Investigations of porous oxides as an antireflective coating for glass surfaces

There is no inorganic material that would satisfy the low index requirement of a single-layer antireflective coating for commercial soda-lime glasses. Such an antireflective coating would increase transmission 4-8% and cause corresponding efficiency increase in devices where energy is transmitted by radiation, e.g., solar collectors, and cathode ray tubes. MgF(2) with an index of 1.38 (vs 1.23 needed) is the lowest index coating material available and widely used by the industry. In this work, possible applications of porous oxide films as an antireflective coating were investigated. A porous aluminum oxide film is deposited on glass surfaces from a clear organometallic derived sol. The index of the oxide coating is reduced by the presence of pores hose size is <100 A; this constitutes up to 64% porosity. These pores, being considerably smaller than the wavelength of light, do not interfere with the optical transparency of the material but reduce the index of refraction; thus they make it possible to obtain transparent oxide materials and coatings with very low index.