Chemical vapor deposition of graphene on large-domain ultra-flat copper

Copper foil is the most commonly used substrate for chemical vapor deposition (CVD) growth of graphene, despite the impact of its surface roughness and polycrystalline structure on the resulting graphene. Here we present a method of preparing thick, ultra-flat copper substrates for growing graphene by CVD. We demonstrate the growth of graphene on these substrates using the common Atmospheric Pressure CVD (APCVD) and Low Pressure CVD (LPCVD) methods. We show that compared to copper foil, graphene grown on these thick ultra-flat copper substrates by APCVD results in 50 times smoother graphene on copper. Furthermore, the thick copper substrates have at least 5 times larger copper domains, compared to conventionally prepared copper foil. The evolution of the surface roughness in each growth method is also presented.     

The effect of downstream plasma treatments on graphene surfaces

This paper reports on the effects of growth, transfer and annealing procedures on graphene grown by chemical vapour deposition. A combination of Raman spectroscopy, electrical measurements, atomic force microscopy, and X-ray photoemission spectroscopy allowed for the study of inherent characteristics and electronic structure of graphene films. Contributions from contaminants and surface inhomogeneities such as ripples were also examined. A new cleaning and reconstruction process for graphene, based on plasma treatments and annealing is presented, opening a new pathway for control over the surface chemistry of graphene films. The method has been successfully used on contacted graphene samples, demonstrating its potential for in situ cleaning, passivation and interface engineering of graphene devices.     

A novel mechanical cleavage method for synthesizing few-layer graphenes

A novel method to synthesize few layer graphene from bulk graphite by mechanical cleavage is presented here. The method involves the use of an ultrasharp single crystal diamond wedge to cleave a highly ordered pyrolytic graphite sample to generate the graphene layers. Cleaving is aided by the use of ultrasonic oscillations along the wedge. Characterization of the obtained layers shows that the process is able to synthesize graphene layers with an area of a few micrometers. Application of oscillation enhances the quality of the layers produced with the layers having a reduced crystallite size as determined from the Raman spectrum. Interesting edge structures are observed that needs further investigation.     

Synthesis of graphene on silicon carbide substrates at low temperature

A method for the synthesis of millimeter-scaled graphene films on silicon carbide substrates at low temperatures (750 °C) is presented herein. Ni thin films were coated on a silicon carbide substrate and used to extract the substrate’s carbon atoms under rapid heating. During the cooling stage, the carbon atoms precipitated on the free surface of the Ni and formed single-layer or few-layer graphene. The result shows that the number of graphene layers might be further controlled by appropriate process conditions. In contrast to the epitaxial graphene synthesis on single crystal silicon carbide, the graphene prepared here are continuous over the entire Ni-coated area, and can be stripped from the substrate much more easily for further characterization. The large-scaled, low temperature and transferable features of our method suggest the potential for future graphene-based applications.     

Exploitation of Nanobifiller in Polymer/Graphene Oxide–Carbon Nanotube,Polymer/Graphene Oxide–Nanodiamond,and Polymer/Graphene Oxide–Montmorillonite Composite: A Review

In this article, a comprehensive review is presented regarding structure, synthesis, and properties of nanofillers such as graphene oxide, nanobifiller of graphene oxide, and their polymeric nanocomposite. The information about hybrid properties and synthesis of graphene oxide–carbon nanotube, graphene oxide–montmorillonite, and graphene oxide–nanodiamond is presented. Use of nanobifiller in polymer/graphene oxide–carbon nanotube, polymer/graphene oxide–montmorillonite, and polymer/graphene oxide–nanodiamond composites was summarized. Area of polymer and graphene oxide-based nanobifiller composites is less studied in literature. Therefore, nanobifiller technology limitations and research challenges must be focused. Polymer/graphene oxide nanobifiller composites have a wide range of unexplored potential in technological areas such as automobile, aerospace, energy, and medical industries.     

