Nobel metal alloyed thin-films with optical properties on demand

Metallic materials with tunable optical responses can enable the unprecedented control of optoelectronic and nanophotonic devices with enhanced performance, such as thin-film solar cells, metamaterials and metasurfaces for tunable absorbers and optical filters, among others. Here we present the alloying of noble metals, Ag, Au and Cu, to develop a novel class of material with optical response not achieved by pure metals. We fabricate binary mixtures with controlled chemical composition by co-sputtering. Ellipsometry and surface plasmon polariton coupling angle measurements are in excellent agreement when determining the real part of the dielectric function ($\varepsilon $1). Surprisingly, in some cases, a mixture provides a material with higher surface plasmon polariton quality factor than the corresponding pure metals. Our approach paves the way to implement metallic nanostructures with tunable absorption/transmission, overcoming the current limitation of the dielectric function of noble metals.