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Comparison of NO2 gas sensing properties of three different ZnO nanostructuressynthesized by on-chip low-temperature hydrothermal growth
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Three different ZnO nanostructures, dense nanorods, dense nanowires, and sparsenanowires, were synthesized between Pt electrodes by on-chip hydrothermal growth at90 °C and below. The three nanostructures were characterized by scanning electronmicroscopy and X-ray diffraction to identify their morphologies and crystal structures.The three ZnO nanostructures were confirmed to have the same crystal type, but theirdimensions and densities differed. The NO2 gas-sensing performance of the threeZnO nanostructures was investigated at different operation temperatures. ZnOnanorods had the lowest response to NO2 along with the longest response/recoverytime, whereas sparse ZnO nanowires had the highest response to NO2 and theshortest response/recovery time. Sparse ZnO nanowires also performed best at 300°C and still work well and fast at 200 °C. The current-voltage curves of the three ZnOnanostructures were obtained at various temperatures, and results clearly showed thatsparse ZnO nanowires did not have the linear characteristics of the others. Analysis ofthis phenomenon in connection with the highly sensitive behavior of sparse ZnOnanowires is also presented.

National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:uu:diva-320153OAI: oai:DiVA.org:uu-320153DiVA: diva2:1088832
Available from: 2017-04-16 Created: 2017-04-16 Last updated: 2017-04-24
In thesis
1. Microfabricated Gas Sensors Based on Hydrothermally Grown 1-D ZnO Nanostructures
Open this publication in new window or tab >>Microfabricated Gas Sensors Based on Hydrothermally Grown 1-D ZnO Nanostructures
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, gas sensors based on on-chip hydrothermally grown 1-D zinc oxide (ZnO) nanostructures are presented, to improve the sensitivity, selectivity, and stability of the gas sensors.

Metal-oxide-semiconductor (MOS) gas sensors are well-established tools for the monitoring of air quality indoors and outdoors. In recent years, the use of 1-D metal oxide nanostructures for sensing toxic gases, such as nitrogen dioxide, ammonia, and hydrogen, has gained significant attention. However, low-dimensional nanorod (NR) gas sensors can be enhanced further. Most works synthesize the NRs first and then transfer them onto electrodes to produce gas sensors, thereby resulting in large batch-to-batch difference.

Therefore, in this thesis six studies on 1-D ZnO NR gas sensors were carried out. First, ultrathin secondary ZnO nanowires (NWs) were successfully grown on a silicon substrate. Second, an on-chip hydrothermally grown ZnO NR gas sensor was developed on a glass substrate. Its performance with regard to sensing nitrogen dioxide and three reductive gases, namely, ethanol, hydrogen, and ammonia, was tested. Third, three 1-D ZnO nanostructures, namely, ZnO NRs, dense ZnO NWs, and sparse ZnO NWs, were synthesized and tested toward nitrogen dioxide. Fourth, hydrothermally grown ZnO NRs, chemical vapor deposited ZnO NWs, and thermal deposited ZnO nanoparticles (NPs) were tested toward ethanol. Fifth, the effect of annealing on the sensitivity and stability of ZnO NR gas sensors was examined. Sixth, ZnO NRs were decorated with palladium oxide NPs and tested toward hydrogen at high temperature.

The following conclusions can be drawn from the work in this thesis: 1) ZnO NWs can be obtained by using a precursor at low concentration, temperature of 90 °C, and long reaction time. 2) ZnO NR gas sensors have better selectivity to nitrogen dioxide compared with ethanol, ammonia, and hydrogen. 3) Sparse ZnO NWs are highly sensitive to nitrogen dioxide compared with dense ZnO NWs and ZnO NRs. 4) ZnO NPs have the highest sensitivity to ethanol compared with dense ZnO NWs and ZnO NRs. The sensitivity of the NPs is due to their small grain sizes and large surface areas. 5) ZnO NRs annealed at 600 °C have lower sensitivity toward nitrogen dioxide but higher long-term stability compared with those annealed at 400 °C. 6) When decorated with palladium oxide, both materials form alloy at a temperature higher than 350 °C and decrease the amount of ZnO, which is the sensing material toward hydrogen. Thus, controlling the amount of palladium oxide on ZnO NRs is necessary.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 60 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1513
Keyword
gas sensor, zinc oxide, on-chip, hydrothermal growth, nanorods, nanowires, annealing, palladium oxide, photoluminescence, alloy, sensitivity, selectivity, stability
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:uu:diva-320183 (URN)978-91-554-9908-2 (ISBN)
Public defence
2017-06-09, 2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
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Available from: 2017-05-16 Created: 2017-04-17 Last updated: 2017-06-07

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