Variation in electrical resistance versus strain of an individual multiwalled carbon nanotubeThermal 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 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 6 150 W/m-K. The results highlight the importance of MWCNT quality in thermal management applications. V C 2012 American Institute of Physics.

The three omega method has proven to provide accurate and reliable measurements of thermal conductivity of thin films and other materials. However, if the films are soft and conductive, conventional methodologies to prepare samples for the measurement technique are challenging and often unachievable. Various modifications to the sample preparation to employ this technique for soft conducting films are reported in this paper including the use of shadow masks for metal heater deposition and a process for preparation of low temperature insulating films required between film and heater. In this work, thick (∼5μm) and ultrathin (∼110nm) films of polyaniline as well as a thin (∼300nm) film of low temperature plasma enhanced chemical vapor deposited SiO2 as a function of temperature were measured. Though not considered a soft material, the silicon dioxide film was utilized for comparison with previous data. Results indicate that the SiO2 film exhibits a thermal conductivity slightly lower than others’ data [S. M. Lee and D. G. Cahill, J. Appl. Phys. 81, 2590 (1997); H. Yan et al., Chem. Lett. 2000, 392; H. Yan et al., Anal. Calorim. 69, 881 (2002); J. E. de Albuquerque et al., Rev. Sci. Instrum. 74, 306 (2003)], which is likely due to the low temperature processing conditions that results in additional disorder in the film. The polyaniline films exhibit an increase in thermal conductivity with temperature, which is largely due to increasing heat capacity. The thick film thermal conductivity is many times the value corresponding to the thin film, which is likely due to significant phonon boundary scattering present in the ultrathin film.

Nanostructures have been shown theoretically, and to a certain extent experimentally, to exhibit enhanced thermoelectric properties. While the use of thermoelectric devices is not widespread today, even marginal improvements in performance could lead to a revolution in small-scale energy conversion and generation and heat removal applications. The potential integration of nanostructures into actual thermoelectric devices has not been fully realized since these devices generally require larger scale materials for the thermoelectric elements. Therefore, a focused investigation into thermal, electrical and thermoelectric characteristics of nanocomposites comprised of nanostructures that, in their bulk form, exhibit good thermoelectric characteristics, was conducted. The presented research explores the thermal and electrical properties of nanocomposites comprised of bismuth nanoparticles that were embedded in a conducting polymer matrix. The thermal and electrical conductivities as well as the thermopower of thin films of polyaniline (the conducting polymer) with different volume fractions of nanoparticles were measured. Results demonstrate that the thermal and electrical properties of polyaniline may be significantly influenced by the presence of the nanoparticles.

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Recently, tin has been identified as an attractive electrode material for energy storage/conversion technologies. Tin thin films have also been utilized as an important constituent of thermal interface materials in thermal management applications. In this regards, in the present paper, we investigate thermal conductivity of two nanoscale tin films, (i) with thickness 500 ± 50 nm and 0.45% porosity and (ii) with thickness 100 ± 20 nm and 12.21% porosity. Thermal transport in these films is characterized over the temperature range from 40 K–310 K, using a three-omega method for multilayer configurations. The experimental results are compared with analytical predictions obtained by considering both phonon and electron contributions to heat conduction as described by existing frequency-dependent phenomenological models and BvK dispersion for phonons. The thermal conductivity of the thicker tin film (500 nm) is measured to be 46.2 W/m-K at 300 K and is observed to increase with reduced temperatures; the mechanisms for thermal transport are understood to be governed by strong phonon-electron interactions in addition to the normal phonon-phonon interactions within the temperature range 160 K–300 K. In the case of the tin thin film with 100 nm thickness, porosity and electron-boundary scattering supersede carrier interactions, and a reversal in the thermal conductivity trend with reduced temperatures is observed; the thermal conductivity falls to 1.83 W/m-K at 40 K from its room temperature value of 36.1 W/m-K. In order to interpret the experimental results, we utilize the existing analytical models that account for contributions of electron-boundary scattering using the Mayadas-Shatzkes and Fuchs-Sondheimer models for the thin and thick films, respectively. Moreover, the effects of porosity on carrier transport are included using a previous treatment based on phonon radiative transport involving frequency-dependent mean free paths and the morphology of the nanoporous channels. The systematic modeling approach presented in here can, in general, also be utilized to understand thermal transport in semi-metals and semiconductor nano-porous thin films and/or phononic nanocrystals.