Electron energy loss spectroscopy theory including the effect of electromagnetic retardation

We have developed a theory of electron energy loss spectra (EELS) for reflection geometry that includes the electromagnetic retardation effect. This theory analytically reduces to the standard EELS result when \(\frac{\omega}{c}\) is much smaller than | k ∥ | , where ω and k ∥ are the frequency and the wavevector parallel to the sample surface, respectively, of an elementary excitation created in the scattering process. As a concrete example we calculate the energy loss probability for a Au sample including the electromagnetic retardation effect.