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Nanoscale Metal Oxide Semiconductors for Gas SensingA report describes the fabrication and testing of nanoscale metal oxide semiconductors (MOSs) for gas and chemical sensing. This document examines the relationship between processing approaches and resulting sensor behavior. This is a core question related to a range of applications of nanotechnology and a number of different synthesis methods are discussed: thermal evaporation- condensation (TEC), controlled oxidation, and electrospinning. Advantages and limitations of each technique are listed, providing a processing overview to developers of nanotechnology- based systems. The results of a significant amount of testing and comparison are also described. A comparison is made between SnO2, ZnO, and TiO2 single-crystal nanowires and SnO2 polycrystalline nanofibers for gas sensing. The TECsynthesized single-crystal nanowires offer uniform crystal surfaces, resistance to sintering, and their synthesis may be done apart from the substrate. The TECproduced nanowire response is very low, even at the operating temperature of 200 C. In contrast, the electrospun polycrystalline nanofiber response is high, suggesting that junction potentials are superior to a continuous surface depletion layer as a transduction mechanism for chemisorption. Using a catalyst deposited upon the surface in the form of nanoparticles yields dramatic gains in sensitivity for both nanostructured, one-dimensional forms. For the nanowire materials, the response magnitude and response rate uniformly increase with increasing operating temperature. Such changes are interpreted in terms of accelerated surface diffusional processes, yielding greater access to chemisorbed oxygen species and faster dissociative chemisorption, respectively. Regardless of operating temperature, sensitivity of the nanofibers is a factor of 10 to 100 greater than that of nanowires with the same catalyst for the same test condition. In summary, nanostructure appears critical to governing the reactivity, as measured by electrical resistance of these SnO2 nanomaterials towards reducing gases. With regard to the sensitivity of the different nascent nanostructures, the electrospun nanofibers appear preferable
Document ID
20110012204
Acquisition Source
Glenn Research Center
Document Type
Other - NASA Tech Brief
External Source(s)
http://www.techbriefs.com/component/content/article/9152
Authors
Hunter, Gary W. (NASA Glenn Research Center Cleveland, OH, United States)
Evans, Laura (NASA Glenn Research Center Cleveland, OH, United States)
Xu, Jennifer C. (NASA Glenn Research Center Cleveland, OH, United States)
VanderWal, Randy L. (Pennsylvania State Univ. PA, United States)
Berger, Gordon M. (National Center for Space Exploration Research on Fluids and Combustion Cleveland, OH, United States)
Kulis, Michael J. (National Center for Space Exploration Research on Fluids and Combustion Cleveland, OH, United States)
Date Acquired
August 25, 2013
Publication Date
February 1, 2011
Publication Information
Publication: NASA Tech Briefs, February 2011
Subject Category
Man/System Technology And Life Support
Report/Patent Number
LEW-18492-1
Distribution Limits
Public
Copyright
Public Use Permitted.

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IDRelationTitle20110012198Collected WorksNASA Tech Briefs, February 2011
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