Effects of heat treatment and contact resistance on the thermal conductivity of individual multiwalled carbon nanotubes using a Wollaston wire thermal probe
MFP Bifano and J Park and PB Kaul and AK Roy and V Prakash, JOURNAL OF APPLIED PHYSICS, 111, 054321 (2012).
Thermal conductivity measurements in commercially available, chemical vapor deposition-grown, heat-treated and non-heat-treated multiwalled carbon nanotubes (MWCNTs) are reported. The thermal conductivity of individual samples is measured using a suspended platinum wire as a thermal resistance probe in a "T-type" configuration. Changes in third harmonic voltage are measured across the heated suspended platinum wire as a specimen is attached to the platinum wire's midpoint. An analytic model is used to correlate the reduction in the average temperature of the probe wire to the thermal resistance (and thermal conductivity) of the attached sample. Experiments are implemented inside a scanning electron microscope equipped with nanomanipulators for sample selection, and a gas injection system for platinum based electron beam-induced deposition to improve thermal contact resistances. The results indicate a nearly 5-fold increase in the average thermal conductivity of MWCNT samples annealed with a 20-h 3000 degrees C annealing heat treatment compared to the as-grown samples. However, specimen-specific morphological defects, such as kinking, Y-branches, etc., are found to negate, to a large degree, the advantage of the heat treatment process. The thermal contact resistance between the MWCNT and the electron beam- induced deposition contacts is estimated using an anisotropic diffusive mismatch model that includes the effect of fin resistance. Adjusting the thermal conductivity to include the effect of thermal contact resistance is found to increase the thermal conductivity by approximately 5%. Once adjusted for thermal contact resistance, the average thermal conductivity of the heat-treated MWCNT specimens is 228 W/m-K, with the highest measured thermal conductivity being 765 +/- 150 W/m-K. The results highlight the importance of MWCNT quality in thermal management applications. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.3691607
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