Optical properties of selectively absorbing Ni/Al2O3 composite films

Abstract

Composite films of Ni particles embedded in an Al₂O₃ matrix have been produced by controlled coevaporation. The optical properties of the Ni/Al₂O₃ composites measured over the range of the solar spectrum are in good accord with the predictions of Maxwell‐Garnett theory provided the Ni volume fraction is ≲0.2. The composite films have excellent spectral selectivity for the absorption of solar radiation, with a solar absorptivity of 0.94 obtained for a film produced with a composition gradient. Low‐temperature emissivities of ∼0.1 have been obtained with composite films evaporated on highly reflecting metal substrates.