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Curvature dependence of electric and thermal conductivity in carbon nanotubes

Curvature dependence of electric and thermal conductivity in carbon nanotubes. Wan-Ju Li Phys 570X Proposal presentation 04/22/2009. Outline. Motivation Introduction Conductivities under strain Summary. Motivation.

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Curvature dependence of electric and thermal conductivity in carbon nanotubes

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  1. Curvature dependence of electric and thermal conductivity in carbon nanotubes Wan-Ju Li Phys 570X Proposal presentation 04/22/2009

  2. Outline • Motivation • Introduction • Conductivities under strain • Summary

  3. Motivation • Structure deformations are common in the growth of CNTs as well as in developing CNT-based nano devices. • Dependences of electric and thermal conductivities on the radius of the CNTs and the curvature radius are essential for estimating the preperties of our designed nano device.

  4. Introduction-electric conductivity M: number of transport channels G: electric conductance E: energy of electrons When E lies inside a band gap we can use quantum mechanical penetration or thermal activation transport to obtain the transmission coefficient and then get electric conductance. J X Cao, X H Yan, J W Ding and D L Wang, J. Phys.: Condens. Matter 13 (2001) L271–L275

  5. Introduction-electric(cont.) Liu Yang and Jie Han, Phys.Rev.Lett. 5,154(2000) E. D. Minot,et al (McEuen group) Phys.Rev.Lett.90.156401(2003)

  6. Introduction-Molecule Dynamics • Computer Simulation • Interatomic potential form • Newtonian dynamics Example of a molecular dynamics simulation in a simple system: deposition of a single Cu atom on a Cu (001) surface. Each circle illustrates the position of a single atom; http://en.wikipedia.org/wiki/Molecular_dynamics

  7. Introduction-Molecule Dynamics Potential form for our problem Parameters, except R and D, are chosen to fit the cohesive energy, lattice constant, and bulk modulus of diamond. For carbon we choose R=1.95A D=0.15A, where R is chosen to include only the first neighbor shell. J. Tersoff, PRB 37, 6991(1988)

  8. Introduction-thermal conductivity Thermal conductivity λ is related to the thermal current correlation function. Savas Berber, Young-Kyun Kwon,* and David Tománek, Phys.Rev.Lett.84,4613(2000)

  9. r R Electric conductivity under strain • Tight binding model for band structure • Add band gap modification • Get electric conductance (conductivity) as a function of incident energy • Also include effects of tube radius and curvature radius

  10. r R Thermal conductivity under strain • Specify the geometry under strain • Molecule Dynamics simulation Michael C H Wu and Jang-Yu Hsu, nanotechnology 20 145401(2009)

  11. Summary • In order to predict the behaviors of designed nano devices it is necessary to understand the influence of curvature • Electric conductivity- Tight-binding model + change of gap by strain • Thermal conductivity- Molecule dynamics simulation R. Heyd. et al, PRB 55,6820(1997)

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