Thermal conductivity of multiwalled carbon nanotubes ͑CNT's͒ prepared using a microwave plasma chemical vapor deposition system is investigated using a pulsed photothermal reflectance technique. We find that the average thermal conductivity of carbon nanotube films, with the film thickness from 10 to 50 m, is around 15 W/m K at room temperature and independent of the tube length. Taking a small volume filling fraction of CNT's into account, the effective nanotube thermal conductivity could be 2ϫ10 2 W/m K, which is smaller than the thermal conductivity of diamond and in-plane graphite by a factor of 9 and 7.5, respectively.

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Articles you may be interested inOn the induced microstructure changes of the amorphous carbon nitride films during annealing Plasma enhanced metalorganic chemical vapor deposition of amorphous aluminum nitride Effects of microwave power on the structural and emission properties of hydrogenated amorphous silicon carbide deposited by electron cyclotron resonance chemical vapor depositionWe have investigated the growth of a-Si 1Ϫx C x :H using the electron cyclotron resonance chemical vapor deposition ͑ECR-CVD͒ technique, under the conditions of high microwave power and strong hydrogen (H 2 ) dilution. The microwave power used is 900 W and a gas mixture of CH 4 and SiH 4 diluted in H 2 is varied to give carbon ͑C͒ fractions x ranging from 0 to 1. We aim to understand the effects of these deposition conditions on the characteristics of ECR-CVD grown a-Si 1Ϫx C x :H films at different x. Their microstructure and optical properties are investigated using infrared absorption, Raman scattering, UV-visible spectrophotometry, and photothermal deflection spectroscopy. Information on the atomic fraction x is obtained with Rutherford backscattering spectrometry. The B parameter in the Tauc relation is found to decrease and the Urbach energy E u increase with x, which are indicative of a higher degree of disorder with C incorporation. At intermediate x, the presence of SiuC bonds can be clearly seen from the IR absorption and Raman scattering results. The T peak around 1200 cm Ϫ1 is observed in the Raman spectra of the C-rich samples, with a redshift noted at increasing x. This suggests an increased presence of sp 3 CuC bonds in these films, which is attributed to the high microwave power and strong H 2 dilution that enhance C sp 3 bonding and indirectly limit the number of C sp 2 sites. This accounts for the large E 04 gaps of more than 3.2 eV observed in such films, which are nearly saturated at large x, instead of exhibiting a maximum at an intermediate x as are commonly reported. Blue photoluminescence ͑PL͒ is observed, and the PL peak energies (E PL ) are correlated to the E 04 gap. The full width at half maximum of the PL are also correlated to the Urbach energy E u . These results support that the PL broadening is attributed to the disorder broadening arising from the broad band tails.