Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session W36: Focus Session: Graphene Structure, Dopants, and Defects: Graphene Oxide and Fluoride |
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Sponsoring Units: DMP Chair: Masahiro Ishigami, University of Central Florida Room: C142 |
Thursday, March 24, 2011 11:15AM - 11:51AM |
W36.00001: Properties of Dilute Fluorinated Graphene Invited Speaker: I will discuss our recent studies on dilute fluorinated graphene (DFG). Fluorine adatoms are covalently added to a graphene sheet using a controlled and reversible approach to create a dilute coverage on the order of 10$^{12}$/cm$^2$, as determined by scanning tunneling microscopy studies. These adatoms are atomically sharp defects, interact strongly with the electronic states of graphene and drastically modify the transport properties of pristine graphene. This unusual 2D system exhibits several remarkable properties. Mid-gap state scattering dominates conduction at high temperature, the magnitude of which is determined by the adatom density and is correlated with Raman spectra. The temperature-dependent conductivity of the DFG sample follows weak localization at high carrier density and variable-range hopping at low carrier density. The transition is strongly correlated with the fluorine adatom density. In the variable-range hopping regime, DFG samples exhibit very large, negative magnetoresistance, which shows unusual staircase-like field dependence at low temperature. In the weak localization regime, we observe anomalous phase breaking behavior. I will discuss possible origins of these observations in the context of magnetism and localization. (In collaboration with S.-H. Cheng, C. Herding, and J. Zhu.) [Preview Abstract] |
Thursday, March 24, 2011 11:51AM - 12:03PM |
W36.00002: Electronic and structural properties of fluorinated graphene Chad E. Junkermeier, Stefan C. Badescu, Thomas L. Reinecke Experiments have shown that the electronic structure of graphene can be tailored from that of a semimetal to that of a wide bandgap semiconductor through adsorption of fluorene. This makes fluorinated graphene C$_{x}$F (x$\ge $1) attractive for electronics applications. Here we present first-principle calculations that reveal the dependence of C$_{x}$F electronic structure on the degree of fluorination in the range 1 $\le $ x $\le $ 8. We present a systematic analysis of bandgap opening and p-doping, as well as of adsorption energies, lattice constants, bulk modulus and surface corrugation for single-face and two-face functionalization. We rationalize these with a band-interpolation scheme in terms of localized orbitals that clarify the C-C, C-F and F-F bonding. We discuss the relevance of tunable Young modulus for nanomechanical resonators. [Preview Abstract] |
Thursday, March 24, 2011 12:03PM - 12:15PM |
W36.00003: Patterning nanoroads and quantum dots on fluorinated graphene Morgana Ribas, Abhishek Singh, Pavel Sorokin, Boris Yakobson Graphene nanoroads [1] and quantum dots [2] patterned on functionalized graphene combine metallic and semiconducting properties on a same mechanically intact sheet. Using density functional methods we investigate different stoichiometric phases of fluorinated graphene and find that the complete ``2D-teflon'' CF phase is thermodynamically more stable. The formation of fluorinated graphene favors the nucleation of aromatic ``magic'' clusters, but unlike hydrogenated graphene [3] it does not have a nucleation barrier. The CF is an insulator and turns out to be a perfect matrix-host for patterning nanoroads and quantum dots of pristine graphene. Depending upon the edge orientation and width the electronic and magnetic properties of the nanoroads can be tuned. The HOMO-LUMO energy gaps are size dependent and show a typical confinement of Dirac fermions. Furthermore, we study the effect of different coverage of F on graphene (CF and C$_{4}$F) on the band gaps, and show their suitability to host quantum dots of graphene with unique electronic properties. References: [1] Singh, A. K.; Yakobson, B. I., Nano Lett. 2009, 9 (4), 1540.[2] Singh, A. K.; Penev, E. S.; Yakobson, B. I., ACS Nano 2010, 4 (6), 3510. [3] Lin, Y.; Ding, F.; Yakobson, B. I., Phys. Rev. B 2008, 78 (4), 041402. [Preview Abstract] |
