A photo-thermoelectric technique for anisotropic thermal diffusivity characterization of nanowire/nanotube composites

Thermal properties of nanowire and nanotube arrays and their composites formed by deposition in a nanochannel alumina matrix have attracted a great research interest due to possible applications in high efficiency thermoelectric energy conversion and thermal management. A photo-thermoelectric technique was employed recently to perform anisotropic thermal diffusivity measurements in aligned carbon nanotube arrays, nanochannel alumina, and Bi and BiTe nanowire alumina composites. In this technique a thermal wave is produced into the specimen by absorption of laser radiation while the thermal wave is detected using a fast thermoelectric effect at the junction between a sharp wire probe and the sample surface. To allow effective heating and signal detection, additional thin-film layers may need to be deposited onto the samples. However, heat transport through the layers and the thermoelectric probe may affect the thermal transport measurements. This work discusses a heat conduction model that takes these effects into account and can be used to guide the selection of the probe and thin-film materials and thicknesses such that the accuracy of the thermal measurements is minimally affected. The discussion is illustrated with simulation results, calibration experiments, and examples of anisotropic thermal diffusivity characterization in aligned multiwall carbon nanotube arrays.