Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session J5: Focus Session: Computational Discovery and Design of New Materials: Graphene |
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Sponsoring Units: DMP DCOMP Chair: Richard Hennig, Cornell University Room: 301 |
Tuesday, March 19, 2013 2:30PM - 2:42PM |
J5.00001: Electronic structure and lattice matching in graphene/h-BN stacked thin films Yuki Sakai, Susumu Saito, Marvin Cohen In this work, we study the electronic structure and possibility of lattice matching of thin films composed of graphene and hexagonal boron nitride (h-BN) within the framework of the density functional theory. Since graphene and h-BN have different in-plane lattice constants intrinsically, we first study relative stabilities of commensurate thin films with lattice matching and incommensurate thin films without lattice matching by comparing total energies in order to clarify the stable geometries of graphene/h-BN thin films. As a result, we find some stacking patterns where commensurate thin films are more stable than incommensurate thin films. We also find that the energy gain due to interlayer interaction depends on the number of layers in thin films. In addition, we report electronic properties of these thin film systems. Some commensurate thin films are found to possess finite band gaps, while induced band gaps should be almost canceled out in incommensurate phases. We also discuss the electric field effect on the electronic properties of graphene/h-BN thin films. [Preview Abstract] |
Tuesday, March 19, 2013 2:42PM - 2:54PM |
J5.00002: Accessing the Strong-Coupling Regime in Graphene on hBN Substrate Andrey Shytov, Justin Song, Leonid Levitov Recent experiments [1,2] report on an insulating behavior at charge neutrality in single-layer graphene on hBN substrate. Ref.[1] attributed this behavior to weak localization due to residual short-range disorder. However, in Ref.[2] a much stronger insulating behavior was observed at a larger separation between graphene and the gates, in the regime when interactions are largely unscreened. This suggests that interactions play a decisive role in the observed phenomena, ruling out the weak localization scenario. We propose an alternative mechanism in which a gap opens up due to a combined effect of sublattice modulation in hBN [3] and electron-electron interactions. We argue that sublattice modulation in hBN amplifies the effective fine structure constant enhancing electron-electron interactions. In this regime, a weak gap induced by sublattice modulation can be strongly enhanced by interactions, giving rise to near-spontaneous excitonic order. \\[4pt] [1] L.A.Ponomarenko et al., Nature Physics {\bf 7}, 958 (2011) \\[0pt] [2] F.Amet et al, arXiv:1209.6364 \\[0pt] [3] M.Kindermann, B.Uchoa, and D.Miller, arXiv:1205.3194 [Preview Abstract] |
Tuesday, March 19, 2013 2:54PM - 3:06PM |
J5.00003: Observation of a Massive Dirac Spectrum in Monolayer Graphene on Boron Nitride Benjamin Hunt, Javier D. Sanchez-Yamagishi, Andrea F. Young, T. Taniguchi, K. Watanabe, Pablo Jarillo-Herrero, Raymond Ashoori Graphene on hexagonal boron nitride (hBN) has emerged as the new standard for high-mobility graphene devices. However, the role of the hBN substrate in modifying the electronic properties of the graphene has only recently been investigated, with particular attention paid to the effects of the Moire produced by the interplay between the graphene and hBN lattices. Here we show that the hBN substrate can have a dramatic effect on the electronic structure of monolayer graphene, leading to the formation of superlattice Dirac points (SLDPs) and an insulating state at charge neutrality in zero magnetic field. The SLDPs imply that the insulator is related to the presence of a long-wavelength Moire. In samples which show the zero-field insulator, we also observe incompressible features associated with fractional quantum Hall (FQH) states at filling fractions $\nu$=$\pm$5/3. Their absence in previous measurements has been attributed to the presence of low-energy valley excitations; in our measurement we find the strength of the $\nu$=5/3 gap is comparable to that of all other observed FQH states. Taken together, these observations imply that for small twist angles between the graphene and hBN substrates, the appropriate low-energy theory describing monolayer graphene features a mass. [Preview Abstract] |
Tuesday, March 19, 2013 3:06PM - 3:18PM |
