Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session B29: Graphene Functionalization and Adsorbates |
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Sponsoring Units: DCMP Chair: Dan Dougherty, North Carolina State University Room: 603 |
Monday, March 3, 2014 11:15AM - 11:27AM |
B29.00001: Graphene functionalization with nitrogen and oxygen: controlled modification of the electronic properties Peter Brommer, Alexander Marsden, Neil Wilson, Gavin Bell, David Quigley For many applications it is essential to modify the electronic properties of graphene in a controlled fashion. This can be achieved via oxygen and nitrogen functionalization in ultra-high vacuum, leading to a system in which electronic and structural properties can be systematically studied. Here we present insights from DFT calculations on functionalized graphene systems, such as the low-energy configurations and simulated transmission electron microscopy (TEM) images, binding energies and effective band structures (EBS) of the N and O decorated graphene sheets. We directly compare our results with experiments on CVD grown graphene. Angle-resolved photoemission spectroscopy (ARPES - performed at the Antares beamline of Synchrotron SOLEIL, France) resolves the band structure changes on functionalization, whilst the simulated TEM images provide feedback for the interpretation of low-voltage aberration-corrected TEM measurements. Combined, the computational and experimental results have important implications for the manipulation of electronic properties in graphene by controlled functionalization. [Preview Abstract] |
Monday, March 3, 2014 11:27AM - 11:39AM |
B29.00002: Density functional theory investigation of cyclohexane as a potential functionalizing agent on graphene Ceren Sibel Sayin, Daniele Toffoli, Hande \"Ust\"unel Single molecules can functionalize graphene both covalently and non-covalently for use in various applications. Their adsorption properties also become important in graphene-based catalysis. In this talk, we present density functional theory (DFT) results of the interaction of cyclohexane, cyclohexyl and cyclohexene with pristine and defected graphene. We investigate structural and electronic changes induced in graphene upon adsorption and explore the potentiality of graphene to be employed in the catalytic oxidation/hydrogenation of these molecules. [Preview Abstract] |
Monday, March 3, 2014 11:39AM - 11:51AM |
B29.00003: Ab Initio Study of Covalently Functionalized Graphene and Carbon Nanotubes Sanjiv Jha, Mahmoud Hammouri, Igor Vasiliev, Igor Magedov, Liliya Frolova, Nikolai Kalugin The electronic and structural properties of carbon nanomaterials can be affected by chemical functionalization. We apply {\it ab initio} computational methods based on density functional theory to study the properties of graphene and single-walled carbon nanotubes functionalized with benzyne. Our calculations are carried out using the SIESTA electronic structure code combined with the generalized gradient approximation for the exchange correlation functional. The calculated binding energies, densities of states, and band structures of functionalized graphene and carbon nanotubes are analyzed in comparison with the available experimental data. The surfaces of carbon nanotubes are found to be significantly more reactive toward benzyne molecules than the surface of graphene. The strength of interaction between benzyne and carbon nanotubes is affected by the curvature of the nanotube sidewall. The binding energies of benzyne molecules attached to both semiconducting zigzag and metallic armchair nanotubes increase with decreasing the nanotube diameter. [Preview Abstract] |
Monday, March 3, 2014 11:51AM - 12:03PM |
B29.00004: Graphene functionalization by single atoms doping - a theoretical study Amir Natan, Elad Segev, Mark Hersam, Tamar Seideman We present first principles results and analysis for the electronic structure of chemically modified graphene. We analyze the cases of fluorine adsorption and nitrogen substitution and show that a simple analytical model can describe the doping level as a function of dopant concentration for both cases. We show the relationship between different physical parameters and the electronic band structure of the modified material and its doping level. Finally, we discuss the possible effects of substrate and of different dopant patterns on the band structure and possible applications. [Preview Abstract] |
Monday, March 3, 2014 12:03PM - 12:15PM |
