The electronic thickness of graphene

When two dimensional crystals are atomically close, their finite thickness becomes relevant. Using transport measurements, we investigate the electrostatics of two graphene layers, twisted by θ = 22° such that the layers are decoupled by the huge momentum mismatch between the K and K′ points of the two layers. We observe a splitting of the zero-density lines of the two layers with increasing interlayer energy difference. This splitting is given by the ratio of single-layer quantum capacitance over interlayer capacitance Cm and is therefore suited to extract Cm. We explain the large observed value of Cm by considering the finite dielectric thickness dg of each graphene layer and determine dg ≈ 2.6 Å. In a second experiment, we map out the entire density range with a Fabry-Pérot resonator. We can precisely measure the Fermi wavelength λ in each layer, showing that the layers are decoupled. Our findings are reproduced using tight-binding calculations.

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SOME FACTORS LEADING TO ASYMMETRY IN ELECTRONIC SPECTRA OF BILAYER GRAPHENE

International Journal of Modern Physics B ◽

10.1142/s0217979211100060 ◽

2011 ◽

Vol 25 (14) ◽

pp. 1877-1888

Author(s):

RUPALI KUNDU

Keyword(s):

Graphene Layer ◽

Nearest Neighbor ◽

Tight Binding ◽

Energy Difference ◽

Bilayer Graphene ◽

Electron Hole ◽

Binding Model ◽

Site Energy ◽

Coupling Parameters ◽

Electronic Dispersion

We have investigated the effects of in-plane and interplane nearest neighbor overlap integrals (s0 and [Formula: see text]) and the site energy difference (Δ) between atoms in two different sublattices in the same graphene layer on the electronic dispersion of bilayer graphene within tight binding model. We then extended the calculation to include the in-plane next nearest neighbor interactions (γ1, s1) and next to next nearest neighbor interactions (γ2, s2) for bilayer graphene bands. It is observed that [Formula: see text] introduces further asymmetry in energy values of top conduction band and bottom valence band at the K point in addition to the asymmetry due to Δ. In general there is noticeable electron–hole asymmetry in the slope of the bands away from the K point, and also the changes in band widths due to [Formula: see text] as well as the other in-plane coupling parameters. The density of states of bilayer graphene has also been calculated within the same model.

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Towards Perfect Absorption of Single Layer CVD Graphene in an Optical Resonant Cavity: Challenges and Experimental Achievements

Materials ◽

10.3390/ma15010352 ◽

2022 ◽

Vol 15 (1) ◽

pp. 352

Author(s):

Abedin Nematpour ◽

Maria Luisa Grilli ◽

Laura Lancellotti ◽

Nicola Lisi

Keyword(s):

Incident Angle ◽

Resonant Cavity ◽

Experimental Studies ◽

Single Layer ◽

Absorption Enhancement ◽

Perfect Absorption ◽

Cvd Graphene ◽

Graphene Layers ◽

Absorption Increase ◽

Fabry Perot

Graphene is emerging as a promising material for the integration in the most common Si platform, capable to convey some of its unique properties to fabricate novel photonic and optoelectronic devices. For many real functions and devices however, graphene absorption is too low and must be enhanced. Among strategies, the use of an optical resonant cavity was recently proposed, and graphene absorption enhancement was demonstrated, both, by theoretical and experimental studies. This paper summarizes our recent progress in graphene absorption enhancement by means of Si/SiO2-based Fabry–Perot filters fabricated by radiofrequency sputtering. Simulations and experimental achievements carried out during more than two years of investigations are reported here, detailing the technical expedients that were necessary to increase the single layer CVD graphene absorption first to 39% and then up to 84%. Graphene absorption increased when an asymmetric Fabry–Perot filter was applied rather than a symmetric one, and a further absorption increase was obtained when graphene was embedded in a reflective rather than a transmissive Fabry–Perot filter. Moreover, the effect of the incident angle of the electromagnetic radiation and of the polarization of the light was investigated in the case of the optimized reflective Fabry–Perot filter. Experimental challenges and precautions to avoid evaporation or sputtering induced damage on the graphene layers are described as well, disclosing some experimental procedures that may help other researchers to embed graphene inside PVD grown materials with minimal alterations.

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Tuning the electrical properties of exfoliated graphene layers using deep ultraviolet irradiation

Journal of Materials Chemistry C ◽

10.1039/c4tc00522h ◽

2014 ◽

Vol 2 (27) ◽

pp. 5404-5410 ◽

Cited By ~ 30

Author(s):

M. Z. Iqbal ◽

M. F. Khan ◽

M. W. Iqbal ◽

Jonghwa Eom

Keyword(s):

Electrical Properties ◽

Ultraviolet Irradiation ◽

Single Layer ◽

Single Layer Graphene ◽

Graphene Bilayer ◽

Graphene Layers ◽

Exfoliated Graphene ◽

Deep Ultraviolet ◽

Trilayer Graphene ◽

Unique Band

Deep ultraviolet irradiation tunes the electronic properties of mechanically exfoliated single-layer graphene, bilayer graphene, and trilayer graphene while maintaining their unique band structure and electrical properties.

