Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session J1: Focus Session: Graphene: Surface Functionalization and Other Topics |
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Sponsoring Units: DMP Chair: Jinglei Ping, University of Pennsylvania Room: 001A |
Tuesday, March 3, 2015 2:30PM - 3:06PM |
J1.00001: Hybridized Graphene Materials Invited Speaker: Jeremy Robinson Graphene's high-quality structure and properties continue to motivate intensive research to mold it into the electronic material of the future. Analogous to other electronic materials, however, defects are a tool to engineer graphene's properties and tune its response to various stimuli. In this talk I discuss our efforts to engineer and manipulate defects in hybrid graphene materials for applications ranging from sensing to nanomechanical structures. First, I will present our results using chemically modified graphene to not only improve chemical sensing, but also achieve new functionality for electronic systems. In particular, we hybridize graphene via the addition of fluorine atoms [1] and show the subsequent formation of nanoribbons and tunnel barriers exploiting property changes from the fluorine adsorbates. Second, I will present results on the electronic hybridization of stacked graphene layers, where the moir\'{e} pattern formed by the relative twist between layers is responsible for new properties of the bilayer system [2]. Defects specific to this system include rotational disorder, strain, and chemical doping [3]. These defects modify, but do not destroy the strong interlayer coupling. Finally, I will present results on the influence of chemistry and defects on the properties of graphene nanomechanical systems. By measuring the response of high-quality nanomehcanical resonators, we can extract relevant mechanical properties including tension, yield strength, resilience, and modulus as a function of defect introduction [4]. This work is carried out in collaboration with M. Zalalutdinov, P.E. Sheehan, W.-K. Lee, T. Reinecke, S.W. Schmucker, J.C. Culbertson, and A.L. Friedman at Naval Research Laboratory, and T. Ohta, T.E. Beechem and B. Diaconescu at Sandia National Laboratories. [1] Nano Letters 10, 3001 (2010); [2] ACS Nano 7, 637 (2013); [3] ACS Nano 8, 1655 (2014) [4] Nano Letters 12, 4212 (2012) [Preview Abstract] |
Tuesday, March 3, 2015 3:06PM - 3:18PM |
J1.00002: In Situ Study of Fluorine-Functionalized and Tri-Methyl Aluminum Dosed Epitaxial Graphene on SiC(0001) Zachary Robinson, Virginia Wheeler, Sandra Hernandez, Glenn Jernigan, Rachael Myers-Ward, D. Kurt Gaskill, Tyler Mowl, Eng Wen Ong, Carl Ventrice Jr., Heike Geisler, Ivo Pletikosic, Tonica Valla, Chip Eddy Jr. Graphene growth in Ar on SiC(0001) results in a single rotational orientation film with single-layer thickness control. For many electronic applications, a gate dielectric, such as Al2O3, must be deposited on top of the graphene. To facilitate this, an atomic layer deposition process was developed to deposit Al2O3 on a fluorine-functionalized graphene surface [1]. The functionalization process was necessary for deposition of the Al2O3. Angle resolved photoelectron spectroscopy and low energy electron diffraction were used to study the functionalized surfaces of bilayer and single layer graphene grown on SiC(0001). It was found that the fluorine had a negligible effect on the electronic structure of the graphene, and upon thermal desorption, caused no damage to the graphene film. Additionally, tri-methyl aluminum was dosed on the graphene in a chamber equipped with in situ XPS. This was performed on both fluorine functionalized and as-grown single layer graphene. 1 - Wheeler, Virginia, et al. Carbon, 50(6), 2307-2314 [Preview Abstract] |
Tuesday, March 3, 2015 3:18PM - 3:30PM |
J1.00003: Near-edge X-ray Absorption Fine Structure (NEXAFS) Spectroscopy study on Chlorinated Graphene through Plasma-based Surface Functionalization Xu Zhang, Theanne Schiros, Dennis Nordlund, Yong Cheol Shin, Jing Kong, Mildred Dresselhaus, Tomas Palacios Plasma-based chlorination is a promising technique to realize controllable doping in graphene, while maintaining its high mobility. Meanwhile, synchrotron-based X-ray spectroscopy provides us a sensitive probe to investigate the surface states of functionalizing dopants in graphene. Here, we systematically studied the electronic states of chlorinated graphene on different substrates, including surface binding energy, dopant concentration and work function shift by use of Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy, XPS and photoemission threshold measurements. The concentration of absorbed chlorine is high enough to generate a distinct NEXAFS resonance at 286.2 eV (1s -\textgreater $\pi $* transition for C-Cl bonds). It is remarkable that the sp2 carbon core-hole exciton (291.85eV) retained its sharpness even after treatment, indicating the long-range periodicity in graphene is largely preserved. This distinguishes our approach as a noninvasive and effective doping method. The interaction between Cl and graphene also exhibits strong substrate effects: for Cu, graphene's Fermi level is shifted downwards by 0.35eV, while for graphene on SiO2, the much (4-5 times) higher chlorine concentration causes EF to shift by 0.9eV. [Preview Abstract] |