石墨烯及其复合材料的研究进展

石墨烯是一种新型的碳材料具有优异的光学、电学、热学性能,可制备高性能纳米复合材料。以氧化石墨烯（ GO）为前驱体的一维纤维可提高其柔韧性和导电性。本文针对石墨烯及其复合材料的研究现状进行了简述,评论了石墨烯复合纤维的性能,并展望了其应用领域与发展前景。     

PE-LD/硅烷偶联剂改性石墨烯复合薄膜的制备及性能表征

将硅烷偶联剂KH-560接枝到氧化石墨烯上制得KH-560改性氧化石墨烯（KGO）,通过水合肼还原得到KH 560改性石墨烯（KG）,最后将KG和石墨烯（G）分别与低密度聚乙烯（PE-LD）熔融共混、中空吹塑成PE LD/KG复合薄膜和PE-LD/G复合薄膜。对样品的结构、形貌、光学性能、阻透性能、热性能和力学性能等进行表征。结果表明,KH-560成功接枝到KG上;KG无序度增加,KG的层间距比G增加约80 %;KG在PE-LD中分散均匀,团聚较少;G对复合薄膜的光学性能和阻透性能的增强效果优于KG;而KG对复合薄膜的热性能和力学性能的改善明显优于G;当KG的含量为0.5 %（质量分数,下同）时,PE-LD/KG复合薄膜的结晶度和弹性模量分别比纯PE-LD薄膜提高了8.4 %和63.9 %。     

Analytical modeling of trilayer graphene nanoribbon Schottky-barrier FET for high-speed switching applications

Recent development of trilayer graphene nanoribbon Schottky-barrier field-effect transistors (FETs) will be governed by transistor electrostatics and quantum effects that impose scaling limits like those of Si metal-oxide-semiconductor field-effect transistors. The current–voltage characteristic of a Schottky-barrier FET has been studied as a function of physical parameters such as effective mass, graphene nanoribbon length, gate insulator thickness, and electrical parameters such as Schottky barrier height and applied bias voltage. In this paper, the scaling behaviors of a Schottky-barrier FET using trilayer graphene nanoribbon are studied and analytically modeled. A novel analytical method is also presented for describing a switch in a Schottky-contact double-gate trilayer graphene nanoribbon FET. In the proposed model, different stacking arrangements of trilayer graphene nanoribbon are assumed as metal and semiconductor contacts to form a Schottky transistor. Based on this assumption, an analytical model and numerical solution of the junction current–voltage are presented in which the applied bias voltage and channel length dependence characteristics are highlighted. The model is then compared with other types of transistors. The developed model can assist in comprehending experiments involving graphene nanoribbon Schottky-barrier FETs. It is demonstrated that the proposed structure exhibits negligible short-channel effects, an improved on-current, realistic threshold voltage, and opposite subthreshold slope and meets the International Technology Roadmap for Semiconductors near-term guidelines. Finally, the results showed that there is a fast transient between on-off states. In other words, the suggested model can be used as a high-speed switch where the value of subthreshold slope is small and thus leads to less power consumption.     

Graphene-based composite materials beneficial to wound healing

We use electrospinning to prepare chitosan-PVA nanofibers containing graphene. The nanofibers can be directly used in wound healing: graphene, as an antibacterial material, can be beneficial for this. A possible antibacterial mechanism for graphene is presented.     

Effects of thermal and thermomechanical induced mechanical changes of C/C composites

Carbon fiber reinforced carbon composites are produced by modified chemical vapor infiltration (CVI) of a textile fiber preform. The modified process called rapid CVI (r-CVI) allows a fast production of the matrix as well as the adjustment of graphene orientation of the matrix. At a processing temperature of 1200 °C graphene stacks are produced which are oriented roughly in fiber orientation. Mechanical testing at different temperatures as well as after temperature treatment and optional surface siliconization was carried out on C/C. Thermal treatment leads to growth and realignment of the graphene stacks in the matrix resulting in an intensified anisotropy of the composite. High temperature tests beyond processing temperature on C/C lead to mechanically induced straightening of graphene stacks in loading direction. The improved orientation of the graphene structure which is proven by XRD measurements leads to higher loading capacity and therefore to better mechanical properties in 0/90° fiber direction and to reduced mechanical performance in ±70° fiber orientation. This effect is also shown in transverse tensile tests when the graphene layers in the matrix are loaded perpendicular to their orientation. Furthermore a new method to microstructural assessment is presented.     

