Bismuth nanowire arrays: Synthesis and galvanomagnetic properties

Abstract

This paper reports galvanomagnetic properties of arrays of single-crystal bismuth nanowires, with diameters of 7 to 200 nm, embedded in an amorphous porous anodic alumina matrix. A sample preparation technique is described that makes it possible to obtain nanowires with diameters below 10 nm. The wires are single crystals, with their long axes oriented in the bisectrix/trigonal plane, about 19° from the bisectrix axis. The temperature dependence $(1.4\mathrm{}\mathrm{K}<~T<~300\mathrm{K})$ of the electrical resistance, longitudinal magnetoresistance $(0\mathrm{}\mathrm{T}<~B<~5\mathrm{T}$ with $1.4<~T<~75\mathrm{K},$ and $0T<~B<~1\mathrm{T}$ with $80<~T<~300\mathrm{K})$ and transverse magnetoresistance $(0\mathrm{}\mathrm{T}<~B<~5\mathrm{T}$ with $1.4<~T<~75\mathrm{K})$ of the nanowires are given. The results extend previous work to wires of narrower diameter, and confirm the existence of the semimetal-semiconductor phase transition seen in the magnetoresistance. The data are discussed qualitatively in terms of the interplay between the electron cyclotron radii, electron scattering on the wire walls, size-induced energy level quantization, and the transfer of carriers between the different carrier pockets of the Fermi surface. Nanowires of Bi are theoretically predicted to have a much higher thermoelectric figure of merit than bulk Bi.