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In-situ Raman electrochemistry experimental configuration's scheme. Note that only the top 12C layer is contacted in the current experimental configuration.
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A mass-related symmetry breaking in isotopically labeled bilayer graphene (2LG) was investigated during in-situ electrochemical charging of AB stacked (AB-2LG) and turbostratic (t-2LG) layers. The overlap of the two approaches, isotopic labeling and electronic doping, is powerful tool and allows to tailor, independently and distinctly, the thermal-...
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... Raman spectroelectrochemistry. Next, we discuss the Raman spectroelectrochemistry results for the 12/13 C AB-2LG systems. Figure 3 gives a schematic illustration of the experimental setup used here in which only the 12 C layer is connected to the electrode. Figure 4(b) shows the Raman spectra of 12/13 C AB-2LG at different electrode potentials separated by 0.1 V. Interestingly, the behavior of the Raman spectra for 12/13 C AB-2LG ( Fig. 4(b)) is strongly different from that of 12/13 C t-2LG ( Fig. 4(a)). ...
Context 2
... case will be equilibrated with each other thermodynamically (in other words, both layers are initially at the same potential). In our present work, the device is formed by the add-layer (the 13 C layer) which is located next to the continuous graphene layer, but only the continuous gra- phene layer is contacted to the electrode, as illustrated in Fig. 3 (in this situation the two layer are at two different potentials). In other words, the charge is transported by the 12 C layer to the 12/13 C AB-2LG region. In our experimental setup, we must therefore consider a potential barrier due to the different position of E F in the top layer relative to the bottom layer 1,28 . Therefore the ...
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Here, we study the out-of-plane phonon modes located at 300-700 cm(-1) region in addition to the strong radial breathing-like mode (RBLM) at 150 cm(-1) by employing an Au nanoparticle (NP)-graphene-Au thin film (TF) junction system. Three subsequent peaks from the lower-frequency, called transverse acoustic mode series (TA1, TA2, TA3), can be effic...
Citations
... The 2D band-fitting process seems to be very complex for isotopically labelled 2-LG. Araujo et al. [15] suggested the use of eight Lorentzian peaks, justified by a symmetry breaking in the unit cell, due to the atomic mass difference. Fang et al. [16] discussed how the 2D band for both 12 C-bilayer graphene and 13 C 2-LG can be fit with four Lorentzians. ...
... Hence, the mechanism that leads to the increase in the number of peaks in the 2D band upon isotope labelling still remains unclear. Moreover, both works mentioned above [15,16] were based on a four-peak fitting of the 2D band, while it has recently been shown that a three-peak fitting of the 2D mode is more appropriate [6]. The components of the 2D mode have not been studied yet. ...
The most important bands for the evaluation of strain in graphene (the 2D and 2D prime modes) are investigated. It is shown that for Bernal-stacked bilayers, the two-phonon Raman features have three different components that can be assigned to processes originating solely from the top graphene layer, bottom graphene layer, and from a combination of processes originating both from the top and bottom layers. The individual components of the 2D and 2D prime modes are disentangled. The reported results enable addressing the properties of individual graphene layers in isotopically labelled turbostratic and Bernalstacked graphene systems.
... To explain the strong intensity of the D band in the presumably undefected bottom graphene layer, we suggest that for 2-LG AB the phonons in the bottom layer can be scattered by the defects in the top layer. It has been shown that phonons from different layers in AB-stacked bilayer graphene can interact in one scattering process [35]. For instance, the 2D mode in graphene, where one phonon can originate in the top layer and the second phonon in the bottom layer. ...
Correct defect quantification in graphene samples is crucial both for fundamental and applied re-search. Raman spectroscopy represents the most widely used tool to identify defects in graphene. However, despite its extreme importance the relation between the Raman features and the amount of defects in multilayered graphene samples has not been experimentally verified. In this study we intentionally created defects in single layer graphene, turbostratic bilayer graphene and Bernal stacked bilayer graphene by oxygen plasma. By employing isotopic labelling, our study reveals substantial differences of the effects of plasma treatment on individual layers in bilayer graphene with different stacking orders. In addition Raman spectroscopy evidences scattering of phonons in the bottom layer by defects in the top layer for Bernal-stacked samples, which can in general lead to overestimation of the number of defects by as much as a factor of two.
