Interference coating by hydrophobic aerogel-like SiO2 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 aerogel-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 ≤2% in the wavelength range 1000–2000 nm. A minimum transmittance of ≤2% in the wavelength range between 995 and 1085 nm, and the maximum transmittance of ≥80% in the visible range has been obtained from the deposited 12-layer SiO2–TiO2 NIR multilayer reflective coatings.