On a dielectric approach to understand Electron Energy Loss Spectra from carbon materials

A phenomenological approach to understand the low energy Electron Energy Loss Spectra (EELS) from carbon materials is proposed. Within certain approximations, expressions relating the pi and pi+sigma plasmon energy to the material mass density and sp(2) fraction are derived. The characteristic excitation energies of pi and sigma electrons as well as the screening of pi electrons by the sigma electron polarizability are shown to be crucial factors needed to reproduce the experimental dependence of plasmon energies on mass density. A comparison with earlier results shows the more general character of the present ones and allows a better understanding of previous proposals to characterize amorphous carbon by low energy EELS. (c) 2006 Elsevier B.V. All rights reserved.