INSTITUTE OF PHYSICS PUBLISHING NANOTECHNOLOGY Nanotechnology 17 (2006) 1922–1926 doi:10.1088/0957-4484/17/8/020 Electrochemical fabrication of single-crystalline and polycrystalline Au nanowires: the influence of deposition parameters J Liu 1 , J L Duan 1 , M E Toimil-Molares 2 , S Karim 3 , T W Cornelius 2 , D Dobrev 2 , H J Yao 1 , Y M Sun 1 , M D Hou 1 , D Mo 1 , Z G Wang 1 and R Neumann 2 1 Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, People’s Republic of China 2 Gesellschaft f¨ ur Schwerionenforschung (GSI), Darmstadt, Germany 3 Department of Chemistry, Philipps University, Marburg, Germany E-mail: j.liu@impcas.ac.cn Received 15 December 2005 Published 15 March 2006 Online at stacks.iop.org/Nano/17/1922 Abstract We report the electrochemical growth of gold nanowires with controlled dimensions and crystallinity. By systematically varying the deposition conditions, both polycrystalline and single-crystalline wires with diameters between 20 and 100 nm are successfully synthesized in etched ion-track membranes. The nanowires are characterized using scanning electron microscopy, high resolution transmission electron microscopy, scanning tunnelling microscopy and x-ray diffraction. The influence of the deposition parameters, especially those of the electrolyte, on the nanowire structure is investigated. Gold sulfite electrolytes lead to polycrystalline structure at the temperatures and voltages employed. In contrast, gold cyanide solution favours the growth of single crystals at temperatures between 50 and 65 ◦ C under both direct current and reverse pulse current deposition conditions. The single-crystalline wires possess a [110] preferred orientation. 1. Introduction Research on nanowires is currently motivated by the novel size-dependent properties of nanostructures and by their promising technological applications in fields such as electronics, optoelectronics, and chemical and biological sensors [1–6]. Gold possesses, in particular, very good electrical and thermal conductivity, high ductility and chemical inertness, all these characteristics being important for the fabrication of reliable electrical nanocontacts. Thanks to its specific chemical properties, gold enables the creation of nanowires with chemically inert walls, which can be suitably modified for attaching various chemical ligands or biomolecules. Nanowires altered in this way may be used as sensors [7] or spectroscopic probes [8]. A number of different methods for producing gold nanowires have been reported up to now, comprising electroless deposition in the channels of mesoporous silica thin films [9], assembly of gold nanoparticles [10], microwave synthesis [11] and lithography [12]. However, these techniques lead in most cases to polycrystalline structures, and do not allow the control of the crystallographic properties of the wires. The maximal aspect ratio is also limited in all cases. Since the electrical, thermal and mechanical properties of the wires depend strongly on their crystallographic and morphological characteristics, further synthesis techniques are needed to fabricate nanostructures with well-controlled crys- tallinity. The template method, i.e. filling the pores of a host membrane with a certain material, is suitable for this purpose. In the recent past, nanowires of various metals, semiconduc- 0957-4484/06/081922+05$30.00 © 2006 IOP Publishing Ltd Printed in the UK 1922