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