Resonant absorption effects in the diffraction of low energy electrons

Contrary to X-ray diffraction, electron diffraction studies have not incorporated the influences of resonances on the diffracted intensities. In this paper the resonant absorption effect in the diffraction of electrons from surfaces has been studied. The electron absorption of Si(001) was measured in the energy interval 0–250 eV and it shows a large absorption edge around 125 eV. This is compared with the specular reflected beam of a low energy electron diffraction pattern of Si(001) that was measured as a function of electron energy. The intensity of the specular reflected beam has three maxima on the expected Bragg positions and two peaks at electron energies of 102 and 125 eV that cannot be associated with Bragg reflections. The non-bragg peaks are explained as Fano resonance effects due to the configuration interaction of a discrete state with two continua.