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Synthesis and Solid-State NMR Structural Characterization of 13C-Labeled Graphite Oxide
Cai, W.,Piner, R. D.,Stadermann, F. J.,Park, S.,Shaibat, M. A.,Ishii, Y.,Yang, D.,Velamakanni, A.,An, S. J.,Stoller, M.,An, J.,Chen, D.,Ruoff, R. S. American Association for the Advancement of Scienc 2008 Science Vol.321 No.5897
<P>The detailed chemical structure of graphite oxide (GO), a layered material prepared from graphite almost 150 years ago and a precursor to chemically modified graphenes, has not been previously resolved because of the pseudo-random chemical functionalization of each layer, as well as variations in exact composition. Carbon-13 (13C) solid-state nuclear magnetic resonance (SSNMR) spectra of GO for natural abundance 13C have poor signal-to-noise ratios. Approximately 100% 13C-labeled graphite was made and converted to 13C-labeled GO, and 13C SSNMR was used to reveal details of the chemical bonding network, including the chemical groups and their connections. Carbon-13-labeled graphite can be used to prepare chemically modified graphenes for 13C SSNMR analysis with enhanced sensitivity and for fundamental studies of 13C-labeled graphite and graphene.</P>
van der Waals Interactions of Graphene Membranes with a Sharp Silicon Tip
석지원,김태영,Richard D. Piner 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.12
Adhesive interactions of suspended graphene membranes were studied by using non-contact atomic force microscopy (AFM) with a sharp silicon tip. Circular graphene membranes were prepared by transferring large-area monolayer graphene onto a perforated substrate. The non-contact AFM imaging showed a fluctuation of the graphene membrane. The maximum deflection of a 2.7- μm-diameter membrane was about 26.8 nm. The dynamic deflection of the membrane is attributed to the van der Waals interactions between the graphene membrane and the silicon tip of the AFM, and the interaction force was estimated to be about 3.0 nN.
FABRICATION AND MEASUREMENT OF SUSPENDED SILICON CARBIDE NANOWIRE DEVICES AND DEFLECTION
정인화,JAE-HYUN CHUNG,RICHARD PINER,석지원,RODNEY S. ROUFF 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2009 NANO Vol.4 No.6
In this paper, we report the measurement of the deflection of β-SiC nanowires supported at both ends. Such wires hold promise as active elements in NEMS/MEMS devices. To ensure the stable mechanical clamping and electrical contacts between electrodes and nanowires, we have developed a method of metal deposition to improve the contacts. This method consists of multiple depositions at different angles in order to avoid the shadow effect and reduce the compressive residual stress. The improvement of the contacts was verified via SEM observation and electrical transport measurements. To suspend the nanowire, a dielectric layer underneath was removed, followed by critical point drying. The change of electrical resistance was measured when the suspended nanowires were deflected by either capillary forces arising from the surface tension or electrostatic forces.
Lee, Sun Hwa,Dreyer, Daniel R.,An, Jinho,Velamakanni, Aruna,Piner, Richard D.,Park, Sungjin,Zhu, Yanwu,Kim, Sang Ouk,Bielawski, Christopher W.,Ruoff, Rodney S. WILEY-VCH Verlag 2010 Macromolecular Rapid Communications Vol.31 No.3
<P>A method for growing polymers directly from the surface of graphene oxide is demonstrated. The technique involves the covalent attachment of an initiator followed by the polymerization of styrene, methyl methacrylate, or butyl acrylate using atom transfer radical polymerization (ATRP). The resulting materials were characterized using a range of techniques and were found to significantly improve the solubility properties of graphene oxide. The surface-grown polymers were saponified from the surface and also characterized. Based on these results, the ATRP reactions were determined to proceed in a controlled manner and were found to leave the structure of the graphene oxide largely intact.</P><P> <img src='wiley_img/10221336-2010-31-3-MARC200900641-gra001.gif' alt='wiley_img/10221336-2010-31-3-MARC200900641-gra001'> </P> <B>Graphic Abstract</B> <P>The covalent attachment of ATRP initiators to graphene oxide followed by a surface-initiated polymerization affords derivatives with surface-attached polymer brushes. The product is found to have dramatically increased solubility without altering the structural properties inherent to graphene oxide. <img src='wiley_img/10221336-2010-31-3-MARC200900641-content.gif' alt='wiley_img/10221336-2010-31-3-MARC200900641-content'> </P>
Solution-based production of graphene nano-platelets containing extremely low amounts of heteroatoms
Han, J.,Lee, S.,Zhang, L.L.,Oh, J.,Potts, J.R.,Piner, R.D.,Ruoff, R.S.,Park, S. Elsevier 2013 Solid state sciences Vol.25 No.-
We developed a new route for scalable production of graphene-based nano-platelets containing extremely low amounts of heteroatoms via treatment of graphene oxide suspensions with ammonia borane at low temperatures without further thermal annealing. The C/O atomic ratio measured by combustion-based elemental analysis is the highest value among published data on graphene-based nano-platelets using solution processes. Resulting materials showed a very high electrical conductivity.