B29.00005: Transport properties of chemically functionalized graphene Georgi Diankov, Francois Amet, Yongtao Cui, Zhi-Xun Shen, David Goldhaber-Gordon We use low-temperature transport measurements and microwave impedance microscopy to investigate the properties of graphene on hBN substrates. In particular, we study the Quantum Hall-insulator transition in pristine graphene and then study its evolution as the graphene is hydrogenated, observing the effect of the interplay between inter-defect distance and magnetic length. Using real-space imaging with microwave impedance microscopy, we observe well-defined edge states and suppression of conductivity in the bulk. We correlate the results from microwave impedance imaging with transport measurements. The study elucidates mechanisms that can be used to introduce controlled amounts of defects and thus, to tune the quantum transport properties of graphene. [Preview Abstract] |
Monday, March 3, 2014 12:15PM - 12:27PM |
B29.00006: Electrical transport in indium-decorated graphene sheets U. Chandni, E.A. Henriksen, J.P. Eisenstein Heavy adatoms on graphene are expected to alter its intrinsic properties in many novel ways. Here we report magneto-transport measurements on single layer graphene sheets which have been decorated with dilute concentrations of indium adatoms. These measurements are made using a custom-built evaporator housed in an ultra-high vacuum cryostat. This apparatus allows for the annealing of the graphene sample, the controlled deposition and removal of the In adatoms, and the actual transport measurements to all be done \textit{in situ}. As expected, we find that the In adatoms donate electrons to the graphene sheet, thereby shifting the location of the Dirac peak. More interestingly, our measurements clearly reveal how the In adatoms influence the scattering environment experienced by the Dirac electrons. Beyond merely reducing the sample mobility via enhanced charged impurity scattering, we find that the In adatoms alter the ``puddle'' landscape near the Dirac point and modify the low field magneto-resistance signatures of weak localization and anti-localization. [Preview Abstract] |
Monday, March 3, 2014 12:27PM - 12:39PM |
B29.00007: Pseudo-spin Winding Number in Hydrogenated Graphene Keyan Bennaceur, Jonathan Guillemette, Pierre L. L\'evesque, Farzaneh Mahvash, Cyril Proust, Mohamed Siaj, Richard Martel, Guillaume Gervais, Thomas Szkopek The quantum Hall effect (QHE) has been previously observed in highly resistive hydrogenated graphene, with an estimated hydrogen coverage up to 0.1\% that is sufficient to impart strongly insulating behaviour in zero magnetic field [1]. The opening of an impurity induced gap in graphene upon hydrogenation is anticipated to break local sub-lattice symmetry, and it may thus alter the Berry phase of Shubnikov-de Haas (SdH) oscillations and lead to a different Landau level (LL) sequence. Here we report the observation of SdH oscillations in a magnetic field up to 55 Tesla in graphene samples hydrogenated to different degree. The low temperature electron mobility ranges from $\sim$1 $cm^2/V.s$ to $\sim$1000 $cm^2/V.s$. Analysis of SdH oscillation frequency in 1/B indicates that the LL sequence remains four-fold degenerate. We also observe the $\nu=2$ Hall plateau in all samples. We therefore conclude that the topological part of the Berry phase, meaning the pseudo-spin winding number that determines the LL sequence [2], is preserved in hydrogenated graphene. \\[4pt] [1] J. Guillemette et al, PRL 110, 176801 (2013).\\[0pt] [2] J.N Fuchs et al Eur. Phys. J. B 77, 351-362 (2010). [Preview Abstract] |
Monday, March 3, 2014 12:39PM - 12:51PM |
B29.00008: Triangular Lattices of Transition Metals Adsorbed on Graphene Matheus P. Lima, Carlos M. Acosta, Roberto H. Miwa, Ant\^onio J.R. da Silva, Adalberto Fazzio It is possible to control the electronic properties of graphene (GR) via adsorption. For instance, the increasing of the Spin-Orbit Coupling (SOC) in GR by adsorption of heavy atoms. When these atoms are adsorbed in GR, the SOC leads to a non-trivial opening of a band gap higher than the predicted in pristine GR. Indeed, there are several works addressed to investigate the adsorption of adatoms in GR, where the geometric arrangement of the atoms plays a quite important role. In this work, using ab initio DFT calculations, we present a detailed picture of how the electronic properties of GR are connected to the atomic lattice geometry of TMs (3d , 4d, and 5d) adatoms. Particularly, we show that triangular arrangements of ``Ru'' and ``Os'' atoms on GR give rise to: i) two Dirac cones at K-point due to the crystal field, ii) broken of the spin degeneracy due to the exchange field, leading to four Dirac cones, and iii) a non-trivial band gap opens due to the SOC, resulting the Quantum Anomalous Hall phase. The Dirac cones are ruled by a suitable coupling between the TM triangular lattice, and the GR hexagonal lattice. The electronic states near the Dirac points appear in the Local Density of States as peaks or valleys at geometric center of the TM triangles (barycenters). [Preview Abstract] |
