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Qi, Zhikai,Shi, Haohao,Zhao, Mingxing,Jin, Hongchang,Jin, Song,Kong, Xianghua,Ruoff, Rodney S.,Qin, Shengyong,Xue, Jiamin,Ji, Hengxing American Chemical Society 2018 Chemistry of materials Vol.30 No.21
<P>Bernal-stacked bilayer graphene is uniquely suited for application in electronic and photonic devices because of its tunable band structure. Even though chemical vapor deposition (CVD) is considered to be the method of choice to grow bilayer graphene, the direct synthesis of high-quality, large-area Bernal-stacked bilayer graphene on Cu foils is complicated by overcoming the self-limiting nature of graphene growth on Cu. Here, we report a facile H<SUB>2</SUB>O-assisted CVD process to grow bilayer graphene on Cu foils, where graphene growth is controlled by injecting intermittent pulses of H<SUB>2</SUB>O vapor using a pulse valve. By optimizing CVD process parameters fully covered large area graphene with bilayer coverage of 77 ± 3.6% and high AB stacking ratio of 93 ± 3% can be directly obtained on Cu foils, which presents a hole concentration and mobility of 4.5 × 10<SUP>12</SUP> cm<SUP>-2</SUP> and 1100 cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>, respectively, at room temperature. The H<SUB>2</SUB>O selectively etches graphene edges without damaging graphene facets, which slows down the growth of the top layer and improves the nucleation and growth of a second graphene layer. Results from our work are important both for the industrial applications of bilayer graphene and to elucidate the growth mechanism of CVD-graphene.</P> [FIG OMISSION]</BR>
Jiang, Yi,Oh, Inseon,Joo, Se Hun,Buyukcakir, Onur,Chen, Xiong,Lee, Sun Hwa,Huang, Ming,Seong, Won Kyung,Kwak, Sang Kyu,Yoo, Jung-Woo,Ruoff, Rodney S. American Chemical Society 2019 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.141 No.42
<P>We report the synthesis and characterization of a two-dimensional (2D) conjugated Ni(II) tetraaza[14]annulene-linked metal organic framework (<B>NiTAA-MOF</B>) where <B>NiTAA</B> is a macrocyclic MN<SUB>4</SUB> (M = metal, N = nitrogen) compound. The structure of <B>NiTAA-MOF</B> was elucidated by Fourier-transform infrared, X-ray photoemission, and X-ray diffraction spectroscopies, in combination with density functional theory (DFT) calculations. When chemically oxidized by iodine, the insulating bulk <B>NiTAA-MOF</B> (σ < 10<SUP>-10</SUP> S/cm) exhibits an electrical conductivity of 0.01 S/cm at 300 K, demonstrating the vital role of ligand oxidation in the electrical conductivity of 2D MOFs. Magnetization measurements show that iodine-doped <B>NiTAA-MOF</B> is paramagnetic with weak antiferromagnetic coupling due to the presence of organic radicals of oxidized ligands and high-spin Ni(II) sites of the missing-linker defects. In addition to providing further insights into the origin of the induced electrical conductivity in 2D MOFs, both pristine and iodine-doped <B>NiTAA-MOF</B> synthesized in this work could find potential applications in areas such as catalase mimics, catalysis, energy storage, and dynamic nuclear polarization-nuclear magnetic resonance (DNP-NMR).</P> [FIG OMISSION]</BR>
Graphitization of graphene oxide films under pressure
Chen, Xianjue,Deng, Xiaomei,Kim, Na Yeon,Wang, Yu,Huang, Yuan,Peng, Li,Huang, Ming,Zhang, Xu,Chen, Xiong,Luo, Da,Wang, Bin,Wu, Xiaozhong,Ma, Yufei,Lee, Zonghoon,Ruoff, Rodney S. Elsevier 2018 Carbon Vol.132 No.-
<P><B>Abstract</B></P> <P>Lightweight, flexible graphite foils that are chemically inert, high-temperature resistant, and highly electrically and thermally conductive can be used as component materials in numerous applications. “Graphenic” foils can be prepared by thermally transforming graphene oxide films. For this transformation, it is desirable to maintain a densely packed film structure at high heating rates as well as to lower the graphitizing temperatures. In this work, we discuss the pressure-assisted thermal decomposition of graphene oxide films by hot pressing at different temperatures (<I>i.e.</I>, 300 °C, 1000 °C, or 2000 °C). The films pressed at 1000 °C or 2000 °C were subsequently heated at 2750 °C to achieve a higher degree of graphitization. The combination of heating and pressing promotes the simultaneous thermal decomposition and graphitic transformation of G-O films. Films pressed at 2000 °C as well as films further graphitized at 2750 °C show high chemical purity, uniformity, and retain their flexibility. For films pressed at 2000 °C and then further heated at 2750 °C, the mechanical performances outperform the reported values of the “graphite” foils prepared by calendering exfoliated graphite flakes; the electrical conductivity is ∼3.1 × 10<SUP>5</SUP> S/m and the in-plane thermal conductivity is ∼1.2 × 10<SUP>3</SUP> W/(m·K).</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
BORON NANOWIRES AND NOVEL TUBE–CATALYTIC PARTICLE–WIRE HYBRID BORON NANOSTRUCTURES
RODNEY S. RUOFF,TERRY T. XU,ALAN W. NICHOLLS 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2006 NANO Vol.1 No.1
Catalyst-assisted growth of boron nanowires and novel tube–catalytic particle–wire hybrid boron nanostructures were achieved by pyrolysis of diborane at 820–890°C and ~ 200 mTorr in a quartz tube furnace. Electron microscopy imaging and diffraction analysis reveal that most of the nano-structures are amorphous. Elemental analysis by EELS and EDX shows that the nanostructures consist of boron with a small amount of oxygen and carbon. Possible growth mechanisms for the tube–catalytic particle–wire hybrid boron nanostructures are discussed.
