Black metal coatings are metallic coatings that exhibit high absorption in a certain region of the electromagnetic spectra. They are of interest in a wide range of applications such as radiative heat exchangers, solar energy absorbers, photovoltaic cells electrodes, separators to avoid cross effects in optical devices, thermal light emitters, or biosensors electrodes, to name a few. In particular, gold is frequently used due to its high resistance to oxidation.
In this work, we report the fabrication of black gold coatings in the visible range using glancing angle deposition with substrate rotation by magnetron sputtering. The morphological characterization was obtained by scanning electron microscopy (SEM) and atomic force microscopy (AFM), whereas spectral ellipsometry and reflectivity measurements were performed to study the optical behavior. We will present the optical properties of the nanostructured films, showing that high tilt angle is needed to achieve the black metal behavior with reflectivity below 10% in the 400-700 nm range for gold films deposited on Si. We will also analyze the morphological differences between the two obtained optical regimes in order to understand the main features responsible of this black metal behavior.