Confinement effects and surface-induced charge carriers in Bi quantum wires

Abstract

We present measurements of Shubnikov-de Haas oscillations in arrays of bismuth nanowires. For 80-nm wires, the hole concentration is less than 30% of that for bulk Bi, a finding that is consistent with current models of quantum confinement effects. However, 30-nm-diameter nanowires, which are predicted to be semiconductors, show a nearly isotropic short period of 0.025 T -1 , consistent with a heavy carrier concentration five times that of bulk Bi. These results are discussed in terms of surface-induced charge carriers in a spherical Fermi surface pocket that are uniformly distributed in the 30-nm nanowire volume and that inhibit the semimetal-tosemiconductor transition.

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

“…However, In the case of the semimetal Bi, the metallic and semiconducting characteristics coexist because of the small carrier concentration of Bi (2.7 × 10 17 -3.0 × 10 18 cm −3 at 2-300 K). 5,7,12,15 The temperature dependence of the resistance is determined by the competition between the mobility and the carrier concentration. 7,12,14 Moreover, in Bi NWs, the mobility could be varied not only by the carrier scattering from the non-specular surface but also by the strong coupling effect in the L-point sub-bands.…”

“…For small diameters (d < 30 nm), however, the temperature dependence of resistance returned to metallic. In Bi NWs [12][13][14]16 and Bi thin films 31,32 with dimensions below 50 nm, the metallic surface-state effects reportedly influence the bulk characteristics owing to their large surface/ volume ratio and SMSC transition. In the Bi NWs along the [100] direction, the critical diameter was found to be less than 40 nm.…”

“…Alternatively, Huber et al fabricated arraytype [12][13][14] and individual 15,16 single-crystalline Bi NWs using the AAO templates and the Ulitovsky method, respectively. These NWs with diameters less than 50 nm displayed transport properties, which were predominantly governed by surface states, including electrical conductivity and the Seebeck coefficient, in quantum oscillations such as Shubnikov-de Haas (SdH) 12,13 and Aharonov-Bohm 16 oscillations. However, the maximum measured Seebeck coefficient 14,15 was similar to the value in bulk Bi (2004Bi ( -2011.…”

Electronic structure and Fermi surface of Bi(100)

“…Similar surface states could inhibit predicted 8 semimetal-to-semiconductor transitions in Bi nanowires. 9 With the use of Fig. 6, one can try to construct the Fermi surface from the calculated band structure and compare it with the measured plot in Fig.…”

“…Such interesting changes of the electronic structure have indeed been predicted and observed for thin films, [3][4][5] clusters, 6 and nanotubes. [7][8][9] Other cases in which structural changes can be expected to lead to interesting consequences for the electronic structure are the surfaces of Bi. For the surface orientations studied so far, ͑110͒ and ͑111͒, the surface is a much better metal than the bulk due to the presence of electronic surface states.…”