Design, Fabrication and Testing of a Novel Gas Sensor utilizing Vertically Aligned Zinc Oxide Nanowire Arrays
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0951-E08-09
Design, Fabrication and Testing of a Novel Gas Sensor Utilizing Vertically Aligned Zinc Oxide Nanowire Arrays Prahalad Parthangal1,2, Richard Cavicchi2, and Michael Zachariah1,2 1 Mechanical Engineering and Chemistry, University of Maryland, College Park, MD, 20742 2 Process Measurements Division, NIST, Gaithersburg, MD, 20899
ABSTRACT We report on a novel, non-destructive, in-situ approach toward connecting and electrically contacting vertically aligned zinc oxide nanowire arrays using conductive gold nanoparticles. A chemical gas-sensing device was constructed and tested using this nanoarchitecture. Well-aligned, single-crystalline zinc oxide nanowires were grown through a direct thermal evaporation process at 550 °C on gold catalyst layers. Electrical contact to the top of the nanowire array was established by creating a contiguous nanoparticle film through electrostatic attachment of conductive gold nanoparticles exclusively onto the tips of nanowires. The gassensing device fabricated through this approach was found to be sensitive to both reducing (methanol) and oxidizing (nitrous oxides) gases. This assembly approach is amenable to any array of one-dimensional nanostructures for which a top contact electrode is needed. INTRODUCTION Despite significant advancements in nanowire (NW) growth techniques and device descriptions, establishment of electrical contacts to NW assemblies through non-destructive methods has not yet been successfully realized. The commonly employed method involves physically removing NWs from the sample, dispersing them in solution, and transferring them onto another surface containing probe pads, and depositing contact electrodes onto individual NWs through some form of lithography. Such a series of steps are not only destructive, but also expensive and tedious. Another method described in the literature involves burying the NW array in an insulating matrix such as spin-on glass or polystyrene, followed by plasma etching to expose the NW tips [1,2]. However, this approach prevents access to the surface of the NWs, which would be necessary for applications like gas sensing. In this paper, we describe a simple method for growing contact electrodes in-situ to the top of a vertically aligned NW assembly by selectively attaching gold nanoparticles to the tips of NWs and forming a continuous film. The electric field enhancements around the sharp tips of NWs as well as their high aspect ratios are exploited in this procedure, which is generic to a wide range of nanomaterials and nanostructures. The result is a device, which is an ensemble of single NW devices connected in parallel. For sensor applications there may be signal to noise advantages in such an arrangement compared to single NW devices. Previous NW-based sensors have involved disordered NW networks, where electrical contact is determined primarily by the contacts between individual NWs [3-6]. In contrast, this new device’s properties reflect the electrical transport along isolated NWs.
ZnO is a wide-bandgap semiconducto
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