Diameter-dependent thermopower of Bi nanowires

TL;DR

This study investigates how the thermopower of bismuth nanowires varies with diameter, temperature, and magnetic field, revealing size-dependent effects and surface scattering influences on electronic transport.

Contribution

It provides the first detailed analysis of diameter-dependent thermopower in Bi nanowires, highlighting surface scattering effects and magneto-thermopower phenomena.

Findings

Thermopower is positive below 150 K in nanowires, unlike bulk Bi.

Magneto-thermopower effects are observed due to surface scattering.

Surface scattering impacts mobility more than electron-hole scattering.

Abstract

We present a study of electronic transport in individual Bi nanowires of large diameter relative to the Fermi wavelength. Measurements of the resistance and thermopower of intrinsic and Sn-doped Bi wires with various wire diameters, ranging from 150-480 nm, have been carried out over a wide range of temperatures (4-300 K) and magnetic fields (0-14 T). We find that the thermopower of intrinsic Bi wires in this diameter range is positive (type-p) below about 150 K, displaying a peak at around 40 K. In comparison, intrinsic bulk Bi is type-n. Magneto-thermopower effects due to the decrease of surface scattering when the cyclotron diameter is less than the wire diameter are demonstrated. The measurements are interpreted in terms of a model of diffusive thermopower, where the mobility limitations posed by hole-boundary scattering are much less severe than those due to electron-hole scattering.