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 first two-dimensional transition metal nitride, Ti4N3-based MXene is synthesised using a molten fluoride salt to etch Al from a Ti4AlN3 powder precursor at 550 °C under an argon atmosphere and delaminated the resulting MXene to produce few-layered nanosheets and monolayers of Ti4n3Tx.
Abstract: We report on the synthesis of the first two-dimensional transition metal nitride, Ti4N3-based MXene. In contrast to the previously reported MXene synthesis methods – in which selective etching of a MAX phase precursor occurred in aqueous acidic solutions – here a molten fluoride salt is used to etch Al from a Ti4AlN3 powder precursor at 550 °C under an argon atmosphere. We further delaminated the resulting MXene to produce few-layered nanosheets and monolayers of Ti4N3Tx, where T is a surface termination (F, O, or OH). Density functional theory calculations of bare, non-terminated Ti4N3 and terminated Ti4N3Tx were performed to determine the most energetically stable form of this MXene. Bare and functionalized Ti4N3 are predicted to be metallic. Bare Ti4N3 is expected to show magnetism, which is significantly reduced in the presence of functional groups.
690 citations
TL;DR: In this paper, it is shown that the high wavenumber "bump" can be resolved into the conventional 2D band and several defect activated peaks such as G*, D+D+D′ and 2D′.
Abstract: Graphene sheets that are now routinely obtained by the exfoliation/reduction of graphite oxide exhibit Raman spectra unlike traditional graphene systems. The general attributes of the Raman spectra of these ‘wrinkled graphene’ are first reaffirmed by evaluating the spectra of samples prepared by seven different exfoliation-reduction methods. These graphene sheets exhibit highly broadened D and G Raman bands and in addition, have a modulated bump in place of the conventional 2D (G′) band. It is shown that the high wavenumber ‘bump’ can be resolved into the conventional 2D band and several defect activated peaks such as G*, D+D′ and 2D′. The broad G band could also be deconvoluted into the actual G band and the D′ band, thereby attributing the broadening in the G band to the presence of this defect activated band. Two additional modes, named as D* at 1190 cm-1 and D** at ∼1500 cm-1 could be identified. These peculiar features in the Raman spectrum of ‘graphene’ are attributed to the highly disordered and wrinkled (defective) morphology of the sheets. The affect of defects are further augmented due to the finite crystallite size of these graphene sheets. The dispersion in the band positions and peak intensities with respect to the laser energy are also demonstrated.
689 citations
TL;DR: It is shown that the quality of CVD-grown graphene depends critically on the used transfer process, and an advanced transfer technique is reported on that allows both reusing the copper substrate of the CVD growth and making devices with mobilities as high as 350,000 cm2 V–1 s–1, thus rivaling exfoliated graphene.
Abstract: Graphene research has prospered impressively in the past few years, and promising applications such as high-frequency transistors, magnetic field sensors, and flexible optoelectronics are just waiting for a scalable and cost-efficient fabrication technology to produce high-mobility graphene. Although significant progress has been made in chemical vapor deposition (CVD) and epitaxial growth of graphene, the carrier mobility obtained with these techniques is still significantly lower than what is achieved using exfoliated graphene. We show that the quality of CVD-grown graphene depends critically on the used transfer process, and we report on an advanced transfer technique that allows both reusing the copper substrate of the CVD growth and making devices with mobilities as high as 350,000 cm2 V–1 s–1, thus rivaling exfoliated graphene.
687 citations
TL;DR: Graphene layers with AB stacking, FLG with arbitrary stacking, is considered to possess distinct properties arising from its different crystalline structure and p electron interactions, and it has been observed that the electroand magnetotransport properties for folded graphene sheets are different to those ofAB stackedbilayers.
Abstract: Graphene is a two-dimensional material defined as a planar honeycomb lattice of close-packed carbon atoms, where the electrons exhibit a linear dispersion near Dirac K points and behave as massless Dirac fermions. However, the valence and conduction bands in an AB stacked graphene bilayer split into two parabolic branches near the K point originating from the interaction of p electrons, and the electrons are hence described by massive Dirac fermions. Moreover, a graphene bilayer is a tunable-gap semiconductor under electric-field biasing. With a further increase in the number of layers along with AB stacking, the electronic structure reveals stepwise variations that eventually approach that of the three-dimensional counterpart. Considering the close relation between the electronic properties and layer number of few-layer graphene (FLG), the ability to accurately determine the layer number and correlating this with the electronic structure is a prerequisite in understanding the evolution of the electronic properties from twoto threedimensional graphitic materials. In addition to graphene layers with AB stacking, FLG with arbitrary stacking (Figure 1) is considered to possess distinct properties arising from its different crystalline structure and p electron interactions. Experimentally, it has been observed that the electroand magnetotransport properties for folded graphene sheets are different to thoseofAB stackedbilayers. Furthermore,FLG grown on SiC, Ni, and Ru also have non-AB stacking order. Therefore, elucidating the detailed character-
679 citations
TL;DR: In this article, a CMOS-compatible photodetector based on graphene with multi-gigahertz operation ranging from the O-to U-band of telecommunication bands is demonstrated, highlighting the promise of graphene as a new material for integrated photonics.
Abstract: A CMOS-compatible photodetector based on graphene with multi-gigahertz operation ranging from the O- to U-band of telecommunication bands is demonstrated, highlighting the promise of graphene as a new material for integrated photonics.
675 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