Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session X28: Carbon Nanotubes and Related Materials: Theoretical and Computational Studies |
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Sponsoring Units: DCMP Chair: Tahir Cagin, Texas A&M University Room: C156 |
Thursday, March 24, 2011 2:30PM - 2:42PM |
X28.00001: Electron-phonon renormalization of the electronic structure of diamond Feliciano Giustino, Steven G. Louie, Marvin L. Cohen The calculation of band structures from first-principles has reached a high level of accuracy. Calculations combining density-functional theory with many-body perturbation theory often are in good agreement with measurements by photoemission, tunneling, and other spectroscopic probes. While significant efforts have been devoted to improving the description of electron-electron interactions in these calculations, the effect of lattice vibrations has largely been overlooked so far. In this work we study from first principles the electron-phonon renormalization of the band gap of diamond. The calculated temperature dependence of the gap and the broadening of the absorption edge are in excellent agreement with spectroscopic ellipsometry data. Interestingly we find a gap renormalization due to zero-point vibrations as large as 0.6 eV. We discuss the implications of our findings for the electronic structure of other carbon-based bulk materials and nanostructures. [Preview Abstract] |
Thursday, March 24, 2011 2:42PM - 2:54PM |
X28.00002: Intrinsic Twisting and Electronic Properties of Carbon Nanotubes : A First-Principles Study Koichiro Kato, Takashi Koretsune, Susumu Saito We report the energetics and electronic structures of twisted single-walled CNTs in the framework of the density functional theory (DFT) with the local density approximation. As for very thin CNTs, we use conventional plane-wave DFT computational code. In order to utilize the periodic boundary condition implemented in the plane-wave DFT code, we study CNTs under several discretized twisting conditions. On the other hand, in the case of thicker nanotubes including experimentally abundant nanotube sizes, we use a real-space DFT computational code which can deal with twisted CNTs with only two atoms per ``helical'' unit cell. As a result, it is found that chiral CNTs become more stable in slightly twisted geometry. Our results suggest that chiral nanotubes would possess the intrinsic twisting. We also report the twisting-level dependence of the electronic structures. It is found that the fundamental gaps of most kinds of CNTs sensitively depend on twisting level. Importantly, the directions of the intrinsic twisting are the same as the directions of enlarging the fundamental gap except for very thin CNTs. [Preview Abstract] |
Thursday, March 24, 2011 2:54PM - 3:06PM |
X28.00003: Excitonic Hierarchies in Gapped Carbon Nanotubes Robert Konik We present evidence that the strong electron-electron interactions in gapped carbon nanotubes lead to a hierarchy of excitons within a given nanotube subband. We study these hierarchies by employing a field theoretic reduction of the gapped carbon nanotube permitting electron-electron interactions to be treated exactly. We analyze this reduction by employing a Wilsonian-like numerical renormalization group. We are so able to determine the gap ratios of the one-photon excitons as a function of the effective strength of interactions. We also determine within the same subband the gaps of the two-photon excitons, the single particle gaps, as well as a subset of the dark excitons. The strong electron-electron interactions in addition lead to strongly renormalized dispersion relations where the consequences of spin-charge separation can be readily observed. [Preview Abstract] |
Thursday, March 24, 2011 3:06PM - 3:18PM |
X28.00004: Biexcitonic Non-Linearities in Semiconducting Carbon Nanotubes Toros Torosyan, Igor Bondarev We obtained an analytical expression for the biexciton binding energy as a function of the inter-exciton distance and binding energy of constituent quasi-one-dimensional excitons in single-wall semiconducting carbon nanotubes. This allows one to trace biexciton energy variation and relevant non-linear absorption under external conditions whereby the exciton binding energy varies. In particular, we show the biexciton-plasmon coupling tunability by means of the quantum confined Stark effect, both for the ground-ground state and for the ground-excited state biexcitonic configurations. The non-linear absorption lineshapes calculated exhibit characteristic asymmetric Rabi splitting as the exciton energy is tuned to the nearest interband plasmon resonance. These results are useful for tunable optoelectronic device applications of optically excited semiconducting carbon nanotubes, including the strong excitation regime with optical non-linearities. [Preview Abstract] |
