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 KрTр300 K) of the electrical resistance, longitudinal magnetoresistance (0 TрBр5 T with 1.4рTр75 K, and 0TрBр1 T with 80рTр300 K͒ and transverse magnetoresistance ͑0 TрBр5 T with 1.4рTр75 K͒ 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.

Diameter-dependent thermoelectric figure of merit in single-crystalline Bi nanowires

“…In particular, single-crystalline Bi has been considered as a potential thermoelectric material for nanostructures because of its unusual intrinsic properties, 3,4 i.e., its anisotropic Fermi pocket (L-point electron and T-point hole pocket in the Brillouin zone), 4 small band overlap (38 meV), 5 small effective mass (∼0.001 m e ), 6 long mean free path (MFP ∼ 1 mm), 7 and large Fermi wavelength (∼70 nm). 8 These properties cause the semimetal-to-semiconductor (SMSC) transition to occur more easily (diameter < 50 nm), compared to conventional metals.…”

Spontaneous growth of bismuth nanowires on a sputter-deposited thin bismuth film

“…Pressure injection can result in single crystal nanowires grown along the length of the alumina template, but requires dissolving the template and manipulation of the solution in order to obtain single, separated nanowires [16]. Similar methods using electro-deposition have also been very successful [17,18,5] and good-quality nanowires have been manufactured by a template-free process [19].…”

“…Secondly, conduction electrons in bismuth have a very small effective mass. Thirdly they have a long carrier mean free path (~100 nm at 300 K and ~400 μm at 4 K) [2] and finally the wavelength of electrons at the Fermi level is very long giving rise to more prominent quantum confinement effects in bismuth nanowires than in other materials. Bismuth has a small band overlap energy between its L-point conduction band and T-point valence band (38 meV at 77 K) [3], anisotropic Fermi surface [4], low density of states [5] and high carrier mobility [6].…”

Low-Dimensional Thermoelectricity

“…The data from aligned anodic Al 2 O 3 composites with d ≥ 38 nm are from Ref. [29], those in composites with d ≤ 15 nm from [31] for the various diameters indicated. Two distinct behaviors are observed.…”

“…Two distinct behaviors are observed. [29]; the data on wires of diameters 15 nm are on composites based on porous SiO 2 or Al2O3 with random pores (after Ref. [31]).…”