Curvature dependence of electric and thermal conductivity in carbon nanotubes
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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

Curvature dependence of electric and thermal conductivity in carbon nanotubes

Wan-Ju Li

Phys 570X Proposal presentation

04/22/2009


Outline

Outline

  • Motivation

  • Introduction

  • Conductivities under strain

  • Summary


Motivation

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.


Introduction electric conductivity

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


Introduction electric cont

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)


Introduction molecule dynamics

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


Introduction molecule dynamics1

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)


Introduction thermal conductivity

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)


Electric conductivity under strain

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


Thermal conductivity under strain

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)


Summary

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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