Elastic and inelastic backscattering of slow electrons from W(001)

Abstract

We have studied angle resolved electron energy loss spectra obtained from EELS experiments on W(001) surfaces. The measurements were carried out for primary energies of 40–600 eV and for various angles of incidence. The inelastically scattered electrons were detected either in the specular direction or in the (11) beam. The main objective of the present study was to gain insight into the combined action of elastic and inelastic scattering. The experimental results are by and large consistent with the well-known two-step model. It is shown that this model can be justified within a one-particle approximation which includes exchange and correlation effects of the ( N +1) electron system. The experimental results lead to the conclusion that the effective potential governing the elastic part of the combined scattering process is different from that of the purely elastic process. The spectra mainly reflect features of the DL (diffraction before loss) contributions to the inelastic scattering. This is understandable if one assumes a finite momentum transfer q in the majority of scattering processes. The q dependence observed for the excitation probabilities of certain losses supports this assumption. We discuss the dispersion of some particularly prominent peaks in the loss spectra. All losses which can safely be correlated with elementary excitations of the N-electron system are compared with corresponding structures that occur in the loss functions.