Backscattering yield paradox for samples with perpendicular layers

Abstract

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.

Calculations of Auger intensity versus beam position for a sample with layers perpendicular to its surface

“…These results can be explained qualitatively. In [13] we analysed the dependence of the BY versus beam position for the Au|Si|Au and Au|Cu|Au systems. The BY is the ratio of the total number of electrons emitted from the sample with energies greater than 50 eV to the total number of electrons incident at a given energy and angle of incidence [18].…”

“…We propose the MC simulation which makes it possible to determine the Auger current versus the electron beam position which omits the problem of the BF calculation. Although a theoretical description of the electron transport phenomenon in a solid is now well known, an algorithm applicable to samples with layers perpendicular to its surface has not been developed yet, with the exception of a report devoted to a paradox of backscattering yield (BY) dependence on the electron beam position for the same kind of samples [13].…”

“…In a recent publication, the Monte Carlo (MC) strategy was proposed for the simulation of electron trajectories in a surface region of idealized samples with perfectly flat surface and layers perpendicular to their surface having infinitesimally thin interfaces [13]. Here, we extend this model for calculating the Auger electron signal intensity during the primary beam scan perpendicular to the interfaces.…”