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 alpha and the incident energy E-0. With change in alpha and E-0, 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 alpha fixed and with E-0 varied in a broad range, we can scan a sharply narrowed probed region on the wave number-energy (Q-omega) 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 E-0. When the parameter h omega /2E(0) becomes appreciable compared with the aperture angle, presence of the aperture causes a certain decrease in the width of the probed Q region. (C) 2001 Elsevier Science B.V. All rights reserved.