Interference coating by hydrophobic aerogel-likeSiO(2) thin films

The present paper presents a novel method of preparation of hydrophobic aer ogel-like SiO2 thin films by means of a two-step acid/base derived silica s ol at an ambient pressure without any supercritical drying. Crack free aero .-el-like SiO2 thin films having thickness of 100-400 nm, and refractive in dices of 1.13-1.25 have been obtained upon heating at different temperature s. By using the silica aerogel-like thin films as low-refractive index comp onent and sol-gel derived TiO2 as high-refractive index component, a two-la yer 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 rang e 1000-2000 mn. A minimum transmittance of less than or equal to2% in the w avelength range between 995 and 1085 nm, and the maximum transmittance of g reater 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.