Relationship of the energy-loss function in Au and Ag to transverse and longitudinal excitations

Abstract

A Drude–Lorentz model for the interaction of transverse electromagnetic radiation with a solid is used to study the structural relationships between the energy-loss function and other optical parameters. The presence of interband transitions is shown to lead to the replacement of the peak in the loss function associated with the free-electron-plasma resonance by several peaks and in particular one below and one above the region of interband absorption. These results are consistent with low-energy structure in the loss function for Ag and Au and for these elements containing transitional impurities. Structure in reflectivity is shown to be closely related to structure in the loss function and not to be uniquely determined by the onset of interband transitions. It is argued that there will be a bulk collective plasma mode in Au at 2.5 eV, similar to that in Ag at 3.8 eV, but much more heavily damped.