Thursday, March 24, 2011 12:15PM - 12:27PM |
W36.00004: Anomalous Phase Breaking in Dilute Fluorinated Graphene Xia Hong, Shih-Ho Cheng, Jun Zhu Quantum interference induced weak localization and phase breaking measurements are sensitive tools to probe the existence of magnetic impurities in mesoscopic systems. In this work, we study the low-field magnetoresistance of dilute fluorinated graphene (DFG), with a fluorine adatom density of $\sim$~10$^{12}$/cm$^2$. In the DFG samples, the phase breaking time $\tau_\phi$ follows $T^{-1}$ at high temperature and saturates at $T$ $\sim$ 10 K. The former is consistent with electron-electron interaction. The latter cannot be accounted for by conventional theories based on sample size and charge inhomogeneity. We show the dependence of the saturated $\tau_\phi$ on the carrier density and fluorine coverage and discuss the effects of spin-flip scattering and localization in phase breaking. Our observations point to the presence of adatom induced local magnetic moments in dilute fluorinated graphene. [Preview Abstract] |
Thursday, March 24, 2011 12:27PM - 12:39PM |
W36.00005: Functionalization of exfoliated graphene by grafting aryl groups Hang Zhang, Elena Bekyarova, Zeng Zhao, Wenzhong Bao, Jhao-Wun Huang, Mikhail Itkis, Sandip Niyogi, Xiaoliu Chi, Huazhou Wei, Fenglin Wang, Robert Haddon, Chun Ning Lau We studied the transport properties of aryl functionalized exfoliated graphene. For the functionalization the graphene devices were immersed in a solution of diazonium salt. The attachment of aryl free radical to the basal carbon atoms changes the hybridization of the graphitic atoms from sp2 to sp3 thereby~modifying the lattice's electronic structure. We observe that this opens a Coulomb gap at low temperatures and transport measurements indicate a variable range hopping mechanism. In suspended graphene, which allows for functionalization on both sides, we observe a large transport gap. [Preview Abstract] |
Thursday, March 24, 2011 12:39PM - 12:51PM |
W36.00006: Field emission from atomically thin edges of reduced graphene oxide Hisato Yamaguchi, Katsuhisa Murakami, Goki Eda, Takeshi Fujita, Julien Boisse, Pengfei Guan, Fujio Wakaya, Kyeongjae Cho, Yves Chabal, Mingwei Chen, Mikio Takai, Manish Chhowalla Point sources show the best electron emission properties due to local field enhancement at the tip. A drawback of tip emitters is that they must be positioned sufficiently apart to achieve field enhancement, limiting the number of emission sites and therefore the overall current. In contrast, we report ultra-low threshold voltage emission of multiple electron beams from atomically thin edges of individual reduced graphene oxide (rGO) sheets. The emission sites observed by field emission (FEM) and field ion (FIM) microscopies are atomically spaced along the edge. FEM measurements indicate evidence for interference, suggesting that the emitted electron beams are coherent. Based on our spectroscopy, high-resolution transmission electron microscopy and theory results, field emission is attributed to the aggregation of oxygen groups in the form of cyclic edge ethers. Such closely spaced electron beams from rGO offer prospects for novel applications and understanding the physics of linear electron sources. [Preview Abstract] |
Thursday, March 24, 2011 12:51PM - 1:03PM |