J5.00004: Ideal strength and phonon instability of atomically-thin materials under strain Eric B. Isaacs, Chris A. Marianetti Recent \textit{ab initio} calculations suggest that the ideal strength of graphene is limited by a finite-wavevector phonon instability [1]. In order to understand the origin and generality of phonon instabilities in two-dimensional crystals, we investigate the ideal strength of other monolayer materials including boron nitride (BN) and molybdenum disulfide (MoS$_2$) with density functional theory calculations. We find a soft phonon mode at the K-point of the Brillouin zone leading to mechanical failure for both BN and MoS$_2$ under biaxial tensile strain, which suggests that Fermi surface nesting cannot be a universal explanation for this type of phonon instability in monolayer materials since BN and MoS$_2$ have substantial band gaps. While BN distorts similarly to graphene upon mechanical failure, MoS$_2$ undergoes a more complex phase transformation with both in- and out-of-plane atomic displacements. We discuss general features of phonon instabilities in monolayer materials under strain and make connection to results from nanoindentation experiments when available. [1] C. A. Marianetti and H. G. Yevick, Phys. Rev. Lett. \textbf{105}, 245502 (2010). [Preview Abstract] |
Tuesday, March 19, 2013 3:18PM - 3:30PM |
J5.00005: First-Principles Study of Multilayer Lithium and Graphene Compounds for Battery Applications Alper Buldum, Gulcin Tetiker Recently, graphene and graphene based materials have attracted great interest for energy storage applications such as rechargable Li-ion batteries and supercapacitors. However, recent experiments showed that these materials may have different electrochemical mechanism compared to graphite. Porosity and presence of single or few layers of graphene play important roles in carbon based anode materials in lithium ion batteries. In this work, a study of different multilayer lithium-graphene compounds is performed using first-principles density-functional theory(DFT). Relaxed structures are determined, adsorption energies, density of states and charge density are calculated. Possible multilayer structures for energy storage are discussed. [Preview Abstract] |
Tuesday, March 19, 2013 3:30PM - 3:42PM |
J5.00006: Self-assembly mechanisms and even/odd disparity of short atomic chains on graphene V. Ongun Ozcelik, Salim Ciraci Self-assembly mechanisms of carbon chains on boron nitride and short BN chains on graphene are investigated using first-principles plane wave calculations. Once a C$_2$ nucleates on h-BN, the insertion of each additional carbon at its close proximity causes a short segment of carbon atomic chain to grow by one atom at a time in a quaint way: The existing chain leaves its initial position and subsequently is attached from its bottom end to the top of the carbon ad-atom. The electronic, magnetic and structural properties of these chains depend on the number of carbon atoms in the chain, such that they exhibit an even-odd disparity. An individual carbon chain can also modify the electronic structure with localized states in the wide band gap of h-BN. As a reverse situation, the growth of short BN atomic chains on graphene is also examined. These results reveal the interesting self-assembly behavior short atomic chains. Furthermore, we find that these atomic chains enhance the chemical activity of h-BN and graphene sheets by creating active sites and can act as pillars between two and multiple sheets of these honeycomb structures leaving wider spacing between them to achieve high capacity storage of specific molecules.\\[4pt] [1] V.O. Ozcelik and S. Ciraci, Phys. Rev. B 86 155421 (2012). [Preview Abstract] |
Tuesday, March 19, 2013 3:42PM - 3:54PM |
J5.00007: Ab initio Study of the Interactions between Single Vacancies in Graphene Mahmoud Hammouri, Igor Vasiliev Graphene is a promising material for nanoelectronic and spintronic applications. The introduction of point defects such as vacancies can turn graphene into a magnetic material. We present a first-principles computational study of the interactions between single vacancies in graphene. The total energies, lattice deformation energies, and spin magnetic moments of the interacting vacancies are calculated using the SIESTA density functional electronic structure code combined with the generalized gradient approximation for the exchange correlation functional. We discuss the variation of the total energy and the total magnetic moment of defective graphene as a function of the separation distance between vacancies. Our calculations show that the magnetic moment of graphene disappears when the vacancies are located within a certain distance from each other. [Preview Abstract] |
Tuesday, March 19, 2013 3:54PM - 4:06PM |
