Scattering mechanism of electrons interacting with surfaces in specular reflection geometry: Graphite

We have studied the scattering mechanism of electron-energy-loss process in specular reflection geometry highlighting the presence of an elastic collision that always accompanies the inelastic one. It implies that two independent channels contribute to the inelastic cross section depending on whether the inelastic event precedes or follows the elastic one. Our results indicate that neither one of the channels is favored by propensity rules. Nevertheless, suitable experimental conditions permit to enhance contribution to the cross section of one channel with respect to the other. The possibility to single out the contribution of a given channel allows to determine without ambiguity the momentum exchanged in the inelastic collision. This is of fundamental relevance for several electron impact spectroscopies, such as electron-energy-loss spectroscopy and (e,2e), in specular reflection geometry. These results are derived from measuring the current of elastically and inelastically specularly reflected electrons as a function of the primary electron beam kinetic energy (IV curve). The incident beam energy was varied between 150 and 450 eV, the target was an highly oriented pyrolitic graphite and the range of losses investigated was 6-35 eV. A simple kinematics model that accounts for refractive effects due to the surface potential barrier, gives good agreement with the observed diffraction pattern of the elastically reflected electrons. [S0163-1829(99)01519-2].