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: In this article, a new composite structure of graphene-sulfur with a high electrochemical performance is proposed, based on Scotch-tape-like sulfur-assisted exfoliation of graphite.
Abstract: A new composite structure of graphene–sulfur with a high electrochemical performance is proposed. Scotch-tape-like sulfur-assisted exfoliation of graphite is developed to produce the graphene–sulfur composites and freestanding low-defect graphene sheets. The intimate interaction between sulfur and graphene, attributed to the similar electronegativities of the two elements, is stronger than the van der Waals forces between adjacent π–π stacked graphene layers. This causes cleavage of the graphene layers when the sulfur molecules stick to the surface and edges of the graphite, similar to Scotch tape in micromechanical exfoliation processes. This approach enables us to obtain graphene with an electrical conductivity as high as 1820 S cm−1 and a Hall mobility as high as 200 cm2 V−1 s−1, superior to most reported graphene. Furthermore, the graphene sheets which uniformly anchor sulfur molecules provide a superior confinement ability for polysulfides, sufficient space to accommodate sulfur volumetric expansion, a large contact area with the sulfur and a short transport pathway for both electrons and Li+. The unique structure containing 73 wt.% sulfur exhibits excellent overall electrochemical properties of 615 mA h g−1 at the 1 C (1 C = 1675 mA g−1) rate after 100 cycles (corresponding average Coulombic efficiency of over 96%) and 570 mA h g−1 at 2 C. These encouraging results represent that sulfur molecules bound onto graphene sheets could be a promising cathode material for lithium batteries with a high energy density.
243 citations
TL;DR: In this article, the buckling strain of single flakes of different geometries was measured by simultaneous Raman measurements through the shift of either the G or 2D phonons of graphene.
Abstract: Central to most applications involving monolayer graphene is its mechanical response under various stress states. To date most of the work reported is of theoretical nature and refers to tension and compression loading of model graphene. Most of the experimental work is indeed limited to bending of single flakes in air and the stretching of flakes up to typically ~1% using plastic substrates. Recently we have shown that by employing a cantilever beam we can subject single graphene into various degrees of axial compression. Here we extend this work much further by measuring in detail both stress uptake and compression buckling strain in single flakes of different geometries. In all cases the mechanical response is monitored by simultaneous Raman measurements through the shift of either the G or 2D phonons of graphene. In spite of the infinitely small thickness of the monolayers, the results show that graphene embedded in plastic beams exhibit remarkable compression buckling strains. For large length (l)-to-width (w) ratios (> 0.2) the buckling strain is of the order of -0.5% to -0.6%. However, for l/w <0.2 no failure is observed for strains even higher than -1%. Calculations based on classical Euler analysis show that the buckling strain enhancement provided by the polymer lateral support is more than six orders of magnitude compared to suspended graphene in air.
243 citations
TL;DR: In this paper, the authors investigated the Raman spectra of single-layer and multi-layer graphene under ultraviolet laser excitation at the wavelength of 325 nm and found that while the G peak of graphene remains pronounced in UV Raman, the 2D band intensity undergoes severe quenching.
Abstract: We investigated Raman spectra of single-layer and multi-layer graphene under ultraviolet laser excitation at the wavelength of 325 nm. It was found that while the G peak of graphene remains pronounced in UV Raman spectra, the 2D band intensity undergoes severe quenching. The evolution of the ratio of the intensities of the G and 2D peaks, I(G)/I(2D), as the number of graphene layers n changes from n=1 to n=5, is different in UV Raman spectra from that in conventional visible Raman spectra excited at the 488 nm and 633 nm wavelengths. The 2D band under UV excitation shifts to larger wave numbers and is found near 2825 1/cm. The observed UV Raman features of graphene were explained by invoking the resonant scattering model. The obtained results contribute to the Raman nanometrology of graphene by providing an additional metric for determining the number of graphene layers and assessing its quality.
243 citations
TL;DR: In this article, the authors reported a hybrid structure employing a CVD SLG film and a network of silver nanowires (AgNWs), achieving a sheet resistance as low as 22 Ω/□ (stabilized to 13 Ω /□ after 4 months).
Abstract: Transparent conducting electrodes (TCEs) require high transparency and low sheet resistance for applications in photovoltaics, photodetectors, flat panel displays, touch screen devices and imagers. Indium tin oxide (ITO), or other transparent conductive oxides, have typically been used, and provide a baseline sheet resistance (RS) vs. transparency (T) relationship. However, ITO is relatively expensive (due to limited abundance of Indium), brittle, unstable, and inflexible; moreover, ITO transparency drops rapidly for wavelengths above 1000 nm. Motivated by a need for transparent conductors with comparable (or better) RS at a given T, as well as flexible structures, several alternative material systems have been investigated. Single-layer graphene (SLG) or few-layer graphene provide sufficiently high transparency (≈97% per layer) to be a potential replacement for ITO. However, large-area synthesis approaches, including chemical vapor deposition (CVD), typically yield films with relatively high sheet resistance due to small grain sizes and high-resistance grain boundaries (HGBs). In this paper, we report a hybrid structure employing a CVD SLG film and a network of silver nanowires (AgNWs): RS as low as 22 Ω/□ (stabilized to 13 Ω/□ after 4 months) have been observed at high transparency (88% at λ = 550 nm) in hybrid structures employing relatively low-cost commercial graphene with a starting RS of 770 Ω/□. This sheet resistance is superior to typical reported values for ITO, comparable to the best reported TCEs employing graphene and/or random nanowire networks, and the film properties exhibit impressive stability under mechanical pressure, mechanical bending and over time. The design is inspired by the theory of a co-percolating network where conduction bottlenecks of a 2D film (e.g., SLG, MoS2) are circumvented by a 1D network (e.g., AgNWs, CNTs) and vice versa. The development of these high-performance hybrid structures provides a route towards robust, scalable and low-cost approaches for realizing high-performance TCE.
243 citations
TL;DR: In this article, the authors demonstrate inkjet printing of nanosheets of both graphene and MoS2 prepared by liquid exfoliation, and demonstrate the printing of semiconducting traces using solvent-exfoliated, size-selected MoS 2 nanoheets.
Abstract: Here we demonstrate inkjet printing of nanosheets of both graphene and MoS2 prepared by liquid exfoliation. We describe a protocol for the preparation of inks of nanosheets with well-defined size distribution and concentration up to 6 mg ml−1. Graphene traces were printed at low temperature (<70 °C) with no subsequent thermal or chemical treatment. Thin traces displayed percolation effects while traces with thickness above 160 nm displayed thickness-independent conductivity of 3000 S m−1. We also demonstrate the printing of semiconducting traces using solvent-exfoliated, size-selected MoS2 nanosheets. Such traces can be combined with inkjet-printed graphene interdigitated array electrodes to produce all-printed photodetectors.
242 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