Paper NS-TuP14
Segmented Nanowire Fabrication Through Templated Electrodeposition

Tuesday, October 16, 2007, 6:00 pm, Room 4C

Metal oxide nanowires have recently attracted considerable attention in electrochemical sensing. Templated electrodeposition of metals within porous aluminum oxide (PAO) membranes has proven to be a simple and reliable method of nanowire synthesis.¹ The PAO self ordered pore array consists of honeycomb packed hexagonal cells with central cylindrical pores. Pore diameters exhibit high uniformity across the membrane can be easily tailored from 4 to 400 nm, while a pore depth of several hundred nanometers has been achieved. Electrodeopsition of WO₃ has been explored for its electrochromic effects. Application of WO₃ to gas sensing was first explored by Reyes et al.² We here report on the development of WO₃ segmented nanowires for chemical sensing. The basic layout of these sensing structures consists of a short metal oxide segment intercalated between gold electrical contacts. During the initial step, a 500 nm silver layer is sputtered onto the back of Whatman Anodisc 25 PAO filters. The resistive nature of aluminum oxide forces wire growth to initiate at the seeding layer, the deepest point within each pore, and continue towards the surface of the membrane. Silver (Technic Inc. Cy-less Silver RTU Plating solution) is backfilled into the pores and acts as a sacrificial contact, restricting gold and metal oxide growth to a uniform portion of the membrane. 3 µm of gold is subsequently deposited from Techni-Gold 25 E (Technic Inc.) at a current density of 250 µm/cm². A 0.1 molar aqueous sodium tungstate (Na₂WO₃) solution is then prepared and subsequently deposited at 0.5 mA/cm². Plating is completed with a final 3 µm Au deposition. The resulting wires are then released by selective etching of the silver seeding layer and the porous alumina template. Extensive structural characterization of these nanowires using XPS, SEM and Auger will be presented. We plan to present both morphological material analysis as well as preliminary electrical response and chemical sensing results.

¹ A. Kolmakov, Y. Zhang, G. Cheng, M. Moskovits, "Detection of CO and O2 using tin oxide nanowire sensors", Adv. Mater. 15(12), 997-1000 (2003).
² L.F. Reyes, A. Hoel, S Saukko, P. Heszler, V. Lantto, C.G. Granqvist, "Gas sensors of pure and activated WO3 nanoparticle films made by advanced reactive gas deposition", Sensors and Actuators B 117, 128-134 (2006).