Plasmon peak inhomogeneous broadening in reflection electron energy loss spectroscopy from carbon materials

Abstract

In addition to the damping effect on plasmon peak broadening in reflection electron energy loss spectroscopy (REELS), the effect of inhomogeneous broadening is considered. The analysis of experimental data from highly oriented pyrolytic graphite (HOPG) shows that the contribution of inhomogeneous broadening is of the same order as the contribution associated with damping. In other words, the width of plasmon peaks cannot be ascribed only to damping, which is just one among several other contributions in this respect. At variance with other broadening contributions, however, damping is responsible not only for the width of plasmon peaks but also for their energy. For this reason, by showing that accounting for inhomogeneous broadening leads to decrease of the damping parameter, we also show that the plasmon peak-shift associated with damping is less than one could expect otherwise.

High-energy plasmon spectroscopy of freestanding multilayer graphene

“…A three-dimensional (3D) version of the phenomenological two-fluid polarizability function was used in the ADS model to build a dielectric tensor in the optical limit with suitable Drude-Lorentz parameters 19 for modeling of the EEL spectra of multilayer fullerene molecules 20 and MWCNTs. 21,22 In other applications, such a 3D version of the two-fluid model was used to study the variable degree of the sp 2 hybridization for applications in different carbon materials 41 and the in-plane plasmons in HOPG, 42 as well as to deduce the optical conductivity of graphene in order to calculate Casimir forces between graphene layers. 43 However, we need here a strictly 2D version of the two-fluid model with suitable Drude-Lorentz parameters, similar to that used to describe plasmon excitations in single-layer fullerene molecules 44,45 and singlewall carbon nanotubes (SWCNTs).…”

Optical excitations in electron microscopy

“…Finally, there are other configurations that make use of electrons to perform spectroscopy. For instance, reflection electron energy-loss spectroscopy (REELS) has been recently used to determine optical properties of noble metals (Went et al, 2008;Werner, 2006;Werner et al, 2007) and graphite (Calliari et al, 2008) after careful data analysis.…”

Effective medium theory for REELS analysis of amorphous carbon films

“…[10] Before discussing the comparison between experimental and calculated curves, we should note however that thorough reproduction of experimental spectra is beyond the scope of this work. In fact, we are neglecting important spectral contributions, such as inhomogeneous broadening, [5] momentum dispersion and surface excitations. Moreover, multiple scattering was not deconvoluted from experimental spectra to get the single scattering energy distribution.…”

“…[4] and damping constants from Ref. [5] For polycrystalline graphite, parameters are optimized by successive approximations, without error evaluation Bethe-Born factor was calculated for θ c = ω E. Upper curves refer to unirradiated polycrystalline graphite (dotted line) and lower curves to ion-irradiated polycrystalline graphite (dotted line). Experimental spectra are normalized to unit height of the zero loss peak.…”