Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session R31: Properties of Carbon Nanotubes |
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Sponsoring Units: DCMP Chair: Nicola Marzari, Massachusetts Institute of Technology Room: Baltimore Convention Center 328 |
Wednesday, March 15, 2006 2:30PM - 2:42PM |
R31.00001: Neon adsorption on single walled carbon nanohorns V. Krungleviciute, K. Lask, A. D. Migone, B. Buller, T. Beattie, U. Venkateswaran We present results for Ne adsorbed on single walled carbon nanohorns (SWNHs) purchased from NanoCraft, Inc. The as-received SWNHs were characterized with Raman spectroscopy. The spectra show two peaks attributable to the D and G-bands, with the G-band exhibiting a shoulder in contrast to a single Lorentzian peak reported in the literature. A portion of the SWNHs was sonicated in methanol for twenty minutes and heated under vacuum at 60oC for 12 hours (this treatment was followed to produce ``nanohorn- paper''). Full adsorption isotherms were measured on this sample between 22 and 31 K, and low coverage isotherms were measured between 40 and 49 K. Neon measurements were also performed at 31 K on a sample of SWNHs that was not subjected to the methanol treatment, for comparison. We found no difference between the results obtained on these two sets of samples. We will also present isotherm data on SWNHs that were heated to 520 K under vacuum. [Preview Abstract] |
Wednesday, March 15, 2006 2:42PM - 2:54PM |
R31.00002: Carbon nanotube -- metal cluster bond strengths: implications for catalytic growth. Peter Larsson, Feng Ding, J. Andreas Larsson, Arne Rosen, Rajeev Ahuja, Kim Bolton Catalysts play a crucial role in the production of carbon nanotubes (CNTs). Although a lot of experimental effort has been devoted to finding metals and alloys to optimize CNT growth, the importance of the CNT-metal interactions at the microscopic level are not well understood. Previous simulations based on analytic force fields indicate that a critical role of the catalyst particle is to maintain an open end of the growing CNT, and that sufficiently strong CNT-metal bond strengths are required for this criterion to be met. Here we report CNT-metal bond strengths obtained from density functional theory for a variety of metal clusters. In agreement with the simulations, these calculations reveal that CNT interactions with metals used for production (e.g., Fe and Ni) are stronger than for other metals (e.g. Au). These bond strengths are also compared to the C-C bond energies that form when a cap forms at the end of the growing CNT. [Preview Abstract] |
Wednesday, March 15, 2006 2:54PM - 3:06PM |
R31.00003: Uncatalyzed Etching of Single Walled Carbon Nanotubes on Surfaces Sean Pheasant, Valerie Moore, Robert Hauge, Richard Smalley Aside from burning, the only way single walled carbon nanotubes (SWNTs) have been etched is with the use of a catalyst nanoparticle at high temperatures in an oxidative or reducing atmosphere. The catalyst is a particle close in size to the diameter of the nanotube, and is usually composed of iron, molybdenum, nickel or cobalt, or a combination of these metals. The catalyst operates at the ends of the SWNTs, where it dissociates molecules from the atmosphere on its surface, and combines them with carbon atoms from the tube to form a gas. It has been found that SWNTs can be oxidatively etched with CO2 at a high temperature (900C) in the absence of catalyst particles. The reverse of the Boudard reaction occurs at high temperatures to produce two molecules of CO from a molecule of CO2 and a C atom. When the ends of the tubes are closed, no etching is observed, indicating that only the open ends of the tubes can be attacked by CO2 and not the sidewalls. Experiments were done on both SiO2 and highly oriented pyrolytic graphite (HOPG). Results suggest the tubes etch faster on HOPG than they do on the oxide surface. [Preview Abstract] |
Wednesday, March 15, 2006 3:06PM - 3:18PM |
R31.00004: Defects in carbon nanotubes Rodrigo G. Amorim, Ant\^{o}nio J. R. da Silva, A. Fazzio, Alex Antonelli It is a consensus that defects can alter in a significant way the mechanical properties of carbon nanotubes. We here will investigate, using ab initio total energy density functional theory calculations, some defects and their properties, such as: 1) an interstitial carbon atom right besides a vacancy that can connect tubes in bundles or in multiwall nanotubes; 2) two vacancies that can connect tubes in bundles; 3) a variety of configurations for two vacancies in one nanotube, and how their energies vary with separation. In particular, we will compare the formation energies of the 5-8-5 and 555-777 two-vacancy defects as a function of nanotube diameter. [Preview Abstract] |
Wednesday, March 15, 2006 3:18PM - 3:30PM |
