Peculiarities of thermopower in Bi microwires at low temperatures

Abstract

The temperature dependence (4.2 -300 K) of the thermopower of thin Bi wires was investigated. The cylindrical Bi crystals ranging in size from 0.19 to 3 µm were prepared by high-frequency liquid-phase casting in a glass capillary. The nanowires are single crystal and are oriented with the (1011) crystalline axis along the wire axis. For temperatures below ~12 K the thermopower is dominated by phonon drag and a maximum is observed at around 6 K. The position of this maximum and its value depends on the wire's diameter and the length of the samples. In the temperature range 8 -11 K the phonon-drag contribution follows an exponential temperature dependence that is characteristic of a two-stage mechanism. The positive thermopower maxima of the order of 10 µV K -1 are explained in terms of the phonon drag of carriers. Several mechanisms that may account for the data are discussed.

Thermoelectric Characterization of Electronic Properties of GaMnAs Nanowires

“…We were able to estimate the hole carrier density from thermopower measurements to be p ∼ 10 17 -10 18 cm −3 in our NW. In addition, we find a dramatic rise in the resistance and thermopower of the NW below 120 K [17][18][19]. The resistance versus temperature measurements point to the role of Mott variable range hopping (VRH) transport with activation energy 62 meV at 100 K and hopping lengths of 11 nm.…”

Diameter-dependent thermopower of bismuth nanowires

“…5,6 Therefore, the electronic transport properties and the thermopower of Bi NWs, specifically, are the subject of intense investigation. [7][8][9][10][11][12][13][14][15][16] With the exception of temperatures below 10 K, [17][18][19][20] the thermopower of bulk Bi is due to the difference in broadening of the Fermi distribution between hot and cold regions of the sample or diffusion thermopower. [21][22][23][24] Because the mobility is larger for electrons than for holes, overall, in bulk samples, the thermopower of bulk Bi is negative.…”

Thermoelectric prospects of nanomaterials with spin-orbit surface bands

“…17 In Bi nanowires, out-of-equilibrium effects like the phonon-drag effect are of negligible importance since phonon scattering is mainly phonon-boundary rather than phonon-carrier. 23 This model for decreased phonon drag has been observed to apply in other cases of thermopower of nanowires, notably sub-100 nm diameter Si point contacts, 24 and Si and Ni nanowires, respectively. 25,26 This is relevant because Equation (1) is not applicable in the case that there are phonon drag effects and also because such nonequilibrium effects limit zT to values that are much less than one.…”