Analytical applications of elastic electron backscattering from surfaces

Abstract

Measurements of probability of elastic electron backscattering from surfaces can provide information on physical properties of the surface region with thickness comparable to the inelastic mean free path (IMFP) of electrons. The analytical technique, based on such measurements, is known as elastic peak electron spectroscopy (EPES). The most frequent application of EPES is the determination of the IMFP in solids. However, this technique can also be used to measure overlayer thickness, or to determine surface composition. Quantitative applications of EPES, addressed here, require a reliable theoretical model describing the elastic backscattering probability from surfaces with a given structure and composition. Unfortunately, there is no simple analytical model which describes the elastic backscattering probability with an acceptable accuracy. Values of the elastic backscattering probability are usually estimated from Monte Carlo (MC) simulations of elastic backscattering events, since the theoretical model implemented in the MC scheme seems closest to reality, as compared with models leading to different analytical expressions. It is shown that the reliability of the theory is associated with accuracy of the parameters needed in the calculations. The most important parameters are the differential elastic scattering cross-sections which are presently known, especially in some angular regions, with limited accuracy. The IMFP values, determined in different laboratories via EPES, exhibit a considerable scatter, which may be due to the fact that different experimental geometries are used in measurements. Other sources of errors are briefly discussed.