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 development of this still-young technique, from early experiments to recent achievements concerning inorganic, organic, and biological materials, is addressed and an assessment of the frontiers and new concepts of TERS, which aim towards rendering it a general and widely applicable technique that combines the highest possible lateral resolution and extreme sensitivity are provided.
Abstract: An analytical technique operating at the nanoscale must be flexible regarding variable experimental conditions while ideally also being highly specific, extremely sensitive, and spatially confined. In this respect, tip-enhanced Raman scattering (TERS) has been demonstrated to be ideally suited to, e.g., elucidating chemical reaction mechanisms, determining the distribution of components and identifying and localizing specific molecular structures at the nanometre scale. TERS combines the specificity of Raman spectroscopy with the high spatial resolution of scanning probe microscopies by utilizing plasmonic nanostructures to confine the incident electromagnetic field and increase it by many orders of magnitude. Consequently, molecular structure information in the optical near field that is inaccessible to other optical microscopy methods can be obtained. In this general review, the development of this still-young technique, from early experiments to recent achievements concerning inorganic, organic, and biological materials, is addressed. Accordingly, the technical developments necessary for stable and reliable AFM- and STM-based TERS experiments, together with the specific properties of the instruments under different conditions, are reviewed. The review also highlights selected experiments illustrating the capabilities of this emerging technique, the number of users of which has steadily increased since its inception in 2000. Finally, an assessment of the frontiers and new concepts of TERS, which aim towards rendering it a general and widely applicable technique that combines the highest possible lateral resolution and extreme sensitivity, is provided.
175 citations
TL;DR: This work demonstrates the use of an interfacial trapping technique to assemble laterally macroscopic films of pristine graphene that are up to 95% transparent and have long-range structure with conductivities on the order of 400 S/cm.
Abstract: Graphite’s insolubility in conventional solvents is a major obstacle to its utilization. This challenge is typically addressed by chemical modification such as oxidation, followed by reduction. However, pristine graphene possesses superior properties as oxidation and reduction lead to degradation of the graphene. Here we demonstrate the use of an interfacial trapping technique to assemble laterally macroscopic films of pristine graphene that are up to 95% transparent. This is accomplished by modest sonication of natural flake graphite in a water/heptane mixture to form continuous films at the interface between two immiscible liquids. Furthermore, the graphene sheets readily climb hydrophilic solid substrates, forming a homogeneous thin film one to four layers thick. These films are composed of a network of overlapping graphene sheets and shown to have long-range structure with conductivities on the order of 400 S/cm.
175 citations
TL;DR: This work directly image hot spot formation in functioning mono- and bilayer graphene field effect transistors using infrared thermal microscopy and finds that thermal imaging combined with self-consistent simulation provide a noninvasive approach for more deeply examining transport and energy dissipation in nanoscale devices.
Abstract: We directly image hot spot formation in functioning mono- and bilayer graphene field effect transistors (GFETs) using infrared thermal microscopy. Correlating with an electrical-thermal transport model provides insight into carrier distributions, fields, and GFET power dissipation. The hot spot corresponds to the location of minimum charge density along the GFET; by changing the applied bias, this can be shifted between electrodes or held in the middle of the channel in ambipolar transport. Interestingly, the hot spot shape bears the imprint of the density of states in mono- vs bilayer graphene. More broadly, we find that thermal imaging combined with self-consistent simulation provide a noninvasive approach for more deeply examining transport and energy dissipation in nanoscale devices.
175 citations
TL;DR: This work offers the first opportunity to experimentally confirm the validity of the Raman theory for graphene edges by performing confocal Raman spectroscopy on hexagonal holes obtained after the anisotropic etching of prepatterned pits using carbothermal decomposition of SiO(2).
Abstract: Theory has predicted rich and very distinct physics for graphene devices with boundaries that follow either the armchair or the zigzag crystallographic directions. A prerequisite to disclose this physics in experiment is to be able to produce devices with boundaries of pure chirality. Exfoliated flakes frequently exhibit corners with an odd multiple of 30°, which raised expectations that their boundaries follow pure zigzag and armchair directions. The predicted Raman behavior at such crystallographic edges however failed to confirm pure edge chirality. Here, we perform confocal Raman spectroscopy on hexagonal holes obtained after the anisotropic etching of prepatterned pits using carbothermal decomposition of SiO2. The boundaries of the hexagonal holes are aligned along the zigzag crystallographic direction and leave hardly any signature in the Raman map indicating unprecedented purity of the edge chirality. This work offers the first opportunity to experimentally confirm the validity of the Raman theory ...
175 citations
TL;DR: In this article, a composite of fluorine-doped SnO2 and reduced graphene oxide (F-SnO2@RGO) was synthesized using a cheap F-containing Sn source, Sn(BF4)2, through a hydrothermal process.
Abstract: For the first time, a composite of fluorine-doped SnO2 and reduced graphene oxide (F-SnO2@RGO) was synthesized using a cheap F-containing Sn source, Sn(BF4)2, through a hydrothermal process. X-ray photoelectron spectroscopy and X-ray diffraction results identified that F was doped in the unit cells of the SnO2 nanocrystals, instead of only on the surfaces of the nanoparticles. F doping of SnO2 led to more uniform and higher loading of the F-SnO2 nanoparticles on the surfaces of RGO sheets, as well as enhanced electron transportation and Li ion diffusion in the composite. As a result, the F-SnO2@RGO composite exhibited a remarkably high specific capacity (1277 mA h g–1 after 100 cycles), a long-term cycling stability, and excellent high-rate capacity at large charge/discharge current densities as anode material for lithium ion batteries. The outstanding performance of the F-SnO2@RGO composite electrode could be ascribed to the combined features of the composite electrode that dealt with both the electrode ...
175 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