INSTITUTE OF PHYSICS PUBLISHING NANOTECHNOLOGY Nanotechnology 13 (2002) 1–6 PII: S0957-4484(02)39918-5 Making electrical contacts to nanowires with a thick oxide coating Stephen B Cronin 1 , Yu-Ming Lin 2 , Oded Rabin 3 , Marcie R Black 2 , Jackie Y Ying 4 , Mildred S Dresselhaus 1,2 , Pratibha L Gai 5 , Jean-Paul Minet 6 and Jean-Paul Issi 6 1 Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA 2 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA 3 Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA 4 Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA 5 Dupont Central Research and Development, Wilmington, DE 19880, UK 6 Unit´ e PCPM, CERMIN, Universit´ e Catholique de Louvain, Louvain-la-Neuve, Belgium E-mail: millie@mgm.mit.edu Received 24 July 2002, in final form 27 August 2002 Published Online at stacks.iop.org/Nano/13/1 Abstract Techniques are presented for making ohmic contacts to nanowires with a thick oxide coating. Although experiments were carried out on Bi nanowires, the techniques described in this paper are generally applicable to other nanowire systems. Metal electrodes are patterned to individual Bi nanowires using electron beam lithography. Imaging the chemical reaction on the atomic scale with in situ high-resolution transmission electron microscope shows that annealing in H 2 or NH 3 can reduce the nanowires’ oxide coating completely. The high temperatures required for this annealing, however, are not compatible with the lithographic techniques. Low-resistance ohmic contacts to individual bismuth nanowires are achieved using a focused ion beam (FIB) to first sputter away the oxide layer and then deposit Pt contacts. By combining electron beam lithography and FIB techniques, ohmic contacts stable from 2 to 400 K are successfully made to the nanowires. A method for preventing the burnout of nanowires from electrostatic discharge is also developed. (Some figures in this article are in colour only in the electronic version) Processing/NAN/na139918-xsl/PAP Printed 4/9/2002 Issue no Total pages First page Last page File name NA .TEX Date req (Ed: EMILY) 1. Introduction The fabrication of nanowires within porous alumina templates has recently become a very popular area of research. During Q.1 the past few years, researchers have filled these templates with a number of materials ranging from carbon nanotubes to superconductors and magnetic materials [1–3]. Our motivation for studying the Bi nanowire system is based on the unique properties of bulk Bi. In particular, the very long mean free path in bulk Bi (∼0.4 mm at 4 K and 100 nm at 300 K) makes the Bi nanowires a suitable system for the study of low-dimensional transport phenomena. Since the diameter of the nanowires is much smaller than the mean free path of the electrons, the electrons will be confined by the boundary of the nanowire, thereby resulting in a reduction in mean free path as the wire diameter decreases. Also, the small effective masses of Bi (which are as small as 0.001m e ) result in very pronounced quantum size effects [4]. For these reasons, the Bi nanowire system is attractive for the fundamental investigation of classical and quantum size effects that are becoming more and more relevant to the semiconductor industry as devices become smaller and smaller. 0957-4484/02/000001+06$30.00 © 2002 IOP Publishing Ltd Printed in the UK 1