Angle-resolved elastic-peak electron spectroscopy: Solid-state effects

Abstract

It has been frequently reported that characteristics of electrons elastically backscattered from solid surfaces (e.g., the angular distribution) are well described by Monte Carlo simulations of electron trajectories in solids. The theoretical model implemented in these simulations requires knowledge of accurate differential elastic-scattering cross sections (DCSs). In computational practice, the DCSs for isolated neutral atoms constituting the solid are used to simplify the calculations. In reality, the interaction potential between an electron and an atom inside a solid is different from the interaction between an electron and an isolated atom. In the present work, we study changes of the DCSs due to agglomeration of atoms. The interaction between an atom and an electron in the solid is approximated by the muffin-tin potential. It has been found that the DCSs are considerably influenced by the agglomeration of atoms for small scattering angles. The difference for silicon reaches 500% for silicon at 200 eV. On the other hand, electron elastic-backscattering probabilities calculated using DCSs from two potentials were only slightly affected. Calculations and measurements of elastically backscattered intensity were compared for 10 elemental solids, a number of emission angles from 35° to 74°, and three energies (200 eV, 500 eV, and 1000 eV). The experimental angular distributions compare very well with the calculated distributions; the mean percentage deviation between them was about 10% at 200 eV, and decreased to about 5% at 1000 eV. Agreement between theory and experiment was not improved when DCSs determined from muffin-tin potentials were used in the calculations. This result justifies the use of DCSs for isolated atoms in theoretical description of elastic-electron backscattering from surfaces.