Monday, March 3, 2014 12:51PM - 1:03PM |
B29.00009: Quantum Monte Carlo study of magnetic correlations between adatom impurities in graphene A.D. G\"u\c{c}l\"u, Nejat Bulut We study the interaction between two adatom impurity spins in graphene within the framework of the Anderson model. In particular, we calculate the inter-impurity magnetic correlations by using the quantum Monte Carlo (QMC) technique [1]. We find that, at high temperatures, the QMC results for the magnetic correlations between the impurities are in agreement with the Ruderman-Kittel-Kasuya-Yoshida (RKKY) predictions for graphene [1]. However, as the temperature is lowered, the inter-impurity magnetic correlations become strongly enhanced over the RKKY results, which points to the significance of the electronic correlations.\\[4pt] [1] R.M. Fye and J.E. Hirsch, PRB v38, 433 (1988).\\[0pt] [2] S. Saremi, PRB v76, 184430 (2007). [Preview Abstract] |
Monday, March 3, 2014 1:03PM - 1:15PM |
B29.00010: The sonication of graphite in various solvents and surfactants to synthesize high quality graphene as well as the nitrogen doping of graphene Daniel R. Soden, Jincheng Bai, Lifeng Dong The emergence of graphene in the scientific community has been the cause of much excitement among material scientists due to its unusual physical and photovoltaic properties. However, the much sought after monolayer graphene has proven to be difficult to produce in sufficient quantities This experiment aims to correct some of these problems, concerning itself with the synthesis of high quality graphene through continuous sonication with surfactant or solvent added throughout, as well as the issue of graphene quality as a function of sonication time. This was accomplished through the creation and addition of a solvent or surfactant solution to a graphite suspension during sonication lasting for 50, 80, 110,140, 170, and 200 minutes. The resulting suspension was then filtrated to separate out the graphene. Following this, the graphene was then doped through various methods with nitrogen to alter its properties. This completely physical method of graphene synthesis and doping provides a much simpler and more environmentally safe way to achieve the highly desired few layer graphene, and will hopefully allow for greater use of the substance in industry and its implementation into new technology. [Preview Abstract] |
Monday, March 3, 2014 1:15PM - 1:27PM |
B29.00011: Theory of spin-orbit coupling in fluorinated graphene Martin Gmitra, Tobias Frank, Susanne Irmer, Denis Kochan, Jaroslav Fabian We performed first-principles calculations of the spin-orbit coupling in graphene with fluorine adatom. The chemisorption of fluorine modifies the structural symmetry of graphene by breaking the pseudospin symmetry and inducing local corrugation towards $sp^3$ hybridization. We show that there are two dominant contributions to the spin-orbit field -- Rashba term and a term due to pseudospin inversion asymmetry (PIA). In addition to the $sp^3$ induced spin-orbit coupling enhancement the spin-orbit split of the fluorine $p$ orbitals is substantially transferred to graphene. Using group theoretical arguments we propose a realistic minimal Hamiltonian that reproduce the relevant spin-orbit effects calculated from first-principles. Our realistic effective Hamiltonian should be useful for spin transport and spin relaxation investigations. [Preview Abstract] |
Monday, March 3, 2014 1:27PM - 1:39PM |
B29.00012: Attraction-repulsion transition in the interaction of adatoms and vacancies in graphene Stephan LeBohec, Justin Talbot, Eugene Mishchenko The interaction of two resonant impurities in graphene has been predicted to have a long-range character with weaker repulsion when the two adatoms reside on the same sublattice and stronger attraction when they are on the same sublattice. We reveal that a single impurity level is responsible for such attraction. This opens up a possibility of controlling the sign of the impurity interaction via the adjustment of the chemical potential. For many randomly distributed impurities (adatoms or vacancies) this may offer a way to achieve a controlled transition from aggregation to dispersion. [Preview Abstract] |
