An Analytic Model for the Dielectric Function of Au, Ag, and their Alloys

An analytical model for the prediction of the dielectric properties of gold–silver alloys is developed. This multi‐parametric model is a modification of the usual Drude–Lorentz model that takes into account the band structure of the metals. It is fitted by a genetic algorithm to the dielectric function of thin alloy films of different gold–silver ratio obtained by ellipsometry. The model is validated for arbitrary alloy compositions by comparing the experimental extinction spectra of alloy nanoparticles with the spectra predicted by Mie theory. Through analysis of the band structure of Au and Ag and the subsequent fitting of measured dielectric functions of alloy thin films, an analytic model for the dielectric function of AuAg alloys is obtained. The model is validated for arbitrary alloy compositions by comparing the experimental extinction spectra of alloy nanoparticles with the spectra predicted by Mie theory.