Probing the electrostatic environment of bilayer graphene using Raman spectra

Gava, Paola; Lazzeri, Michele; Saitta, A. Marco; Mauri, Francesco

doi:10.1103/physrevb.80.155422

Cited by 43 publications

(71 citation statements)

References 36 publications

(35 reference statements)

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“…It is known that G mode splitting or two-peak G mode occurs when the graphene layers are highly and asymmetrically doped at top and bottom layers, which causes the breaking inverse symmetry and consequently the phonon mixing. [48][49][50][51] Applying substantially large uniaxial strain could also split the G mode by breaking the symmetry of the lattice and subsequently breaking the degeneracy of the two-fold symmetric E 2g phonons. [15][16]48 However, for this work, neither of the above two substances should apply since we did not highly dope or substantially stretch the samples as reflected by the absence of large amount of blue-shift, the response of doping 12 nor the red-shift of the G mode, the response of tensile strain.…”

Section: Resultsmentioning

confidence: 99%

Evolution of RamanGandG′(2D) modes in folded graphene layers

Cong

2014

Phys. Rev. B

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Bernal-and non-Bernal-stacked graphene layers have been systematically studied by Raman imaging and spectroscopy. Two dominant Raman modes, G and G' (or 2D) of folded graphene layers exhibit three types of spectral features when interlayer lattice mismatches, defined by a rotational angle varies. Among these folded graphene layers, the most interesting one is the folded graphene layers that present an extremely strong G mode enhanced by a twist-induced Van Hove singularity. The evolution of Raman G and G' modes of such folded graphene layers are probed by changing the excitation photon energies. For the first time, doublet splitting of the G' mode in folded double-layer (1 + 1) and of the G mode in folded tetra-layer (2 + 2) graphene are clearly observed and discussed. The G' mode splitting in folded double-layer graphene is attributed to the coexistence of inner and outer scattering processes and the trigonal warping effect as well as further downwards bending of the inner dispersion branch at visible excitation energy.While the two peaks of the G mode in folded tetra-layer graphene are assigned to Ramanactive mode (E 2g ) and lattice mismatch activated infrared-active mode (E 1u ), which is further verified by the temperature-dependent Raman measurements. Our study provides a summary and thorough understanding of Raman spectra of Bernal-and non-Bernal-2 stacked graphene layers and further demonstrates the versatility of Raman spectroscopy for exploiting electronic band structures of graphene layers.

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Section: Resultsmentioning

confidence: 99%

Evolution of RamanGandG′(2D) modes in folded graphene layers

Cong

2014

Phys. Rev. B

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“…The doping n of the sample can be determined from the G-line position ω G using the calculated relations n (ω G ) for single-layer 31 and bilayer graphene. 32 The G-line shift is nearly symmetric and positive for electron and hole doping, therefore the sign of the doping cannot be extracted from the measured G-line shift. However, assuming a hole doping on this flake, we find a doping level of n ≈ −(2.5 ± 1)× 10 12 cm −2 for the single-layer and n ≈ −(7.5 ± 1.5)×10 12 cm −2 for the bilayer.…”

Section: Setups and Measurementsmentioning

confidence: 99%

Variations in the work function of doped single- and few-layer graphene assessed by Kelvin probe force microscopy and density functional theory

et al. 2011

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We present Kelvin probe force microscopy measurements of single-and few-layer graphene resting on SiO 2 substrates. We compare the layer thickness dependency of the measured surface potential with ab initio density functional theory calculations of the work function for substrate-doped graphene. The ab initio calculations show that the work function of single-and bilayer graphene is mainly given by a variation of the Fermi energy with respect to the Dirac point energy as a function of doping, and that electrostatic interlayer screening only becomes relevant for thicker multilayer graphene. From the Raman G-line shift and the comparison of the Kelvin probe data with the ab initio calculations, we independently find an interlayer screening length in the order of four to five layers. Furthermore, we describe in-plane variations of the work function, which can be attributed to partial screening of charge impurities in the substrate, and result in a nonuniform charge density in single-layer graphene.

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“…The self-energy of the S and AS phonons for different Fermi energies is calculated by Ando. He found a hardening of the symmetric and asymmetric phonons, strongly influenced by carrier doping [7].…”

Section: Identification Of Monolayer and Bilayer Graphenementioning

confidence: 99%

“…The changes in the Fermi level make charge transfer split the G peak for the E 2g phonon mode. This mode shows very strong coupling between electrons and phonons [7]. The Raman G peak will have two components, which are associated with symmetric (S) and asymmetric (AS) vibration of the atoms in the two sheets of bilayer graphene.…”

Section: Identification Of Monolayer and Bilayer Graphenementioning

confidence: 99%

“…In the bilayer, usually a single peak is detected that can split if the two sheets are doped differently. When we have a doped bilayer, we can find two components in the G peak because the symmetry is broken by doping due to different n top and n bottom [7]. The self-energy of the S and AS phonons for different Fermi energies is calculated by Ando.…”

Section: Identification Of Monolayer and Bilayer Graphenementioning

confidence: 99%

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Multi-Wavelength Raman Characterization of Back-Gated Monolayer and Bilayer Graphene

Arvani¹

2014

AJMP

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Abstract:In this work, we investigate the Raman spectrum of gated monolayer and bilayer graphene devices. We used Raman spectroscopy with three different excitation wavelengths: (488nm, 514nm and 633nm). After producing graphene sheets by scotch tape technique, Raman spectrometry used to distinguish between bilayer, mono layer and other few layer of graphene. We contact the wires on the flakes using micro-soldering method then we applied gate voltage on monolayer and bilayer graphene and investigate the changes in peak of the Raman spectra in different wavelengths in different voltages. Raman spectroscopy probes phonons as well as electronic states. If the electronic dispersion changes, the Raman spectrum will also changes. The shifts of the Raman spectra peaks of the monolayer and bilayer are explained in the current work. Charge carrier concentration as a function of gate voltage in gated graphene is shown as well as the position of the G peak and 2D peak graphene versus gate voltage. For monolayer devices we observed the expected behavior for doped devices. For bilayer devices, we present a comparison between the theoretical model and our experimental results.

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Probing the electrostatic environment of bilayer graphene using Raman spectra

Cited by 43 publications

References 36 publications

Evolution of RamanGandG′(2D) modes in folded graphene layers

Evolution of RamanGandG′(2D) modes in folded graphene layers

Variations in the work function of doped single- and few-layer graphene assessed by Kelvin probe force microscopy and density functional theory

Multi-Wavelength Raman Characterization of Back-Gated Monolayer and Bilayer Graphene

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