Bismuth nanowire arrays: Synthesis and galvanomagnetic properties

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. 4K<~T<~300K) of the electrical resistance, longitudinal magnetoresistance (0T<~B<~5T with 1. 4<~T<~75K, and 0T<~B<~1T with 80<~T<~300K) and transverse magnetoresistance (0T<~B<~5T with 1. 4<~T<~75K) 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.