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 colli sion that always accompanies the inelastic one. It implies that two indepen dent channels contribute to the inelastic cross section depending on whethe r the inelastic event precedes or follows the elastic one. Our results indi cate that neither one of the channels is favored by propensity rules. Never theless, suitable experimental conditions permit to enhance contribution to the cross section of one channel with respect to the other. The possibilit y to single out the contribution of a given channel allows to determine wit hout ambiguity the momentum exchanged in the inelastic collision. This is o f fundamental relevance for several electron impact spectroscopies, such as electron-energy-loss spectroscopy and (e,2e), in specular reflection geome try. These results are derived from measuring the current of elastically an d inelastically specularly reflected electrons as a function of the primary electron beam kinetic energy (IV curve). The incident beam energy was vari ed between 150 and 450 eV, the target was an highly oriented pyrolitic grap hite and the range of losses investigated was 6-35 eV. A simple kinematics model that accounts for refractive effects due to the surface potential bar rier, gives good agreement with the observed diffraction pattern of the ela stically reflected electrons. [S0163-1829(99)01519-2].