IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Electrochemistry and Fluid-Solid Interfaces Monday Sessions
       Session EC-MoA

Paper EC-MoA6
Electrochemical Deposition of Molybdenum Nanowires for Use as Sensors

Monday, October 29, 2001, 3:40 pm, Room 111

Session: Electrochemical Control of Surface Structure: Growth and Dissolution
Presenter: M.P. Zach, University of California, Irvine
Authors: M.P. Zach, University of California, Irvine
K. Inazu, University of California, Irvine
J.C. Hemminger, University of California, Irvine
R.M. Penner, University of California, Irvine
Correspondent: Click to Email
Electrodeposition of molybdenum dioxide (using the step edges of highly oriented pyrolytic graphite as nucleation templates) is used to form precursor nanowires ranging in diameter from 10 nm to one micron with many exceeding one-half millimeter in length. Subsequent treatment with hydrogen gas above 500°C reduces the wires to conductive metallic molybdenum.@footnote 1@ Currently, this is the only method that exists to create millions of ordered nanowires with such high aspect ratios. A polymer film is used to lift the wires off of the conductive substrate thus isolating the wires electronically. The discovery of a method to deposit nanowires is just the beginning. A sensor device can be made by embedding the reduced wires in a polymer, laying a shadow mask over this array, and sputter-coating gold over the unmasked area. In the end, only the nanowires provide a conductive path across the gap left by the mask. The electronic properties of single wires can also be studied using a gold coated probes. The probes can also manipulate individual wires showing flexibility and mechanical properties of the reduced molybdenum and allowing conductivity measurements of single nanowires. Both the sensors and the single wire probe methods for measuring conductivity show decrease of conductivity as a function of time. Understanding the changes in resistance is imperative if these wires or wires made from other materials are to be integrated in functional devices. TEM, EDAX and XPS measurements have allowed characterization of the re-oxidation process in air. Freshly reduced molybdenum wires, upon exposure to oxygen and/or moisture, start to oxidize yielding thinner molybdenum metal wires with a insulating sheath of molybdenum trioxide. This data is important in order to understand the conduction and analyte adsorption properties of wires used in sensor devices. @FootnoteText@ @footnote 1@M.P. Zach and R.M. Penner, Science, December 15, 2000, 290 (5499) 2120.