Thursday, March 24, 2011 3:18PM - 3:30PM |
X28.00005: Spin manipulation in carbon nanotubes: All electrical spin filtering through spin-orbit interactions G. S. Diniz, A. Latg\'e, S. E. Ulloa Carbon nanotubes (CNTs) are known to exhibit interesting physical properties, such as metallic or insulating behavior for different chiral vectors. Application of external electric fields and the presence of spin-orbit interaction (SOI) result in modification of the energy level structure of CNTs and their conductance profiles. SOI couples spin and orbital degrees of freedom in these nanostructures, and we explore this effect in this work. We present calculations of the electronic transport of different single-wall CNTs in the presence of SOI. Our calculation uses a single-orbital tight-binding Hamiltonian representation and the equilibrium surface Green's function formalism [1] to calculate electronic transport. We consider the effects of both Rashba and intrinsic SOIs. Our results show possible implementations of carbon nanotubes as spin filtering devices for spatially asymmetric electric fields. We further discuss the spin polarization for different CNT size, chirality, field strength, and the spatially varying fields induced by the adsorption of DNA on their surface.\\ $\left[1\right]$ M. B. Nardelli, Phys. Rev. B \textbf {60}, 7828 (1999). [Preview Abstract] |
Thursday, March 24, 2011 3:30PM - 3:42PM |
X28.00006: Substantial reduction of thermal conductivity of defected carbon nanotubes Cem Sevik, Haldun Sevincli, Justin B. Haskin, Alper Kinaci, Gianaurelio Cuniberti, Tahir Cagin The influence of the structural details and defects on the thermal transport properties of carbon nanotubes (CNTs) are explored by molecular dynamics and real-space Kubo methodologies. A variety of randomly oriented and distributed defects, (mono- and di-vacancies, Stone Wales defects) on lattice thermal conductivity and anharmonic phonon mean free paths are studied for model systems in sizes up to 1000 nm. Substantial reduction in thermal conductivity, up to $\sim $80{\%} reduction compared to the pristine CNTs, is observed for $\sim $0.5$\backslash ${\%} defect concentrations. Additionally, nearly the same saturation value of lattice thermal conductivity for CNTs with different type of defects is predicted. [Preview Abstract] |
Thursday, March 24, 2011 3:42PM - 3:54PM |
X28.00007: All About Chlorinated Carbon Nanotubes Dogan Erbahar, Savas Berber The halogens are viable alternatives to harsher chemicals in the post-process of purification of carbon nanotube production. However the chlorine is known to bind less agresively to carbon nanotubes than fluorine and hydrogen. Therefore, in principle the residual Cl left after the halogen gas treatment of the nanotubes can be removed without damaging the nanotube walls easier. We report ab initio density functional calculation results about pure and defective carbon nanotubes of various diameters interacting with single and multiple chlorine atoms. We first focus on pure nanotubes and investigate the adsorption of additional Cl atoms near the first adsorbtion site, investigate the clustering tendency and most favourable configurations. We report the energetics results as well as the alteration of electronic properties. We then focus on monovacancy and divacancy defects on carbon nanotubes. It is a known fact that the defective site to be more active in this case. We apply the same procedure as in the pure nanotubes but also investigate the effect of chlorination on reconstruction process and also electronic transport properties. [Preview Abstract] |
Thursday, March 24, 2011 3:54PM - 4:06PM |
