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Real-time evolution of the buckled Stone-Wales defect in graphene  [PDF]
L. A. Openov,A. I. Podlivaev
Physics , 2015, DOI: 10.1016/j.physe.2015.03.010
Abstract: Dynamics of the buckled Stone-Wales defect in graphene is studied by means of computer simulation. Thermally activated switching between two degenerate sine-wave-like configurations of the defect is traced in real time. Transition trajectory is found to be rather complex and pass through a multitude of near-planar, wave-like, and irregular configurations. Surprisingly, the switching time fluctuates strongly and can be up to an order of magnitude longer or shorter than the value given by the Arrhenius formula. This is due to a peculiar shape of the potential relief in the neighborhood of sine-wave-like configurations and, as a result, the occurrence of two radically different characteristic times.
Graphene-templated approach to ultrathin silica nanosheets
LanYan Kan,BingNa Zheng,Chao Gao
Chinese Science Bulletin , 2012, DOI: 10.1007/s11434-012-5252-6
Abstract: Graphene, a perfect two-dimensional (2D) nanostructure, is an ideal template for 2D material design. We developed a graphene- templated method to synthesize 2D silica nanosheets through the crosslinking of poly(3-methacryloxypropyl trimethoxysilane)-grafted graphene oxide (GO-g-PMPS), followed by pyrolysis at 700°C for 10 h.
Vacuum Ultraviolet Assisted Photoreduction of Graphene Oxide Nanosheets  [cached]
Vasilets V.N.,Baskakov S.A.,Shulga Y.M.
Proceedings of the International Conference Nanomaterials : Applications and Properties , 2012,
Abstract: Films of graphene oxide nanosheets have been prepared by deposition from an aqueous alcohol emulsion onto a Teflon FEP substrate. The behavior of the films exposed to monochromatic vacuum UV radiation at a wavelength of 123.6 nm has been studied. The decrease of water content and the amount of hydroxyl (OH) groups as well as the increases of the concentration of double bonds in the film has been found after irradiation. At the same time the amount of C=O remains constant in the carboxyl and ketone groups.
Colorful Polymer Compositions with Dyed Graphene Oxide Nanosheets  [PDF]
Y. M. Shulga,S. A. Baskakov,V. E. Muradyan,D. N. Voylov,V. A. Smirnov,A. Michtchenko,J. G. Caba?as-Moreno,K. G. Belay,C. A. Weatherford,G. L. Gutsev
ISRN Optics , 2012, DOI: 10.5402/2012/647849
Abstract: A water suspension of graphene oxide nanosheets (GONSs) obtained via exfoliation of a graphite oxide was treated with a solution of rhodamine 6G. It was found that adding the dye results in the destruction of the GONS water suspension and the precipitation of dyed graphene oxide. The precipitate, washed out of the excess dye and subjected to a second dispersal via sonification, provides a stable suspension of dyed GONS in water or dimethylformamide. The GONS dyeing produces shifts of major absorption bands of the dye in solutions or in polymer compositions toward larger wavelengths. We also found that the stability of a dye subjected to ultraviolet irradiation increases if the dye is bound to a GONS. The increased stability resulted from excitation transfer from dye to a GO nanosheet and its subsequent reduction. 1. Introduction Graphite oxide is known since the 19th century [1]. The current surge of interest to graphite oxide is due to not only its application as a prospective material for electrodes, membranes, and polymer additives [2–7] but also to a new avenue which opened after the discovery of the unique properties of graphene [8–10]. Contrary to many other carbon materials, graphite oxide is hydrophilic and is capable of forming colloidal solutions in water, spirits, and other polar solvents, where GO splits into thin sheets of up to one carbon layer thickness [11–13]. Graphite oxide “solubility” is due to a large number of oxygen-containing groups chemically bound to graphene layers. The presence of these groups deteriorates the mechanical and conducting properties of GO nanosheets with respect to those of graphene. A hydrazine processing restores [14–16] the GONS π-system and results in properties similar to those of graphene. Generally, the GO nanosheets possess [17] sites with different reaction abilities; therefore, it is difficult to predict beforehand the results of interactions between a GONS and different molecules. This letter describes the products of interactions between a GONS and the dye rhodamine 6G (R6G, C28H31ClN2O3) and then discusses some properties of this product. The goal of this work was to produce dyed GONSs in transparent polymer compositions. We prepared films of polymethylmethacrylate (PMMA) modified using both dye and dyed GONSs. The film samples were characterized using spectral methods. 2. Experimental Details Our GO samples were prepared according to Hummers and Offeman’s method [18] using a procedure whose details are described elsewhere [19]. Suspensions were prepared by mixing GO (100?mg) with water (100?mL) in
Graphene defect formation by extreme ultraviolet generated photoelectrons  [PDF]
A. Gao,C. J. Lee,F. Bijkerk
Physics , 2014, DOI: 10.1063/1.4892485
Abstract: We have studied the effect of photoelectrons on defect formation in graphene during extreme ultraviolet (EUV) irradiation. Assuming the major role of these low energy electrons, we have mimicked the process by using low energy primary electrons. Graphene is irradiated by an electron beam with energy lower than 80 eV. After e-beam irradiation, it is found that the D peak, I(D), appears in the Raman spectrum, indicating defect formation in graphene. The evolution of I(D)/I(G) follows the amorphization trajectory with increasing irradiation dose, indicating that graphene goes through a transformation from microcrystalline to nanocrystalline and then further to amorphous carbon. Further, irradiation of graphene with increased water partial pressure does not significantly change the Raman spectra, which suggests that, in the extremely low energy range, e-beam induced chemical reactions between residual water and graphene is not the dominant mechanism driving defect formation in graphene. Single layer graphene, partially suspended over holes was irradiated with EUV radiation. By comparing with the Raman results from e-beam irradiation, it is concluded that the photoelectrons, especially those from the valence band, contribute to defect formation in graphene during irradiation.
