Thermal conductivity of nanotubes revisited: Effects of chirality, isotope impurity, tube length, and temperature

Abstract

We study the dependence of thermal conductivity of single walled nanotubes (SWNT) on chirality, isotope impurity, tube length and temperature by nonequilibrium molecular dynamics method with accurate potentials. It is found that, contrary to electronic conductivity, the thermal conductivity is insensitive to the chirality. The isotope impurity, however, can reduce the thermal conductivity up to 60% and change the temperature dependence behavior. We also found that the tube length dependence of thermal conductivity is different for nanotubes of different radius at different temperatures.PACS numbers: 65.80+n, 66.70.+f, 44.10.+i Carbon nanotube is one of exciting nano-scale materials discovered in the last decade. It reveals many excellent mechanical, thermal and electronic properties 1 . Depends on its chirality 2,3 , the nanotube can be either metallic or semiconducting. For example, for zigzag (9,0) and (10,0) tubes, their radius are almost the same, but (9,0) tube behaves metallic and (10,0) tube semiconducting. At room temperature, the electronic resistivity is about 10 −4 − 10 −3 Ωcm for the metallic nanotubes, while the resistivity is about 10Ωcm for semiconducting tubes 4 . The 10% difference in radius induces the change of electronic conductivity in four orders of magnitude. One may ask, whether thermal conductivity is also very sensitive to the chirality like its electronic counterpart?On the other hand, the isotope impurity reduces thermal conductivity of most materials, such as germanium and diamond 5,6 . It is surprising that 1% 13 C in diamond leads to a reduction of thermal conductivity up to 30% 7 . Is there same effect in carbon nanotubes?Moreover, in electronic conductance, SWNT reveals many 1D characters 1 . However in thermal conduction, it is still not clear whether the conduction behavior is like that one of 1D lattice or a quasi 1D (1D lattice with transverse motions) or that one in a 2D lattice.These questions and many other relevant properties of nanotubes are very important and should be understood before the nanotubes are put into any practical application. Indeed, recent years have witnessed increasing interesting in thermal conductivity of nanotubes 8,9,10,11,12,13,14,15,16,17,18,19 , the questions raised here are still open.In this paper, we study the effects of the chirality, isotope impurity, tube length and temperature on SWNTs' thermal conductivity by using the nonequilibrium molecular dynamics (MD) method with bond order potential. This approach is valid as it shows that at finite temperature, phonon has a dominating contribution to thermal conduction than electron does 20,21 . We should pointed out that the thermal conductivity calculated in this paper is exclusively from lattice vibration. Of course, for the metallic nanotubes, the electrons may give some but limited contributions 20,21 , but this is not the main concern in our paper.The Hamiltonian of the carbon SWNT is:where] is the Tersoff empirical bond order potential. V R (r ij ), and V A (r ij ) are the repulsive and ...

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