Morphology dependence of the thermal transport properties of single-walled carbon nanotube thin films.

The thermal transport properties of random network, single-walled carbon nanotube (SWNT) films were assessed using Raman spectroscopy. Two types of SWNT films were investigated: single-layer and stacked. The single-layer films were fabricated by aerosol chemical vapour deposition and subsequent direct dry deposition, while the stacked films were prepared by placing the single-layer films on top of one another. The anisotropy of the network structures of each of these films was evaluated based on the angular dependence of the optical absorbance spectra. The results show that the anisotropy of the films decreases with increasing film thickness in the case of the single-layer films, and that the film anisotropy is preserved during the stacking process. The sheet thermal conductance is proportional to the SWNT area density in the case of stacked films, but is reduced with increasing thickness in the case of single-layer films. This effect is explained by a change in the network morphology from a two-dimensional anisotropic structure to the more isotropic structure. This work demonstrates the fabrication of low-density films with high sheet thermal conductance through the stacking of thin SWNT films.

Exciton diffusion in air-suspended single-walled carbon nanotubes.

Direct measurements of the diffusion length of excitons in air-suspended single-walled carbon nanotubes are reported. Photoluminescence microscopy is used to identify individual nanotubes and to determine their lengths and chiral indices. Exciton diffusion length is obtained by comparing the dependence of photoluminescence intensity on the nanotube length to numerical solutions of diffusion equations. We find that the diffusion length in these clean, as-grown nanotubes is significantly longer than those reported for micelle-encapsulated nanotubes.

Superconductivity in entirely end-bonded multiwalled carbon nanotubes.

We report that entirely end-bonded multiwalled carbon nanotubes (MWNTs) can exhibit superconductivity with a transition temperature (T(c)) as high as 12 K, which is approximately 30 times greater than T(c) reported for ropes of single-walled nanotubes. We find that the emergence of this superconductivity is highly sensitive to the junction structures of the Au electrode/MWNTs. This reveals that only MWNTs with optimal numbers of electrically activated shells, which are realized by end bonding, can allow superconductivity due to intershell effects.