Secondary Electron Emission by Plasmon Induced Symmetry Breaking in Highly Oriented Pyrolitic Graphite (HOPG)

TL;DR

This study links plasmon-induced symmetry breaking in HOPG to changes in secondary electron emission, revealing how plasmon excitation affects unoccupied band structure and hybridizes interlayer resonances with $\sigma^*$ bands, supported by spectroscopy and theoretical calculations.

Contribution

It demonstrates the causal relationship between plasmon excitation and symmetry breaking, leading to hybridization effects observable in secondary electron spectra in HOPG.

Findings

Plasmon spectrum correlates with unoccupied band structure.

Final state effects influence secondary electron spectrum.

Hybridization of interlayer resonances with $\sigma^*$ bands occurs due to plasmon excitation.

Abstract

Two-particle spectroscopy with correlated electron pairs is used to establish the causal link between the secondary electron spectrum, the $(\pi+\sigma)-$plasmon peak and the unoccupied band structure of highly oriented pyrolitic graphite. The plasmon spectrum is resolved with respect to the involved interband transitions and clearly exhibits final state effects, in particular due to the energy gap between the interlayer resonances along the $\Gamma$A-direction. The corresponding final state effects can also be identified in the secondary electron spectrum. Interpretation of the results is performed on the basis of density functional theory and tight binding calculations. Excitation of the plasmon perturbs the symmetry of the system and leads to hybridisation of the interlayer resonances with atom-like $\sigma^*$ bands along the $\Gamma A$-direction. These hybrid states have a high density of states as well as sufficient mobility along the graphite $c$-axis leading to the sharp $\sim$3\ eV resonance in the spectrum of emitted secondary electrons reported throughout the literature.