Prospects for bismuth nanowires as thermoelectrics

The small effective mass of Bi, high anisotropy of its Fermi surface, and the high aspect ratio (length/diameter) of Bi nanowires make this an excellent system for studying quantum confinement effects of a one-dimensional (1D) electron gas in relation to electrical conductivity, thermoelectric power, and thermal conductivity. A theoretical model based on the basic electronic band structure of bulk Bi is suitably modified to describe 1D bismuth nanowires and is used to predict the dependence of these transport properties on nanowire diameter, temperature and crystalline orientation of the bismuth nanowires. Experiments have been carried out on ultra-fine single crystal Bi nanowires (10-120 nm diameter) with a packing density as high as 7 x 10(10) wires/cm(2) to test the quantum confinement assumptions of the model and the occurrence of a quantum confinement-induced semimetal-to-semiconductor transition as the wire diameter becomes less than 100 nm. Prospects for the use of bismuth nanowires for thermoelectric applications are discussed.