Theory of electron energy loss spectroscopy at the surface of a planar stratified medium, application to semiconductor superlattices

Abstract

The nonretarded, macroscopic surface and interface optical vibrational modes of a layered material are theoretically investigated via their electron energy loss spectrum (EELS) in the reflection geometry. For this purpose, a continued-fraction representation of the relevant effective dielectric function of an arbitrarily stratified medium is obtained. For a semi-infinite superlattice two distinct types of vibrational excitations are predicted. The first gives rise to weak EELS continua and consists in Bloch-like interface modes propagating throughout the layered medium. The second type is responsible for strong EELS lines outside the above continua and is associated with evanescent, Fuchs-Kliewer-like surface modes of the superlattice. Application to a model GaAs/InAs superlattice is given for illustration.