ROLE OF MULTIPLE DIPOLE SCATTERING IN HIGH-RESOLUTION ELECTRON-ENERGY-LOSS SPECTROSCOPY

A cleaved crystal of GaSe was analyzed by high-resolution electron-ene rgy-loss spectroscopy (HREELS) and its optical parameters were deduced by using the dielectric theory. The angular and intensity distributio ns of the multiple energy losses and gains of low-energy electrons sca ttered on GaSe(0001) were examined in detail, in order to assess the r elevance of the dielectric theory for describing higher-order excitati ons than the first Born approximation. We find a high linear correlati on between the angular shift of the successive peaks recorded on the s pectrum, and we demonstrate that peak intensities are underestimated i n specular measurements. Experimental as well as theoretical implicati ons for HREELS are discussed.