Plasmon features in electron energy loss spectra from carbon materials

A phenomenological approach is proposed to derive plasmon energies for C materials as a function of mass density rho and sp(2) fraction It is shown that the energy of the graphite in-plane (pi and pi + sigma) and out-of-plane plasmons, as well as the energy of the diamond bulk (sigma) plasmon are correctly reproduced by the model. Crucial factors in this respect - and responsible for the deviation from a free electron picture - are the energy of interband transitions associated with plasmon excitation and the screening of pi electrons due to sigma electron polarization. Plasmon energies, derived as a function of rho and f, are discussed. (c) 2007 Elsevier Ltd. All rights reserved.