High temperature optical degradation of Cr, Ni and Ge films deposited at oblique angle of incidence

Abstract Solar selectivity of three obliquely evaporated materials was measured before and after heat-treatment up to 400°C in air. In the present study, chromium, nickel or germanium films were deposited on aluminium or chromium evaporated substrates. All the films were deposited at 80° oblique angle of incidence on plane substrates. The absorption mechanism for all the coatings is simply believed to be intrinsic. High absorption was found to be dependent on the substrate material, the coating thickness and the preparation conditions. Those coatings prepared in an oxygen atmosphere degraded rapidly upon heating in air at a temperature of about 200°C. Both germanium and chromium surfaces were found to be stable after heat treatment in air up to 300°C. Some nickel films were stable up to 200°C depending upon the preparation conditions. The chemical composition of the surfaces were investigated before and after heat treatment via AES profiling.