Modeling thermoelectric behavior in Bi nano-wires

The small effective mass of Bi and high anisotropy of its Fermi surface make Bi nano-wires an excellent system for studying quantum confinement effects on the transport properties of a quasi one-dimensional (1D) electron gas, such as the electrical conductivity, magnetoresistance, thermoelectric power, and thermal conductivity. A theoretical model based on the basic band structure of bulk Bi, suitably modified for the 1D situation, is developed to predict the dependence of these quantities on wire diameter, temperature and crystalline orientation of the Bi nano-wires. Experiments have been carried out on ultra-fine single-crystalline Bi nano-wires (10-120 nm in diameter) with packing densities as high as 7×10¹⁰ nanowires/cm² to test the quantum confinement assumptions of the model. Strong experimental evidence has been observed for an interesting quantum confinement-induced semimetal-to-semiconductor transition in Bi nano-wires with diameters less than 100 nm.