ABSTRACT
Retarded dielectric theory gives an explicit but complicated formula for the electron energy loss probability in the case of cross-sectional incidence on a multilayer.
This formula predicts suppression of longitudinal bulk modes in thin layers, but experiment suggests that even stronger fìnite-size effects are present. Here we obtain an energy loss formula for the limiting case of an infinite superlattice; the result is much simpler than for a large multilayer and, being expressed in terms of integrals overkz, is well-suited to investigations based on a wavenumber cut-off.
