Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session V27: Theory of Nanotubes & Carbon Based Nanostructures |
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Sponsoring Units: DCOMP DMP Chair: Vincent Meunier, Oak Ridge National Lab Room: LACC 501C |
Thursday, March 24, 2005 11:15AM - 11:51AM |
V27.00001: Mesoscopic transport in carbon nanotubes with boron and nitrogen substitutions Invited Speaker: This theoretical study is devoted to the electronic structure and (magneto)transport properties of carbon nanotubes containing boron or nitrogen substitutions. It addresses large devices with a mesoscopic approach, in order to tune the density of substitutionnal atoms and to take random multiple interference effects into account. The electronic properties are treated within a modified tight-binding model, with parameters adjusted on ab initio results, allowing to treat correctly charge transfer due to impurities. The transport properties were calculated using the Kubo formalism. The evolution of the generic transport properties (conduction regime, conductance, etc.) versus the density of substitutional atoms has been studied. The regime is found to be highly sensitive upon the energy and the density of dopants: following the cases, it may be quasi-ballistic, diffusive (here, the mean free paths follow usual scalings), or strongly localized. Finally, when a magnetic field is applied along the nanotube axis, an anomalous Aharonov-Bohm phenomenon in the conduction properties has been pointed out. [Preview Abstract] |
Thursday, March 24, 2005 11:51AM - 12:27PM |
V27.00002: Optimization of the Properties of Carbon Nanotube-Based Structures by Electron and Ion Beam Irradiation Invited Speaker: There is considerable interest in building new nanostructures for electronic devices and incorporating nanostructured fibers and particles into composites. Here, classical molecular dynamics simulations are used to study the production of new carbon nanotube junctions or cross-links through electron irradiation, in addition to the chemical modification of carbon nanotube-based structures and composites through ion and polyatomic ion beam deposition. In particular, electron irradiation is used to produce junctions between carbon nanotubes. The specific reactions that lead to junction-formation and the mechanical and electronic properties of the resulting junctions will be discussed. Additionally, the chemical modification of multi-walled nanotubes, single-walled and multi-walled nanotube bundles, nanopeapods, and nanotube-polymer composites from polyatomic fluorocarbon ions, which are commonly present in low-energy fluorocarbon plasmas, and Ar will be presented. Multi-walled carbon nanotubes usually fail through the so-called ``sword-and-sheath'' mechanism and nanotube-polymer composites often fail through nanotube pullout. In both cases the failure mechanism is due to the weak van der Waals bonds between either the nanotube shells in the multi-walled tube or between the nanotubes and polymer matrix in the composite. The simulation results show that ion beam deposition produces cross-links between shells in multi-walled nanotubes and between otherwise unfunctionalized nanotubes and polymer backbone chains, which ultimately toughens the composites. The conditions that are predicted to be optimum for effective chemical modification of the system will be discussed. [Preview Abstract] |
Thursday, March 24, 2005 12:27PM - 1:03PM |
V27.00003: Magnetic Properties of Carbon Nanostructures: The Role of Negative and Positive Curvature Invited Speaker: A Pi-orbital nearest-neighbor tight-binding Hamiltonian in conjunction with the London approximation is used to study uniform external magnetic field effects on different graphitic nanostructures with negative and positive Gaussian curvature. Ring currents and the induced magnetic moment are calculated on toroidal structures formed by coalescing C60 structures (peapod- like) and Haeckelite-tubules (structures containing heptagons, hexagons and pentagons of carbon). It is found that coalesced C60 fullerenes connected along the five-fold symmetry axes and Haeckelites tubes are metallic and exhibit large magnetic moments. These results have important implications in the magnetic properties of corrugated carbon nanotubes (coalesced peapods). The magnetism observed experimentally in rombohedral C60 is also discussed in the context of ring currents generated by the sp2 polymerization of C60. Finally, the possiblity of witnessing magnetism in interconnected graphene layers is also studied. [Preview Abstract] |
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