Estimating refractive index of thin-film alloys of Cu, Ag, and Au by extension from those of the main metal

Abstract

Due to dependence of nanostructural material properties on the deposition conditions, the refractive index (RI) of a thin-metal alloy can vary by over 100×. For a more accurate RI estimation of thin-film alloys under a specific deposition condition, a model of RI for untested alloys is derived by extension from the alloy’s main element properties. One of the key derivations is to simplify RI polynomial equations into monomial expressions through four assumptions. Thus, a ratio method can accurately predict the RI of thin-film alloys from the properties of their main metals under the same deposition condition. The model is valid in the red to infrared spectrum for thin-film alloys MX where M is one of copper, silver, or gold and X is one or more elements with total concentration <10%.