OPTICAL PROPERTIES OF SELECTIVELY ABSORBING METAL/INSULATOR COMPOSITE FILMS.

The optical properties of Ni/Al//2O//3, V/Al//2O//3, V/SiO//2, V/MgO, Fe/Al//2O//3 and Fe/MgO composite films have been studied with consideration given to their applicability as selective solar energy absorbers. Thin films were produced by coevaporation and the microstructure examined by electron microscopy. The optical properties of Ni/Al//2O//3 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 APP 1STH 0. 2. The Ni/Al//2O//3 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 graded composition. Low-temperature emissivities of similar 0. 1 have been obtained for Ni/Al//2O//3 on a highly reflecting metal backing. The composite Ni/Al//2O//3 is stable at high temperatures in air. The V and Fe composite studies have optical properties different in character from the predictions of Maxwell-Garnett theory and are not as suitable for solar energy applications as Ni composites.