Kinematic analysis of a dispersion region probed in reflection electron energy-loss spectroscopy

In high-resolution electron energy-loss spectroscopy (HREELS) with the specular-reflection geometry, a probed dispersion region determined kinematically depends upon the incident angle α and the incident energy E0. With change in α and E0, we make a kinematic analysis of the probed dispersion region with special attention to its width. Simultaneously, we evaluate the effect of the image force (IMF) and the analyzer aperture on the probed region. Our analysis shows that, with a grazing angle α fixed and with E0 varied in a broad range, we can scan a sharply narrowed probed region on the wave number–energy (Q–ω) plane to make a close observation of the dispersion relation of surface-excitation modes. Even at grazing incidence, the IMF has no substantial influence on the probed region, though it operates to reduce the energy-loss intensity remarkably at low E0. When the parameter ℏω/2E0 becomes appreciable compared with the aperture angle, presence of the aperture causes a certain decrease in the width of the probed Q region.