Tuesday, March 3, 2015 3:30PM - 3:42PM |
J1.00004: First Principles Study of Chemically Functionalized Graphene Sanjiv Jha, Igor Vasiliev The electronic, structural and vibrational properties of carbon nanomaterials can be affected by chemical functionalization. We applied {\it ab initio} computational methods based on density functional theory to study the covalent functionalization of graphene with benzyne, carboxyl groups and tetracyanoethylene oxide (TCNEO). Our calculations were carried out using the SIESTA and Quantum-ESPRESSO electronic structure codes combined with the local density and generalized gradient approximations for the exchange correlation functional and norm-conserving Troullier-Martins pseudopotentials. The simulated Raman and infrared spectra of graphene functionalized with carboxyl groups and TCNEO were consistent with the available experimental results. The computed vibrational spectra of graphene functionalized with carboxyl groups showed that the presence of point defects near the functionalization site affects the Raman and infrared spectroscopic signatures of functionalized graphene. [Preview Abstract] |
Tuesday, March 3, 2015 3:42PM - 3:54PM |
J1.00005: The influence of selective chemical doping on clean, low-carrier density SiC epitaxial graphene Chiashain Chuang, Yanfei Yang, Lung-I Huang, Chi-Te Liang, Randolph E. Elmquist The charge-transfer effect of ambient air on magneto-transport in polymer-free SiC graphene was investigated. Interestingly, adsorption of atmospheric gas molecules on clean epitaxial graphene can reduce the carrier density to near charge neutrality, allowing observation of highly precise $v=$ 2 quantum Hall plateaus. The atmospheric adsorbates were reproducibly removed and pure gases (N$_{\mathrm{2}}$, O$_{2}$, CO$_{2}$, H$_{2}$O) were used to form new individual adsorbates on SiC graphene. Our experimental results ($\tau _{\mathrm{t}}$/$\tau_{\mathrm{q}}\approx $ 2) support the theoretical predictions for the ratio of transport relaxation time $\tau _{\mathrm{t}}$ to quantum lifetime $\tau_{\mathrm{q}}$ in clean graphene. The analysis of Shubnikov-de Haas oscillations at intermediate doping levels indicates that the carrier scattering is reduced by water and oxygen so as to increase both the classical and quantum mobility. This study points to the key dopant gases in ambient air and also paves the way towards extremely precise quantized Hall resistance standards in epitaxial graphene systems with carrier density tuned by exposure to highly pure gases and vacuum annealing treatment. [Preview Abstract] |
Tuesday, March 3, 2015 3:54PM - 4:06PM |
J1.00006: ABSTRACT WITHDRAWN |
Tuesday, March 3, 2015 4:06PM - 4:18PM |
J1.00007: Electroless deposition of metal nanoparticles on graphene with substrate-assisted techniques Anna M. Zaniewski, Christie J. Trimble, Veronica Meeks, Robert J. Nemanich We present the electroless reduction of solution-based metal ions for nanoparticle deposition on a variety of substrates.~ The substrates include graphene-coated metals, insulators, doped semiconductors, and patterned ferroelectrics. We find that the metal ions are spontaneously reduced on a wide variety of graphene substrates, and the substrates play a large role in the nanoparticle coverage. For example, the reduction of gold chloride to gold nanoparticles on graphene/lithium niobate results in 3{\%} nanoparticle coverage compared to 20{\%} coverage on graphene/silicon and 60{\%} on graphene/copper. Given that the work function of graphene is approximately 4.4eV, the Fermi level is -0.1 V vs the normal hydrogen electrode (NHE). Since the reduction potential of gold chloride is $+$1.002 V, the spontaneous transfer of electrons from the graphene to the metal ion is energetically favorable. However, we find substrates with similar work functions nevertheless result in varied deposition rates, which we attribute to electron availability. We also find that patterned ferrolectrics can be used as a template for patterned nanoparticle deposition, with and without graphene. [Preview Abstract] |
Tuesday, March 3, 2015 4:18PM - 4:54PM |
