Absorption of infrared radiation by a giant enhancement of two-phonon lattice modes at a dielectric-conductor interface

Abstract

Recent experimental work has shown that, at certain frequencies of infrared radiation, there is a giant absorption at the interface between a nanosize graphite substrate doped with copper and diamond nanocrystals grown on the substrate. We propose a model for this absorption based on the Born approach which uses a set of dynamie surface dipoles induced in a conducting medium at its interface with a dielectric and where the frequency of radiation corresponds to a combination of two-lattice vibrations. The wavenumber at which the enhancement oceurs can be determined from the fundamental freauency of the vibrations and the functional dependence of the extinction coefficient as a function of wavenumber can be determined from the relaxation times and the plasma frequencies. An analytical expression for the enhancement absorption factor is derived and it is shown how the cut-off of the absorption band can be used to ascertain the size and shape of conductive nanocrystals.