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 q and sp2 fraction f. It is shown that the energy of the graphite in-plane (p and p + r) and out-of-plane plasmons, as well as the energy of the diamond bulk (r) 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 p electrons due to r electron polarization. Plasmon energies, derived as a function of q and f, are discussed.