Origin of solar thermal selectivity and interference effects in nickel–alumina nanostructured films

Selective surfaces for solar to thermal conversion were studied for understanding the main parameters affecting selectivity. For this purpose samples of Ni inclusions into nanoporous anodized aluminum were electrochemically prepared. Their optical reflectance from 200 nm to 17 μm was measured showing a step-like behavior and several interference fringes. Different models were used to interpret this behavior varying several of the involved parameters. The composition of Ni/alumina film is the first cause for selectivity. Interference effects occurring in this film strengthen the step-like behavior of the reflectance spectra and therefore, the selectivity.