氧化还原法制备石墨烯工艺参数的研究

氧化还原法制备石墨烯是目前被广泛采用的一种方法.但用此方法制备的石墨烯片比较容易产生皱褶或出现折叠现象,厚度偏大、有很多缺陷.所以用此方法制备的石墨烯缺陷偏多、导电性不理想,使其在电极材料方面的应用受到了很大的限制.本文对采用氧化还原法制备石墨烯过程中的主要工艺参数进行了研究,并通过拉曼光谱的测试结果来表征和分析石墨烯的缺陷程度,最终确定石墨烯的结构与主要工艺参数之间的关系.     

Process intensification of uniform loading of SnO2 nanoparticles on graphene oxide nanosheets using a novel ultrasound assisted in situ chemical precipitation method

In this paper, a novel ultrasound assisted, solution-based chemical synthesis method for the preparation of SnO₂–graphene nanocomposite is presented. Graphene oxide (GO) was prepared by the modified Hummers–Offeman method in presence of ultrasonic irradiation. Further loading of SnO₂ on GO was carried out with an ultrasound assisted solution-based synthesis route. The prepared GO and SnO₂–graphene nanocomposite were characterized by XRD, TEM, FTIR spectra, TGA and DTA analysis in order to confirm the formation of graphene–SnO₂ nanocomposite. TEM analysis of ultrasonically prepared graphene–SnO₂ composite shows the uniform and fine loading of SnO₂ particles (3–5 nm) on graphene nanosheets. However agglomerated morphology was observed in case of conventionally prepared graphene–SnO₂ composite. The cavitational effects generated due to the ultrasonic irradiations during the synthesis of graphene–SnO₂ composite improve the fine and uniform loading of SnO₂ on graphene nanosheets by oxidation–reduction reaction between GO and SnCl₂·2H₂O compared to conventional synthesis methods. The formed material was used for the preparation of anode in lithium ion batteries and its electrochemical performance was characterized by cyclic voltammetry and charge/discharge cycles. It is found that the capacity of SnO₂–graphene nanocomposite based Li-battery is stable for around 120 cycles, and the battery could repeat stable charge–discharge reaction.     

改性氧化石墨烯对废水中重金属的吸附

简述了石墨烯的基本结构以及氧化石墨烯在结构上的优越性。概述了氧化石墨烯的主要改性方法。针对不同的影响因素,总结了改性氧化石墨烯对废水中重金属的吸附效果。对去除水体中重金属的反应机理进行了归纳,指出了改性氧化石墨烯目前应用在污水处理中存在的问题及应用前景。     

石墨烯复合浆料应用于ABS塑料电镀前表面处理

采用石墨烯等碳纳米材料与溶剂及多种助剂混合研磨,制备了稳定的石墨烯复合导电浆料.将导电浆料喷涂于丙烯腈-丁二烯-苯乙烯共聚物(ABS)表面获得ABS/石墨烯材料,赋予ABS塑料优良的导电性能,继而进行电镀处理.为了提高石墨烯涂层与ABS塑料表面的结合力,对ABS塑料进行了不同的表面处理,包括磨砂、有机溶剂微腐蚀和化学粗...     

Advances in Epoxy/Graphene Nanoplatelet Composite with Enhanced Physical Properties: A Review

In this review, development from graphene nanoplatelet, that is, comprised of short bulk of single layer graphene, into modified-polymer/graphene nanoplatelet composite is presented. Preparation methods of graphite, graphene, and graphene nanoplatelets have also been discussed. Graphene nanoplatelet and modified graphene nanoplatelet commend unique properties to composites such as excellent thermal and electrical conductivity as well as mechanical and barrier properties. Graphene nanoplatelet fabrication techniques by solution mixing, melt blending, and in situ polymerization are also discussed. Excellent dispersion of nanoplatelets in polymer/graphene nanoplatelet depends upon the selection of suitable fabrication technique. Moreover, the corresponding significance, exploitation, challenges, and future aspect of polymer/graphene nanoplatelet-based material is overviewed.     

