Infra-red reflectance and transmittance by thin film coatings of some selected metals on glass substrate

Abstract

Reflection and transmission of light serve as key parameters in thin films coatings meant for temperature regulation in warm climates. In this study, the infrared reflectance and transmittance for three different thicknesses of thin films of palladium and platinum were determined. The thin films were made by thermally evaporating various masses of the platinum and palladium on glass substrates. A Shimadzu UV-VIS-NIR Spectrophotometer was used to determine the reflectance and transmittance of the samples from which the spectra were determined. Ex situ measurements, using Point wise Unconstrained Minimization Approach (PUMA) were made to determine the exact thicknesses of the films. Reflectance was found to vary with film thickness. The results showed that the 60 nm film of palladium had a maximum reflectance of 33%, 140 nm film, a maximum reflectance of 39% and 230 nm film, a maximum reflectance of 72%. For platinum, the 140 nm film had a maximum reflectance of 28%, 146 nm film a maximum of 35% and 395 nm film a maximum reflectance of 42%. In all the cases, the reflectance in the infrared part of the spectra (800-2500 nm) was higher than in the visible region which suggests that palladium and platinum thin films may be used as heat mirrors. The transmittances of palladium and platinum thin films were high (over 80%) an indication that the thin films probably had voids. The study also showed that for the same thickness of palladium and platinum films (Palladium film of 140 nm and platinum film of 140 nm), palladium has greater reflectance than platinum showing dependence of reflectance of thin film on material used for its fabrication.