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Title: Scanning tunnelling microscopy/spectroscopy and X-ray photoelectron spectroscopy investigations of nanocrystalline tin dioxide gas sensors
Author: Owen, G. T.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2004
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Gas sensors fabricated from Tin Dioxide (SnO2) nanoparticles were studied in UHV environments using scanning tunnelling microscopy/spectroscopy (STM/S) and x-ray photoelectron spectroscopy in an attempt to mimic real working conditions. The sensor fabrication process was investigated, where it was determined that the optimum condition for the formation of sintering necks between consecutive grains was at a firing temperature of 400oC for 20 minutes. The effect of introducing oxygen and reducing gases (CH4, CO) was studied at both room and elevated temperatures using XPS and resistance measurements; where chemisorption of these gaseous species caused upward bandbending of 0.2eV upon O2 exposure followed by a 0.1eV bandbending decrease as reducing gases were introduced. Respective resistance variations of 50MΩ and 20MΩ were observed upon exposure to these gases. Simultaneous use of STM and STS techniques revealed the apparent surface band gap measured by STS was significantly narrower at nanoparticles boundaries than at centres. Changes in the conduction band edge position were much more pronounced than for the valence band and were mostly responsible for the variation in band gap. The preferential chemisorption of oxygen at sintering necks causing an increase in surface state density has been suggested as a possible interpretation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available