AN IMPROVED METHOD FOR TRANSFERRING GRAPHENE GROWN BY CHEMICAL VAPOR DEPOSITION
YUJIE REN,CHAOFU ZHU,WEIWEI CAI,HUIFENG LI,YUFENG HAO,YAPING WU,SHANSHAN CHEN,QINGZHI WU,RICHARD D. PINER,RODNEY S. RUOFF 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2012 NANO Vol.7 No.1
In this paper, we report an improved transfer of graphene by directly picking up the graphene with target substrates and the comparison of such transferred graphene samples with other graphene samples transferred by the commonly used "PMMA-based transfer" method. Raman spectroscopy studies show that this "direct transfer method" does not degrade the graphene structure and field effect transistor measurements show that it does not introduce any extra doping in graphene; in contrast, PMMA-based transfer samples have strong n-type doping. We also find that graphene samples achieved by this direct transfer method show higher mobility than graphene obtained from the PMMA-based transfer method.
Selective-Area Fluorination of Graphene with Fluoropolymer and Laser Irradiation
Lee, Wi Hyoung,Suk, Ji Won,Chou, Harry,Lee, Jongho,Hao, Yufeng,Wu, Yaping,Piner, Richard,Akinwande, Deji,Kim, Kwang S.,Ruoff, Rodney S. American Chemical Society 2012 Nano letters Vol.12 No.5
<P>We have devised a method to selectively fluorinate graphene by irradiating fluoropolymer-covered graphene with a laser. This fluoropolymer produces active fluorine radicals under laser irradiation that react with graphene but only in the laser-irradiated region. The kinetics of C–F bond formation is dependent on both the laser power and fluoropolymer thickness, proving that fluorination occurs by the decomposition of the fluoropolymer. Fluorination leads to a dramatic increase in the resistance of the graphene while the basic skeletal structure of the carbon bonding network is maintained. Considering the simplicity of the fluorination process and that it allows patterning with a nontoxic fluoropolymer as a solid source, this method could find application to generate fluorinated graphene in graphene-based electronic devices such as for the electrical isolation of graphene.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2012/nalefd.2012.12.issue-5/nl300346j/production/images/medium/nl-2012-00346j_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl300346j'>ACS Electronic Supporting Info</A></P>
Selective surface functionalization at regions of high local curvature in graphene
Wu, Qingzhi,Wu, Yaping,Hao, Yufeng,Geng, Jianxin,Charlton, Matthew,Chen, Shanshan,Ren, Yujie,Ji, Hengxing,Li, Huifeng,Boukhvalov, Danil W.,Piner, Richard D.,Bielawski, Christopher W.,Ruoff, Rodney S. The Royal Society of Chemistry 2013 Chemical communications Vol.49 No.7
<P>Monolayer graphene was deposited on a Si wafer substrate decorated with SiO<SUB>2</SUB> nanoparticles (NPs) and then exposed to aryl radicals that were generated <I>in situ</I> from their diazonium precursors. Using micro-Raman mapping, the aryl radicals were found to selectively react with the regions of graphene that covered the NPs. The enhanced chemical reactivity was attributed to the increased strain energy induced by the local mechanical deformation of the graphene.</P> <P>Graphic Abstract</P><P>Due to the increased strain energy caused by local mechanical deformation, aryl radicals were found to selectively react with regions of graphene that were curved by underlying SiO<SUB>2</SUB> nanoparticles. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2cc36747e'> </P>
Thermal Oxidation of WSe<sub>2</sub> Nanosheets Adhered on SiO<sub>2</sub>/Si Substrates
Liu, Yingnan,Tan, Cheng,Chou, Harry,Nayak, Avinash,Wu, Di,Ghosh, Rudresh,Chang, Hsiao-Yu,Hao, Yufeng,Wang, Xiaohan,Kim, Joon-Seok,Piner, Richard,Ruoff, Rodney S.,Akinwande, Deji,Lai, Keji American Chemical Society 2015 NANO LETTERS Vol.15 No.8
<P>Because of the drastically different intralayer versus interlayer bonding strengths, the mechanical, thermal, and electrical properties of two-dimensional (2D) materials are highly anisotropic between the in-plane and out-of-plane directions. The structural anisotropy may also play a role in chemical reactions, such as oxidation, reduction, and etching. Here, the composition, structure, and electrical properties of mechanically exfoliated WSe<SUB>2</SUB> nanosheets on SiO<SUB>2</SUB>/Si substrates were studied as a function of the extent of thermal oxidation. A major component of the oxidation, as indicated from optical and Raman data, starts from the nanosheet edges and propagates laterally toward the center. Partial oxidation also occurs in certain areas at the surface of the flakes, which are shown to be highly conductive by microwave impedance microscopy. Using secondary ion mass spectroscopy, we also observed extensive oxidation at the WSe<SUB>2</SUB>–SiO<SUB>2</SUB> interface. The combination of multiple microcopy methods can thus provide vital information on the spatial evolution of chemical reactions on 2D materials and the nanoscale electrical properties of the reaction products.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2015/nalefd.2015.15.issue-8/acs.nanolett.5b02069/production/images/medium/nl-2015-02069p_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl5b02069'>ACS Electronic Supporting Info</A></P>