Coupling and Decoupling of Bilayer Graphene Monitored by Electron Energy Loss Spectroscopy

Lin, Yung‐Chang; Motoyama, Amane; Solís‐Fernández, Pablo; Matsumoto, Rikio; Ago, Hiroki; Suenaga, Kazu

doi:10.1021/acs.nanolett.1c03689

Cited by 13 publications

(15 citation statements)

References 37 publications

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“…When two layers of graphene are stacked and coupled, the interlayer interaction perturbs the bands, leading to the hybridization of the energy band structures. 22 Twisted bilayer graphene consists of two hexagonal Brillouin zones, which can be attributed to the different layers of graphene stacked at a twisted angle. The original K points of each graphene layer are denoted as K 1 and K 2 , whereas the intersections of the hexagons are denoted as A and B, which represent the regions where interlayer interactions and energy bands overlap (Figure 1b).…”

Section: Resultsmentioning

confidence: 99%

Direct Observation of Locally Modified Excitonic Effects within a Moiré Unit Cell in Twisted Bilayer Graphene

Liu,

Senga,

Koshino

et al. 2023

ACS Nano

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Bilayer graphene, which forms moiré superlattices, possesses distinct electronic and optical properties owing to its hybridized energy band and the emergence of van Hove singularities depending on its twist angle. Extensive research has been conducted on the global characteristics of moiré superlattices induced by their long-range periodicity. However, the local properties, which differ owing to the variations in the three-dimensional atomic arrangement, within a moiré unit cell have been rarely explored. In this study, we demonstrate the highly localized excitation of carbon 1s electrons to unoccupied van Hove singularities in twisted bilayer graphene by electron energy loss spectroscopy using a monochromated transmission electron microscope. The core-level excitations associated with the van Hove singularities exhibit a systematic twist-angle dependence analogous to optical excitations. Furthermore, local variations in the core-level van Hove singularity peaks, which can originate from the core-exciton lifetimes and band modifications corresponding to the local stacking geometry within a moiré unit cell, are unambiguously corroborated.

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Section: Resultsmentioning

confidence: 99%

Direct Observation of Locally Modified Excitonic Effects within a Moiré Unit Cell in Twisted Bilayer Graphene

Liu,

Senga,

Koshino

et al. 2023

ACS Nano

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“…In addition, the surface-adsorbed molecules are easily oxidized, but the oxygen concentration was low in the areas of intercalation. Second, electron energy loss spectroscopy (EELS) analysis indicated decoupling of the two graphene layers due to insertion of the metal chlorides between them …”

Section: Resultsmentioning

confidence: 99%

“…Second, electron energy loss spectroscopy (EELS) analysis indicated decoupling of the two graphene layers due to insertion of the metal chlorides between them. 37 An annular dark field (ADF) image of CuCl 2 intercalated in BLG is shown in Figure 5a. The bottom left region with darker ADF contrast is the BLG grain containing no intercalant.…”

Section: Structures Of the Metal Chlorides In The Interlayermentioning

confidence: 99%

Twist Angle-Dependent Molecular Intercalation and Sheet Resistance in Bilayer Graphene

et al. 2022

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Bilayer graphene (BLG) has a two-dimensional (2D) interlayer nanospace that can be used to intercalate molecules and ions, resulting in a significant change of its electronic and magnetic properties. Intercalation of BLG with different materials, such as FeCl3, MoCl5, Li ions, and Ca ions, has been demonstrated. However, little is known about how the twist angle of the BLG host affects intercalation. Here, by using artificially stacked BLG with controlled twist angles, we systematically investigated the twist angle dependence of intercalation of metal chlorides. We discovered that BLG with high twist angles of >15° is more favorable for intercalation than BLG with low twist angles. Density functional theory calculations suggested that the weaker interlayer coupling in high twist angle BLG is the key for effective intercalation. Scanning transmission electron microscope observations revealed that co-intercalation of AlCl3 and CuCl2 molecules into BLG gives various 2D structures in the confined interlayer nanospace. Moreover, before intercalation we observed a significantly lower sheet resistance in BLG with high twist angles (281 ± 98 Ω/□) than that in AB stacked BLG (580 ± 124 Ω/□). Intercalation further decreased the sheet resistance, reaching values as low as 48 Ω/□, which is the lowest value reported so far for BLG. This work provides a twist angle-dependent phenomenon, in which enhanced intercalation and drastic changes of the electrical properties can be realized by controlling the stacking angle of adjacent graphene layers.

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“…They intercalated AlCl 3 molecules into CVD-BLG and observed their atomic structures using a scanning transmission electron microscope (STEM). Interestingly, they discovered three new AlCl 3 crystalline structures in the interlayer 2D nanospace as shown in Figure 7(h) , which are completely different from the structure of the bulk AlCl 3 crystal [ 11 , 86 ]. In addition, these structures showed phase transitions upon excitation by an electron beam.…”

Section: Synthesis and Chemistry Of 25d Materialsmentioning

confidence: 99%

Science of 2.5 dimensional materials: paradigm shift of materials science toward future social innovation

Ago

Okada

Miyata

et al. 2022

Science and Technology of Advanced Materials

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The past decades of materials science discoveries are the basis of our present society – from the foundation of semiconductor devices to the recent development of internet of things (IoT) technologies. These materials science developments have depended mainly on control of rigid chemical bonds, such as covalent and ionic bonds, in organic molecules and polymers, inorganic crystals and thin films. The recent discovery of graphene and other two-dimensional (2D) materials offers a novel approach to synthesizing materials by controlling their weak out-of-plane van der Waals (vdW) interactions. Artificial stacks of different types of 2D materials are a novel concept in materials synthesis, with the stacks not limited by rigid chemical bonds nor by lattice constants. This offers plenty of opportunities to explore new physics, chemistry, and engineering. An often-overlooked characteristic of vdW stacks is the well-defined 2D nanospace between the layers, which provides unique physical phenomena and a rich field for synthesis of novel materials. Applying the science of intercalation compounds to 2D materials provides new insights and expectations about the use of the vdW nanospace. We call this nascent field of science ‘2.5 dimensional (2.5D) materials,’ to acknowledge the important extra degree of freedom beyond 2D materials. 2.5D materials not only offer a new field of scientific research, but also contribute to the development of practical applications, and will lead to future social innovation. In this paper, we introduce the new scientific concept of this science of ‘2.5D materials’ and review recent research developments based on this new scientific concept.

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Coupling and Decoupling of Bilayer Graphene Monitored by Electron Energy Loss Spectroscopy

Cited by 13 publications

References 37 publications

Direct Observation of Locally Modified Excitonic Effects within a Moiré Unit Cell in Twisted Bilayer Graphene

Direct Observation of Locally Modified Excitonic Effects within a Moiré Unit Cell in Twisted Bilayer Graphene

Twist Angle-Dependent Molecular Intercalation and Sheet Resistance in Bilayer Graphene

Science of 2.5 dimensional materials: paradigm shift of materials science toward future social innovation

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