... Consequently, their vibrational properties (and any other property which is mass dependent) will be different. Moreover, this isotope labeling of CVD carbon layers may also be used as a characterization technique [14,[88][89][90][91][92][93][94][95][97][98][99][100]. Li et al. were pioneers on using 12 C and 13 C to study the dynamics of SLG and bilayer graphene (BLG) on bulk Cu surface and bulk Ni surface [90]. ...
... Another signature for the 12 C/ 13 C AB-BLG is observed in the spectral range between 1650 cm-1 and 2100 cm-1. AB-BLG systems have non-negligible interlayer interactions [97,98]. The vibrations related to these interlayer interactions, which are known as the ZO' (symmetric breathing of the layers) and ZO (antisymmetric vibrations of the layers), are observed around 1700 cm 1 and 1800 cm 1 as a combination mode (LOZO') and an overtone (2ZO). ...
Recent progress in the synthesis of carbon nanostructures has triggered a large number of studies aiming to elucidate their fundamental properties and to pave their way to possible applications. The successful isolation of single graphite sheets, called graphene (Geim and Novoselov Nat Mater 6:183–191, 2007), has attracted worldwide attention due to its exceptional and unique charge transport and thermal, optical, and mechanical properties. Graphene and its derivatives are being studied in nearly every field of science and engineering (Singh et al. Prog Mater Sci 56:1178–1271, 2011). Recent progress has shown that graphene nanoribbons – narrow- and straight-edged stripes of graphene – exhibit special electronic properties that make them attractive for the fabrication of nanoscale electronic device due to their sizeable bandgap which overcomes many of the limitations of graphene (Cai et al. Nature 466:470–473, 2010). Due to their outstanding properties, graphene and GNRs can be potentially applied in several research areas such as high-frequency analog circuits; spintronic, nanoelectronic, chemical, and biological sensing; energy storage; and switching devices (Cai et al. Nature 466:470–473, 2010; Biro et al. Nanoscale 4:1824–1839,2012; Cai et al. Nat Nanotechnol 9:896–900, 2014). Characterization techniques play a fundamental role in graphene and graphene-based material research, since these allow the detailed knowledge about the number of layers of graphene; the width, length, and distribution of GNRs; the purity and homogeneity of the sample; the absence or presence of surface defects; as well as their electronic and optical behavior. This is a critical step to further develop those materials, understand their properties, and move toward application (Terrones et al. Nano Today 5:351–372, 2014). In this chapter, we will review the main properties of graphene-based materials based on their dimensionality. We will discuss the effect of dimensionality on the electronic and optical properties of these materials as well as a novel route to tune properties and characterize the growth of carbon layers and stacking orders.
... The 2D band-fitting process is complex for isotopically labeled 2-LG. Araujo et al [15] suggested the use of eight Lorentzian peaks, justified by a symmetry breaking in the unit cell, due to the atomic mass difference. Fang et al [16] suggested a fitting procedure of the 2D band for both 12 Cbilayer graphene and 13 C 2-LG using four Lorentzians. ...
... However, in the case of isotopically labeled AB 2-LG the atomic mass difference can break the degeneracy of some modes, and up to eight peaks would be necessary to fit fully the 2D band. Both works mentioned above [15,16] were based on a four-peak fitting of the 2D band, while it has recently been shown that a threepeak fitting of the 2D mode is more appropriate [6]. ...
In this report important Raman modes for the evaluation of strain in graphene (the 2D and 2D') are analyzed. The isotope labeling is used to disentangle contribution of individual graphene layers of graphene bilayer to the studied Raman modes. It is shown that for Bernal-stacked bilayers, the 2D and the 2D' Raman modes have three distinct components that can be assigned to processes originating solely from the top graphene layer, bottom graphene layer, and from a combination of processes originating both from the top and bottom layers. The reported results thus enable addressing the properties of individual graphene layers in graphene bilayer by Raman spectroscopy.
... The control of DWNT and TWNT diameters is also in an advanced stage, although there is still a way to go as it comes to the chirality-specific growth of such systems. However, as mentioned above, the synthesis of DWNTs and TWNTs did reach a stage in which more sophisticated science can now be carried out, not only in terms of applications, but also in terms of fundamental science related to electrons, phonons, electron-electron interactions, electron-phonon interactions and phonon-phonon interactions (also known as many-body interactions), which are well understood in monolayer graphene and its multi-layer counterparts [199][200][201][202][203]. Both DWNTs and TWNTs, which are concentric SWNTs, have interesting phenomena related to their IL interactions [202][203][204][205]. ...
