Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session G6: Focus Session: CVD Graphene - Doping and Defects |
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Sponsoring Units: DMP Chair: Abhay Pasupathy, Columbia University Room: 302 |
Tuesday, March 19, 2013 11:15AM - 11:51AM |
G6.00001: Dopants in Chemically Doped Monolayer Graphene Invited Speaker: Liuyan Zhao In monolayer graphene, substitutional doping during chemical vapor deposition (CVD) growth can be used to alter the electronic properties of graphene. To gain full understanding of such chemically doped monolayer graphene, it is essential to learn how the dopants distribute from at atomic scale up to at micron-meter scale, how the dopants modify the electronic structures of the graphene, and how the quasiparticles in graphene behave in the vicinity of the dopants. We use Scanning Tunneling Microscopy/Spectroscopy (STM/S), Micro-Raman spectroscopy, and X-ray absorption spectroscopy to address these questions. In this presentation, we will first show both Nitrogen and Boron atoms dope graphene in the graphitic form, and contribute electron and hole carriers into graphene respectively. Secondly, we will discuss the nature of inter-valley and intra-valley scattering in Nitrogen doped graphene due to the presence of graphitic Nitrogen dopants. Finally, we will show that Nitrogen dopants show sub-lattice clustering and avoid structural features such as domain boundaries of a graphene polycrystal. [Preview Abstract] |
Tuesday, March 19, 2013 11:51AM - 12:03PM |
G6.00002: Nitrogen incorporation into epitaxial graphene formed on SiC Edward Conrad, Wang Wang, Gang Liu, Sara Rothwell, Leonard C. Feldman, Phil Cohen Substitutional doping is an important way to modify the electronic, chemical, optical and magnetic property of graphene. A significant body of work has shown that nitrogen can be introduced into the graphene structure during CVD growth or by plasma treatments [1,2]. These methods produce a variety of nitrogen defect sites. We present new results on the direct incorporation of nitrogen into graphene as it grows from SiC. The starting material is a sub-monolayer of N at the SiC/SiO2 interface introduced by NO annealing at 1175C [3]. The oxygen is chemically removed to leave $\sim$0.5 ML nitrogen layer that is stable on the SiC(000-1) surface up to 1550C. When heated to 1450C, nitrogen is introduced into the graphene as it grows from the SiC. Post growth studies with Raman Spectroscopy, ARPES, XPS, and LEED show that the N-doped graphene is entirely pyridinic and has a small finite bandgap. This method has an advantage in that the SiC/nitrogen surface can be pre-patterned to high resolution prior to graphene fabrication.\\[4pt] [1] Zhao, L. Y. et al. Science 333, 999-1003 (2011); [2] Lin, Y. C. et al. Appl. Phys. Lett. 96, 133110 (2010); [3] J. Rozen et al, IEEE Transactions on Electron Devices, 0018-9383, 2011 [Preview Abstract] |
Tuesday, March 19, 2013 12:03PM - 12:15PM |
G6.00003: Nitrogen-doped graphene: beyond single substitution and enhanced molecular sensing Simin Feng, Junjie Wang, Ruitao Lu, Qing Li, Andr\'es R. Botello-M\'endez, Xavier Declerck, Aur\'elien Lherbier, Ayse Berkdemir, Ana Laura El\'Ias, Rodolfo Cruz-Silva, Morinobu Endo, Humberto Terrones, Jean Christophe Charlier, Minghu Pan, Jun Zhu, Mauricio Terrones Large-area ($\sim$ 4 cm$^{2})$ and highly-crystalline~monolayer nitrogen-doped graphene (NG) sheets have been synthesized on copper foils by ambient-pressure chemical vapor deposition (AP-CVD) method. Scanning tunneling microscopy (STM) and spectroscopy (STS) reveal that the nitrogen dopants in as-synthesized NG samples are separated by one carbon atom and sit consequently on the same sub-lattice of graphene. Based on our first principles and tight binding calculations, this unbalanced distribution of dopants on one of the graphene sub-lattices will promote the opening of an electronic band gap. We control the synthesis parameters and use Raman spectroscopy and electrical transport measurements to monitor the nitrogen doping levels. Finally, we will demonstrate that NG behaves as an efficient molecular sensor, especially when performing graphene-enhanced Raman scattering (GERS) of various organic and bio-molecules. [Preview Abstract] |
