Influence of surface states and size effects on the Seebeck coefficient and electrical resistance of Bi_1−xSb_xnanowire arrays

Abstract

The Seebeck coefficient and electrical resistance of BiSb nanowire arrays electrodeposited in etched ion-track membranes have been investigated as a function of wire diameter (40-750 nm) and composition (0 ≤ x ≤ 1). The experimental data reveal a non-monotonic dependence between thermopower and wire diameter for three different compositions. Thus, the thermopower values decrease with decreasing wire diameter, exhibiting a minimum around ∼60 nm. This non-monotonic dependence of the Seebeck coefficient is attributed to the interplay of surface and bulk states. On the one hand, the metallic properties of the surface states can contribute to decreasing the thermopower of the nanostructure with increasing surface-to-volume ratio. On the other hand, for wires thinner than ∼60 nm, the relative increase of the thermopower can be tentatively attributed to the presence of quantum-size effects on both surface and bulk states. These measurements contribute to a better understanding of the interplay between bulk and surface states in nanostructures, and indicate that the decrease of Seebeck coefficient with decreasing diameter caused by the presence of surfaces states can possibly be overcome for even thinner nanowires.

Effects of Size Reduction on the Electrical Transport Properties of 3D Bi Nanowire Networks

“…In turn, the theoretical predictions did not take into account the presence of surface states, which may play a role due to the large surface to volume ratio of the nanowires. [ 22,40,49 ] In addition, the crystalline structure of wires with different diameters may vary and as such also contribute to the discrepancy between theoretical prediction and experiment. Usually wires with smaller diameter exhibit a stronger texture along the wire axis.…”

“…The Seebeck coefficient and the electrical resistance of the samples were measured using a custom‐built setup described in. [ 8,40,48,63 ] A schematic of the setup is shown in Figure . For these measurements, the nanowire network remained embedded in the polymer membrane and was placed between two copper blocks.…”

“…[ 38,39 ] The transition is also interesting for thermoelectric and topological insulator applications, as the effect might be used to generate larger Seebeck coefficients in very thin wires when compared to bulk material. [ 13,30,35,40 ]…”

“…Bismuth nanowires can be prepared by several methods including hydro‐ and solvothermal synthesis, stress‐induced growth, vapor liquid solid methods, the Taylor process and the so‐called template method. [ 1–3,35,40–51 ] The template method, applied in this work, is based on the deposition of material into nanochannels of a given matrix. Thus, wire diameter, density number and alignment are determined by the properties of the hosting membrane.…”

Novel Principles and Nanostructuring Methods for Enhanced Thermoelectrics

“…Therefore, comprehensively assembled heterostructures of nanosheets with thin layers may be good target materials. Recent reports that surface effects in BiTe nanowires apparently negated any large TE enhancement indicate that such effects may not always be easily realized. However, thinner nanosheet heterostructures should be fabricated to test this.…”