The effect of molecular oxygen on the thermal conductance of multi-walled nanotubes – a preliminary investigation

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Abstract

Whilst the effect of oxygen adsorption on the electrical properties of carbon nanotubes has been investigated extensively, little is known about how oxygen changes the thermal properties of nanotubes.

Here we present a preliminary investigation on the effect of molecular oxygen on the electrical and thermal conductance of multi-walled nanotubes (MWNTs) measured simultaneously.

The nanotubes were placed in a vacuum chamber (pressures <1 × 10–5 mbar) for a prolonged period of time (>7 days) and continuously heated above 100 °C to ensure oxygen desorption. Then pure oxygen was introduced in the chamber using a needle valve (the pressure in the chamber was always <3 × 10–4 mbar) and the heating of the nanotube was stopped to allow oxygen adsorption.

Thermal and electrical conductance measurements were taken simultaneously on the nanotubes when degassed and in the presence of oxygen.

The thermal conductance of the nanotubes increased by a maximum of about 20% upon addition of oxygen. The percentage increase was initially linearly dependent on the amount of oxygen added then at oxygen pressures >1 × 10−4 mbar saturation of the effect was observed.

The reasons for these changes are proposed to be: (i) oxygen adsorption caused a change in the nanotubes' phonon modes; (ii) the presence of oxygen molecules facilitated the inter-shell transfer of heat in the nanotube. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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