Secondary Electron Emission by Plasmon-Induced Symmetry Breaking in Highly Oriented Pyrolytic Graphite

Werner, Wolfgang; Astašauskas, Vytautas; Ziegler, Philipp; Bellissimo, Alessandra; Stefani, Giovanni; Linhart, Lukas; Libisch, Florian

doi:10.1103/physrevlett.125.196603

Cited by 11 publications

(13 citation statements)

References 54 publications

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“…Moreover, the exchange correlation effects may blue-shift the plasmon by approximately 0.5 eV [ 63 ]. In [ 64 ] ( Figure 2 b), they directly measured the electronic transition in K-space, leading to the π + σ plasmon. While this was carried out on highly oriented pyrolytic graphite, it is nonetheless a confirmation of the red arrow in Figure 9 b corresponding to the σ-σ* transition.…”

Section: Resultsmentioning

confidence: 99%

Low-Energy Electron Inelastic Mean Free Path of Graphene Measured by a Time-of-Flight Spectrometer

et al. 2021

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The detailed examination of electron scattering in solids is of crucial importance for the theory of solid-state physics, as well as for the development and diagnostics of novel materials, particularly those for micro- and nanoelectronics. Among others, an important parameter of electron scattering is the inelastic mean free path (IMFP) of electrons both in bulk materials and in thin films, including 2D crystals. The amount of IMFP data available is still not sufficient, especially for very slow electrons and for 2D crystals. This situation motivated the present study, which summarizes pilot experiments for graphene on a new device intended to acquire electron energy-loss spectra (EELS) for low landing energies. Thanks to its unique properties, such as electrical conductivity and transparency, graphene is an ideal candidate for study at very low energies in the transmission mode of an electron microscope. The EELS are acquired by means of the very low-energy electron microspectroscopy of 2D crystals, using a dedicated ultra-high vacuum scanning low-energy electron microscope equipped with a time-of-flight (ToF) velocity analyzer. In order to verify our pilot results, we also simulate the EELS by means of density functional theory (DFT) and the many-body perturbation theory. Additional DFT calculations, providing both the total density of states and the band structure, illustrate the graphene loss features. We utilize the experimental EELS data to derive IMFP values using the so-called log-ratio method.

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Section: Resultsmentioning

confidence: 99%

Low-Energy Electron Inelastic Mean Free Path of Graphene Measured by a Time-of-Flight Spectrometer

et al. 2021

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“…The white curve is the singles loss-and secondary electron spectrum. Indices "1" and "2" are used to indicate respectively fast and slow electrons arriving at detector 1, the hemispherical mirror analyser (HMA), and 2, the time of flight analyser (TOF) [40]. The green line labeled "E2 = ∆E − φ" indicates the minimum energy loss needed for the slow liberated electron ("2") to reach the vacuum level from the Fermi-level for a given energy loss ∆E where φ = 4.6 eV is the work function of HOPG.…”

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“…We use time-correlated two-electron spectroscopy to establish a causal relationship between energy losses and secondary electron emission [35][36][37][38][39] on a sample of highly oriented pyrolitic graphite (HOPG). In particular, secondary electron-electron energy loss coincidence spectroscopy (SE2ELCS) is employed (see supplemental information [40]) to investigate the relationship between energy losses suffered by exciting a plasmon and the concomitant emission of a secondary electron. Note that for a given energy loss of the primary electron to be feasible, corresponding initial and final states need to exist in order to satisfy energy conservation.…”

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“…The electronic transitions taking place in resonance with the plasmon are explicitly identified experimentally. The experimental results highlight the influence of the complex band structure of HOPG on the plasmon spectrum and the ejection of a secondary electron in the course of the associated interband transition and are interpreted with the aid of density functional theory (DFT) and tight binding (TB) calculations [40]. In particular, when the symmetry of the system is broken in our tight binding model, the resulting hybridisation of the interlayer states with the atom-like σ * 2 -band leads to the ∼3 eV resonance in the SE spectrum.…”

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“…Our experimental results are summarized in Figs. 1-3(a) showing different portions of the electron coincidence spectrum taken in specular reflection geometry at the Bragg maximum for a primary energy of E 0 − E vac = 173 eV (see Ref [40] for details). The white curve in Figs.…”

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

Werner,

Astašauskas,

Ziegler

et al. 2020

Preprint

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Two-particle spectroscopy with correlated electron pairs is used to establish the causal link between the secondary electron spectrum, the (π + σ)−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 ΓA-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 σ * bands along the ΓA-direction. These hybrid states have a high density of states as well as sufficient mobility along the graphite c-axis leading to the sharp ∼3 eV resonance in the spectrum of emitted secondary electrons reported throughout the literature.

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Optical constants of organic insulators in the UV range extracted from reflection electron energy loss spectra

Ridzel

Kalbe

Astašauskas

et al. 2022

Surface & Interface Analysis

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Reflection electron energy loss spectroscopy (REELS) spectra were measured for seven insulating organic compounds (DNA, Irganox 1010, Kapton, polyethylene [PE], poly(methyl methacrylate) [PMMA], polystyrene [PS] and polytetrafluoroethylene [PTFE]). Optical constants and energy band gaps were extracted from the measured REELS spectra after elimination of multiple electron scattering via a deconvolution and fitting the normalised single scattering energy loss spectra to Drude and Drude–Lindhard model dielectric functions, constrained by the Kramers–Kronig sum and f‐sum rules. Satisfactory agreement is found for those optical constants for which literature data exists. For PTFE, the observed features in the optical data correspond to its electronic structure.

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Secondary Electron Emission by Plasmon-Induced Symmetry Breaking in Highly Oriented Pyrolytic Graphite

Cited by 11 publications

References 54 publications

Low-Energy Electron Inelastic Mean Free Path of Graphene Measured by a Time-of-Flight Spectrometer

Low-Energy Electron Inelastic Mean Free Path of Graphene Measured by a Time-of-Flight Spectrometer

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

Optical constants of organic insulators in the UV range extracted from reflection electron energy loss spectra

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