Electron Interaction Mechanisms in High Resolution Electron Energy Loss Spectroscopy

Three aspects of the interaction of a low energy electron beam with surface excitations are described. The long range dipolar scattering concentrates the inelastic electrons in a narrow lobe close to the specular reflection. The resulting spectra are quantitatively interpreted by the macroscopic dielectric theory in order to retrieve the infrared dielectric response of the target. Dipolar HREEL spectra of adsorbates obey the metal surface selection rule. Short range impact scattering disperses the inelastic electrons in a broad isotropic distribution. It allows the observation of short wavelength excitations and cancels the dipolar selection rule. Resonance scattering is a particular scattering mechanism which is observed for certain conditions of electron beam energy.