Role of Nondipole Transitions in Formation of K-Edge Extended Electron Energy Loss Fine Structure

For extended electron energy loss fine structure (EELFS) in the case of ionized K-level, the effects of nondipole processes are estimated at different excitation energies and scattering angles of incident electron. A multiplet resolution converging fast for any scattering angles of incident electron is suggested, and simple analytical expressions up to the quadrupole term are derived. Using these estimates, we have calculated the Al K-edge EELFS spectrum and compared the calculated data with the experimental results. The problem of violation of the dispersion law of secondary electrons is discussed; this problem is caused by the finite lifetime of the excited electronic subsystem of the sample compared to the dispersion law of free electrons.