IOP PUBLISHING NANOTECHNOLOGY Nanotechnology 18 (2007) 245305 (6pp) doi:10.1088/0957-4484/18/24/245305 Step-edge like template fabrication of polyelectrolyte supported nickel nanowires Devesh Srivastava, Troy R Hendricks and Ilsoon Lee 1 Department of Chemical Engineering and Materials Science, Michigan State University, 2527 Engineering, East Lansing, MI 48824, USA E-mail: leeil@egr.msu.edu Received 15 March 2007, in final form 18 April 2007 Published 18 May 2007 Online at stacks.iop.org/Nano/18/245305 Abstract A method to produce novel polymer supported nickel nanowires, which are asymmetric (or anisotropic) in shape and function, using an alumina membrane as a template is presented. This paper reports a step-edge like fabrication technique using anodized alumina membranes. First the membrane is treated with fluorosilanes to make the surface completely hydrophobic. It is then cleaved to expose the freshly prepared alumina edges, which are hydrophilic. These freshly cleaved hydrophilic edges are used as templates for the deposition of polyelectrolyte multilayers and nickel. We selectively deposit polyelectrolyte multilayers on those hydrophilic edges. Then the electroless deposition of nickel is used to create nickel nanowires. After dissolving the membranes, we obtain nanostructures which are asymmetric in shape and function. (Some figures in this article are in colour only in the electronic version) 1. Introduction One of the biggest challenges in the field of nanotechnology is the cost-effective fabrication of nanowires. To date there are many methods that use top-down approaches or involving elaborate equipment to form nanowires such as dip-pen [1] and electron beam lithography [2], but both are expensive and slow. Cost-effective methods such as soft-lithography [3, 4] and nanoimprint lithography [5–7] are also being developed. The bottom-up approach involves the self-assembly of molecules based on various interactions such as electrostatic, hydrogen bonding or covalent bonding. It offers a more cost-effective method for the fabrication of nanostructures. It also provides more control over the variety of nanostructures that can be fabricated. Nanowires and nanotubes of various materials have also been fabricated using template assisted techniques such as filling the membrane pores of anodized alumina [8–13], track etched polymer membranes [14, 15] and decoration of step-edges [16–19]. Most methods using membranes as a template involve electrodeposition. This is done by coating one side with a metal to make it conductive, followed by electrodeposition of the metal inside the pores. Electroless methods are slightly more difficult, especially in depositing 1 Author to whom any correspondence should be addressed. metal inside the pores, as the process is hindered by the slow diffusion of metal ions into pores. There are a variety of metals that are being used to make nanowires such as gold [20, 21], copper [22, 23] and silver [24, 25]. Nickel nanowires are also finding great interest among researchers due to there unique magnetic properties. Also at the nanometre scale, quantum confinement leads to unique properties. For example, the band gap of nanowires varies as the inverse square of its diameter [26]. Biological molecules can also be attached to nanowires to form nano- machines [27]. Most fabrication methods for nickel nanowires and nanotubes involve filling pores of membranes [28], step- edge [19] and also using biomolecules such as DNA [29]. In this paper, we report a step-edge like methodology for the fabrication of polyelectrolyte supported nanowires. Polyelectrolytes provide flexible support to metallic nanowires and prevent them from falling apart. Our method is simple, can be performed on a lab-bench top and does not require any equipment for metal deposition. In our method an alumina membrane was functionalized with hydrophobic molecules and then broken to expose freshly cleaved hydrophilic edges along the broken pore walls. Then, polyelectrolyte multilayers (PEMs) were built on the hydrophilic edge of the pore membrane and an electroless nickel bath was used for the deposition of nickel onto the multilayers to form nickel 0957-4484/07/245305+06$30.00 1 © 2007 IOP Publishing Ltd Printed in the UK