... The control of DWNT and TWNT diameters is also in an advanced stage, although there is still a way to go as it comes to the chirality-specific growth of such systems. However, as mentioned above, the synthesis of DWNTs and TWNTs did reach a stage in which more sophisticated science can now be carried out, not only in terms of applications, but also in terms of fundamental science related to electrons, phonons, electron-electron interactions, electron-phonon interactions and phonon-phonon interactions (also known as many-body interactions), which are well understood in monolayer graphene and its multi-layer counterparts [199][200][201][202][203]. Both DWNTs and TWNTs, which are concentric SWNTs, have interesting phenomena related to their IL interactions [202][203][204][205]. These IL interactions are mediated by van der Waals forces, and they change as the chirality of the tubes composing the DWNTs and TWNTs changes, which therefore modifies how strongly the electronic and vibrational structures of each SWNT constituent will mix together in DWNT and TWNT systems. ...
... These IL interactions are mediated by van der Waals forces, and they change as the chirality of the tubes composing the DWNTs and TWNTs changes, which therefore modifies how strongly the electronic and vibrational structures of each SWNT constituent will mix together in DWNT and TWNT systems. In fact, these IL interactions when well understood can be used in device applications, which work in the infrared regime [202][203][204][205]. ...
Double- and triple-walled carbon nanotubes (DWNTs and TWNTs) consist of coaxially-nested two and three single-walled carbon nanotubes (SWNTs).They act as the geometrical bridge between SWNTs and multi-walled carbon nanotubes (MWNTs), providing an ideal model for studying the coupling interactions between different shells in MWNTs. Within this context, this article comprehensively reviews various synthetic routes of DWNTs' and TWNTs' production, such as arc discharge, catalytic chemical vapor deposition and thermal annealing of pea pods (i.e., SWNTs encapsulating fullerenes). Their structural features, as well as promising applications and future perspectives are also discussed.
... The non-zero V D is ascribed to unintentional extrinsic doping from the Si substrate and the ion gel electrolyte. 32,35 The positive and negative signs of the (V TG -V D ) correspond to n-and p-doping in graphene, respectively. Doping dependence of the G and 2D bands from the SLG in our device is in good agreement with previous reports. ...
... 32,33 In tBLG, the AB sublattice symmetry is naturally broken because of the relative rotation between the two layers regardless of the charge doping. However, the E u mode has not been observed in Raman studies of tBLG under zero gate voltage, 21,22,32,35,42 suggesting this E u mode remains Raman-inactive or silent in tBLG. Araujo, et al. and Kalbac, et al. studied the Raman features of twisted bilayer 12 C/ 13 C graphene with large twist angle using electrochemical doping method. ...
... Araujo, et al. and Kalbac, et al. studied the Raman features of twisted bilayer 12 C/ 13 C graphene with large twist angle using electrochemical doping method. 35,42 No obvious signature of the E u mode has been observed. In addition, the doublet G lines observed in our doped tBLG sample are different from those reported on AB-BLG (due to optical phonon mixing) in which the two G Raman peaks give opposite frequency shift, while simultaneously a reversal of resonance intensities occurs with increasing doping density. ...
Twisted bilayer graphene (tBLG) devices with ion gel gate dielectrics are
studied using Raman spectroscopy in the twist angle regime where a resonantly
enhanced G band can be observed. We observe prominent splitting and intensity
quenching on the G Raman band when the carrier density is tuned away from
charge neutrality. This G peak splitting is attributed to asymmetric charge
doping in the two graphene layers, which reveals individual phonon self-energy
renormalization of the two weakly-coupled layers of graphene. We estimate the
effective interlayer capacitance at low doping density of tBLG using an
interlayer screening model. The anomalous intensity quenching of both G peaks
is ascribed to the suppression of resonant interband transitions between the
two saddle points (van Hove singularities), that are displaced in the momentum
space by gate-tuning. In addition, we observe a softening (hardening) of the R
Raman band, a superlattice-induced phonon mode in tBLG, in electron (hole)
doping. Our results demonstrate that gate modulation can be used to control the
optoelectronic and vibrational properties in tBLG devices.