W36.00007: Electronic structure of graphite oxide Hae Kyung Jeong, Cheolsoo Yang, Bong Soo Kim, Ki-jeong Kim We have investigated the electronic structure of graphite oxide by photoelectron spectroscopy at the Pohang Accelerator Laboratory, Korea. The typical sp$^{2}$ hybridization states found in graphite were also seen in graphite oxide. However, the $\pi $ state disappeared near the Fermi level because of bonding between the $\pi $ and oxygen-related states originating from graphite oxide, indicating electron transfer from graphite to oxygen and resulting in a downward shift of the highest occupied molecular orbital (HOMO) state to higher binding energies. The band gap opening increased to about 1.8 eV, and additional oxygen-related peaks were observed at 8.5 and 27 eV.\\[4pt] This research was supported by the Basic Science Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education, Science and Technology (2010-0004592), and partly by the MEST (2009-0087138). Experiments at the PLS were supported in part by POSTECH and MEST. [Preview Abstract] |
Thursday, March 24, 2011 1:03PM - 1:15PM |
W36.00008: Computational Studies for Reduced Graphene Oxide in Alcohol- and Hydrogen-Rich Environments Ramin Abolfath, Cheng Gong, Muge Acik, Yves Chabal, Kyeongjae Cho We employ \textit{ab-initio} molecular dynamic simulations to analyze the chemical reaction mechanisms for the oxygen removal process of graphene oxide upon annealing in the presence of water molecules and compare various thermal pathways in alcohol- and hydrogen-rich environments. Our first principles calculation shows damage-repair mechanisms of sp$^{2}$-C bonds in the etch holes of reduced graphene oxide and formation of dangling and/or sp$^{3}$-C bonds. The initial oxygen-abstraction results in the propagation of broken bonds and multi-site sp$^{2}$-C bond damage driven by the cascade of chemical reactions. The interplay between the environmentally induced damages and self-repair mechanisms of sp$^{2}$-C bonds determines the quality of the sheets after chemical treatments in alcohols or with hydrogen-rich environment. Water molecules form C=O and C-H bonds in the etch holes. We show that the alcohol- and hydrogen-rich environment provide an efficient transformation of C=O to the C-O bonds, and the removal of oxygen that is rarely observed with alcohol-rich environment alone. [Preview Abstract] |
Thursday, March 24, 2011 1:15PM - 1:27PM |
W36.00009: Electron Phonon Coupling Mechanism in Thermally Reduced Graphene Muge Acik, Geunsik Lee, Cecilia Mattevi, Manish Chhowalla, Kyeongjae Cho, Yves J. Chabal Infrared absorption of atomic and molecular vibrations in solids can be affected by electronic contributions through non-adiabatic interactions, such as the Fano effect. Typically, the IR absorption lineshapes are modified or IR forbidden modes are detectable as a modulation of the electronic absorption. In contrast to such known phenomena, we report here the observation of a giant IR absorption band in reduced graphene oxide (GO), arising from the coupling of electronic states to the asymmetric stretch mode of a yet unreported structure [1], consisting of oxygen atoms aggregated at edges of defects. DFT calculations show that free electrons are induced by the displacement of the oxygen atoms, leading to a strong IR absorption that is in-phase with the phonon mode. This new phenomenon is only possible when all other oxygen-containing chemical species including hydroxyl, carboxyl, epoxide and ketonic functional groups are removed from the region adjacent to the edges, i.e. clean graphene patches are present. *The authors acknowledge funding from the NRI SWAN program and Texas Instruments. [1] Acik, M.; Lee, G.; Mattevi, C.; Chhowalla, M.; Cho, K.; Chabal, Y. J. \textit{Nature Materials}. \textbf{9,} 840-845 (2010) [Preview Abstract] |
Thursday, March 24, 2011 1:27PM - 1:39PM |
W36.00010: Grain-boundary unzipping by oxidation in polycrystalline graphene Simone Alexandre, Aline Lucio, Ricardo Nunes The need for large-scale production of graphene will inevitably lead to synthesis of the polycrystalline material [1,2]. Understanding the chemical, mechanical, and electronic properties of grain boundaries in graphene polycrystals will be crucial for the development of graphene-based electronics. Oxidation of this material has been suggested to lead to graphene ribbons, by the oxygen-driven unzipping mechanism [3]. A cooperative-strain mechanism, based on the formation of epoxy groups along