Experimental evidence of a size-dependent sign change of the Seebeck coefficient of Bi nanowire arrays

Abstract

The electrical transport in bismuth nanowires is strongly influenced by both sample geometry and crystallinity. Compared to bulk bismuth, the electrical transport in nanowires is dominated by size effects and influenced by surface states, which gain increasing relevance with increasing surface-to-volume ratios, i.e. with decreasing wire diameter. Bismuth nanowires with tailored diameter and crystallinity constitute, therefore, excellent model systems, allowing to study the interplay of the different transport phenomena. Here, we present temperature-dependent Seebeck coefficient and relative electrical resistance measurements of parallel bismuth nanowire arrays with diameters between 40 and 400 nm synthesized by pulsed electroplating in polymer templates. Both electrical resistance and Seebeck coefficient exhibit a non-monotonic temperature dependence, with the sign of the Seebeck coefficient changing from negative to positive with decreasing temperature. The observed behavior is size-dependent and is attributed to limitations of the mean free path of the charge carriers within the nanowires. The observed size-dependent Seebeck coefficient and in particular the size-dependent sign change opens a promising avenue for single-material thermocouples with p- and n-legs made from nanowires with different diameters.

Polycrystalline bismuth nanowire networks for flexible longitudinal and transverse thermoelectrics

“…2,8,9 Although the study of the dependence of thermoelectric power on the diameter of individual Bi NWs and parallel NW arrays has been the subject of several previous studies, the experimental results are very contrasted, not allowing the identification of a clear trend. 1,5,6,10–18 Several factors are likely to be at the origin of the puzzling results obtained on Bi NW arrays. Firstly, most measurements have been made on single crystal Bi NWs, some of which display different crystal orientations.…”