Thermal conductivity (kappa) of isolated carbon nanotubes (CNTs) is higher than the kappa of diamond; however, in this Letter we show that the kappa of a packed bed of three-dimensional random networks of single and multiwall CNTs is smaller than that of thermally insulating amorphous polymers. The thermoelectric power (Sigma) of the random network of CNTs was also measured. The Sigma of a single wall nanotube network is very similar to that of isolated nanotubes and, in contrast with kappa, Sigma shows a strong dependence on the tube diameter.

Molecular dynamics (MD) is a numerical simulation technique based on classical mechanics. It has been taken for granted that its use is limited to a large temperature regime where classical statistics is valid. To overcome this limitation, the authors introduce in a universal way a quantum thermal bath that accounts for quantum statistics while using standard MD. The efficiency of the new technique is illustrated by reproducing several experimental data at low temperatures in a regime where quantum statistical effects cannot be neglected.

The surface phonon-polaritons contribution to the thermal conductivity of a nano thin film of silicon dioxide is investigated based on the Maxwell equations and the Boltzmann transport equation. It is shown that: (1) a small difference between the permittivities of the substrate and superstrate of the film can generate giant propagation lengths and therefore remarkably enhances its thermal conductivity with respect to values obtained for a freestanding one. (2) The propagation of surface phonon-polaritons is present in a broad band of frequencies and exhibits its largest propagation lengths at the frequency where the absorption of energy is minimal. (3) The increase of the thermal conductivity of the film as its thickness decreases is higher when it is deposited on potassium bromide instead of being suspended in air. The difference in the thermal conductivity for these two systems increases with increasing temperature and reducing the film thickness. A thermal conductivity as high as 2.5 W/m K is obtained for a 30 nm-thick thin film at room temperature, which is about 1.8 times larger than its bulk phonon value. The obtained results show that the propagation of surface phonon-polaritons has the potential not only to offset the reduction of the phonon thermal conductivity of a nano thin film, when its sizes are scaled down, but also to enhance it, by choosing properly the permittivity of its substrate. V C 2013 American Institute of Physics. [http://dx.