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.