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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
18 Jan 2010-Small
TL;DR: It is demonstrated that rGO films with a higher conductivity have a smaller work function and show a better performance in the fabricated solar cells.
Abstract: Monocrystalline ZnO nanorods (NRs) with high donor concentration are electrochemically deposited on highly conductive reduced graphene oxide (rGO) films on quartz. The film thickness, optical transmittance, sheet resistance, and roughness of rGO films are systematically studied. The obtained ZnO NRs on rGO films are characterized by X-ray diffraction, transmission electron microscopy, photoluminescence, and Raman spectra. As a proof-of-concept application, the obtained ZnO NRs on rGO are used to fabricate inorganic-organic hybrid solar cells with layered structure of quartz/rGO/ZnO NR/poly(3-hexylthiophene)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (P3HT/PEDOT:PSS)/Au. The observed power conversion efficiency (PCE, eta), approximately 0.31%, is higher than that reported in previous solar cells by using graphene films as electrodes. These results clearly demonstrate that rGO films with a higher conductivity have a smaller work function and show a better performance in the fabricated solar cells.

622 citations

Journal ArticleDOI
TL;DR: The sample of NG-700, obtained at a calcination temperature of 700 °C, showed the highest efficiency in degradation of phenol solutions by metal-free catalytic activation of peroxymonosulfate (PMS).
Abstract: N-Doped graphene (NG) nanomaterials were synthesized by directly annealing graphene oxide (GO) with a novel nitrogen precursor of melamine. A high N-doping level, 8–11 at. %, was achieved at a moderate temperature. The sample of NG-700, obtained at a calcination temperature of 700 °C, showed the highest efficiency in degradation of phenol solutions by metal-free catalytic activation of peroxymonosulfate (PMS). The catalytic activity of the N-doped rGO (NG-700) was about 80 times higher than that of undoped rGO in phenol degradation. Moreover, the activity of NG-700 was 18.5 times higher than that of the most popular metal-based catalyst of nanocrystalline Co3O4 in PMS activation. Theoretical calculations using spin–unrestricted density functional theory (DFT) were carried out to probe the active sites for PMS activation on N-doped graphene. In addition, experimental detection of generated radicals using electron paramagnetic resonance (EPR) and competitive radical reactions was performed to reveal the PMS...

622 citations

Journal ArticleDOI
TL;DR: It is shown that a graphene-clad microfiber all-optical modulator can achieve a modulation depth of 38% and a response time of ∼ 2.2 ps, limited only by the intrinsic carrier relaxation time of graphene.
Abstract: Graphene is an optical material of unusual characteristics because of its linearly dispersive conduction and valence bands and the strong interband transitions. It allows broadband light-matter interactions with ultrafast responses and can be readily pasted to surfaces of functional structures for photonic and optoelectronic applications. Recently, graphene-based optical modulators have been demonstrated with electrical tuning of the Fermi level of graphene. Their operation bandwidth, however, was limited to about 1 GHz by the response of the driving electrical circuit. Clearly, this can be improved by an all-optical approach. Here, we show that a graphene-clad microfiber all-optical modulator can achieve a modulation depth of 38% and a response time of ∼2.2 ps, limited only by the intrinsic carrier relaxation time of graphene. This modulator is compatible with current high-speed fiber-optic communication networks and may open the door to meet future demand of ultrafast optical signal processing.

619 citations

Journal ArticleDOI
22 Dec 2009-ACS Nano
TL;DR: It is shown that strong photoluminescence can be induced in single-layer graphene using an oxygen plasma treatment, and the PL is spatially uniform across the flakes and connected to elastic scattering spectra distinctly different from those of gapless pristine graphene.
Abstract: We show that strong photoluminescence (PL) can be induced in single-layer graphene using an oxygen plasma treatment. The PL is spatially uniform across the flakes and connected to elastic scattering spectra distinctly different from those of gapless pristine graphene. Oxygen plasma can be used to selectively convert the topmost layer when multilayer samples are treated.

608 citations


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

  • ...The number of layers is determined by a combination of optical microscopy and Raman spectroscopy.(20,21) Optical imaging at 473 and 514 nm is done in an inverted confocal microscope....

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  • ...This is a single band in monolayer graphene, whereas it splits in four in bilayer graphene, reflecting the evolution of the band structure.(21) The 2D peak is always seen, even when no D peak is present, since no defects are required for the activation of two phonons with the same momentum, one backscattering from the other....

    [...]

Journal ArticleDOI
01 Sep 2008-Carbon
TL;DR: In this article, the authors focused on the imaging mechanism of tapping mode AFM (TAFM) when measuring graphene and few layer graphene (FLG) flakes on silicon oxide surfaces, and showed that at certain measurement parameters significant deviations can be introduced in the measured thickness of FLG flakes.

607 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