Infrared properties of sol–gel derived zirconia film

Abstract

We examined infrared transmission characteristics of a sol–gel derived zirconia film and the antireflective (AR) effect of this film for an Si substrate in the midinfrared region. The surface reflection loss of an Si plate is high (∼30%) because of the high refractive index (3.42) in the infrared region. We employed zirconia nanoparticle dispersion with 15 wt. % (1-butanol solvent) as starting sol solution. Then, the dispersion was coated with Si substrate at a spin-coating speed of 2000 rpm, and the substrate was heated to 150°C. The number of coatings was repeated seven times. As a result, the transmittance at 5.6-μm wavelength was enhanced to 66.2%, and we found that the coated film worked efficiently as the AR film up to 10-μm wavelength. Additionally, by heating the substrate to 800°C, the large absorptions at 2.9-, 6.4-, and 6.9-μm wavelengths could be suppressed because the hydroxy group in the film was reduced. Its peak transmittance was 67.9% at 4.9-μm wavelength.