Long-range atomic ordering and variable interlayer interactions in two overlapping graphene lattices with stacking misorientations

Ohta, Taisuke; Beechem, Thomas E.; Robinson, Jeremy T.; Kellogg, G. L.

doi:10.1103/physrevb.85.075415

Cited by 32 publications

(38 citation statements)

References 41 publications

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“…As we saw via low energy electron diffraction, the twist angle in our samples varied slightly, over a few µm length-scale. 33,34,59 Because of the small superlattice BZ, the experimentally observed states from slightly different twist angles would be broadened with their intensity decaying rapidly, especially for those created by folding at superlattice BZ boundaries. The likelihood of observing these folded states would decrease correspondingly.…”

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confidence: 99%

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Evidence for Interlayer Coupling and Moiré Periodic Potentials in Twisted Bilayer Graphene

et al. 2012

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confidence: 99%

“…33. This fabrication procedure results in >100µm domains with random rotational orientation between two graphene lattices.…”

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Evidence for Interlayer Coupling and Moiré Periodic Potentials in Twisted Bilayer Graphene

et al. 2012

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“…Transfer techniques yielding large domains of twisted bilayers over a macroscopic sample [28] and quantitative, fast, Raman characterization tools [29,30] have recently been proposed. However, despite the fact that rotated graphene layers are readily available and a number of measurements have confirmed that large twist angles lead to an electronic decoupling of stacked graphene layers [3,11,24,[31][32][33][34], few experiments tackle the electronic properties for sufficiently small angles ( < 15 ) [13,35,36].…”

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Unraveling the Intrinsic and Robust Nature of van Hove Singularities in Twisted Bilayer Graphene by Scanning Tunneling Microscopy and Theoretical Analysis

et al. 2012

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Extensive scanning tunneling microscopy and spectroscopy experiments complemented by firstprinciples and parametrized tight binding calculations provide a clear answer to the existence, origin, and robustness of van Hove singularities (vHs) in twisted graphene layers. Our results are conclusive: vHs due to interlayer coupling are ubiquitously present in a broad range (from 1 to 10 ) of rotation angles in our graphene on 6H-SiC(000-1) samples. From the variation of the energy separation of the vHs with the rotation angle we are able to recover the Fermi velocity of a graphene monolayer as well as the strength of the interlayer interaction. The robustness of the vHs is assessed both by experiments, which show that they survive in the presence of a third graphene layer, and by calculations, which test the role of the periodic modulation and absolute value of the interlayer distance. Finally, we clarify the role of the layer topographic corrugation and of electronic effects in the apparent moiré contrast measured on the STM images. DOI: 10.1103/PhysRevLett.109.196802 PACS numbers: 73.22.Pr, 61.48.Gh, 68.37.Ef, 73.20.At Soon after the discovery of the unique electronic properties of graphene [1-3], suggestions were made for engineering the band structure of this material. It has been proposed that periodic potentials with wavelengths in the nanometer range could lead to anisotropic renormalization of the velocity of low energy charge carriers [4] or to the generation of new massless Dirac fermions [5]. Experimental works intended for verifying these theoretical predictions were recently reported [6][7][8], where the periodic perturbation was generated either by a lattice mismatch with the supporting material or by a self-organized array of clusters. An alternative route for modifying graphene's band structure would be to exploit a rotation between stacked graphene layers [9]. According to calculations, for large angles ( !15 ) the low energy band structure of graphene should be preserved [10][11][12]. For intermediate angles (1 15 ), it is predicted that, while the linear dispersion persists in the vicinity of the Dirac points of both layers, the band velocity is depressed and two saddle points appear in the band structure, giving rise to two logarithmic van Hove singularities (vHs) in the density of states (DOS) [9,[13][14][15][16][17][18]. For smaller angles ( 1 ) weakly dispersive bands appear at low energy [19,20] with sharp DOS peaks very close to the Dirac point [17,18].Twisted graphene layers are commonly found on different substrates, such as metals [13,21,22], the C face of SiC [23][24][25], or graphite surfaces [26,27]. Transfer techniques yielding large domains of twisted bilayers over a macroscopic sample [28] and quantitative, fast, Raman characterization tools [29,30] have recently been proposed. However, despite the fact that rotated graphene layers are readily available and a number of measurements have confirmed that large twist angles lead to an electronic decoupling of stacked graphene layers [...

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“…The sampled area then includes domains 2 and 1, and it is obvious that two grains of different azimuthal orientations are now probed since this LEED pattern just represents a superposition of the patterns shown in the upper two panels. The characteristic additional diffraction spots, 41 originating from rotated/twisted layers are not discernable. To further emphasize that grains of six layers of graphene can form on the C-face and be stacked in such a way that no rotational disorder exists between adjacent layers, some PADs of the p-band were also recorded.…”

Section: (D)mentioning

confidence: 93%

“…In selected area LEED, not only two rotated (1 Â 1) patterns would then be seen but also characteristic additional diffraction spots, originating from the sum and difference between the two sets of reciprocal lattice vectors, would appear. 41 Thus, both in selected area LEED patterns and selected area PAD images, it is possible to directly reveal if adjacent graphene layers are rotationally disordered, i.e., if they are rotated azimuthally relative to each other by an angle different than 60°Â integer.…”

Section: A Si-face Graphenementioning

confidence: 99%

Properties of epitaxial graphene grown on C-face SiC compared to Si-face

Johansson

Virojanadara

2013

J. Mater. Res.

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Epitaxial graphene of uniform thickness prepared on SiC is of great interest for various applications. On the Si-face, large area uniformity has been achieved, and there is a general consensus about the graphene properties. A similar uniformity has yet not been demonstrated on the C-face where the graphene has been claimed to be fundamentally different. A rotational disorder between adjacent graphene layers has been reported and suggested to explain why multilayer C-face graphene show the p-band characteristic of monolayer graphene. Utilizing low energy electron microscopy, x-ray photoelectron electron microscopy, low energy electron diffraction, and photoelectron spectroscopy, we investigated the properties of C-face graphene prepared by sublimation growth. We observe the formation of micrometer-sized crystallographic grains of multilayer graphene and no rotational disorder between adjacent layers within a grain. Adjacent grains are in general found to have different azimuthal orientations. Effects on C-face graphene by hydrogen treatment and Na exposure were also investigated and are reported. Why multilayer C-face graphene exhibits single layer electronic properties is still a puzzle, however.

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Long-range atomic ordering and variable interlayer interactions in two overlapping graphene lattices with stacking misorientations

Cited by 32 publications

References 41 publications

Evidence for Interlayer Coupling and Moiré Periodic Potentials in Twisted Bilayer Graphene

Evidence for Interlayer Coupling and Moiré Periodic Potentials in Twisted Bilayer Graphene

Unraveling the Intrinsic and Robust Nature of van Hove Singularities in Twisted Bilayer Graphene by Scanning Tunneling Microscopy and Theoretical Analysis

Properties of epitaxial graphene grown on C-face SiC compared to Si-face

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