Anisotropic Thermal Diffusivity Measurements in Nanostructured Samples Using a Photothermoelectric Technique

Knowledge of the thermal transport properties in thin films and nanostructures is critical for a wide range of applications in microelectronics, photonics, micro-electro-mechanical-systems, and thermoelectrics. The last twenty years have seen significant developments in thin-film thermal characterization techniques. Despite these advances, the characterization of the thermal transport properties in low-dimensional systems remains a challenging task. Recently, thermal properties of nanowire/nanotube nanocomposites such as thermoelectric nanowires and aligned carbon nanotubes (CNT) deposited on silicon substrates or in alumina or polymer matrix have attracted a great interest due to their possible applications in high efficiency thermoelectric energy conversion and thermal management applications. However, a major challenge for thermal characterization of nanowire/nanotube composites is their thermal anisotropy. This work presents measurements of anisotropic thermal properties using a photothermoelectric technique.

Thermophysical Properties of Ni Films for LIGA Microsystems

ABSTRACTThis work reports temperature dependent thermophysical properties characterization of electrodeposited Ni and NiMn alloys intended for LIGA Microsystems applications. A steady-state method is used to determine the in-plane thermal conductivity. Anisotropic thermal diffusivity characterization is performed using a photothermoelectric technique. The measured thermal properties are dependent on the deposition method and also on subsequent temperature annealing steps. The thermal transport measurement results are correlated with scanning electron microscopy studies of the grain structure and measurements of the electrical transport properties.

Anisotropic Thermal Diffusivity of Aligned Multiwalled Carbon Nanotube Arrays

This work employs a photothermoelectric technique to measure the anisotropic thermal diffusivity of an aligned multiwalled carbon nanotube array. A modulated laser beam incident to the front surface of the sample creates a thermal wave which is detected by a fast responding thermocouple formed between the back surface of the sample and the tip of a sharp metallic probe. The anisotropic thermal diffusivity values are obtained by fitting the radial and frequency dependent thermal signals with an anisotropic heat conduction model. The room temperature thermal diffusivity measured perpendicular to the alignment direction is 0.246×10−5m2/s, an order of magnitude smaller than thermal diffusivity along the CNTs alignment direction 4.4×10−5m2/s. However, the thermal diffusivity of the aligned multiwalled CNT is two orders of magnitude smaller than expected for an individual multiwalled CNT.