Electron back-scattering contribution to the electron emission anisotropy by keV range electron beams

The dependence of the electron-excited Auger emission intensity on the incidence direction for surfaces and ultra-thin overlayers has been investigated. The interpretation of the intensity distribution curves is not straightforward due to the superposition of true overlayer focusing-diffraction effects and back-scattering of the beam electrons by the substrate atoms. A multi-step mechanism that involves forward-focusing of the beam electrons in the sub-surface region and their subsequent back-scattering to the surface region has been proposed to explain the non-zero anisotropy of the surface signal. In this work, we systematically test the different assumptions contained in the multi-step model both by direct measure of some of the relevant physical parameters such as the intensity and the anisotropy of the back-scattered electrons by computer modelling of the experimental conditions. Monte Carlo simulations of the electron trajectories and single-scattering cluster calculations helped to get information about the physical quantities which are not directly accessible by experiments. The relationship between the angular anisotropy of the surface signal and the surface structure itself is also discussed. (C) 2001 Elsevier Science B.V. All rights reserved.