Heat-reflecting windows using gold and bismuth oxide films

Thin gold films sandwiched between certain metal oxide layers possess a high electrical conductivity and high optical transparency. They also have a high infra-red reflectance, and may be used as transparent heat-reflecting coatings if their yellowish tinted colour in transmitted light can be tolerated. The observation window of an enclosure exposed to infra-red radiation was coated with different film combinations, and their effectiveness in reducing the internal temperature rise determined. The reflectance and transmittance of the coatings were measured at λ = 0.56 μ and in the infra-red region using a photometer with a broad bandwidth (0.8-2 μ). Results are given for the following: plain glass; a high reflecting bismuth oxide film on glass; gold film on glass; and gold films sandwiched between bismuth oxide and silicon monoxide coatings. Optimum performance was obtained with a Bi 2 O 3 /Au/Bi 2 O 3 multi-layer of 450/130/450 Å thickness which had a transmittance of 73% for green light and a reflectance of 74% in the near infra-red region, compared with values of 55 and 35% respectively for a gold film of the same thickness without the oxide layers.