MEASUREMENT OF THE SPECTRAL MOMENTUM DISTRIBUTION OF VALENCE-ELECTRONS IN AMORPHOUS-CARBON BY (E, 2E) SPECTROSCOPY

The spectral momentum density of the valence band of are evaporated amorphous carbon has been measured by (e, 2e) spectroscopy with significantly improved energy resolution relative to earlier studies. The valence band has been studied over a range of momenta from 0 to 1.6 a.u. with a resolution of 0.15 a.u. and over a range of binding energies from 9 eV above to 35 eV below the Fermi energy with a resolution of 1.5 eV. As seen in earlier studies, two major peaks are observed in the spectral momentum density which previously have been associated with sigma and pi bands in graphite. A third feature in the spectra, a weak shoulder approximately 4 eV below the Fermi energy, is observed. A heuristic model is introduced based on the assumption that the spectral momentum density of evaporated amorphous carbon is an angular average of the spectral momentum density of graphite. The behavior of the strongest feature in the experimental spectra is described well by this model, but the other two features, which are in the energy range of the graphitic pi, sigma(2), and sigma(3) bands, are poorly represented by the model. It is suggested that the poor agreement is due to rehybridization of these graphitic bands.