Electrodeposition and device incorporation of bismuth antimony nanowire arrays

Thermoelectric materials have the unique property where the application of a potential difference across the material results in the formation of a temperature gradient, and vice versa. There is continued interest in bulk thermoelectric materials for power generation and refrigeration applications, however these materials are not currently in widespread use due to their low conversion efficiency. It has been predicted that nanostructured thermoelectric materials will show enhanced performance over their bulk counterparts. In this study, bismuth antimony (Bi1-xSbx) nanowire arrays have been synthesized and assembled into devices in order to demonstrate an enhanced performance in nanostructured thermoelectric materials.; Bi1-xSbx nanowire arrays were fabricated by potentiostatic electrodeposition into porous alumina templates from a dimethyl sulfoxide (DMSO) solution. The nanowire composition and texture were studied as a function of the electrodeposition conditions in order to maximize their thermoelectric performance. Energy dispersive spectrometry and electron microprobe analysis were used to study the nanowire composition as a function of the electroactive and non-electroactive species in solution. Texturing in the nanowire arrays was observed by X-ray diffraction and controlled by the applied voltage and presence of supporting electrolyte. The nanowire arrays were also optimized for device incorporation by maximizing the number of nanowires and minimizing their length distribution. The areal density of nanowire arrays was on the order of 1010 wires/cm2 due to the high density of pores in the alumina and the high degree to which those pores were filled with electrodeposited material. A narrow distribution of nanowire lengths was observed by scanning electron microscopy across millimeter-length portions of the arrays.; A hybrid nanowire-bulk thermoelectric device was assembled after electrical contacts were electrodeposited over Bi1-xSbx nanowire arrays. Nickel was used as the contact material and its electrodeposition was studied with respect to the applied potential (direct and pulsed) and the deposition bath contents. The thermoelectric performance of hybrid devices assembled from these nanowire composites was determined by the Harman method. An unoptimized Bi1-xSbx nanowire array produced a temperature difference of 7°C and the hybrid device had a ZT of 0.12, which is on par with an equivalent bulk couple. The results of this work illustrate the proof of concept where a thermoelectric nanowire array was taken from fabrication to device to measurement.