Changing character of electronic transitions in graphene: From single-particle excitations to plasmons

Novko, Dino; Despoja, Vito; Šunjić, Marijan

doi:10.1103/physrevb.91.195407

Cited by 61 publications

(94 citation statements)

References 35 publications

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“…Two energy ranges are generally distinguished, with a π plasmon peak in the 6-8 eV range and a σ + π peak at about 25 eV for bulk h-BN and also for graphite [43][44][45][46][47], the position and intensity of the latter peak being strongly dependent on the number of sheets in thin samples. The position of some structures can also be associated with specific interband transitions, particularly if they are correlated with the behavior of ε(q,ω) itself through Kramers-Kronig analyses [43], but some controversy has appeared recently between these two interpretations concerning the nature of the observed signals in 2D systems such as graphene [48][49][50][51]. Actually, deriving well-defined dispersion relations and deciding between the two possibilities is not obvious.…”

Section: B Low-loss Regionmentioning

confidence: 99%

Angle-resolved electron energy loss spectroscopy in hexagonal boron nitride

et al. 2017

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Electron energy loss spectra were measured on hexagonal boron nitride single crystals employing an electron energy loss spectroscopic setup composed of an electron microscope equipped with a monochromator and an in-column filter. This setup provides high-quality energy-loss spectra and allows also for the imaging of energy-filtered diffraction patterns. These two acquisition modes provide complementary pieces of information, offering a global view of excitations in reciprocal space. As an example of the capabilities of the method we show how easily the core loss spectra at the K edges of boron and nitrogen can be measured and imaged. Low losses associated with interband and/or plasmon excitations are also measured. This energy range allows us to illustrate that our method provides results whose quality is comparable to that obtained from nonresonant x-ray inelastic scattering but with advantageous specificities such as an enhanced sensitivity at low q and a much greater simplicity and versatility that make it well adapted to the study of two-dimensional materials and related heterostructures. Finally, by comparing theoretical calculations to our measures, we are able to relate the range of applicability of ab initio calculations to the anisotropy of the sample and assess the level of approximation required for a proper simulation of our acquisition method.

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Section: B Low-loss Regionmentioning

confidence: 99%

Angle-resolved electron energy loss spectroscopy in hexagonal boron nitride

et al. 2017

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“…The v GG terms have been proved to efficiently cut off the spurious interaction between replicas of planar graphenebased systems [18,[45][46][47]. Finally, the EL spectra were computed by…”

Section: Local Density Calculations and Geometry Optimizationmentioning

confidence: 99%

“…A serious drawback stems from the long-range character of the Coulomb potential, which allows nonnegligible interactions between repeated planar arrays even at large distances. To cut off this unwanted phenomenon, we replace v 0 GG by the truncated Fourier integral [18,19,[45][46][47] …”

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confidence: 99%

Plasmon Modes of Graphene Nanoribbons with Periodic Planar Arrangements

et al. 2016

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Among their amazing properties, graphene and related low-dimensional materials show quantized charge-density fluctuations-known as plasmons-when exposed to photons or electrons of suitable energies. Graphene nanoribbons offer an enhanced tunability of these resonant modes, due to their geometrically controllable band gaps. The formidable effort made over recent years in developing graphene-based technologies is however weakened by a lack of predictive modeling approaches that draw upon available ab initio methods. An example of such a framework is presented here, focusing on narrow-width graphene nanoribbons organized in periodic planar arrays. Time-dependent density-functional calculations reveal unprecedented plasmon modes of different nature at visible to infrared energies. Specifically, semimetallic (zigzag) nanoribbons display an intraband plasmon following the energy-momentum dispersion of a two-dimensional electron gas. Semiconducting (armchair) nanoribbons are instead characterized by two distinct intraband and interband plasmons, whose fascinating interplay is extremely responsive to either injection of charge carriers or increase in electronic temperature. These oscillations share some common trends with recent nanoinfrared imaging of confined edge and surface plasmon modes detected in graphene nanoribbons of 100-500 nm width. Plasmons are quantized oscillations of the valence electron density in metals, metal-dielectric interfaces and nanostructures, being usually excited by light or electronbeam radiation. Plasmon-related technologies are expected to receive a burst from nanocarbon architectures [1-10], due to one of the fascinating features of monolayer graphene (MG) [11], i.e., its extrinsic plasmon modes at terahertz (THz) frequencies [12][13][14][15][16][17][18][19][20]. These show much stronger confinement, larger tunability and lower losses [21] compared to conventional plasmonic materials, such as silver or gold. Nowadays plasmons are launched, controlled, manipulated and detected in a variety of graphene-related materials and heterostructures, which suggests that graphene-based plasmonic devices are becoming closer to reality, with the potential to operate on the "THz gap", forbidden by either classical electronics or photonics [4,22,23]. Plasmons with widely tunable frequencies have been observed in graphene nanoribbons (GNRs)-from the nano-to microrange in width [12,14,24,25]. On the theoretical side, density functional and tight-binding (TB) approaches have explored the electronic structure of zigzag and armchair GNRs, with particular attention to the band-gap values of the intrinsic systems, being a major control factor of their plasmonic properties [26][27][28][29][30]. Far fewer studies have been focused on plasmon resonances in GNRs using either a semiclassical electromagnetic picture [31] or a TB scheme [5,32,33], and specializing to THz frequencies. A comprehensive characterization of the dielectric properties of such systems is, however, lacking.Here, we provide an ab initio study o...

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“…[35]). Thus the observed VHS EELS peak values can be rationalized by the contribution of the real part of the dielectric function to the loss function [32,36], effectively shifting VHS EELS peaks away from the corresponding optical values (given by maxima in the imaginary part of the dielectric function).…”

Section: Resultsmentioning

confidence: 99%

Momentum- and space-resolved high-resolution electron energy loss spectroscopy of individual single-wall carbon nanotubes

et al. 2017

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The ability to probe the electronic structure of individual nano-objects at high energy resolution using momentum-and space-resolved electron energy loss spectroscopy in the scanning transmission electron microscope is demonstrated through the observation of confinement of the π plasmon in individual single-wall carbon nanotubes. While confinement perpendicular to the tube axis was identified for all investigated tubes, a variable degree of confinement parallel to the tube axis was attributed to the concentration of topological defects. Spatially resolved valence loss spectra allowed for the identification of a loss peak attributed to a chirality-dependent radial interband transition. Furthermore, the importance of a careful consideration of loss peak momentum dispersions for the interpretation of spatially resolved valence loss spectra is discussed.

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Changing character of electronic transitions in graphene: From single-particle excitations to plasmons

Cited by 61 publications

References 35 publications

Angle-resolved electron energy loss spectroscopy in hexagonal boron nitride

Angle-resolved electron energy loss spectroscopy in hexagonal boron nitride

Plasmon Modes of Graphene Nanoribbons with Periodic Planar Arrangements

Momentum- and space-resolved high-resolution electron energy loss spectroscopy of individual single-wall carbon nanotubes

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