Investigation of epitaxial graphene via Raman spectroscopy: Origins of phonon mode asymmetries and line width deviations

Hähnlein, Bernd; Лебедев, С. П.; Eliseyev, I. A.; Смирнов, А. Н.; Davydov, V. Yu.; Zubov, A. V.; Лебедев, А. А.; Pezoldt, Jörg

doi:10.1016/j.carbon.2020.07.016

Cited by 13 publications

(12 citation statements)

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“…In addition, mapping also revealed homogenous morphology and significant graphene film peaks [84]. Shen et al studied the synthesis of bilayer graphene on Cu substrate using a hot filament CVD technique [85] and reported the synthesis of Haehnlein et al investigated epitaxial graphene of different types, such as defective/ single-layer graphene to multilayer graphene with small defect densities by Raman spectroscopy and determined graphene layer numbers using strain types [74]. A novel correlation was observed between the 2D mode line width and the inverse I D /I G ratio, which allowed the determination of strain type and layer number [74].…”

Section: Raman Mappingmentioning

confidence: 99%

“…Shen et al studied the synthesis of bilayer graphene on Cu substrate using a hot filament CVD technique [85] and reported the synthesis of Haehnlein et al investigated epitaxial graphene of different types, such as defective/ single-layer graphene to multilayer graphene with small defect densities by Raman spectroscopy and determined graphene layer numbers using strain types [74]. A novel correlation was observed between the 2D mode line width and the inverse I D /I G ratio, which allowed the determination of strain type and layer number [74]. Kolomiytsev et al employ Raman spectroscopy to investigate the layer numbers of multilayer graphene, and found that there were 10 layers per multilayer graphene flake [75].…”

Section: Raman Mappingmentioning

confidence: 99%

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Estimation of Number of Graphene Layers Using Different Methods: A Focused Review

et al. 2021

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Graphene, a two-dimensional nanosheet, is composed of carbon species (sp2 hybridized carbon atoms) and is the center of attention for researchers due to its extraordinary physicochemical (e.g., optical transparency, electrical, thermal conductivity, and mechanical) properties. Graphene can be synthesized using top-down or bottom-up approaches and is used in the electronics and medical (e.g., drug delivery, tissue engineering, biosensors) fields as well as in photovoltaic systems. However, the mass production of graphene and the means of transferring monolayer graphene for commercial purposes are still under investigation. When graphene layers are stacked as flakes, they have substantial impacts on the properties of graphene-based materials, and the layering of graphene obtained using different approaches varies. The determination of number of graphene layers is very important since the properties exhibited by monolayer graphene decrease as the number of graphene layer per flake increases to 5 as few-layer graphene, 10 as multilayer graphene, and more than 10 layers, when it behaves like bulk graphite. Thus, this review summarizes graphene developments and production. In addition, the efficacies of determining the number of graphene layers using various characterization methods (e.g., transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectra and mapping, and spin hall effect-based methods) are compared. Among these methods, TEM and Raman spectra were found to be most promising to determine number of graphene layers and their stacking order.

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Section: Raman Mappingmentioning

confidence: 99%

Section: Raman Mappingmentioning

confidence: 99%

Estimation of Number of Graphene Layers Using Different Methods: A Focused Review

et al. 2021

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“…This decrease of the electron doping concentration can be due to interface states of oxidized silicon at high silicon coverage . The slope of the linear fitting for the different dispersions varies from 1.2 up to 1.7, which is an indication for biaxial strain of the graphene layer, which is expected due to the complex interaction between graphene and the dendritic structures …”

Section: Resultsmentioning

confidence: 92%

“…86 The slope of the linear fitting for the different dispersions varies from 1.2 up to 1.7, which is an indication for biaxial strain of the graphene layer, which is expected due to the complex interaction between graphene and the dendritic structures. 87 We have then annealed Si-ene samples to better understand the mechanism of formation and stabilization of thin Si-ene areas surrounded by 3D dendrites. Annealings were performed (both in situ just after Si deposition and in another UHV setup after the samples have been exposed to air) for samples with a deposited thickness of 0.5 ML since the most intense Raman peaks resulting from the most extended 2D Si-ene areas are obtained at this coverage.…”

