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Electrical Properties of Nanocrystalline WO3 for Gas Sensing Applications
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Tungsten trioxide is a material with a variety of application areas. For example, the material is used within thin film technologies as electrochromic material in smart windows, as electrochemically functional material in thermal control applications or as active layer in gas sensing application. Metal-oxide semiconductor gas sensors are of significant interest to detect toxic and hazardous gases. The use of small and cheep sensors is preferable since a large number of sensors easily can be placed at different sites to monitor the concentration of different species without involving huge investments.

In this work, WO3 nanoparticle films were produced using an advanced gas deposition unit for gas sensing applications. The structure of the WO3 nanoparticle films was determined using X-ray diffraction, neutron scattering, X-ray photoelectron spectroscopy, elastic recoil detection analysis and electron microscopy. The as deposited films consist of sub-stoichiometric WO3 and exhibit a large degree of porosity, which together with the small particle size of about 5 nm results in a large surface area and therefore excellent prospects for gas sensor applications.

Investigations on the optical properties and temperature dependence of the resistance indicate hopping conduction in the WO3 films. The bandgaps for tetragonal and monoclinic WO3 were found to be direct, which is in accordance with band structure calculations.

Sensor properties were investigated using resistance measurements upon test gas exposures. The experiments were performed at fixed operating temperatures as well as on temperature modulated sensors. The films of WO3 showed excellent sensitivity to H2S gas and selectivity to other gases. The responses of temperature modulated sensors were further analyzed using mathematical transformations and pattern recognition methods whereby different gases could be distinguished.

We also present a sensing technique using conduction noise as a tool for detection of alcohol vapor. The relative change of the noise, due to the inserted alcohol, can be as large as two orders of magnitude.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2004. , p. 86
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 948
Keywords [en]
Engineering physics, Nanoparticle, Gas sensors, Tungsten trioxide
Keywords [sv]
Teknisk fysik
National Category
Other Engineering and Technologies
Identifiers
URN: urn:nbn:se:uu:diva-4051ISBN: 91-554-5894-7 (print)OAI: oai:DiVA.org:uu-4051DiVA, id: diva2:164180
Public defence
2004-03-26, Polhemsalen, Ångström Laboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30
Opponent
Supervisors
Available from: 2004-03-03 Created: 2004-03-03Bibliographically approved
List of papers
1. Current and voltage noise in WO3 nanoparticle films
Open this publication in new window or tab >>Current and voltage noise in WO3 nanoparticle films
2002 In: Journal of Applied Physics, Vol. 91, p. 5221-5226Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-91441 (URN)
Available from: 2004-03-03 Created: 2004-03-03Bibliographically approved
2. Conduction invasion noise in nanoparticle WO3/Au thin-film devices for gas sensing application
Open this publication in new window or tab >>Conduction invasion noise in nanoparticle WO3/Au thin-film devices for gas sensing application
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2002 In: Smart Materials and Structures, Vol. 11, p. 640-644Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-91442 (URN)
Available from: 2004-03-03 Created: 2004-03-03Bibliographically approved
3. Gas sensing properties of nanocrystalline WO3 films made by advanced reactive gas deposition
Open this publication in new window or tab >>Gas sensing properties of nanocrystalline WO3 films made by advanced reactive gas deposition
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2001 In: Journal of the American Ceramic Society, Vol. 84, p. 1504-1508Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-91443 (URN)
Available from: 2004-03-03 Created: 2004-03-03Bibliographically approved
4. Gas sensing properties of films consisting of nanocrystalline WO3 and Pd made by advanced reactive gas deposition
Open this publication in new window or tab >>Gas sensing properties of films consisting of nanocrystalline WO3 and Pd made by advanced reactive gas deposition
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In: Sensors and ActuatorsArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-91444 (URN)
Available from: 2004-03-03 Created: 2004-03-03Bibliographically approved
5. Gas sensor response of pure and activated WO3 nanoparticle films made by advanced reactive gas deposition
Open this publication in new window or tab >>Gas sensor response of pure and activated WO3 nanoparticle films made by advanced reactive gas deposition
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2006 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 117, no 1, p. 128-134Article in journal (Refereed) Published
Abstract [en]

Pure and activated (doped) nanocrystalline WO3 films, produced by advanced reactive gas deposition, were investigated for gas sensing applications. Activation took place by co-evaporation of Al or Au with tungsten oxide as the particles were produced. Structural characterization of the films was performed by electron microscopy and X-ray diffractometry. Sensitivity, response time, and recovery time of the sensors were systematically investigated as a function of annealing and operating temperature, using H2S, CO, and NO, as test gases. The sensitivity was found to lie below and around the ppm level for H2S and NO2, respectively.

Keywords
microstructure, electrical properties, WO3, Au, sensor
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-91445 (URN)10.1016/j.snb.2005.11.008 (DOI)000239255400018 ()
Available from: 2004-03-03 Created: 2004-03-03 Last updated: 2017-12-14Bibliographically approved
6. Low level detection of ethanol and H2S with a WO3 nanoparticle gas sensor driven by square voltages
Open this publication in new window or tab >>Low level detection of ethanol and H2S with a WO3 nanoparticle gas sensor driven by square voltages
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In: Sensors and ActuatorsArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-91446 (URN)
Available from: 2004-03-03 Created: 2004-03-03Bibliographically approved
7. Small Polaron Formation in Purous WO3-x Nanoparticle Films
Open this publication in new window or tab >>Small Polaron Formation in Purous WO3-x Nanoparticle Films
In: Journal of Applied PhysicsArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-91447 (URN)
Available from: 2004-03-03 Created: 2004-03-03Bibliographically approved

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