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Electronic properties of single-layer antimony: Tight-binding model, spin-orbit coupling, and the strength of effective Coulomb interactions

Physical Review B ◽

10.1103/physrevb.95.081407 ◽

2017 ◽

Vol 95 (8) ◽

Cited By ~ 25

Author(s):

A. N. Rudenko ◽

M. I. Katsnelson ◽

R. Roldán

Keyword(s):

Electronic Properties ◽

Tight Binding ◽

Single Layer ◽

Orbit Coupling ◽

Spin Orbit Coupling ◽

Spin Orbit ◽

Tight Binding Model ◽

Coulomb Interactions ◽

Binding Model

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Wedge Radius Effects in Mechanical Exfoliation of HOPG: A Molecular Simulation Study

Volume 1: Materials; Micro and Nano Technologies; Properties, Applications and Systems; Sustainable Manufacturing ◽

10.1115/msec2014-4168 ◽

2014 ◽

Cited By ~ 2

Author(s):

B. Jayasena ◽

S. Subbiah ◽

C. D. Reddy

Keyword(s):

Molecular Dynamics ◽

Pyrolytic Graphite ◽

Single Layer ◽

Layered Material ◽

Critical Depth ◽

Graphene Layers ◽

Highly Ordered Pyrolytic Graphite ◽

Single Sheet ◽

Dynamics Simulations ◽

Atomically Flat

We study the effects of wedge bluntness in mechanically exfoliating graphene layers from highly ordered pyrolytic graphite (HOPG), a layered material. Molecular dynamics simulations show that the layer initiation modes strongly depend on the wedge radius. Force and specific energy signatures are also markedly affected by the radius. Cleaving with a larger wedge radius causes buckling ahead of the wedge; larger the radius more the buckling. A critical depth of insertion of 1.6 A° is seen necessary to cleave a single layer; this is also found to be independent of wedge radius. Hence, with accurate positioning on an atomically flat HOPG surface it is possible to mechanically cleave, using a wedge, a single sheet of graphene even with a blunt wedge.

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Coupling of waveguide mode and graphene plasmons

EPJ Web of Conferences ◽

10.1051/epjconf/202125507002 ◽

2021 ◽

Vol 255 ◽

pp. 07002

Author(s):

Jiří Petráček ◽

Jiří Čtyroký ◽

Vladimír Kuzmiak ◽

Pavel Kwiecien ◽

Ivan Richter

Keyword(s):

Low Power ◽

Graphene Layer ◽

Waveguide Mode ◽

Chemical Potential ◽

Temperature Sensing ◽

Graphene Layers ◽

Optical Wavelength ◽

Electro Optic ◽

Photonic Waveguides ◽

Graphene Plasmons

Photonic waveguides with graphene layers have been recently studied for their potential as fast and low-power electro-optic modulators with small footprints. We show that in the optical wavelength range of 1.55 μm, surface plasmons supported by the graphene layer with the chemical potential exceeding ~0.5 eV can couple with the waveguide mode and affect its propagation. This effect might be possibly utilized in technical applications as a very low-power amplitude modulation, temperature sensing, etc.

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Quasicrystalline 30° twisted bilayer graphene as an incommensurate superlattice with strong interlayer coupling

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1720865115 ◽

2018 ◽

Vol 115 (27) ◽

pp. 6928-6933 ◽

Cited By ~ 55

Author(s):

Wei Yao ◽

Eryin Wang ◽

Changhua Bao ◽

Yiou Zhang ◽

Kenan Zhang ◽

...

Keyword(s):

Electronic Structure ◽

Graphene Layer ◽

Rotational Symmetry ◽

Reciprocal Lattice ◽

Double Resonance ◽

Interlayer Coupling ◽

Bilayer Graphene ◽

Lattice Vector ◽

Graphene Layers ◽

Twisted Bilayer Graphene

The interlayer coupling can be used to engineer the electronic structure of van der Waals heterostructures (superlattices) to obtain properties that are not possible in a single material. So far research in heterostructures has been focused on commensurate superlattices with a long-ranged Moiré period. Incommensurate heterostructures with rotational symmetry but not translational symmetry (in analogy to quasicrystals) are not only rare in nature, but also the interlayer interaction has often been assumed to be negligible due to the lack of phase coherence. Here we report the successful growth of quasicrystalline 30° twisted bilayer graphene (30°-tBLG), which is stabilized by the Pt(111) substrate, and reveal its electronic structure. The 30°-tBLG is confirmed by low energy electron diffraction and the intervalley double-resonance Raman mode at 1383 cm−1. Moreover, the emergence of mirrored Dirac cones inside the Brillouin zone of each graphene layer and a gap opening at the zone boundary suggest that these two graphene layers are coupled via a generalized Umklapp scattering mechanism—that is, scattering of a Dirac cone in one graphene layer by the reciprocal lattice vector of the other graphene layer. Our work highlights the important role of interlayer coupling in incommensurate quasicrystalline superlattices, thereby extending band structure engineering to incommensurate superstructures.

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