Silica thin Films Obtaining by Sol-Gel Dip Coating with Controlled Optical Properties

Abstract

Transparent oxide films are widely employed as antireflection or high reflection coatings, band-pass filters and narrow-band-filters in various optical and electronic devices. The performances of these devices are based on interference effects obtained by alternating layers of high and low refractive indices. Different deposition techniques have been employed for coating glasses with different thin films materials. The metal oxides optical coatings can be deposed on glass substrate by CVD and PVD processes. The heterogeneity between the deposit and the glass substrate is the principal cause of the lack of durability of these coatings. Mono or multilayers materials could be used as colored glazing, which is slightly opaque to the human eye but highly transparent to solar energy. The glazing colors are based on interference in the thin-film coating(s) on the reverse side of the glass. Our research group focuses on investigation of single SiO2 and SiO2-TiO2 multilayers, obtained by dip-coating (DC) deposition technique using sol-gel precursors, as suitable glazing for colored solar-thermal collectors. By optimizing the deposition parameters (number of deposition sequences, time between deposition sequences, immersion and extraction rate, temperature) and the precursor properties (concentration, additives, etc.) we are able to tailor the morphological and optical properties of silica coated glass. Consequently the transmittance has increased up to 93% in UV-VIS and IR regions and the reflectance is < 5% in VIS and IR regions. The samples show various morphologies (mostly dense with grains around 30- 40 nm) function of the precursor composition (presence of additives) and concentration.