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 am orphous carbon has been measured by (e, 2e) spectroscopy with signific antly improved energy resolution relative to earlier studies. The vale nce band has been studied over a range of momenta from 0 to 1.6 a.u. w ith a resolution of 0.15 a.u. and over a range of binding energies fro m 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 sp ectral momentum density which previously have been associated with sig ma and pi bands in graphite. A third feature in the spectra, a weak sh oulder approximately 4 eV below the Fermi energy, is observed. A heuri stic model is introduced based on the assumption that the spectral mom entum density of evaporated amorphous carbon is an angular average of the spectral momentum density of graphite. The behavior of the stronge st feature in the experimental spectra is described well by this model , but the other two features, which are in the energy range of the gra phitic pi, sigma(2), and sigma(3) bands, are poorly represented by the model. It is suggested that the poor agreement is due to rehybridizat ion of these graphitic bands.