... One of the challenges regarding few layers graphene systems is the difficulty to address and probe individual layers. This problem can be promptly solved by isotope labeling of individual layers, as has been recently demonstrated [73][74][75]. One can easily tune the frequency of the phonons by an exchange of the 12 C isotope with a 13 C isotope with essentially no change to the electronic structure. ...
... In such a sample, we are able to address individual layers by Raman spectroscopy, follow the effect of phonon self-energy renormalizations for each individual layer separately and further understand how the interlayer (IL) interactions work in these isotopic systems. In the sample from Reference [75], a small central area is composed only from the 12 C isotope and the border area is composed of the 13 C isotope. The continuous layer that formed first is composed of the 12 C isotope [82]. ...
... and HG (right panel) in AB-2LG as a function of the electrode potential. All insets present information on the intensity dependence with the electrode potential [75]. ...
This review focuses on intra-and interlayer (IL) electron-phonon interactions and phonon self-energy renormalizations in twisted and AB-stacked bilayer graphene (2LG) composed either only of C-12 or a mixing of C-12 and C-13 isotopes. A simple way to imagine a 2LG is by placing one monolayer graphene (1LG) on top of another 1LG. The orientation of one of the layers with relation to the other may originate a twisted 2LG system (known as turbostratic) as well as a AB-stacked system, also known as Bernal stacking. By rotating the layers of a 2LG one can departure from a fully misoriented system to achieve the AB-stacked configuration and their IL interactions can be dramatically different being close to zero in a fully misoriented system and maximum in an AB-stacked system. Interlayer interactions are expected to slightly perturb the intralayer phonons and they also govern the low-energy electronic and vibrational properties, which are of primary importance to phenomena such as transport, infrared (IR) optics and telecommunication bands in the IR range. Therefore, a comprehensive discussion combining intra-and interlayer phenomena is necessary and addressed throughout the text.
... For the latter, the peaks for the 12 C and 13 C layers in the 2D band are well-separated (see Figure 2) and can be fitted with single Lorentzians, whereas for AB 2-LG, the fitting process is more complex. Fang et al. 19 and Araujo et al. 20 both suggested the use of eight Lorentzian peaks, comprising the effects of the 13 C and 12 C presence. If each layer is composed of different isotopes, eight processes can be rationalized directly, four assigned to 12 C and four assigned to 13 C, with frequencies shifted from each other according to eq 1. ...
One of the greatest issues of nanoelectronics today is how to control the
heating of the components. Graphene is a promising material in this area and it
is essential to study its thermal properties. Here, the effect of heating a
bilayer structure was investigated using in situ Raman spectroscopy. In order
to observe the effects on each individual layer, an isotopically labelled
bilayer graphene was synthesized where the two layers are composed of different
carbon isotopes. Therefore, the frequency of the phonons in the Raman spectra
is shifted in relation to each other. This technique was used to investigate
the influence of different stacking order. It was found that in bilayer
graphene grown by chemical vapor deposition (CVD) the two layers behave very
similarly, for both Bernal stacking and randomly oriented structures, while for
transferred samples the layers act more independently. This highlights a
significant dependence on sample preparation procedure.
This paper studies phonon anharmonicities related to the phonon combination LOZO′ and phonon overtone 2ZO in a AB-stacked bilayer graphene (2LG). The results explain in detail the rule of the ZO′ layer breathing mode in the 2LG electron and phonon relaxations, especially at temperatures above 543 K, where anomalous behaviors are observed for the LOZO′ frequencies, linewidths (and therefore, lifetimes), and integrated areas. Surprisingly, the 2ZO frequencies and linewidths do not show any dependence with temperature (ZO is the out-of-phase vibration of the layers). This result is explained via nonsymmetric lattice distortions and via the almost null Grüneisen parameter associated to the ZO mode. Recently, the correct assignments for the phonon combination and overtone modes studied here have been put in debate once again in a theoretical work by Popov [Carbon 91, 436 (2015)]. This work shows how temperature-dependent Raman spectroscopy is used to propose a solution for these recent assignment problems. Finally, although 2LG is the system used here, the measurements and discussions to approach electron and phonon relaxations have the potential to be extended to any other multilayered structure that presents ZO′- and ZO-like phonon modes.