J5.00008: Ab Initio Study of the Interactions between Dopant Atoms and Vacancies in Graphene Tarek Tawalbeh, Igor Vasiliev We apply a first-principles computational method based on density functional theory to study the interaction of substitutional boron and nitrogen atoms with single vacancies in graphene. Our calculations are carried out using a pseudopotential technique combined with the generalized gradient approximation for the exchange-correlation functional implemented in the SIESTA electronic structure package. The equilibrium geometries, total energies, electronic structures, magnetization, and spin-polarized densities of states of doped and defective graphene sheets are examined as a function of the separation distance between dopant atoms and vacancies. Our study shows the presence of attractive interaction between dopant atoms and vacancies. Furthermore, we found that boron dopants enhance the magnetism of graphene sheets containing single vacancies, whereas nitrogen dopants reduce it. The influence of dopant site location on both the interaction energy and magnetization is discussed. [Preview Abstract] |
Tuesday, March 19, 2013 4:06PM - 4:18PM |
J5.00009: Doping of graphene nanomeshes by ion-chelation Ahmed Maarouf, Razvan Nistor, Ali Afzali, Marcelo Kuroda, Dennis Newns, Glenn Martyna Graphene nanomeshes (GNM's) are formed by the creation of a superlattice of pores in graphene. Depending upon the pore shape, size, superlattice constant and symmetry, GNM's can be semimetallic, or semiconducting with a fractional eV band gap, allowing them to be fruitfully employed in applications that pristine graphene cannot. In this work, first principles calculations are used to study the doping of semiconducting GNM's using a chemically motivated approach. It is shown that {\it ion-chelation} leads to a stable doping of the GNM's, and that it occurs within a rigid band doping picture. Such chelated or ``crown'' GNM structures are thus stable, high mobility semiconducting materials which can serve as building blocks for novel graphene-based nanoelectronics applications. [Preview Abstract] |
Tuesday, March 19, 2013 4:18PM - 4:30PM |
J5.00010: Magnetism of single and divacancies in graphene nanoflakes Silvia Fernandez-Sabido, M.E. Cifuentes-Quintal, Carlos Ramos, Romeo de Coss Vacancy-induced magnetism in graphene is a recent topic of great scientific relevance because of the potential applications of spin-polarized graphene-based systems. In this work, we have studied by means of DFT calculations, the structural, electronic and magnetic properties of single and divacancies in hexagonal zigzag graphene nanoflakes $C_{6n^2}H_{6n} (n=2,\dots,7)$. We have found that, when a single carbon atom is removed, the structure undergoes a magnetic 5-9 reconstruction where the interatomic distances depend on the nanoflake size. The charge density distribution suggests that there is not a complete bond reconstruction in the vacancy zone, however, the existence of a partial bond is sufficient to conclude that only two electrons remain unpaired, resulting in the $2\mu_B$ spin moment. The spin moment is equally distributed over the localized-$sp^2$ and delocalized-$p_z$ orbitals. For a carbon-divacancy, we have varied the distance between the vacancies and we have found magnetic structural reconstructions (9-4-9, 5-9-9-5, 5-9-6-5) which have not been reported for graphene layer with magnetic moments between $2$ and $4\mu_B$; although the most stable is the nonmagnetic 5-8-5 reconstruction. [Preview Abstract] |
Tuesday, March 19, 2013 4:30PM - 4:42PM |
J5.00011: Scattering by periodic defect lines in graphene J.N.B. Rodrigues, N.M.R. Peres, J.M.B. Lopes dos Santos Recently, Tsen et al. [1] demonstrated how one can probe the electric properties of a single grain boundary in graphene. Following this remarkable possibility, we study, from a theoretical point of view, the electronic transport across periodic defect lines in graphene. In the continuum low-energy limit, such defects act as infinitesimally thin stripes separating two regions where the Dirac Hamiltonian governs the low-energy phenomena. The behaviour of these systems is determined by the boundary condition imposed by the defect on the massless Dirac fermions. We demonstrate how this low-energy boundary condition can be computed from the tight-binding model of the defect line. We illustrate this procedure by considering a simple zigzag oriented defect line solely composed by pentagons: the {\it pentagon-only} defect line. The recently observed $zz(558)$ defect line [2], as well as the $zz(5757)$ defect line will also be considered [3].\\[4pt] [1] A. W. Tsen et al., Science 336, 1143 (2012).\\[0pt] [2] J. Lahiri et al., Nature Nanotechnology 5, 326 (2010).\\[0pt] [3] J. N. B. Rodrigues et al., arXiv:1208.0822 (2012). [Preview Abstract] |
