Composition and degradation of graded metal-carbon solar selective absorbing surfaces

Abstract An investigation of magnetron sputtered graded stainless steel-carbon on copper solar selective absorbing surfaces by Auger electron spectroscopy is described. The composition of the dielectric layer of these surfaces is shown to be almost pure carbon. Optical measurements and Auger spectroscopy of selective surfaces annealed in a continuously evacuated furnace has isolated two degradation mechanisms: oxidation of the metal rich layers of the metal-carbon film, and diffusion of metal components into the copper substrate. Analysis of these results and previous experimental work suggest that this type of selective surface should experience negligible deterioration during the lifetime of a suitably outgassed permanently sealed evacuated collector operating at temperatures below 300°C.