Tuesday, March 19, 2013 12:15PM - 12:27PM |
G6.00004: Temperature-dependent gap opening in doped graphene Choongyu Hwang, Chris Jozwiak, Swanee J. Shin, Eugene H. Haller, Alessandra Lanzara Fundamental physical properties of a material are strongly affected by electronic correlations, which typically reveal their origins through a temperature-dependence study. By using angle-resolved photoemission spectroscopy, we study unusual gap opening in doped graphene as a function of temperature, which poses a strong constraint on the charge carrier scattering mechanism in this system. Our finding provides a potentiality to realize new correlated states with unusual properties. [Preview Abstract] |
Tuesday, March 19, 2013 12:27PM - 12:39PM |
G6.00005: Mapping the Electron Transport of Graphene Boundaries Using Scanning Tunneling Potentiometry Kendal Clark, Xiaoguang Zhang, Ivan Vlassiouk, Guowei He, Gong Gu, Randall Feenstra, An-Ping Li The symmetry of the graphene honeycomb lattice is a key element for determining many of graphene's unique electronic properties. Topological lattice defects, such as grain boundaries and step edges, break the sublattice symmetry and can affect the electronic properties, especially the transport of graphene. A complete understanding of the physical and electronic properties of defects and boundaries of graphene is needed for future applications. Using a scanning tunneling potentiometry method with a low temperature four-probe scanning tunneling microscope, two-dimensional maps of electrochemical potentials have been measured across individual grain boundaries of graphene films on SiO$_{2}$, as well as across 1ML to 1ML substrate steps and 1ML to 2ML transitions of graphene on SiC. An Atomic Force Microscope (AFM) is implemented to image the grain boundary that forms between coalesced individual graphene flakes on insulating surfaces where as a Scanning Tunneling Microscopy (STM) is implemented for characterizing the SiC grown graphene samples. Results of the influence that various boundaries have on the electronic transport of graphene will be presented. [Preview Abstract] |
Tuesday, March 19, 2013 12:39PM - 12:51PM |
G6.00006: Chemically decorated line defect as a transport barrier in graphene Carter White, Smitha Vasudevan, Daniel Gunlycke Graphene exhibits itinerant electrons propagating ballistically across its surface. To control electrons injected at a source contact, one needs transport barriers. With reliable transport barriers, electron flow could be directed and modified, a key requirement in nanoelectronics applications. In this presentation, we show that chemically decorated line defects in graphene could act as effective atomically-thin transport barriers. The considered 5-5-8 line defect has both been observed and controllably fabricated. Our density functional theory calculations indicate that diatomic hydrogen, oxygen, and fluorine react exothermically with the 5-5-8 defect inducing effective potentials along this line defect. Transport calculations show that these potentials reduce the electron transmission probability across the line defect converting it from semi-transparent to highly reflective to incoming electrons. [Preview Abstract] |
Tuesday, March 19, 2013 12:51PM - 1:03PM |
G6.00007: Characterization of line defects in CVD graphene films with scanning plasmon interferometry Zhe Fei, Aleksandr Rodin, Will Gannett, Siyuan Dai, William Regan, Alexander McLeod, Martin Wagner, Benji Aleman, Mark Thiemens, Gerardo Dominguez, Antonio Castro-Neto, Alex Zettle, Fritz Keilmann, Michael Fogler, Dimitri Basov Line defects that are omnipresent in graphene films fabricated with chemical vapor deposition method (CVD) were studied with scanning plasmon interferometry (SPI)---a technique capable of convenient nano-characterization of graphene devices in ambient conditions. The characteristic SPI patterns of line defects are plasmonic twin fringes, which are generated due to interference between surface plasmons (SPs) of graphene launched by a scanning probe and reflected by the line defects. The twin fringes allow us to visualize and distinguish various types of line defects including cracks, wrinkles, and even grain boundaries. Further modeling of the twin fringes provides detailed information on the electronic properties associated with these line defects. [Preview Abstract] |