J1.00008: Quantum Transport in Few-Layer Graphene and Phosphorene Devices Invited Speaker: Chun Ning (Jeanie) Lau I will present our results on transport measurements in bilayer and trilayer graphene devices with mobility as high as 400,000 cm2/Vs. We demonstrate the presence of an intrinsic gapped state in bilayer and trilayer graphene at the charge neutrality point, a ``new'' spectroscopy technique for measuring the Landau level gaps, the distinct competing states at filling factor 2 and crossing between symmetry-broken Landau levels. Our results underscore the fascinating many-body physics in these 2D membranes. Finally, I will present our recent results on fabrication of air-stable few-layer phosphorene heterostructures and observation of quantum oscillations in these devices. [Preview Abstract] |
Tuesday, March 3, 2015 4:54PM - 5:06PM |
J1.00009: Multi-mode Fabry-P\'erot Interferences in SiO$_2$-supported Single Layer Graphene, in Large Aspect Ratio 2-terminal Devices Joseph Lambert, Steven Carabello, Roberto Ramos The Fabry-P\'erot (F-P) interference of charge carriers in graphene occur in 2-dimensional cavities defined between $pn$ interfaces. Typically, $pn$ interfaces form by local doping of metallic contacts, and serve as partially reflecting mirrors for ballistic charge carriers. Here, we report on observed F-P resonances in very large aspect ratio devices. For all devices studied, the inter-lead distance is $L \approx 0.2$ $\mathrm{\mu}$m, and the graphene channel widths range from $W \approx 5$ to $17$ $\mathrm{\mu}$m, resulting in aspect ratios up to $W/L \approx 74$. In maps of conductance versus source-drain and gate voltages, we observe long-range tapestry patterns, extending over the gate voltage range from $V_{\mathrm{g}} = -60$ V to $20$ V. These features onset at a temperature of $T \approx 20$ K. Upon lowering the temperature, an additional mode appears around $T \approx 3$ K, and remains fairly unchanged down to $T \approx 30$ mK. From the lowest energy features, we estimate the phase coherence length to be on the order of $1$ to $2$ $\mathrm{\mu}$m. Using FFT, we have identified two modes: the fundamental longitudinal, and one of the transverse modes, which we propose is a result of smaller cavities formed by the disorder-induced charge puddles. [Preview Abstract] |
Tuesday, March 3, 2015 5:06PM - 5:18PM |
J1.00010: Graphene Transport Under the Influence of Polar Molecules Barrett Worley, Seohee Kim, Saungeun Park, Peter Rossky, Deji Akinwande, Ananth Dodabalapur Charged defects and impurities play a very important role in charge transport in graphene field-effect transistors (FETs). They influence the mobility, residual doping, and the Dirac voltage. Long-range scattering by charged impurities in fabricated graphene FETs lowers the mobility of charge carriers, while short range scattering affects the value of residual carrier concentration. Our group has shown that the electrical properties of graphene FETs are significantly improved upon exposure to fluoropolymers or polar organic vapors. We have demonstrated favorable Dirac voltage shifts, increases in mobility, and reduction in residual carrier concentration as a result of polar molecules altering the dielectric environment surrounding the graphene/substrate interface of a graphene FET. Screening of charged impurity scattering is hypothesized to be the principal effect by which the polar molecules of the altered dielectric layer bring about improvements. We employ computational chemistry to model polar organic molecule-graphene systems. Such modeling will help explain experimental results. [Preview Abstract] |
Tuesday, March 3, 2015 5:18PM - 5:30PM |
J1.00011: Theory of anharmonic phonons in graphene Sebastian Costamagna, Francois M. Peeters, Karl H. Michel Anharmonic effects in an atomic monolayer thin crystal with honeycomb lattice structure are studied by analytical and numerical lattice dynamical methods. Starting from a semi-empirical model for anharmonic couplings of third and fourth order, we study the in-plane and out-of-plane (flexural) mode components of the generalized wave vector dependent Gr\"uneisen parameters, the thermal tension and the thermal expansion coefficients as function of temperarure and crystal size. From the resonances of the displacement-displacement correlation functions we study the renormalization and decay rate of in-plane and flexural phonons as function of temperature, wave vector and crystal size. Numerical evaluations are made with graphene as a specific model, The work is complementary to crystalline membrane theory and computational studies of anharmonic effects in two-dimensional crystals. [Preview Abstract] |
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