Investigation of MoS2 and Graphene Nanosheets by Magnetic Force Microscopy  [PDF]
Hai Li,Xiaoying Qi,Jumiati Wu,Zhiyuan Zeng,Jun Wei,Hua Zhang
Physics , 2013, DOI: 10.1021/nn400443u
Abstract: For the first time, the magnetic force microscopy (MFM) is used to characterize the mechanically-exfoliated single- and few-layer MoS2 and graphene nanosheets. By analysis of the phase and amplitude shifts, the magnetic response of MoS2 and graphene nanosheets exhibits the dependence on their layer number. However, the solution-processed single-layer MoS2 nanosheet shows the reverse magnetic signal to the mechanically-exfoliated one, and the graphene oxide nanosheet has not shown any detectable magnetic signal. Importantly, graphene and MoS2 flakes become nonmagnetic when they exceed a certain thickness.
Mechanism of intercalation and deintercalation of lithium ions in graphene nanosheets
LeiLei Tian,QuanChao Zhuang,Jia Li,YueLi Shi,JianPeng Chen,Feng Lu,ShiGang Sun
Chinese Science Bulletin , 2011, DOI: 10.1007/s11434-011-4609-6
Abstract: Graphene nanosheets (GNSs) were synthesized by reducing exfoliated graphite oxides. Their structure, surface morphology and lithium storage mechanism were characterized and investigated systematically using X-ray diffraction, atomic force microscopy, scanning electron microscopy, charge-discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy. It was found that the GNSs, which were obtained via chemical synthesis, were primarily less than 10 graphene layers. The GNS electrodes, which were fabricated from the reduced GNSs, exhibited an enhanced reversible lithium storage capacity and good cyclic stability when serving as anodes in lithium-ion batteries. Also, the first-cycle irreversible capacities of the system were relatively high, because of the formation of a solid electrolyte interphase film on the surface of the GNS electrode and the spontaneous stacking of GNSs during the first lithiation. The electrochemical impedance spectroscopy results suggest that the solid electrolyte interphase film on the GNS electrode during first lithiation were primarily formed at potentials between 0.95 and 0.7 V. Also, the symmetry factor of the charge transfer was measured to be 0.446.
Thermal transport in MoS2/Graphene hybrid nanosheets  [PDF]
Zhongwei Zhang,Yuee Xie,Qing Peng,Yuanping Chen
Physics , 2015, DOI: 10.1088/0957-4484/26/37/375402
Abstract: Heat dissipation is a very critical problem for designing nano-functional devices, including MoS2/Graphene heterojunctions. In this paper we investigate thermal transport in MoS2/Graphene hybrid nanosheets under various heating conditions, by using molecular dynamics simulation. Diverse transport processes and characteristics, depending on the conducting layers, are found in these structures. The thermal conductivities can be tuned by interlayer coupling, environment temperature and interlayer overlap. The highest thermal conductivity at room temperature is achieved as more than 5 times of that of single layer MoS2 when both layers are heated and 100% overlapped. Different transport mechanisms in the hybrid nanosheets are explained by phonon density of states, temperature distribution, and ITR. Our results not only could provide clues to master the heat transport in functional devices based on MoS2/Graphene heterojunctions, but also are useful to analyze thermal transport in other van der Waals hybrid nanosheets.
PtCo alloy nanoparticles supported on graphene nanosheets with high performance for methanol oxidation
HuaJie Huang,DongPing Sun,Xin Wang
Chinese Science Bulletin , 2012, DOI: 10.1007/s11434-012-5327-4
Abstract: PtCo alloy nanoparticles are deposited onto graphene sheets through a facile and reproducible hydrothermal method. During the hydrothermal reaction, the reduction of graphene oxide and PtCo alloy nanoparticles loading can be achieved. X-ray diffraction (XRD) analyses reveal a good crystallinity of the supported Pt nanoparticles in the composites and the formation of PtCo alloy. X-ray photoelectron spectra (XPS) results depict that Pt mainly exists in the metallic form, while much of the cobalt is oxidized. Transmission electron microscope (TEM) observations show that the PtCo alloy nanoparticles are uniformly dispersed on graphene nanosheets compared with multiwalled carbon nanotubes (MWNTs). This PtCo-graphene composite exhibits excellent electrocatalytic activity and high poison tolerance toward poisoning species for methanol oxidation reaction, far outperforming the Pt-graphene or PtCo-MWNTs composites with the same feeding ratio of Pt/carbon.
Tert-butylhydroquinone-decorated graphene nanosheets and their enhanced capacitive behaviors
HuanWen Wang,HongYing Wu,YanQin Chang,YanLi Chen,ZhongAi Hu
Chinese Science Bulletin , 2011, DOI: 10.1007/s11434-011-4424-0
Abstract: In the present work, tert-butylhydroquinone (TBHQ) was used to decorate graphene nanosheets to obtain a novel and environmentally friendly electrode material for supercapacitors. The fast redox reactions between hydroquinone and quinone generate pseudocapacitance. Graphene layers which have adsorbed TBHQ interact with each other to construct a three-dimensional network. Through this network, electrolyte ions can easily access the surface of graphene to generate electric double-layer capacitance. Electrochemical measurements have shown that using TBHQ as a redox modifier of graphene can obtain a maximum value of 302 F g-1 and provide a 51% enhancement in specific capacitance. Furthermore, excellent rate capability and cycling ability are achieved using the TBHQ-decorated graphene nanosheet electrode.
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