Effective permittivity of dense random particulate plasmonic composites

摘要

An effective-medium theory (EMT) is developed to predict the effective permittivity ε _(eff) of dense random dispersions of high optical-conductivity metals such as Ag, Au, and Cu. Dependence of ε _(eff) on the volume fraction ?, a microstructure parameter-related to the static structure factor and particle radius a, is studied. In the electrostatic limit, the upper and lower bounds of k correspond to Maxwell-Garnett and Bruggeman EMTs, respectively. Finite size effects are significant when jβ ~2(ka) ~3 becomes O(1), where β, k, and n denote the nanoparticle polarizability, wavenumber, and matrix refractive index, respectively. The coupling between the particle and effective medium results in a red-shift in the resonance peak, a nonlinear dependence of εeff on ?, and Fano resonance in εeff.