Secondary-electron emission spectroscopy and the observation of high-energy excited states in graphite: Theory and experiment

Fine structure in the energy distribution of secondary electrons "back-scattered" from a graphite crystal surface is resolved and shown to be consequence of inelastic electron-electron scattering in which the dominant process is the population of final states above the vacuum level by electron-hole pair production via screened-Coulombic interaction between the incident primary electrons and the valence electrons in the solid. The scattering theory of Kane is applicable and emphasizes that features due to one-electron density of final states should be resolvable in experimental secondary-electron-emission spectra of crystals. Experimental results are presented, which provide strong support for this view. Previous measurements on graphite have been extended and weak secondary-electron-emission structure, resolved in the second derivative of the energy-distribution spectrum, is reported for kinetic energies, $10\lesssim E_{\mathrm{kin}}\lesssim 40$ eV. Maxima are observed at 16.2, 22.2, 29.2, 31.2, 36.2, and 40.7 ± 0.5 eV above the Fermi energy. Details are presented of a first-principles high-energy band-structure calculation of graphite extending over a 80-eV energy range. The observed spectral features correlate closely with final-density-of-states maxima as predicted by the theory.