From Thin Films to Nanopillars: Tunable Morphology of Covellite via Radio Frequency Magnetron Sputtering for Cost-Effective Photothermal Vaporization

Clean water and sanitation are the sixth goal of the United Nation’s sustainable development goals by 2030. Thus, research into expanding clean water supply has been steadily growing. Photothermal vaporization is a technique that utilizes light-to-heat conversion and proper thermal insulation to localize heat and produce steam at accelerated rates at temperatures below 100 °C. Covellite (CuS) has been investigated for this application as it possesses localized surface plasmon resonance (LSPR) in the near-infrared (IR) wavelengths, converting light into heat. However, recent studies on CuS have been limited to preparation via wet chemical methods to achieve nanoscale structures. These methods require an extra step of material transfer, leading to adhesion issues with the working substrate. In this work, we report the growth of polycrystalline CuS nanopillars using rf magnetron sputtering, a high-throughput physical vapor deposition process. By introduction of N2 gas, an etchant, in the plasma, a balance of etching and deposition leads to the formation of CuS nanopillars, thus achieving morphological structures not seen before in other physical vapor deposition techniques. CuS nanopillars were deposited directly onto melamine foam (thermal insulator) with excellent adhesion for photothermal application which achieved a light-to-heat conversion efficiency of 84.8%. Through the optimization of rf magnetron sputtering to fabricate CuS nanopillars, the realization of a cost-effective, industrially scalable photothermal device with batch-to-batch consistency is thus possible.