Thermal treatment of fluorinated graphene: An in situ Raman spectroscopy study

Fluorinated graphene is a promising material for electronic applications, and its thermal properties are of high importance. Here, the resilience of fluorinated graphene to a range of temperatures is presented. The heating/cooling cycles were carried out on fluorinated monolayer, fluorinated bilayer graphene and non-fluorinated graphene as well, for comparison. In order to follow the changes of the properties of the material, in situ Raman spectra were acquired at different temperature steps. The results show that most of fluorine bonded to graphene can be removed at unusually mild temperatures, but not completely, as some fluorine can still be traced even upon heating at 800 K. Additionally, despite monolayer graphene has a higher level of fluorination than bilayer graphene, after the first heating/cooling cycle a similar amount of fluorine is found on both fluorinated graphene samples.     

One-pot in situ ball milling preparation of polymer/graphene nanocomposites

A one-pot method which involves peeling graphite nanosheets (GNs) off into graphenes in polymer solution and in situ forming polymer/graphene sheets nanocomposites by using ball milling is presented. Via this approach, nanocomposites based on maleic anhydride grafted poly (ethylene-co-vinyl acetate) (EVA-g-MAH) and graphene sheets comprising one to five layers were accomplished. The resulted EVA-g-MAH/graphene nanocomposites displayed a percolation threshold around 5.0 wt %, much lower than that of the EVA-g-MAH/GNs nanocomposites prepared by direct solution blending (∼ 13.0 wt %). The nanocomposite containing 10 wt % of graphene sheets exhibited a higher maximum decomposition temperature by ∼ 10°C when compared with the virgin polymer and the corresponding nanocomposite loaded with 10 wt % of GNs. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Enhancement in Performance of Sulfonated PES Cation-Exchange Membrane by Introducing Pristine and Sulfonated Graphene Oxide Nanosheets Synthesized through Hummers and Staudenmaier Methods

Sulfonated polyether sulfone-based cation-exchange membranes are prepared by incorporating different amounts of graphene oxide and sulfonated graphene oxide nanosheets. The graphene oxide nanosheets are synthesized according to Staudenmaier and Hummer methods and functionalized using 3-mercaptopropyl trimethoxysilane. Transport properties of nanocomposite membranes including ion-exchange capacity, transport number, and conductivity as well as their thermal stabilities are enhanced by incorporating sulfonated graphene oxide rather than graphene oxide. Also, the enhancement is more significant for the nanocomposites having functionalized graphene oxide synthesized by Staudenmaier method than those by Hummers method due to higher density of active sites in the Staudenmier graphene oxides for functionalization.     

Polymer and Graphite-Derived Nanofiller Composite: An Overview of Functional Applications

In this article, applications of polymer and graphite-derived nanofiller composite have been presented with special emphasis on epoxy composite. Various types of graphitic nanofillers such as graphite, graphene oxide, graphene, and graphene nanoplatelets are reviewed. Recently, polymer/graphite, polymer/graphene oxide, polymer/graphene, and polymer/graphene nanoplatelet-based materials have gained interest due to high performance. Property enhancement is due to high aspect ratio; high surface area; excellent electrical, thermal, and mechanical properties of nanofillers. The filler dispersion depends upon selection of suitable fabrication technique. We also reported on applications of epoxy/graphite-based filler composites in technical fields such as Li-ion batteries, sensors, and solar cells.     

Layer-by-layer synthesis of large-area graphene films by thermal cracker enhanced gas source molecular beam epitaxy

A thermal cracker enhanced gas source molecular beam epitaxy system was used to synthesize large-area graphene. Hydrocarbon gas molecules were broken by thermal cracker at very high temperature of 1200 °C and then impinged on a nickel substrate. High-quality, large-area graphene films were achieved at 800 °C, and this was confirmed by both Raman spectroscopy and transmission electron microscopy. A rapid cooling rate was not required for few-layer graphene growth in this method, and a high-percentage of single layer and bilayer graphene films was grown by controlling the growth time. The results suggest that in this method, carbon atoms migrate on the nickel surface and bond with each other to form graphene. Few-layer graphene is formed by subsequent growth of carbon layers on top of existing graphene layers. This is completely different from graphene formation through carbon dissolving in nickel and then precipitating from the nickel during rapid substrate cooling in the chemical vapor deposition method.