X28.00008: The origins of nanotube chirality: Is the edge-catalyst in control? Evgeni Penev, Yuanyue Liu, Boris Yakobson The chance for a nanotube of a chiral angle c to emerge from the ``primordial soup'' of carbon atoms on the catalyst is determined by their relative energies. Massive computations allow one to evaluate the ``elastic'' energies of the caps, and the energies of their edges [1], G(c+C), which appears to be dominating. Importantly, the latter contains a ``chemical phase shift'' C, so that the probability of different chiralities is determined by the chemical conditions at the edge. Preference for specific chirality can be achieved by tuning chemical potential of edge terminating chemical. This offers a rational way to control the tube chiral symmetry, a tantalizing yet so far elusive goal. \\[4pt] [1] Y. Liu, A. Dobrinsky, and B.I. Yakobson, Phys. Rev. Lett. in press (Dec 10 2010 issue). [Preview Abstract] |
Thursday, March 24, 2011 4:06PM - 4:18PM |
X28.00009: Laser-Shot-Induced Chemical Reactions inside Nanotubes: a TDDFT investigation Hong Zhang, Yoshiyuki Miyamoto, Angel Rubio We present the application of the time-dependent density functional theory (TDDFT) on ultrafast laser pulse which induces dynamics in molecules encapsulated by a nanotube. A strong laser pulse polarized perpendicular to the tube axis induces a giant bond-stretch of an HCl molecule inside both C and BN nanotubes. Depending on the initial orientation of the HCl molecule, the subsequent laser-induced dynamics is different [1]. We also observed a radial motion of the nanotube and vacancies appear on the tube wall when the HCl is perpendicular to tube axis. Furthermore, the disintegration of HCl molecules took place when their molecular axis tilted to tube axis. These simulations are important to analyze light-induced nanochemistry and manipulation of nanostructures encapsulated in organic and inorganic nanotubes. The computational scheme used in present work was a combination of the molecular dynamics and real-time propagation of electron wave functions under presence of strong optical field [2,3]. The energy conservation rule was checked to monitor the numerical stability. [1] Y. Miyamoto, H. Zhang, and A, Rubio, submitted., [2] O. Sugino and Y. Miyamoto, Phys. Rev. B59, 2579 (1999). [3] A. Castro, E. Rasanen, A. Rubio and E. K. U. Gross, Eur. Phys. Lett. 87, 53001 (2009). [Preview Abstract] |
Thursday, March 24, 2011 4:18PM - 4:30PM |
X28.00010: Ab initio study of the dependence of the reactivity upon carbon nanotube diameter Jonathan Laflamme Janssen, Jason Beaudin, Michel C\^ot\'e, Nicholas D.M. Hine, Peter D. Haynes One of the main research efforts of the recent years has been the development of an efficient way to select desired carbon nanotubes according to their size and their electronic properties. This selectivity would allow easier fabrication of field effect transistor and light-emitting diode devices with appropriate nanotubes. An appealing approach to assess this problem is to use the dependence of chemical functionalization thermodynamics on the material's properties. In this talk, ab initio studies of carbon nanotubes functionalized with bromophenyl will be presented. The radius dependence of the binding and activation energies of this functionalization will be reported. The purpose of this presentation is also to demonstrate the performance of linear-scaling density-functional theory code ONETEP, which provides the possibility carrying out large system simulations (up to several tens of thousands of atoms). Furthermore, the diameter dependence of the oxidation of carbon nanotubes by carbon dioxide will be presented. [Preview Abstract] |
Thursday, March 24, 2011 4:30PM - 4:42PM |
X28.00011: Electric field response on hybrid C/BN nanostructures Miguel Alonso-Pruneda Synthesis of hybrid C/BN nanotubes [1] and nanosheets [2] offer a unique route for material engineering, by combination of the exciting properties of graphene with those of insulating polar BN. First principles (DFT) calculations of the zigzag-terminated edges between C and BN nanodomains will be presented, proving that unconventional physical effects similar to those observed at insulating oxide interfaces [3], can also exist in lower dimensions, opening alternative routes for tuning electronic properties at nanointerfaces. In particular, it will be shown that the magnetic character of the edge states in zigzag shaped graphene nanoribbons, and the polar BN edge, team up to give a spin asymmetric screening that induces half-semimetallicity at the interface [4]. This property is also observed in tubular geometries, where potential magnetoelectric effects will be discussed. \\[4pt] [1] Suenaga et. al. {\it Science} {\bf 278} 5338 (1997); Enouz et. al. {\it Nano Lett.} {\bf 7}, 1856 (2007).\\[0pt] [2] Ci et. al. {\it Nat. Materials} {\bf 9}, 430 (2010).\\[0pt] [3] Ohtomo \& Hwang {\it Nature} {\bf 427}, 423 (2004); Brinkman et. al. {\it Nat. Mater.} {\bf 6}, 493 (2007); Reyren et. al. {\it Science} {\bf 317}, 5842 (2007).\\[0pt] [4] Pruneda {\it Phys. Rev. B} {\bf 81}, 161409(R) (2010). [Preview Abstract] |