Tuesday, March 19, 2013 1:03PM - 1:15PM |
G6.00008: Direct Determination of the Chemical Bonding of Individual Impurities in Graphene Myron Kapetanakis, Wu Zhou, Micah Prange, Sokrates Pantelides, Stephen Pennycook, Juan-Carlos Idrobo Using a combination of Z-contrast imaging and atomically resolved electron energy-loss spectroscopy on a scanning transmission electron microscope, we show that the chemical bonding of individual impurity atoms can be deduced experimentally. We find that when a Si atom is bonded with four atoms at a double-vacancy site in graphene, Si 3d orbitals contribute significantly to the bonding, resulting in a planar sp$^{2}$d-like hybridization, whereas threefold coordinated Si in graphene adopts the preferred sp$^3$ hybridization. The conclusions are confirmed by first-principles calculations and demonstrate that [U+2028] chemical bonding of two-dimensional materials can now be explored an experimental probe at the single impurity level. [Preview Abstract] |
Tuesday, March 19, 2013 1:15PM - 1:27PM |
G6.00009: Effect of Defects on the Intrinsic Strength and Stiffness of Graphene Ardavan Zandiatashbar, Gwan Hyoung Lee, Hamed Parvaneh, Sung Joo An, Sunwoo Lee, Nithin Mathew, Catalin R. Picu, James Hone, Nikhil Koratkar Mechanical properties of defective mono-layer graphene sheets have been studied using experimental and computational tools. In experiments, elastic properties and breaking strength of free standing monolayer defective graphene membranes are measured by nanoindentation using an atomic force microscope. Defects have been introduced by exposure of membranes to oxygen plasma. Density of defects has been quantified using Raman and Auger electron spectroscopy, and also Transmission electron microscopy. Molecular dynamics simulations have been used to investigate the mechanical properties of free standing monolayer graphene membranes using reactive force fields. The effect of boundary conditions, as well as presence of defects in form of vacancies and bonded epoxide groups has been investigated and compared to experiments. Both experiments and simulations show decrease in Young's modulus and strength of graphene membranes by increasing defect density. However, the change in the elastic modulus is small below a certain defect density, which shows defective graphene membrane can still carry load and stay functional in different applications like decorated carbon based MOSFETs and graphene based nanocomposites. [Preview Abstract] |
Tuesday, March 19, 2013 1:27PM - 1:39PM |
G6.00010: Stability and Electronic Structures of Al-, Si- and Au-incorporated Divacancy Graphenes: A First-principles Study Na-Young Kim, Eui-Sup Lee, Yong-Hyun Kim C, N, and O decorated divacancy pores in graphene have been reported as well. Especially, the N4 divacancy pore can strongly bind with the divalent 3d transition metals (TMs) because of the large enough pore size and the strong p-d hybridization. Recently, the Si- and Au-incorporated divacancy pore have been also proposed, but understanding of the stability or electronic properties is largerly lacking. In this work, we invesgated the stability and electronic structure of Al-, Si- and Au-incoporated divacancy graphenes decorated with reactangular CmNn, NnOl, and OlCm, based on first-principles density-functional theory (DFT) calculations. We found that the Al-CN3, Si-C2N2, and Au-CN3 are most stable configurations for each cations because the unpaired electrons of edge atoms of divacancy pore could be completely passivated. The binding energies are also higher than cohessive energies due to the strong p-p or p-d hybridization. Because of the strong hybridizaition, the restoration of $\pi $-network of graphene or small band-gap opening near the fermi-level are also observed. [Preview Abstract] |
Tuesday, March 19, 2013 1:39PM - 1:51PM |
