Effect of Carbon Isotope Abundance on Thermal Conductivity and Raman Scattering of Single-Walled Carbon Nanotubes

We have been studying the heat conduction characteristics along a single-walled carbon nanotube (SWNT) by the molecular dynamics method [1-3] with the simplified form [4] of TersoffBrenner bond order potential [5]. Our preliminary results showed that thermal conductivity was strongly dependent on the nanotube length for realistic length scale for device applications [2, 3]. Furthermore, we have reported the direct calculation of phonon dispersion relations and phonon density of states from molecular dynamics trajectories [2, 3]. The calculated thermal conductivity for a finite length nanotube was not as high as the previously reported result that it might be as high as 6600 W/mK at 300 K [6]. However, the thermal conductivity was much higher than high-thermal conductivity metals. In this study the carbon isotope effect on heat conduction and on Raman scattering are investigated. It is well-known that the inclusion of only 1% of C natural isotope dramatically reduces the thermal conductivity of isotopically pure diamond [7]. However, the previous molecular dynamics result has concluded that the isotope effect was negligible for carbon nanotubes [6]. In order to clarify this point, thermal conductivity of nanotube with randomly distributed C with various ratios was calculated. A preliminary result showed that the dependency of thermal conductivity on isotope ratio was well explained with a simple phonon scattering model. In addition to the molecular dynamics simulations, SWNTs with various amount of C abundance were generated by the alcohol catalytic CVD technique [8, 9] from 1-C and 1,2-C2 ethanol. The Raman scattering of those SWNTs shows a simple shift of Raman scatting frequency for C SWNTs and a complicated broadening for C and C mixture case. Those features are compared with phonon density of states calculated with molecular dynamics method.