Abstract
Black aluminium thin films were prepared by direct current (DC) pulsed magnetron sputtering. The N-2 concentration in the Ar-N-2 mixture that was used as the deposition atmosphere was varied from 0 to 10%, and its impact on the film growth and optical properties was studied.
A strong change in the film growth process was observed as a function of the N-2 concentration. At a specific N-2 concentration of similar to 6%, the Al film growth process favoured the formation of a moth-eye-like antireflective surface.
This surface morphology, which was similar to the structure of a cauliflower, is known to trap incident light, resulting in films with a very low reflectivity. A diffuse reflectivity lower than 4% was reached in the ultraviolet-visible-near infrared (UV-VIS-NIR) spectral range that corresponds to a value observed for an ultrahigh absorber.
We found that for the preparation of black aluminium, the nitrogen content plays an important role in film formation and the resulting film morphology.