lines of parallel bonds in the hexagons of graphene's honeycomb lattice, was proposed to explain the unzipping effect in bulk graphene [3] In this work we employ \textit{ab initio} calculations to study the oxidation of polycrystalline graphene by chemisorption of oxygen at the grain boundaries. Our results indicate that oxygen tends to segregate at the boundaries, and that the unzipping mechanism is also operative along the grain boundaries, despite the lack of the parallel bonds due to the presence of fivefold and sevenfold carbon rings along the boundary core. \\[4pt] [1] J. Cervenka et al., PRB 79, 195429 (2009). \\[0pt] [2] J. da Silva-Ara\'{u}jo and R. W. Nunes, PRB 81, 073408 (2010). \\[0pt] [3] J-L. Li \textit{et al.}, PRL 96, 176101 (2006). [Preview Abstract] |
Thursday, March 24, 2011 1:39PM - 1:51PM |
W36.00011: Influence of Gate Voltage on the diffusion of Oxygen on Graphene Alejandro Suarez, Ljubisa Radovic, Ezra Bar-Ziv, Jorge Sofo We calculate the surface diffusion of Oxygen on Graphene using Density Functional Theory. We find the activation energy for diffusion to be 0.71 eV. Charging the graphene plane causes the diffusion barrier to change substantially. Electron doping graphene lowers the diffusion barrier, resulting in activation energies as low as 0.15 eV for a carrier concentration of 7.6x10$^{13}$ cm$^{-2}$. This barrier reduction yields diffusion coefficients reaching over nine orders of magnitude lower than that of diffusion on neutral graphene. After study of the change in charge density distribution and local density of states, this effect is explained by a mixture of bond weakening under the equilibrium state and bond strengthening during the transition state. With this large fluctuation in diffusivity, patterning of oxidized regions in graphene may be achieved through variation of the gate voltage. [Preview Abstract] |
Thursday, March 24, 2011 1:51PM - 2:03PM |
W36.00012: Coulomb blockade and hopping conduction in graphene quantum dots array Daeha Joung, Lei Zhai, Saiful Khondaker We show from the low temperature electron transport measurements that the transport properties of chemically reduced graphene oxide (RGO) sheets can be explained as a sequential tunneling of charges through a two dimensional polydispersed array of graphene quantum dots (GQD), where graphene domains act like QDs while oxidized domains behave like tunnel barriers between QDs. As the temperature is decreased to lower than 15 K, a complete suppression of current ($I)$ below a threshold voltage ($V_{t})$ was observed due to Coulomb blockade (CB) of charges through GQD array. For $V> \quad V_{t}$, the current follows a scaling behavior, $I \quad \propto [(V-V_{t})/V_{t}]^{\alpha }$ with $\alpha \quad \sim $ 2.8, implying a quasi 2D GQD array. Temperature dependent current -- gate voltage ($I-V_{g})$ curves show reproducible Coulomb oscillations due to a single electron tunneling through GQD array that washes out between 70 and 120 K corresponding to charging energies of 6.2 $\sim $ 10 meV giving estimated GQD sizes of 5 - 8 nm. Temperature dependent resistance data show Efros-Shklovskii variable range hopping (ES VRH) arising from CB, structural and size induced disorder. [Preview Abstract] |
Thursday, March 24, 2011 2:03PM - 2:15PM |
W36.00013: Ink jet printed graphene oxide (GO) coplanar waveguide (CPW) structures for measurement of microwave propagation in GO Kate Duncan, Edwin Barry, Mark Griep, Johhny Daniel, Derek Morris, Shashi Karna Chemically reduced graphene~(CGR) has been successfully inkjet printed using a commercially available printer. The CGR with sheet sizes below 200 nm were dispersed in a mixture of water and ethanol. Coplanar waveguide (CPW) structures were deposited on CGR and plastic substrates, scattering (S) parameters were measured in order to extract material parameter for incorporation into simulation tools. Measurements and modeling of microwave propagation in graphene shall be presented. [Preview Abstract] |
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