Electronic properties of Bi nanowaves

Abstract

Transport properties are reported for Bi nanowires, which have been prepared by the filling of an alumina template with molten Bi. Lithographic processes are devised to pattern 4-point electrodes on single Bi nanowires that have been removed from the alumina template. High resistance non-ohmic contacts are attributed to a thick oxide layer formed on the surface of the nanowires. The non-linear 2-point i(V) response of these contacts is understood on the basis of a tunneling model. Techniques are developed for making ohmic contacts to single bismuth nanowires through the thick oxide coating using a focused ion beam (FIB) to sputter away the oxide and then deposit contacts. By combining the FIB techniques with electron beam lithography we achieve contacts stable from 300K to 2K for nanowires less than 100nm in diameter. Annealing in H2 and also NH3 environments is found to reduce the oxide completely. However, the high tempertures required for this annealing are not compatible with the lithographic techniques. A method for preventing the burnout of nanowires by electrostatic discharge is developed. A lithographic scheme for measuring the Seebeck coefficient of a single Bi nanowire is devised. Techniques are also developed for measuring a single Bi nanowire inside the template. The electronic band structure of Bi nanowires is modeled theoretically based on the quantum confinement of electrons. 4-point resistivity data on single Bi nanowires are reported and understood on the basis of the theoretical model of the quantized electronic band structure and considering the wire boundary and grain boundary scattering not present in bulk bismuth.