Determination of yield ratios of elastically backscattered electrons for deriving inelastic mean free paths in solids

Abstract

Intensity ratios of electrons backscattered elastically from thick, amorphous Si, polycrystalline Ag and Au, as well as various (vacuum evaporated, electrodeposited layers and metallic sheets) polycrystalline Ni samples, were measured using high energy resolution and two different experimental geometries (0° and 50° primary and 50° and 0° scattered beam angles relative to the surface normal, respectively) in the range of 1-5 keV primary electron beam energy. The elastic yield ratios obtained experimentally are compared to the results computed by Monte Carlo simulations using different algorithms and different sets of parameters. In the case of measured elastic yield ratios Si/Ni, Ag/Ni and Au/Ni, systematic differences were observed between the respective values obtained for two experimental geometries, whereas each Monte Carlo calculation predicted similar ratios for the different geometries. For the Si/Ag, Si/Au and Ag/Au elastic yield ratios, however, good agreement is observed between experiment and calculation, resulting in similar ratios for each geometry. As a conclusion to our study, we suggest that when using a polycrystalline Ni standard reference sample for measuring elastic yield ratios the homogeneity of the sample should be ensured. Our results confirm the applicability of elastic peak electron spectroscopy in the case of these solids for deriving IMFP values, i.e. no significant role of surface effects on the elastic yield ratios can be identified in the primary beam energy range studied.