G6.00011: Impact of point defects in graphene systems Miguel Moreno Ugeda, Antonio Mart\'Inez-Galera, Iv\'an Brihuega, Jos\'e Mar\'Ia G\'omez-Rodr\'Iguez Topological defects strongly influence the mechanical, electronic and even magnetic properties of low dimensional carbon-based systems. Taking advantage of the key role of defects in these systems, a unique route based on defect engineering is being developed to broaden the functionalities of graphene. In particular, vacancy-type defects are of an extraordinary importance as they are the key ingredient to understand the new properties shown by functionalized graphene after irradiation. While the role played by these vacancies as single entities has been extensively addressed by theory, experimental data available only refer to statistical properties of the whole heterogeneous collection of vacancies generated in the irradiation process. Scanning tunneling microscopy has great potential in this arena since it enables characterization of point defects at the atomic level. In our work, we first created well characterized individual vacancies on graphene layers by Ar$+$ ion irradiation and then, using low temperature scanning tunneling microscopy/spectroscopy, we individually investigated the impact of each type of such vacancies on the electronic, structural and magnetic properties of several graphene systems [1-3]. [1] M. M. Ugeda, et al, Phys. Rev. Lett 104, 096804 (2010). [2] M. M. Ugeda, et al. Phys. Rev. Lett 107, 116803 (2011). [3] M. M. Ugeda, et al Phys. Rev B,85, 121402 (R) (2012). [Preview Abstract] |
Tuesday, March 19, 2013 1:51PM - 2:03PM |
G6.00012: Defect-induced amorphization of single-layer graphene: structure and mechanical properties Corinne Carpenter, Ashwin Ramasubramaniam, Dimitrios Maroudas Defect engineering of graphene provides a potential route for tuning its mechanical, electronic, and chemical properties. While individual defects in single-layer graphene have been investigated in much detail, collective interactions of multiple defects are less well understood. In this work, we address the effects of introducing populations of vacancies in single-layer graphene using classical molecular-dynamics simulations based on reliable bond-order potentials. We study random distributions of vacancies in a single graphene layer with vacancy concentration and temperature being the key parameters in the analysis. We demonstrate that a crystalline-to-amorphous structural transition occurs at vacancy concentrations of 5-10{\%} leading to complete loss of long-range order in the graphene layer. We conduct a systematic parametric study of this phenomenon accompanied by a detailed structural analysis of the defective sheets. We also present systematic studies of tensile tests on these defective graphene sheets and identify trends for the ultimate tensile strength, failure strength, and toughness as a function of vacancy concentration. The implications of our findings for tuning the mechanical and electronic properties of single-layer graphene are discussed. [Preview Abstract] |
Tuesday, March 19, 2013 2:03PM - 2:15PM |
G6.00013: Heterogeneous Catalysis on Defect-Engineered Graphene M. Samy El-Shall Graphene has attracted great interest for a fundamental understanding of its unique structural and electronic properties and also for important potential applications in nanoelectronics and devices. The combination of thermal, chemical and mechanical stability with the high surface area offers many interesting applications in a wide range of fields including heterogeneous catalysis where metallic and bimetallic nanoparticle catalysts can be efficiently dispersed on the graphene sheets. We have developed facile and scalable chemical and laser reduction methods for the synthesis of defect-engineered graphene, as well as metal and semiconductor nanoparticles dispersed on graphene. We recently discovered a remarkable catalytic activity of metal nanoparticles supported on defect-engineered graphene in a variety of chemical transformation including carbon-carbon cross coupling reactions and Fischer-Tropsch Synthesis of long chain liquid hydrocarbons. The results demonstrate the role of the defect sites on the graphene surface in providing favorable nucleation sites for the selective deposition of the metal nanoparticles and as a result, play a major role in imparting exceptional catalytic properties. [Preview Abstract] |
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