Backscattering yield paradox for samples with perpendicular layers

Special samples with multilayers which are perpendicular to the surface are presently proposed for testing the lateral resolution of surface imaging. Despite considerable progress in theoretical description of the electron transport phenomena in a solid, there is a need for theoretical depiction of the electron transport in samples of this kind. An accurate description can be gained by Monte Carlo (MC) simulations of electron trajectories. We investigated the relation of the backscattering yield (BY) versus the beam position for selected systems with perpendicular layers filled with high, medium and low atomic numbers: Au|Cu|Au, Cu|Au|Cu, Au|Si|Au and Si|Au|Si, for 10 and 5 keV of the primary electron beam. In the MC simulations the BY is of particular importance since it offers a good test of the scattering model. We used the so-called continuous slowing down approximation (CSDA), to account for the inelastic processes. We found a paradox in the calculated relations: the BY may exhibit unexpected values for some beam positions, greater or smaller than those corresponding to elements comprising the layered sample. The origin of this effect is discussed in this work.