2 thin films having thickness of 100-400 nm, and refractive indices of 1.13-1.25 have been obtained upon heating at different temperatures. By using the silica aerogel-like thin films as low-refractive index component and sol-gel derived TiO2 as high-refractive index component, a two-layer refractive index gradient SiO2 hydrophobic anti-reflective (AR) coating and a 12-layer SiO2-TiO2 near infrared reflective (NIR) coatings have been successfully deposited on glass substrates. The obtained AR coatings have shown average reflectance of less than or equal to2% in the wavelength range 1000-2000 mn. A minimum transmittance of less than or equal to2% in the wavelength range between 995 and 1085 nm, and the maximum transmittance of greater than or equal to 80% in the visible range has been obtained from the deposited 12-layer SiO2-TiO2 NIR multilayer reflective coatings. (C) 2001 Elsevier Science B.V. All rights reserved.