Black gold coatings fabricated by glancing angle deposition with sputtering

Abstract

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 the last few years, we have fabricated metallic coatings with nanocolumnar morphology by means of glancing angle deposition with magnetron sputtering [1-4]. This technique allows for obtaining nanostructured coatings onto any kind of flat substrates and it can be scaled up to large areas. Depending on the deposition parameters (such as gas pressure, tilt angle, substrate rotation, etc.), the nanocolumnar structure can be controlled, giving rise to different properties. In this work, we report the fabrication of black gold coatings in the visible range with this fabrication technique [5]. We will present the optical properties of the nanostructured films, showing that high tilt angle is needed to achieve the black metal behaviour (see Figure 1) with reflectivity below 10% in the 400-700 nm range for Au films deposited on Si. We will analyse the morphological characteristics of the samples in order to understand the main features responsible for this black metal behaviour.