Thermal conductivity of carbon nanotubes grown by catalyst-free chemical vapor deposition in nanopores

Abstract

A graphitic structure was synthesized by catalyst-free chemical vapor deposition on an anodized aluminum oxide (AAO) template using acetylene as the carbon source at a temperature of 620 °C. The AAO template was removed by chemical etching, which yielded a three-dimensional structure featuring planar layers seamlessly joined together by nanotube pillars via continuous carbon-carbon bonding. Raman spectroscopy and transmission electron microscopy measurements reveal that the deposited carbon is nanocrystalline graphite with a thickness of about 10 nm. Carbon nanotubes were isolated from the three-dimensional nano-pillar graphitic structure and measured with a thermal four-probe method to obtain the intrinsic thermal conductance. Discrete modulated heating and Fourier transform analysis were used to improve the signal to noise ratio of the thermal measurement of the low-conductance nanostructure. The measured thermal conductivity of the nanotube wall increased with increasing temperature and was 3.9 ± 0.3 Wm−1K−1 at room temperature. Both the temperature dependence and the magnitude are consistent with the nanocrystalline graphitic structure.