Thursday, March 24, 2011 4:42PM - 4:54PM |
X28.00012: Study of Singlet-Triplet Gaps in $\pi$-Conjugated Polymers versus Graphene Nanoribbons and Single-Walled Carbon Nanotubes. The Effect of Dimensionality Karan Aryanpour, Sumit Mazumdar, Hongbo Zhao We compute and compare the gap between the optical singlet and lowest triplet excitons in poly (para-phenylenevinylene) (PPV) with semiconducting graphene nanoribbons (GNRs) and single-walled carbon nanotubes (SWCNTs) within Coulomb correlated model Hamiltonian. The singlet-triplet gaps in semiconducting GNRs and SWCNTs are more than one order of magnitude smaller that in PPV. We ascribe this to two-dimensionality. Spatial distribution of the electron-hole separation in excitons reveals significant localization of the triplet state wave function compared to singlet state in PPV. In GNRs and SWCNTs however, singlet and triplet wave functions exhibit comparably extended spatial distributions. Singlet-triplet gap size is an indicator of the effective Coulomb interaction strength which in turn controls the exciton binding energies of these systems. Exciton binding energy plays a deciding role in light emission and device performance in photovoltaics. [Preview Abstract] |
Thursday, March 24, 2011 4:54PM - 5:06PM |
X28.00013: Carbon-Based Zero-Bandgap Tunnel Transistors Youngki Yoon, Sayeef Salahuddin Tunnel field-effect transistors (TFET) have been proposed as a means of breaking the classical limit of voltage requirement and energy dissipation in electronic devices. However, a tunnel barrier severely reduces the current and hence the speed at which the transistor can be operated. In this work, by performing an atomistic quantum simulation, we propose a novel transistor involving a unique interface between a graphene nanoribbon (GNR) and a metallic carbon nanotube (CNT), such that (i) at low voltages it acts exactly like a tunnel transistor reducing voltage requirement below the classical limit and (ii) at a larger voltage the tunnel barrier is dramatically diminished, resulting in a large flow of current [Appl. Phys. Lett. \textbf{97}, 033102 (2010)]. Indeed, experimental fabrication of such an interface could be possible using recently demonstrated methods where carbon nanotubes are unzipped to open up narrow graphene ribbons. Our results show that orders of magnitude improvement in ON current can be obtained in this structure. [Preview Abstract] |
Thursday, March 24, 2011 5:06PM - 5:18PM |
X28.00014: Josephson current in carbon nanotube quantum dots Ramon Aguado, Jong Soo Lim, Rosa Lopez, Mahn-Soo Choi We study theoretically the Josephson current through a carbon nanotube quantum dot coupled to superconducting leads. Due to the interplay between the curvature-induced spin-orbit effect and external magnetic fields, we find a rich $0-\pi$ phase diagram in various transport regimes ranging from noninteracting to Coulomb Blockade, cotunneling and the Kondo limit. [Preview Abstract] |
Thursday, March 24, 2011 5:18PM - 5:30PM |
X28.00015: Kinetics of Gas Adsorption in Nanopores: A Computer Simulation Study Christopher E. Pueblo, M. Mercedes Calbi Motivated by a variety of experimental results concerning gas adsorption in open-ended carbon nanotubes, we present a series of results for the kinetics of adsorption of a gas inside a nanopore. The study is based on a Kinetic Monte Carlo simulation in combination with a lattice model of adsorption. This allows us to monitor the change in coverage with time and extract corresponding adsorption rates or equilibration times. Adsorption in nanopores presents several distinctive features when compared to open surfaces. The adsorption process is mainly controlled by the energy states close to the ends of the pore; we analyze the consequences of this effect on the equilibration times of the system and also on temperature programmed desorption spectra. [Preview Abstract] |
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