A Noble Metal High-Entropy Alloy for Mid-Infrared Metasurfaces

Abstract

High-entropy alloys (HEAs) are promising materials for photonic applications. In such applications, permittivity is essential for numerical studies. In this work, we experimentally determine the complex permittivity of an HEA composed of five noble metals—Au, Ag, Cu, Pd, and Pt. The measurements are conducted across a broad wavelength spectrum, spanning the ultraviolet, visible, and mid-infrared regions. The experiments, numerical simulations of reflection spectra, and analysis of absorption and scattering cross-sections reveal the potential for fabricating perfect absorber and emitter metasurfaces using this noble HEA. In addition, crystallography studies clearly show the formation of a uniform material. The lattice constant and electron work function of the alloy are found to be 0.396 nm and (4.8 ± 0.4) eV, respectively—results indicate that the formed HEA alloy is well mixed.