Resonant Raman spectroscopy of twisted multilayer graphene

Wu, Jiang; Zhang, Xin; Ijäs, Mari; Han, Wenjuan; Qiao, Xiaoqiang; Li, Xiaoli; Jiang, Desheng; Ferrari, Andrea C.; Tan, Ping‐Heng

doi:10.1038/ncomms6309

Cited by 208 publications

(233 citation statements)

References 57 publications

(95 reference statements)

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“…It was also observed in twisted bilayer graphene that the G band intensity is enhanced in regions of the sample where the separation in energy of the van Hove singularities in the density of states, which are induced by the twisted electronic band structure, match the laser excitation energy [15]. Other authors have suggested that the G band resonance is closely related to the optically allowed electronic transition in twisted bilayer graphene [18,19]. Bernard et al [13] identified several weak Raman peaks in isotope-enriched graphene, ascribed to the double-resonance Raman process, and obtained phonon dispersion for these mixed isotopic materials [13].…”

Section: Introductionmentioning

confidence: 71%

Probing carbon isotope effects on the Raman spectra of graphene with differentC13concentrations

et al. 2015

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A resonance Raman study of graphene samples with different 13 C isotopic concentrations and using different laser excitation energies is presented. The main Raman peaks (D, G, G * , and 2D) of graphene were measured and the dependence of their frequencies on the isotope atomic mass follows a simple harmonic oscillator relation. The G * and 2D double-resonance peak positions were measured as a function of the laser energy, and we observed that the slopes of the laser energy dependence are the same independently of isotope concentration. This result shows that isotopic substitution does not alter the electron and phonon dispersions near the K point of the graphene Brillouin zone. From the linewidth of G and 2D Raman peaks, we have also obtained a dependence of the phonon lifetime on the 13 C isotope concentration.

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Section: Introductionmentioning

confidence: 71%

Probing carbon isotope effects on the Raman spectra of graphene with differentC13concentrations

et al. 2015

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“…Because of technical difficulties, such studies are usually performed at a single excitation wavelength, and a complete picture of the excitation profile of such low energy modes in MX 2 is still lacking. Resonant Raman spectroscopy of such low-energy modes has been performed in semi-metallic twisted graphene, allowing to trace the evolution of its high-energy bands and to quantify the interlayer interaction as a function of the twist angle 50 .…”

Section: Nmmentioning

confidence: 99%

Resonance effects in the Raman scattering of monolayer and few-layerMoSe2

et al. 2016

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Using resonant Raman scattering spectroscopy with 25 different laser lines, we describe the Raman scattering spectra of mono-and multi-layers 2H-molybdenum diselenide (MoSe2) as well as the different resonances affecting the most pronounced features. For high-energy phonons, both A-and E-symmetry type phonons present resonances with A and B excitons of MoSe2 together with a marked increase of intensity when exciting at higher energy, close to the C exciton energy. We observe symmetry dependent exciton-phonon coupling affecting mainly the low-energy rigid layer phonon modes. The shear mode for multilayer displays a pronounced resonance with the C exciton while the breathing mode has an intensity that grows with the excitation laser energy, indicating a resonance with electronic excitations at energies higher than that of the C exciton.

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“…[18][19][20][21][22][23][24] The C and LB modes are the collective vibration modes of all the layers so their frequency (ω C and ω LB ) depends on N and the interlayer coupling.…”

mentioning

confidence: 99%

“…[18][19][20][21][22][23][24] The C and LB modes are the collective vibration modes of all the layers so their frequency (ω C and ω LB ) depends on N and the interlayer coupling. 18,20 By probing such ultralowfrequency (ULF) modes in multilayer 2D materials, it is possible to identify its layer number no matter what kinds of substrates is used to support multilayer flakes.…”

mentioning

confidence: 99%

Substrate-free layer-number identification of two-dimensional materials: A case of Mo0.5W0.5S2 alloy

Qiao

Zhang

et al. 2015

Applied Physics Letters

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Any of two or more two-dimensional (2D) materials with similar properties can be alloyed into a new layered material, namely, 2D alloy. Individual monolayer in 2D alloys are kept together by Van der Waals interactions. The property of multilayer alloys is a function of their layer number. Here, we studied the shear (C) and layerbreathing (LB) modes of Mo 0.5 W 0.5 S 2 alloy flakes and their link to the layer number of alloy flakes. The study reveals that the disorder effect is absent in the C and LB modes of 2D alloys, and the monatomic chain model can be used to estimate the frequencies of the C and LB modes. We demonstrated how to use the C and LB mode frequency to identify the layer number of alloy flakes deposited on different substrates. This technique is independent of the substrate, stoichiometry, monolayer thickness and complex refractive index of 2D materials, offering a robust and substrate-free approach for layer-number identification of 2D materials. [6][7][8][9] The 2D alloys are a rich source of 2D materials because they can exhibit tunable properties because the ratio of two end compositions can be controllable. 6,9 The key to form a good quality of 2D monolayer is mixing the end compositions at atomic scale. Individual monolayers in the 2D alloys are kept together by Van der Waals interations. Similar to graphite and graphene, the property of multilayer alloys is a function of their layer number. How to determine the layer number of ultrathin 2D alloys is thus of primary importance for fundamental science and applications.Several optical techniques have been developed to identify the layer number of 2D materials. [10][11][12][13][14][15][16] Nevertheless, most techniques rely on the specific properties of 2D materials. For example, one can identify the layer number, denoted as N, of MoS 2 by the intensity or peak positions of the corresponding photoluminescence (PL) peak and Raman modes. 14,15 The mostly used technique is based upon optical contrast of 2D materials against dielectric substrates, such as a Si substrate covered with a SiO 2 layers. 10,12 To precisely identify N of few-layer 2D materials, the experimental optical contrast must be compared with the theoretical one for different N. However, the theoretical calculations require predetermined parameters, including thickness of a single layer, complex refractive index of the material and information of the substrate, 11,17 which poses great challenge for research on new 2D materials in early stage. Therefore, it is desirable to develop a novel approach to identify the layer number of fewlayer 2D materials, relying on as little prerequisite parameters as possible.The interlayer modes of multilayer 2D materials originates from the relative motions of the rigid monolayer planes themselves, either perpendicular or parallel to their normal, such as the shear (C) modes and the layer breathing (LB) modes. [18][19][20][21][22][23][24] The C and LB modes are the collective vibration modes of all the layers so their frequency (ω C and ω LB ) depe...

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Resonant Raman spectroscopy of twisted multilayer graphene

Cited by 208 publications

References 57 publications

Probing carbon isotope effects on the Raman spectra of graphene with differentC13concentrations

Probing carbon isotope effects on the Raman spectra of graphene with differentC13concentrations

Resonance effects in the Raman scattering of monolayer and few-layerMoSe2

Substrate-free layer-number identification of two-dimensional materials: A case of Mo0.5W0.5S2 alloy

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