Effect of roughness and nanoporosity on optical properties of black and reflective Al films prepared by magnetron sputtering

•Black Al films were deposited by magnetron sputtering using a N2/Ar gas mixture of ~6.5%.•Microstructure, optical properties, and defect structure of black and classic reflective Al films were investigated.•Black Al films exhibit a moth-eye-like surface capable of> 97% absorption in the wide wavelength range of 190–1200 nm.•The nanoporosity, observed by positron annihilation spectroscopy, is the key property of black films.