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 (similar to 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 degrees C. The number of coatings was repeated seven times. As a result, the transmittance at 5.6-mu m wavelength was enhanced to 66.2, and we found that the coated film worked efficiently as the AR film up to 10-mu m wavelength. Additionally, by heating the substrate to 800 degrees C, the large absorptions at 2.9-, 6.4-, and 6.9-mu m wavelengths could be suppressed because the hydroxy group in the film was reduced. Its peak transmittance was 67.9 at 4.9-mu m wavelength. (c) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)
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