Section: Resultsmentioning

confidence: 99%

Van der Waals Heteroepitaxy of Air-Stable Quasi-Free-Standing Silicene Layers on CVD Epitaxial Graphene/6H-SiC

et al. 2022

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Graphene, consisting of an inert, thermally stable material with an atomically flat, dangling bond-free surface is by essence an ideal template layer for van der Waals heteroepitaxy of two-dimensional materials such as silicene. However, depending on the synthesis method and growth parameters, graphene (Gr) substrates could exhibit, on a single sample, various surface structures, thicknesses, defects, and step heights. These structures noticeably affect the growth mode of epitaxial layers, e.g. turning the layer-by-layer growth into the Volmer Weber growth promoted by defect-assisted nucleation. In this work, the growth of silicon on chemical vapor deposited epitaxial Gr (1 ML Gr/1ML Gr buffer) on 6H-SiC(0001) substrate is investigated by a combination of atomic force microscopy (AFM), scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Raman spectroscopy measurements. It is shown that the perfect control of full-scale almost defect-free 1 ML Gr with a single surface structure and the ultra-clean conditions for molecular beam epitaxy (MBE) deposition of silicon represent key prerequisites for ensuring the growth of extended silicene sheets on epitaxial graphene. At low coverages, the deposition of Si produces large silicene sheets (some hundreds of nanometers large) attested by both AFM and SEM observations and the onset of a Raman peak at 560 cm -1 very close to the theoretical value of 570 cm -1 calculated for freestanding silicene. This vibrational mode at 560 cm -1 represents the highest ever experimentally measured value and is representative of quasi-free standing silicene with almost no interaction with inert non-metal substrates.From a coverage rate of 1ML, the silicene sheets disappear at the expense of 3D Si dendritic islands whose density, size, and thickness increase with the deposited thickness. From this coverage, the Raman mode assigned to quasi-free standing silicene totally vanishes, and the 2D flakes of silicene are no longer observed by AFM. The experimental results are in very good agreement with the results of kinetic Monte-Carlo simulations that rationalize the initial flake growth in solid-state dewetting conditions, followed by the growth of ridges surrounding and covering the 2D flakes. A full description of the growth mechanism is given. This study, which covers a wide range of growth parameters, challenges recent results stating the impossibility to grow silicene on a carbon inert surface and is very promising for large scale silicene growth. It definitely shows that silicene growth can be achieved using perfectly controlled and ultra-clean deposition conditions and an almost defect-free Gr substrate.

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“…On the other hand, nanometer-scale variations of strain within individual spots can also take place and their contribution can be assessed from the broadening and correlations between the full widths at halfmaximums (FWHM) of the G and 2D bands. [39,40] More inhomogeneous strain within the laser spot result in the broadening of both G and 2D bands due to averaging effects, [39] and in the linear correlations between FWHM(G) and FWHM(2D) following the slope value of ≈2.2 (i.e., that of 𝜔 G -𝜔 2D dependence). As shown in Figure 1d and Table 1, we were not able to find a strong linear correlation between FWHM(G) and FWHM(2D) for graphene/water and graphene/hydrogel samples, suggesting that nanometer-scale strains do not play a significant role and other nonlinear effects, such as phononphonon scattering, [39,40] come into play.…”

Section: Relaxation Of Strain In Graphene On Asgarose Hydrogelsmentioning

confidence: 99%

Uniform, Strain‐Free, Large‐Scale Graphene and h‐BN Monolayers Enabled by Hydrogel Substrates

Belyaeva,

Ludwig,

Lai

et al. 2023

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Translation of the unique properties of 2D monolayers from non‐scalable micron‐sized samples to macroscopic scale is a longstanding challenge obstructed by the substrate‐induced strains, interface nonuniformities, and sample‐to‐sample variations inherent to the scalable fabrication methods. So far, the most successful strategies to reduce strain in graphene are the reduction of the interface roughness and lattice mismatch by using hexagonal boron nitride (h‐BN), with the drawback of limited uniformity and applicability to other 2D monolayers, and liquid water, which is not compatible with electronic devices. This work demonstrates a new class of substrates based on hydrogels that overcome these limitations and excel h‐BN and water substrates at strain relaxation enabling superiorly uniform and reproducible centimeter‐sized sheets of unstrained monolayers. The ultimate strain relaxation and uniformity are rationalized by the extreme structural adaptability of the hydrogel surface owing to its high liquid content and low Young's modulus, and are universal to all 2D materials irrespective of their crystalline structure. Such platforms can be integrated into field effect transistors and demonstrate enhanced charge carrier mobilities in graphene. These results present a universal strategy for attaining uniform and strain‐free sheets of 2D materials and underline the opportunities enabled by interfacing them with soft matter.

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Investigation of epitaxial graphene via Raman spectroscopy: Origins of phonon mode asymmetries and line width deviations

Cited by 13 publications

References 73 publications

Estimation of Number of Graphene Layers Using Different Methods: A Focused Review

Estimation of Number of Graphene Layers Using Different Methods: A Focused Review

Van der Waals Heteroepitaxy of Air-Stable Quasi-Free-Standing Silicene Layers on CVD Epitaxial Graphene/6H-SiC

Uniform, Strain‐Free, Large‐Scale Graphene and h‐BN Monolayers Enabled by Hydrogel Substrates

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