R31.00005: Electroabsorption of Single-Walled Carbon Nanotubes W. Joshua Kennedy, Z. Valy Vardeny We have measured the electric field modulated absorption (EA) of single-walled carbon nanotubes (SWNT) isolated in a poly-vinyl alcohol matrix (PVA). The derivative-like structure of the EA indicates that the low energy absorption bands are excitonic in origin. We report the voltage, temperature, and polarization dependence of the EA spectrum. Additionally, the sensitivity of the EA spectrum to the energy levels of the SWNT allows us to use EA spectroscopy to observe shifts in the absorption bands of our sampleS induced by various external fields that are difficult to resolve using CW techniques. Several examples will be discussed. [Preview Abstract] |
Wednesday, March 15, 2006 3:30PM - 3:42PM |
R31.00006: Phases of Ethane Adsorbed on Purified HiPco Single Walled CarbonNanotubes. Dinesh Rawat, Aldo Migone We have measured adsorption isotherms of ethane on purified HiPco SWNTs for coverages in the first layer. We wanted to investigate the existence of different phases for ethane as a function of coverage on this substrate, and to compare the results to those on planar graphite. We measured isotherms at 103, 110,150, 160, and 165K. We used the low-coverage isotherm data to obtain an estimate for the binding energy of ethane on the SWNTs; we found a value of 363 meV for this quantity. This binding energy value is 1.81 times greater than the corresponding one for this quantity on planar graphite. We have also determined the coverage dependence of isosteric heat of adsorption for ethane using the results for isotherms obtained at above-mentioned temperatures. \newline This work was supported through a grant from NSF, DMR{\#}0089713, and by the Materials Technology Center of SIUC. [Preview Abstract] |
Wednesday, March 15, 2006 3:42PM - 3:54PM |
R31.00007: Single Electron Effects in a Carbon Nanotube Electromechanical Oscillator Arend van der Zande, Rena Zieve, Vera Sazonova, Paul McEuen We have fabricated suspended, doubly clamped, carbon nanotube (NT) transistors to investigate the low temperature coupling between mechanical vibration of the NT and single electron effects. At low temperatures of 0.3K to 4.2K, the NT behaves as a quantum dot. The NT quantum dot displays Coulomb oscillations in the conductance by sweeping a gate voltage. Mechanical vibrations are induced in the NT by applying a high frequency AC voltage relative to the gate [1]. The nonlinear conductance of the Coulomb oscillations can be used as a mixer to detect the NT's own motion. We find that the mechanical resonances of the NT are influenced by the Coulomb oscillations. We observe a dip in the resonance frequency and a dip in the quality factor as the gate voltage is swept through a Coulomb oscillation. We attribute these dips to the forces on the NT from the hopping of single electrons on and off the NT as it moves with respect to the gate. [1] V. Sazonova, Y. Yaish, H. Ustunel, D. Roundy, T.A. Arias, and P.L. McEuen, Nature 431, 284-287 (2004) [Preview Abstract] |
Wednesday, March 15, 2006 3:54PM - 4:06PM |
R31.00008: Anharmonic effects in carbon nanotubes: from thermal expansion to phonon lifetimes N. Bonini, N. Mounet, N. Marzari, M. Lazzeri, F. Mauri We study anharmonic effects in carbon nanotubes using a combination of density-functional theory and density-functional perturbation theory. In particular, we investigate thermal expansion and phonon lifetimes, which are key quantities that govern mechanical and transport properties in these systems. The thermal expansion coefficients are calculated from a minimization of the vibrational free energy in the quasi-harmonic approximation. Our results show that carbon nanotubes contract both in the axial and radial directions at low and room temperature and expand at higher temperatures. The role of different phonon modes in the thermal contraction is discussed together with their Gr\"{u}neisen parameters. Anharmonic phonon lifetimes are evaluated from the cubic terms in the interatomic potential, using density-functional perturbation theory and the 2n+1 theorem. Finally, we discuss the possibility of estimating anharmonic effects using downfolding from graphene. [Preview Abstract] |
Wednesday, March 15, 2006 4:06PM - 4:18PM |
R31.00009: Raman Spectroscopy of Carbon Nanotubes under Axial Strain Rajay Kumar, Hao Zhou, Stephen Cronin We measure the Resonance Raman spectra of individual carbon nanotubes under axial strain. A combination of atomic force microscopy (AFM) and lithography is used to produce strains in nanotubes ranging from 0.1{\%} to 5{\%}. The vibrational and electronic energies of the nanotubes are found to be very sensitive to strain. The D, G and G' band Raman modes are observed to downshift with strain indicating elongation, and hence weakening, of the carbon-carbon bonds. The intensities of the Raman modes are also observed to change as a function of strain, indicating a strain-induced shifting of the electronic subbands. A tight-binding model is presented to explain the changes observed in the Raman intensity in accordance with the Resonance Raman equation. [Preview Abstract] |
