Spectrally selective surfaces of Ni-pigmented anodic Al2O3

Ni pigmentation of anodic Al2O3 is obtained by electrolytic coloration. Durable coatings with good spectral selectivity (a/e≃8) are produced. Scanning electron microscopy, Auger depth profiling, and atomic absorption analysis lead to the formulation of a detailed structural model, its most essential feature being a thin layer comprising a mixture of Ni and Al2O3 located near the bottom of the anodic film. Experimental spectral reflectance data agree well with computer calculations, provided the optical properties of the metal-insulator layer are described with the Bruggeman effective medium theory.