Unusually High Thermal Conductivity of Carbon Nanotubes

Unusually High Thermal Conductivity of Carbon Nanotubes -...

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VOLUME 84, NUMBER20 PHYSICAL REVIEW LETTERS 15M AY 2000 Unusually High Thermal Conductivity of Carbon Nanotubes Savas Berber, Young-Kyun Kwon,* and David Tománek Department of Physics and Astronomy, and Center for Fundamental Materials Research, Michigan State University, East Lansing, Michigan 48824-1116 (Received 23 February 2000) Combining equilibrium and nonequilibrium molecular dynamics simulations with accurate carbon po- tentials, we determine the thermal conductivity l of carbon nanotubes and its dependence on temperature. Our results suggest an unusually high value, l ø 6600 W y m K, for an isolated s 10, 10 d nanotube at room temperature, comparable to the thermal conductivity of a hypothetical isolated graphene monolayer or diamond. Our results suggest that these high values of l are associated with the large phonon mean free paths in these systems; substantially lower values are predicted and observed for the basal plane of bulk graphite. PACS numbers: 61.48.+c, 63.22.+m, 66.70.+f, 68.70.+w With the continually decreasing size of electronic and micromechanical devices, there is an increasing interest in materials that conduct heat efficiently, thus preventing structural damage. The stiff sp 3 bonds, resulting in a high speed of sound, make monocrystalline diamond one of the best thermal conductors [1]. An unusually high thermal conductance should also be expected in carbon nanotubes [2,3], which are held together by even stronger sp 2 bonds. These systems, consisting of seamless and atomically per- fect graphitic cylinders a few nanometers in diameter, are self-supporting. The rigidity of these systems, combined with virtual absence of atomic defects or coupling to soft phonon modes of the embedding medium, should make isolated nanotubes very good candidates for efficient ther- mal conductors. This conjecture has been confirmed by experimental data that are consistent with a very high ther- mal conductivity for nanotubes [4]. In the following, we will present results of molecu- lar dynamics simulations using the Tersoff potential [5], augmented by van der Waals interactions in graphite, for the temperature dependence of the thermal conductivity of nanotubes and other carbon allotropes. We will show that isolated nanotubes are at least as good of heat con- ductors as high-purity diamond. Our comparison with graphitic carbon shows that interlayer coupling reduces thermal conductivity of graphite within the basal plane by 1 order of magnitude with respect to the nanotube value which lies close to that for a hypothetical isolated graphene monolayer. The thermal conductivity l of a solid along a particu- lar direction, taken here as the z axis, is related to the heat flowing down a long rod with a temperature gradient dT y dz by 1 A dQ dt - 2l dT dz , (1) where dQ is the energy transmitted across the area A in the time interval dt . In solids where the phonon contribu- tion to the heat conductance dominates, l is proportional
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Unusually High Thermal Conductivity of Carbon Nanotubes -...

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