Black gold obtained by sputtering glancing angle deposition

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 [1] 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. As the spectrum of the solar radiation exhibits maximum irradiance in the visible range, finding a suitable method to produce black-metal coatings in that range is of fundamental importance. In the last few years, we have followed a low-cost approach to fabricate nanostructured coatings: glancing angle deposition with sputtering. It is energetically efficient, since it takes place at room temperature in one single step and no chemicals are involved (i.e. no recycling problems). Any kind of flat substrate can be used, and with feasible modifications, it can be scaled up to large surfaces. Up to now, we have studied the growth regimes of the nanostructured coatings [2, 3], as well as the antibacterial properties of nanocolumnar films made of titanium [4]. Recently, we have obtained black gold coatings in the visible range with this fabrication technique by rotating the substrate [5]. As it can be seen in the figure, high tilt angle is needed in the deposition to obtain the black behavior. In this work, we will present the optical properties of the black gold films, with reflectivities below 10% in the 400-700 nm range for Au 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 behavior. REFERENCES: [1] A. Y. Vorobyev and C. Guo, J. Appl. Phys. 104, 053516 (2008). [2] R. Alvarez et al., Nanotechnology 24, 045604 (2013). [3] R. Alvarez et al., J. Phys. D: Appl. Phys. 49, 045303 (2016). [4] I. Izquierdo-Barba et al., Acta Biomaterialia 15, 20 (2015). [5 ] A. Vitrey et al., Beilstein J. Nanotechnol. 8, 434 (2017).