Thermopower of Bi Nanowire Array Composites
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Thermopower of Bi Nanowire Array Composites. T.E. Hubera, M.J. Grafb, C.A. Foss, Jr.c , and P. Constanta. a Laser Research, Howard University, Washington, DC 20059, b Department of Physics, Boston College, Chestnut Hill, MA 02467, c Department of Chemistry, Georgetown University, Washington, DC 20059. The small effective mass and high mobility of electrons in Bi, make Bi nanowires a promising system for thermoelectric applications. Dense arrays of 20-200 nm diameter Bi nanowires were fabricated by high pressure injection of the melt. Transport properties and Seebeck coefficient were investigated for Bi nanowires with various wire diameters as a function of temperature (1 K < T < 300 K) and magnetic fields (B< 0.6 T). We discuss the problem of the contact resistance of Bi nanowire arrays.
INTRODUCTION Progress in the study of 1D quantum wire systems has been slow due to the difficulty of fabricating such materials. Since Bi has the smallest electron effective mass among all known materials, quantum confinement effects in Bi are more manifest and can be observed in nanowires of larger diameter than those of any other nanowire material. One technique that is known to be applicable to the problem of fabricating Bi nanowires, and that yields an array of ultrafine nanowires embedded in a porous dielectric template is the high-pressure injection (HPI) of the conducting melt [1] in porous templates. This technique has been applied to fabricate a variety of metal and semiconductor nanowire arrays [2] in insulating porous matrices. The HPI technique was succesfully applied by Gurvitch [3] to the synthesis of single nanowires of Bi in glass pipes. Recently , the HPI technique has been employed has been employed to fabricate fine Bi nanowire arrays for thermoelectric applications [4,5,6,7]. For such applications, it is important to minimize the template contribution to the thermal conductivity and therefore only samples with very high Bi content, such as wire arrays or networks are of interest. Bulk Bi, a semimetal, and Bi-Sb, a semiconducting alloy, have the highest thermoelectric figure-of-merit Z at 100 K. Quantum size effects are predicted to result in an enhancement of Z for fine wires. Bogachek, Scherbakov and Landman [8] studied theoretically the quantum transport in 3D nanowires. For small diameter wires they predict conductance quantization that is manifest by the step-like behavior of the conductance and the appearance of thermopower peaks as a function of constriction diameter. Hicks and Dresselhaus [9] have predicted an enhancement for 1D conductors. These effects are expected to become very relevant for Bi wire diameters d< 30 nm.
Z14.2.1 Downloaded from https://www.cambridge.org/core. Rice University, on 02 Feb 2020 at 21:34:53, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-626-Z14.2
EXPERIMENTS In this work we use porous anodic aluminium oxide (PAAO) templates. These materials support an array of parallel, largely non-interconnected
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