Kim, Hyun Ho,Kang, Boseok,Suk, Ji Won,Li, Nannan,Kim, Kwang S.,Ruoff, Rodney S.,Lee, Wi Hyoung,Cho, Kilwon American Chemical Society 2015 ACS NANO Vol.9 No.5
<P>Pentacene (C<SUB>22</SUB>H<SUB>14</SUB>), a polycyclic aromatic hydrocarbon, was used as both supporting and sacrificing layers for the clean and doping-free graphene transfer. After successful transfer of graphene to a target substrate, the pentacene layer was physically removed from the graphene surface by using intercalating organic solvent. This solvent-mediated removal of pentacene from graphene surface was investigated by both theoretical calculation and experimental studies with various solvents. The uses of pentacene and appropriate intercalation solvent enabled graphene transfer without forming a residue from the supporting layer. Such residues tend to cause charged impurity scattering and unintentional graphene doping effects. As a result, this clean graphene exhibited extremely homogeneous surface potential profiles over a large area. A field-effect transistor fabricated using this graphene displayed a high hole (electron) mobility of 8050 cm<SUP>2</SUP>/V·s (9940 cm<SUP>2</SUP>/V·s) with a nearly zero Dirac point voltage.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-5/nn5066556/production/images/medium/nn-2014-066556_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5066556'>ACS Electronic Supporting Info</A></P>
First-principles investigation of wet-chemical routes for the hydrogenation of graphene
Horbatenko, Yevhen,Choi, Min,Ruoff, Rodney S.,Bielawski, Christopher W.,Park, Noejung Elsevier 2015 Carbon Vol.93 No.-
<P><B>Abstract</B></P> <P>To investigate the microscopic mechanism for the wet-chemical hydrogenation of graphene, first principles density functional calculations were performed for the hydrogen transfer reaction between the graphene surface and a mixture of hydrogen carrier and electron donor. For the hydrogen transfer from CH<SUB>3</SUB>OH to graphene, as commonly used in Birch-type reductions, the presence of alkali atoms is important not only because they donate electrons but also stabilize the CH<SUB>3</SUB>O<SUP>−</SUP>. On the other hand, when a hydrogen carrier becomes charge neutral after the transfer, as for the case of CH<SUB>3</SUB>NH<SUB>3</SUB> <SUP>+</SUP>, the presence of alkali atoms is not essential, and the supply of electrons from an external source can lead to as favorable thermodynamics as that of alkali atoms. We suggest that, based on these results, a potentially more efficient experimental procedure can be designed.</P>
Ultra Long-Range Interactions between Large Area Graphene and Silicon
Na, Seung Ryul,Suk, Ji Won,Ruoff, Rodney S.,Huang, Rui,Liechti, Kenneth M. American Chemical Society 2014 ACS NANO Vol.8 No.11
<P>The wet-transfer of graphene grown by chemical vapor deposition (CVD) has been the standard procedure for transferring graphene to any substrate. However, the nature of the interactions between large area graphene and target substrates is unknown. Here, we report on measurements of the traction–separation relations, which represent the strength and range of adhesive interactions, and the adhesion energy between wet-transferred, CVD grown graphene and the native oxide surface of silicon substrates. These were determined by coupling interferometry measurements of the separation between the graphene and silicon with fracture mechanics concepts and analyses. The measured adhesion energy was 357 ± 16 mJ/m<SUP>2</SUP>, which is commensurate with van der Waals interactions. However, the deduced traction–separation relation for graphene-silicon interactions exhibited a much longer range interaction than those normally associated with van der Waals forces, suggesting that other mechanisms are present.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-11/nn503624f/production/images/medium/nn-2014-03624f_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn503624f'>ACS Electronic Supporting Info</A></P>
Hwang, Sang-Ha,Kang, Dongwoo,Ruoff, Rodney S.,Shin, Hyeon Suk,Park, Young-Bin American Chemical Society 2014 ACS NANO Vol.8 No.7
<P>Poly(dopamine)-treated graphene oxide/poly(vinyl alcohol) (“dG-O/PVA”) composite films were made and characterized. G-O was modified with poly(dopamine) in aqueous solution and then chemically reduced to yield poly(dopamine)-treated reduced G-O. A combination of hydrogen bonding, strong adhesion of poly(dopamine) at the interface of PVA and G-O sheets, and reinforcement by G-O resulted in increases in tensile modulus, ultimate tensile strength, and strain-to-failure by 39, 100, and 89%, respectively, at 0.5 wt % dG-O loading of the PVA. The dG-O serves as a moisture barrier for water-soluble PVA, and the dG-O/PVA composite films were shown to be effective humidity sensors over the relative humidity range 40–100%.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-7/nn500504s/production/images/medium/nn-2014-00504s_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn500504s'>ACS Electronic Supporting Info</A></P>