Enhancement of the VIS-NIR absorption in a sulfurated-high-entropy film

Abstract

This paper introduces a simple method for a high-entropy film to achieve a high optical absorptance in the visible-near-infrared (VIS-NIR) range by means of a sulfuration process. The as-deposited (NiCrCuFeSi)O films were annealed together with S powders in a vacuum and then desulfurized under the conditions of argon flow protection. Rutherford backscattering spectroscopy results confirm that the S element appears in the sulfurated films (NiCrCuFeSi)OS (referred to as (NCCFS)OS below). Furthermore, the distribution of elements along the depth of the films is no longer uniform but gradient. X-ray diffraction indicates that the (NCCFS)OS films have the same face-centered cubic structure as the as-deposited films, while the CuS and SiO₂ type phases may be generated after sulfuration. Scanning electron microscopy reveals the formation of island-like structures on the surface of the (NCCFS)OS films. The VIS-NIR spectrum shows that the (NCCFS)OS films achieve a high absorptance with low reflectance and low transmittance. After sulfuration, the average absorptance of the (NCCFS)OS films can reach up to 0.9 in the range of 300–1700 nm. The high absorptance of the (NCCFS)OS films may be due to joint contributions of the formation of CuS, gradient distribution of elements, and island-like structures.