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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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TL;DR: The g-C3N4-rGO exhibits an unprecedented high, stable and reversible capacity and the superior electrochemical performance is attributed to the specific characteristics of the unique nanostructure of g- covalent interaction between the two moieties, the good conductivity and high special surface area of the nanocomposite.
Abstract: An in situ chemical synthetic approach has been designed for the fabrication of a covalently coupled hybrid consisting of graphitic carbon nitride (g-C3N4) with reduced graphene oxide (rGO) with differing g-C3N4/rGO ratio. The epoxy groups of graphene oxide (GO) undergo a nucleophilic substitution reaction with dicyandiamide (C2H4N4) to form the C2H4N4–GO composite via a covalent C–N bond, and then both the in situ polymerization of C2H4N4 and the thermal reduction of GO can be achieved at higher temperatures, forming the covalently coupled g-C3N4–rGO. FT-IR, CP-MAS NMR and XPS analyses, clearly revealed a covalent interaction between the g-C3N4 and rGO sheets. The g-C3N4–rGO exhibits an unprecedented high, stable and reversible capacity of 1525 mA h g−1 at a current density of 100 mA g−1 after 50 cycles. Even at a large current density of 1000 mA g−1, a reversible capacity of 943 mA h g−1 can still be retained. The superior electrochemical performance of g-C3N4–rGO is attributed to the specific characteristics of the unique nanostructure of g-C3N4–rGO and the concerted effects of g-C3N4 and rGO, including covalent interactions between the two moieties, the good conductivity and high special surface area of the nanocomposite, as well as the template effect of the planar amino group of g-C3N4 for the dispersed decoration of Li+ ions.

178 citations

Journal ArticleDOI
TL;DR: This work presents highly stable and dendrite-free Na metal anodes over a wide current range and long-term cycling via directly applying free-standing graphene films with tunable thickness on Na metal surface and reveals that only a few nanometer differences in the graphene thickness can have decisive influence on the stability and rate capability of Na anodes.
Abstract: Sodium (Na) metal has shown great promise as an anode material for the next-generation energy storage systems because of its high theoretical capacity, low cost, and high earth abundance. However, the extremely high reactivity of Na metal with organic electrolyte leads to the formation of unstable solid electrolyte interphase (SEI) and growth of Na dendrites upon repeated electrochemical stripping/plating, causing poor cycling performance, and serious safety issues. Herein, we present highly stable and dendrite-free Na metal anodes over a wide current range and long-term cycling via directly applying free-standing graphene films with tunable thickness on Na metal surface. We systematically investigate the dependence of Na anode stability on the thickness of the graphene film at different current densities and capacities. Our findings reveal that only a few nanometer (∼2–3 nm) differences in the graphene thickness can have decisive influence on the stability and rate capability of Na anodes. To achieve the...

178 citations

Journal ArticleDOI
TL;DR: A detailed review of the literature for the last 5-10 years on epitaxial growth of graphene is presented in this article, where both experimental and theoretical aspects related to growth on transition metals and on silicon carbide are thoroughly reviewed.

177 citations


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

  • ...Graphene has three main features in its Raman spectrum, the so-called D, G, and 2D (also called G’) modes, appearing respectively at about 1350, 1580 and 2700 cm−1 [119], see Fig....

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  • ...The relative intensity and width of the 2D mode [119], as well as the occurrence of a shear mode for small energy losses in polarized light experiments [122], provide valuable information about the number of layers in graphene stacks....

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Journal ArticleDOI
TL;DR: The results reveal that the growth of macroscopic pristine graphene is not limited by the underlying copper structure, and growth models including a stagnant catalytic surface do not apply to graphene growth on copper.
Abstract: The atomic structure of graphene on polycrystalline copper substrates has been studied using scanning tunneling microscopy. The graphene overlayer maintains a continuous pristine atomic structure over atomically flat planes, monatomic steps, edges, and vertices of the copper surface. We find that facets of different identities are overgrown with graphene’s perfect carbon honeycomb lattice. Our observations suggest that growth models including a stagnant catalytic surface do not apply to graphene growth on copper. Contrary to current expectations, these results reveal that the growth of macroscopic pristine graphene is not limited by the underlying copper structure.

177 citations

Journal ArticleDOI
TL;DR: Combining the X-ray photoelectron spectroscopy, transmission electron microscopy, and electron spin resonance results, it is suggested that the observed magnetization is related to the presence of edge spins on the edges of the nanosheets.
Abstract: Freestanding MoS2 nanosheets with different sizes were prepared through a simple exfoliated method by tuning the ultrasonic time in the organic solvent. Magnetic measurement results reveal the clear room-temperature ferromagnetism for all the MoS2 nanosheets, in contrast to the pristine MoS2 in its bulk form which shows diamagnetism only. Furthermore, results indicate that the saturation magnetizations of the nanosheets increase as the size decreases. Combining the X-ray photoelectron spectroscopy, transmission electron microscopy, and electron spin resonance results, it is suggested that the observed magnetization is related to the presence of edge spins on the edges of the nanosheets. These MoS2 nanosheets may find applications in nanodevices and spintronics by controlling the edge structures.

177 citations


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

  • ...HRTEM investigation in the edge areas was a common and direct method to determine the layer numbers microscopically [28]....

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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