Tuesday, March 19, 2013 4:42PM - 4:54PM |
J5.00012: First-Principles Investigation of Mn and Co Doped Trilayer Graphene Xuan Luo First-principles calculations were performed through ABINIT to investigate trilayer graphene for spintronics materials. We studied two stacking orders for trilayer graphene: Bernal (ABA) and rhombohedra (ABC) by using interstitial and substitution transition metal Mn and Co doped trilayer graphene. We found that the ABC stacking order exhibits larger band gap than that of ABA, the Co doped ABC trilayer graphene possesses a band gap and is ferromagnetic. This results show that interstitial Co doped ABC stacking trilayer graphene has potential applications in spintronics. [Preview Abstract] |
Tuesday, March 19, 2013 4:54PM - 5:06PM |
J5.00013: Oxygen plasma etching of graphene: A first-principles dynamical inspection of the reaction mechanisms and related activation barriers Kenichi Koizumi, Mauro Boero, Yasuteru Shigeta, Atsushi Oshiyama Oxygen plasma etching is a crucial step in the fabrication of electronic circuits and has recently received a renovated interest in view of the realization of carbon-based nanodevices. In an attempt at unraveling the atomic-scale details and to provide guidelines for the control of the etching processes mechanisms, we inspected the possible reaction pathways via reactive first principles simulations. These processes involve breaking and formation of several chemical bonds and are characterized by different free-energy barriers. Free-energy sampling techniques (metadynamics and blue moon), used to enhance the standard Car-Parrinello molecular dynamics, provide us a detailed microscopic picture of the etching of graphene surfaces and a comprehensive scenario of the activation barriers involved in the various steps. [Preview Abstract] |
Tuesday, March 19, 2013 5:06PM - 5:18PM |
J5.00014: Simulating Lattice Image of Suspended Graphene Taken by Helium Ion Microscopy Yoshiyuki Miyamoto, Hong Zhang, Angel Rubio Atomic scale image in nano-scale helps us to characterize property of graphene, and performance of high-resolution transmission electron microscopy (HRTEM) is significant, so far. While a tool without pre-treatment of samples is demanded in practice. Helium ion microscopy (HIM), firstly reported by Word {\it et. al.} in 2006, was applied for monitoring graphene in device structure (Lumme, {\it et. al.}, 2009 ). Motivated by recent HIM explorations, we examined the possibility of taking lattice image of suspended graphene by HIM. The intensity of secondary emitted electron is recorded as a profile of scanned He$^+$-beam in HIM measurement. We mimicked this situation by performing electron-ion dynamics based on the first-principles simulation within the time-dependent density functional theory. He$^+$ ion collision on single graphene sheet at several impact points were simulated and we found that the amount of secondary emitted electron from graphene reflected the valence charge distribution of the graphene sheet. Therefore HIM using atomically thin He-beam should be able to provide the lattice image, and we propose that an experiment generating ultra-thin He$^+$ ion beam (Rezeq {\it et. al.}, 2006) should be combined with HIM technique. [Preview Abstract] |
Tuesday, March 19, 2013 5:18PM - 5:30PM |
J5.00015: Electronic structures and transport properties of silicene on Ag surface Yun-Peng Wang, Hai-Ping Cheng It has been predicted from first-principle that ``silicene'', a two-dimensional buckled honeycomb structure of silicon, is thermally stable and has a graphene-like band structure. In experiments, epitaxial silicene were observed to form at hexagonal Ag(111) and $\mathrm{ZrB_2(0001)}$ surfaces. However, electronic structure and transport properties related to silicene have not been thoroughly studied. In this work, we have studied band structures of silicene on top of Ag surface using density-functional theory. The effective band structure mapped onto $1\times1$ unit cell of monolayer silicene on Ag(111) surface could be compared directly with Angle-Resolved Photoemission Spectra (ARPES). We have also studied electronic transport property across monolayer and bilayer silicene sheets using the Non-Equilibrium Green's Function (NEGF) method. The transmission curve shows a maximum at Fermi energy for the monolayer silicene case, but shows a minimum for the bilayer silicene case, which can be explained by their band structures. [Preview Abstract] |
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