Multiple losses in off-specular electron energy loss spectra of thin NaCl films individually resolved in energy and momentum

A LEED system which provides high resolution in energy and momentum simultaneously has been used to record electron energy loss spectra of thin NaCl films epitaxially grown on Ge(100). While measurements in specular geometry show energetically equidistant dipole losses due to single and multiple excitations of the surface phonon polariton, off-specular spectra show multiple loss features which evidently are the result of a combination of one impact and several dipole scattering processes with individually resolved energy and momentum.