Electron energy-loss spectroscopy study of the electronic structure of alpha-rhombohedral boron

Electron energy-loss spectra of alpha-rhombohedral boron (alpha-r-B) were obtained from perfect crystalline areas of 180 nm diameter, The onset of the spectral intensity was observed at 2.4 eV (band gap energy). The volume plasmon peak due to the sp valence electrons is at 24.5 eV with a full width at half maximum of 7.5 eV. The real Dart epsilon(1)(omega) and imaginary part epsilon(2)(omega) of the dielectric function were obtained from the loss-function by Kramers-Kronig analysis. The value of epsilon(1)(0) was 6.5. epsilon(2)(omega) showed clear peaks, not observed in epsilon(2)(omega) of beta-rhombohedral boron (beta-r-B) and amorphous boron (am-B). K-shell excitation spectra show several peaks, which are not observed in the spectra of beta-r-B and am-B. The characteristic structure of the peaks showed good agreement with a recent ab initio calculation within the local density approximation. (C) 1997 Academic Press.