Comparative study of near and far field e.m. scattering response by Au/Ag alloy and core-shell nanoparticles

Far and near field electromagnetic scattering spectra of core-shell and alloy nanoparticles have been calculated in the context of the theory developed by Kerker. The core-shell particles considered are constituted by a spherical core made by Au or Ag with fixed radius, coated by an Ag or Au, isotropic shell of different radius. The needed dielectric functions of the involved metals have been estimated according to a semiempirical standard treatment. The scattering spectra calculated for core-shell and alloy nanoparticles with the same volume ratio show that the plasmon resonance wavelengths for the two geometries are similar, indicating a modest dependence on the internal structure. Conversely, near field scattering intensities and plasmon resonance widths for alloy or core-shell particles display a different behavior, even qualitatively, as a function of the shell volume. The scattering at the interface between the two metals appears to influence to a larger extent the shape of the scattering band, more than the plasmon resonance wavelength.