Noble metal high-entropy alloy paves the way for mid-infrared metasurfaces
image: The bottom part of the image schematically shows the atomic-level alloying of the HEA, as confirmed by X-ray diffraction (XRD) analysis.
Credit: Yoshiaki Nishijima, Teruaki Sudo, Yasutaka Matsuo, Saulius Juodkazis
A recent study published in Engineering has delved into the properties of a high-entropy alloy (HEA) composed of five noble metals—gold (Au), silver (Ag), copper (Cu), palladium (Pd), and platinum (Pt). This research aimed to explore the potential of such alloys in mid-infrared metasurfaces.
High-entropy alloys, as the name implies, are alloys that consist of multiple principal elements, typically five or more, in approximately equimolar ratios. These alloys have drawn significant attention in recent years due to their unique properties, which can deviate from those of traditional alloys. The current study focuses on the application of a noble metal-based HEA in the field of mid-infrared metasurfaces.
The researchers experimentally determined the complex permittivity of this noble metal HEA. Permittivity is a crucial property that describes how a material responds to an electric field. By measuring the permittivity in a wide range of wavelengths, from ultraviolet through visible to mid-infrared, they were able to gain a comprehensive understanding of the alloy’s optical behavior. The measurements were carried out using sophisticated experimental techniques to ensure accuracy.
For instance, in infrared sensing, perfect absorber metasurfaces can be designed to detect specific infrared wavelengths with high sensitivity. In thermal imaging, emitter metasurfaces can enhance the resolution and accuracy of thermal cameras, enabling better detection of temperature differences in objects.
In addition to permittivity, the researchers also determined other important properties of the noble HEA. The lattice constant of the alloy was found to be 0.396 nm. The lattice constant is a fundamental parameter that describes the size and symmetry of the crystal lattice in a solid material. It affects various physical properties such as mechanical strength, electrical conductivity, and optical behavior.
The electron work function of the alloy was also determined. The work function is the minimum energy required to remove an electron from the surface of a material. This property is significant in understanding the material’s electrical and chemical reactivity, especially in applications involving charge transfer, such as in electronic devices and catalysis.
This study on the noble metal high-entropy alloy provides valuable insights into the potential of such materials in mid-infrared metasurfaces. The findings open up new possibilities for the development of advanced optical devices and systems operating in the mid-infrared range. Further research in this area could lead to the optimization of the alloy’s properties and the realization of more efficient and functional mid-infrared metasurfaces.
The paper “A Noble Metal High-Entropy Alloy for Mid-Infrared Metasurfaces,” is authored by Yoshiaki Nishijima, Teruaki Sudo, Yasutaka Matsuo, Saulius Juodkazis. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.01.017. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.