Monday, March 3, 2014 1:39PM - 1:51PM |
B29.00013: Spin-induced modification of Dirac band on Fe-intercalated graphene system Sijin Sung, Jaewoon Yang, Paengro Lee, Jingul Kim, Mintae Ryu, Heemin Park, Chancuk Hwang, Kwangsu Kim, Jaesam Kim, Jinwook Chung Intercalation of magnetic iron atoms through graphene formed on the SiC(0001) surface is found to induce significant changes in electronic properties of graphene due mainly to the Fe-induced asymmetries in charge as well as spin distribution. From our synchrotron-based photoelectron spectroscopy data together with \textit{ab initio }calculations, we observe that the Fe-induced charge asymmetry results in the formation of a quasi-free-standing bilayer graphene while the spin asymmetry drives multiple spin-split bands. We find that Fe adatoms are best intercalated upon annealing at 600$^{\circ}$C exhibiting split linear $\pi $-bands, characteristic of a bilayer graphene, but much diffused. Subsequent changes in the C 1s, Si 2p, and Fe 3p core levels are consistently described in terms of Fe-intercalation. Our calculations together with a spin-dependent tight binding model ascribe the diffused nature of the $\pi $-bands to the multiple spin-split bands originated from the spin-injected carbon atoms residing only in the lower graphene layer. [Preview Abstract] |
Monday, March 3, 2014 1:51PM - 2:03PM |
B29.00014: Real-Time Optical Observation of Water Diffusion at a Graphene-Silica Janus Interface Sunmin Ryu, DaeEung Lee, Gwanghyun Ahn Because of the dominant role of the surface of molecules and their individuality, molecules behave distinctively in a confined space, which has far-reaching implications in many physical, chemical and biological systems. Here, we demonstrate that graphene forms a unique atom-thick interstitial space that enables the study of molecular diffusion in 2-dimensions with underlying silica substrates. Raman spectroscopy visualized intercalation of water from the edge to the center underneath graphene in real time, which was dictated by the hydrophilicity of the substrates. In addition, graphene undergoes reversible deformation to conform to intercalating water clusters or islands. Atomic force microscopy confirmed that the interfacial water layer is clearly flat and only a few angstroms thick, corresponding to one bilayer unit of normal ice. This study also proves that oxygen species responsible for the ubiquitous hole doping are located below graphene. In addition to serving as a transparent confining wall, graphene and possibly other 2-dimensional materials can be used as an optical indicator sensitive to interfacial mass transport and charge transfer. [Preview Abstract] |
Monday, March 3, 2014 2:03PM - 2:15PM |
B29.00015: Pseudo-magnetic fields in rippled nitrogenated graphene Sara Rothwell, Feng Wang, Edward Conrad, Gang Liu, Leonard Feldman, Philip Cohen We demonstrate a new form of semiconducting graphene which is fabricated via controlled silicon sublimation on carbon face SiC(000$\bar{1}$), previously seeded with a submonolayer of nitrogen. Nitrogenated graphene (NG) films between 2 - 8 layers have been examined [F. Wang et al. Nano Lett. 13, 4827 (2013)]. Scanning tunneling microscopy (STM) shows that NG films have ripples and folds over the entire surface. The ripples are of variable size but typically about 2 nm wide and 2-4 nm high. They meander from 5-20 nm in length. STM images show graphene flowing continuously over all folds. Scanning tunneling spectroscopy (STS) at 50 K shows peaks corresponding to Landau levels, implying a pseudo magnetic field of about 100 T. Little variation in peak position is noted in spectra taken across a fold. Levy et al. observed similar STS spectra taken near graphene nano bubbles [N. Levy et al. Science 329, 544 (2010)]. Near the Dirac point in NG STS spectra, the peaks are weak and broad corresponding to a bandgap of less than 1.5 eV. For a similar film, angle resolved photoemission measures an offset of 0.7 eV, which is a measurement of the portion of the gap below the fermi level. We thank N. Guisinger and T. Low for their support and valuable discussions. [Preview Abstract] |
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