Wednesday, March 15, 2006 4:18PM - 4:30PM |
R31.00010: Synthesis and Raman characterization of Nitrogen doped single walled carbon nanotubes. Adalberto Zamudio, Ana-Laura Elias, Federico Villalpando-Paez, Julio A. Rodriguez-Manzo, Eduardo Cruz-Silva, Humberto Terrones, Takuya Hayashi, Y.A. Kim, Hiroyuki Muramatsu, Morinobu Endo, Mildred S. Dresselhaus, Gene Dresselhaus, Mauricio Terrones We report the production of macroscopic amounts of long strands consisting of SWNT doped with nitrogen, using a CVD approach. We performed series of experiments varying the concentration of the nitrogen precursor in the solution, from 0.01{\%} to 26 {\%} by weight. The materials were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM, and Raman Spectroscopy. We will describe the changes in the Raman spectra caused by the nitrogen content using of different laser lines. First principle calculations on the electronic and vibrational properties of the doped SWNTs with N will also be presented. [Preview Abstract] |
Wednesday, March 15, 2006 4:30PM - 4:42PM |
R31.00011: Raman spectra and thermal stability analysis of 0.4 nm freestanding single-walled carbon nanotubes Jian Ting Ye, Zi Kang Tang Thermal stability of ultra-small 0.4 nm single-walled carbon nanotubes is studied by means of Raman scattering measurement under vacuum. The 0.4 nm SWNTs are very stable when they are confined inside the channels of the AFI crystal. When these SWNTs are extracted from the channels into free space, however, they become thermally unstable because of the strong curvature effect. All three structures of the 0.4 nm-sized SWNTs are destroyed between 730 to 790 K, a temperature range much lower than that of large-sized SWNTs. The (5,0) tube is only destroyed after temperature reaches 790 K and seems slightly stabler than the other two structures: the (3,3) and (4,2) tubes. [Preview Abstract] |
Wednesday, March 15, 2006 4:42PM - 4:54PM |
R31.00012: Effect of Magnetic Field in Carbon Nanotubes Yuriy Malozovsky, Andrew Kinchen We study the effect of magnetic field in the armchair carbon nanotubes (CNT). We model the carbon nanotube as a tubule with electrons confined to the surface of the tubule by an attractive delta-function potential. We derived the dynamic pair interaction potential between two electrons in the tubule in the presence of magnetic field. Dispersion of plasma modes at different values of angular momentum, and single-particle excitations in the presence of the magnetic field are derived as well. The self-energy part due to the interaction of an electron with plasma modes in magnetic field is also discussed. [Preview Abstract] |
Wednesday, March 15, 2006 4:54PM - 5:06PM |
R31.00013: Low-energy dark discharge growth of ultra-thin aligned carbon nanofibers for field emitter and optical antenna arrays Yang Wang, K. Kempa, Z. F. Ren We show experimentally the applicability of using a dc low-energy dark discharge state to grow aligned carbon nanofibers with diameters of less than 10 nm and directly on polyimide and transparent conducting oxides without buffer layers. The average discharge current density used can be 2-3 orders of magnitude lower than that in a typical plasma-enhanced chemical vapor deposition (PECVD), so that the plasma heating and etching effects are greatly alleviated, leading to lower growth temperatures and higher substrate compatibility. The nanofibers grown by dark discharges exhibit similar optical antenna effects to those grown by PECVD methods, and their diameter and density can be reduced to achieve good field emission properties. [Preview Abstract] |
Wednesday, March 15, 2006 5:06PM - 5:18PM |
R31.00014: Electronic and transport properties of carbon-based atomic chain structures R. Tugrul Senger, Engin Durgun, Sefa Dag, Sefaattin Tongay, Salim Ciraci Our first-principles calculations show that monatomic chains of carbon have high cohesive energy and axial strength, and are stable even at high temperatures. Pure carbon chains are metallic, and periodic compounds of carbon with transition- metals exhibit half-metallic properties where the electronic spins are fully polarized at the Fermi level. Finite-length carbon atomic chains capped with single transition metal atoms constitute the ultimately small spin-valve systems with high magnetoresistive ratios. In all these structures the electronic, magnetic and transport properties show interesting variations depending on the number of carbon atoms being odd or even. \\ $^1$ S. Tongay, R.T. Senger, S. Dag, and S. Ciraci, Phys. Rev. Lett. \textbf{93}, 136404 (2004). \\ $^2$ R. T. Senger, S. Tongay, S. Dag, E. Durgun, and S. Ciraci, Phys. Rev. B \textbf{71}, 235406 (2005). \\ $^3$ S. Dag, S. Tongay, T. Yildirim, E. Durgun, R. T. Senger, C. Y. Fong, and S. Ciraci, Phys. Rev. B \textbf{72}, 155444 (2005). [Preview Abstract] |
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