Electronic excitations in graphene in the 1-50 eV range: the π and π + σ peaks are not plasmons.

Nelson, Florence J; Idrobo, Juan-Carlos; Fite, John D; Mišković, Zoran L; Pennycook, Stephen J; Pantelides, Sokrates T; Lee, Ji Ung; Diebold, Alain C · Nano Lett · 2014

basic_science · Level V

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Abstract

The field of plasmonics relies on light coupling strongly to plasmons as collective excitations. The energy loss function of graphene is dominated by two peaks at ∼5 and ∼15 eV, known as π and π + σ plasmons, respectively. We use electron energy-loss spectroscopy in an aberration-corrected scanning transmission electron microscope and density functional theory to show that between 1 to 50 eV, these prominent π and π + σ peaks are not plasmons, but single-particle interband excitations.