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Journal ArticleDOI

Raman spectrum of graphene and graphene layers.

TL;DR: This work shows that graphene's electronic structure is captured in its Raman spectrum that clearly evolves with the number of layers, and allows unambiguous, high-throughput, nondestructive identification of graphene layers, which is critically lacking in this emerging research area.
Abstract: Graphene is the two-dimensional building block for carbon allotropes of every other dimensionality We show that its electronic structure is captured in its Raman spectrum that clearly evolves with the number of layers The D peak second order changes in shape, width, and position for an increasing number of layers, reflecting the change in the electron bands via a double resonant Raman process The G peak slightly down-shifts This allows unambiguous, high-throughput, nondestructive identification of graphene layers, which is critically lacking in this emerging research area

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Journal ArticleDOI
TL;DR: In this paper, the intensity of the G band increases with increased graphene layers, and the shape of 2D band evolves into four peaks of bilayer graphene from a single peak of monolayer graphene.
Abstract: The recent progress using Raman spectroscopy and imaging of graphene is reviewed. The intensity of the G band increases with increased graphene layers, and the shape of 2D band evolves into four peaks of bilayer graphene from a single peak of monolayer graphene. The G band will blue shift and become narrow with both electron and hole doping, whereas the 2D band will blue shift with hole doping and red shift with electron doping. Frequencies of the G and 2D band will downshift with increasing temperature. Under compressed strain, the upshift of the G and 2D bands can be found. Moreover, the strong Raman signal of monolayer graphene is explained by interference enhancement effect. As for epitaxial graphene, Raman spectroscopy can be used to identify the superior and inferior carrier mobility. The edge chirality of graphene can be determined by using polarized Raman spectroscopy. All results mentioned here are closely relevant to the basic theory of graphene and application in nanodevices.

211 citations


Cites background from "Raman spectrum of graphene and grap..."

  • ...Evolution of the 2D peak width with increased layer count of graphene or, at high resolution, its splitting into some Lorentzian components (see Figure 13) can be explained in the framework of the double-resonant Raman model (52, 64, 99)....

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  • ...A 2D peak is the second order of the D peak and caused by the double resonant Raman scattering with two-phonon emissions (52, 57)....

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  • ...(52) explained the phenomenon of splitting of the 2D band of bilayer graphene for the first time....

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  • ...Interestingly, the 2D band, sensitive to the number of graphene layers, is free of defect and has no D peak (52)....

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Journal ArticleDOI
TL;DR: The graphene/polyaniline hybrid exhibited a breakthrough in the improvement of microwave absorption and the interactions between polyanilines and graphene were confirmed by Fourier transform infrared spectroscopy and Raman spectra.
Abstract: A new method is introduced for the preparation of graphene/polyaniline hybrids using a one-step intercalation polymerization of aniline inside the expanded graphite. The structural and morphological characterizations were performed by X-ray diffraction analysis, transmission electron microscopy and field emission scanning electron microscopy. Both the experimental and first-principles simulated results show that the aniline cation formed by aniline and H+ tends to be drawn towards the electron-enriched zone and to intercalate into the interlayer of graphite. Subsequently, an in situ polymerization leads to the separation of graphite into graphene sheet, resulting from the exothermic effect and more vigorous movements of the chain molecules of polyaniline. The interactions between polyaniline and graphene were confirmed by Fourier transform infrared spectroscopy and Raman spectra. In addition, the graphene/polyaniline hybrid exhibited a breakthrough in the improvement of microwave absorption.

211 citations

Journal ArticleDOI
TL;DR: In this paper, the authors studied the thermal stability of single layer graphene synthesized by either chemical vapor deposition or mechanical cleavage and found that the defects are initially sp3 type and become vacancy like at higher temperature.
Abstract: The thermal stability in air of graphene synthesized by either chemical vapor deposition or mechanical cleavage is studied. It is found that single layer graphene prepared by both methods starts to show defects at ~500 °C, indicated by the appearance of a disorder-induced Raman D peak. The defects are initially sp3 type and become vacancy like at higher temperature. On the other hand, bilayer graphene shows better thermal stability, and the D peak appears at ~600 °C. These results are quite different from those annealing in vacuum and controlled atmosphere. Raman images show that the defects in chemical vapor deposition graphene are not homogeneous, whereas those in mechanical cleavage graphene are uniformly distributed across the whole sample. The factors that affect the thermal stability of graphene are discussed. Our results could be important for guiding the future electronics process and chemical decoration of graphene. Copyright © 2013 John Wiley & Sons, Ltd.

211 citations

Journal ArticleDOI
TL;DR: In this paper, a quasi-free-standing graphene on 6H-SiC(0001) was obtained by intercalation of hydrogen under the buffer layer using infrared absorption spectroscopy.
Abstract: We report on an investigation of quasi-free-standing graphene on 6H-SiC(0001) which was prepared by intercalation of hydrogen under the buffer layer. Using infrared absorption spectroscopy we prove that the SiC(0001) surface is saturated with hydrogen. Raman spectra demonstrate the conversion of the buffer layer into graphene which exhibits a slight tensile strain and short range defects. The layers are hole doped (p = 5.0-6.5 x 10^12 cm^(-2)) with a carrier mobility of 3,100 cm^2/Vs at room temperature. Compared to graphene on the buffer layer a strongly reduced temperature dependence of the mobility is observed for graphene on H-terminated SiC(0001)which justifies the term "quasi-free-standing".

211 citations

Journal ArticleDOI
TL;DR: In this article, the use of Raman scattering techniques to study the mechanical properties of graphene films is reviewed, and the determination of Gruneisen parameters of suspended graphene sheets under uni-and bi-axial strain is discussed.
Abstract: The use of Raman scattering techniques to study the mechanical properties of graphene films is reviewed here. The determination of Gruneisen parameters of suspended graphene sheets under uni- and bi-axial strain is discussed, and the values are compared to theoretical predictions. The effects of the graphene−substrate interaction on strain and to the temperature evolution of the graphene Raman spectra are discussed. Finally, the relation between mechanical and thermal properties is presented along with the characterization of thermal properties of graphene with Raman spectroscopy.

211 citations

References
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28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作�ly.
Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1(PfPMP1)与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员,通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

18,940 citations