Fabrication, Characterization, Modeling and Testing of a Nanostructured Bulk Thermoelectric Cooler

Abstract

New generation micro/nano devices are emerging to monitor, control and act on living systems. Particularly, in the field of cryobiology, there is a need to monitor and control temperature at the cellular level. An important step towards achieving this aim is to fabricate a novel bulk nanostructured thermoelectric cooler (TEC). As a first step towards achieving efficient localized control of temperature in biological systems, Bismuth-telluride (Bi2Te3) and Antimony-Telluride (Sb2Te3) arrays of nanowires and nanotubes were fabricated, characterized and modeled. A thermal conductivity model originally developed by Dames and Chen for superlattice nanowires was extended to nanotubes. Based on this model thermal conductivity of Bi2Te3 and Sb2Te3 nanowire or nanotube is determined. Lumped parameter model was also used to determine the performance of a device composed of nanowires or nanotubes. The modeling results suggest that nanotubes would yield higher reduction in thermal conductivity compared to nanowires. Bi2Te3 and Sb2Te3 arrays of nanowires and nanotubes were electrodeposited into the nanochannels of the polycarbonate template as n-type and p-type thermoelectric leg elements of the bulk thermoelectric cooler, respectively. SEM, XRD and WDS were employed to characterize the fabricated Bi2Te3 and Sb2Te3 nanowire or nanotube arrays. A custom built device is developed to characterize the Seebeck coefficient of the electrodeposited nanowires or nanotubes. The Seebeck coefficient values of Sb2Te3 nanowire and nanotube arrays were found to be +359 µV K-1 and +332 µV K-1, respectively. The positive Seebeck coefficient values indicated that electrodeposited Sb2Te3 nanowires and nanotubes were p-type. The Seebeck coefficient values of Bi2Te3 nanowire and nanotube arrays were found to be -118 µV K-1 and -143 µV K-1, respectively. The negative Seebeck coefficient values indicated that electrodeposited Bi2Te3 nanowire and nanotube arrays were n-type. The electrical resistance measurements confirmed that Bi2Te3 and Sb2Te3 nanowire or nanotube arrays resistance were semiconductors. A bulk nanostructured TEC is assembled using the best Bi2Te3 (n-type) and Sb2Te3 (p-type) nanowire or nanotube arrays. The ZT of the thus assembled device is determined by “Harmans Technique”. It is found that a combination of Bi2Te3 nanowires and Sb2Te3 nanotubes yielded highest ZT of around 0.4 at room temperature. Results suggest that there is clearly a need to significantly improve the performance of the nanostructured bulk TEC to compete with commercially available vapor compression coolers.