高分解能電子エネルギー損失分光におけるプローブ分散領域の運動学的解析

Abstract

High-resolution electron energy-loss spectroscopy (HREELS) is a powerful tool for observing an energy dispersion of low-energy surface excitation modes. In the specular-reflection geometry (SRG), a probed dispersion region determined kinematically depends upon the incident angle θ0 and the incident energy E0, while, in the off-specular geometry (OSG) it depends upon θ0 and a scattered angle θS adjusted by the analyzer position. With change in θ0 and E0 in the SRG and with change in θ0 and θS in the OSG, we make a kinematic analysis of the probed dispersion region with special attention to its width. Our analysis shows that, with a grazing angle θ0 fixed and with E0 or θS varied, we can scan a sharply narrowed probed region on a wave number-angular frequency (Q-ω) plane to make an accurate observation of the energy dispersion of surface-excitation modes. An incident electron undergoes an image force, when it incidents on a surface of dielectric material. However, the image force is found to exert no substantial influence on the probed region even at grazing incidence.