Template Synthesis and Electronic Properties of Bismuth Quantum Wire Arrays and Networks

Howard University, Washington DC

Investigators

Abstract

This experimental condensed matter physics project addresses the transport properties of quantum wires (i.e. wires with diameter smaller than the Fermi wavelength). While the theory of such wires is relatively well developed, the experimental situation is less explored, due to the difficulty of fabricating and characterizing such materials. The project focuses on quantum wires of the semimetal bismuth, which is unique because its extremely small effective mass leads to an unusually long Fermi wavelength, 25 nm. Consequently, quantum confinement effects should be readily observed in nanowires whose diameter are below about 25 nm. High-pressure, high-temperature melt injection templates will be used to make arrays and networks of bismuth wires of diameters down to 6 nm. The semimetal-to-semiconductor transition, doping effects, localization, and mesoscopic phenomena will be probed via optical measurements and low-temperature magnetic-field-dependent electronic transport measurements. An important feature of the work is the use of a scanning force microscope with electric force capability for visualization and testing of the nanowires. The research will be carried out by undergraduates from Howard University, Boston College, and Georgetown University. These students will receive scientific training in cutting edge experimental techniques that will prepare them for careers in academe, industry and government. %%% This project is directed at developing a more complete understanding of the properties of ultra-fine nanowires, which are expected to have many applications as electronic circuitry becomes more compact. While several theories of these nanowires have been developed, experimental studies are lacking due to the difficulty of fabricating wires in this so-called quantum regime. In this work, closely packed nanowire arrays and networks will be fabricated by injecting molten bismuth metal under high pressures into porous template materials, where it is subsequently cooled and solidified. Wire diameters down to 6 nm can be achieved with this technique. The optical and electronic transport properties will be measured and comparisons to the various theoretical predictions will be carried out. An important feature of the work is the utilization of a scanning force microscope with electric force capability for visualization and testing of the nanowires. This collaboration between a historically-black university and two collaborating universities will directly impact over 15 undergraduate students who will receive rigorous training in Physics, Chemistry and Materials. Through the interdisciplinary and inter-university character of this program, students will gain a fuller understanding of the scientific enterprise. ***