Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Microfabricated Gas Sensors Based on Hydrothermally Grown 1-D ZnO Nanostructures
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
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 [en]
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: urn:nbn:se:uu:diva-320183ISBN: 978-91-554-9908-2 (print)OAI: oai:DiVA.org:uu-320183DiVA: diva2:1088876
Public defence
2017-06-09, 2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-05-16 Created: 2017-04-17 Last updated: 2017-06-07
List of papers
1. Controlled Synthesis and Understanding of GrowthMechanism: Parameters for Atmospheric PressureHydrothermal Synthesis of Ultrathin SecondaryZnO Nanowires
Open this publication in new window or tab >>Controlled Synthesis and Understanding of GrowthMechanism: Parameters for Atmospheric PressureHydrothermal Synthesis of Ultrathin SecondaryZnO Nanowires
Show others...
2016 (English)In: Journal of Scientific Research and Reports, ISSN 2320-0227, E-ISSN 2320-0227, Vol. 9, no 5, 1-10 p.Article in journal (Refereed) Published
Abstract [en]

Synthesis of ultrathin ZnO nanowires gains great attention from research community because oftheir large potential in applications involving optoelectronics and sensors. In this study, a lowpressure and low-temperature hydrothermal synthesis of ultrathin ZnO nanowires is studied tounderstand the growth mechanisms better. To achieve this aim, an about 10 nm thin Zn seed layerwas sputter-deposited on a silicon (100) wafer for the hydrothermal growth of ZnO nanowires in anequimolar aqueous solution of Zn(NO3)2 and hexamethylenetetramine. X-ray diffraction analysis confirmed that the Zn layer was self-oxidized into ZnO in air soon after deposition and thenfunctioned as the seed for the preferred growth of c-oriented ZnO nanorods. Different growthconditions were investigated to identify how concentration, temperature, and time influence the finalmorphology of the synthesized ZnO nanostructures. It was found that under the atmosphericpressure, concentration and temperature have to be higher than 0.0025 M and 50°C, respectively,for the ZnO nanorods to nucleate and grow densely. Low concentration gives sparse and randomlyoriented nanorods, whereas high concentration gives dense and vertical nanorods. Ultrathin ZnOsecondary nanowires with an average diameter of less than 20 nm were successfully synthesizedin a solution with concentration of 0.005 M at 90°C for about 16 h. By analyzing the scanningelectron microscopy images of the ZnO nanostructures obtained at different growth conditions, amechanism is proposed for the growth of the ultrathin secondary ZnO nanowires. This findingprovides a cost-effective and straightforward pathway to prepare ultrathin ZnO nanowires.

Keyword
ZnO nanowires, growth parameters, growth mechanism
National Category
Nano Technology
Identifiers
urn:nbn:se:uu:diva-286795 (URN)
Available from: 2016-04-21 Created: 2016-04-21 Last updated: 2017-04-24Bibliographically approved
2. On-chip hydrothermal growth of ZnO nanorods at low temperature for highly selective NO2 gas sensor
Open this publication in new window or tab >>On-chip hydrothermal growth of ZnO nanorods at low temperature for highly selective NO2 gas sensor
Show others...
2016 (English)In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 169, 231-235 p.Article in journal (Refereed) Published
Abstract [en]

ZnO nanorods were selectively grown on-chip with a two-step low-temperature hydrothermal method and their gas sensing properties were investigated. Small zinc islands were deposited by sputtering on a glass substrate and used as nucleation sites for the ZnO nanorod growth. An equimolar aqueous solution of 0.005 M Zn(NO3)(2)center dot 6H(2)O and (CH2)(6)N-4 at 85 center dot C was used in two steps. The first step was used for nucleation and growth of short ZnO nanorods for 4 h, whereas the second step was used for elongation of the nanorods for 36 h. Long porous nanorods from neighboring islands connected to each other and formed nanorod junctions. A gas sensor with such nanorods was evaluated towards NO2, ethanol, hydrogen, and ammonia to characterize its sensing properties. It showed that the gas sensor has the highest sensitivity to NO2, and a very high selectivity to this gas when measured at 450 degrees C.

Keyword
Crystal growth, Deposition, Nanocrystalline materials, Sensors, Thin films
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-281470 (URN)10.1016/j.matlet.2016.01.123 (DOI)000370533300058 ()
Available from: 2016-03-24 Created: 2016-03-24 Last updated: 2017-08-10
3. Comparison of NO2 gas sensing properties of three different ZnO nanostructuressynthesized by on-chip low-temperature hydrothermal growth
Open this publication in new window or tab >>Comparison of NO2 gas sensing properties of three different ZnO nanostructuressynthesized by on-chip low-temperature hydrothermal growth
Show others...
(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:nbn:se:uu:diva-320153 (URN)
Available from: 2017-04-16 Created: 2017-04-16 Last updated: 2017-04-24
4. Ethanol-Sensing Characteristics of Nanostructured ZnO: Nanorods, Nanowires, and Porous Nanoparticles
Open this publication in new window or tab >>Ethanol-Sensing Characteristics of Nanostructured ZnO: Nanorods, Nanowires, and Porous Nanoparticles
Show others...
2017 (English)In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 46, no 6, 3406-3411 p.Article in journal (Refereed) Published
Abstract [en]

The morphology and crystalline size of metal oxide-sensing materials arebelieved to have a strong influence on the performance of gas sensors. In thispaper, we report a comparative study on the ethanol-sensing characteristics ofZnO nanorods, nanowires, and porous nanoparticles. The porous ZnOnanoparticles were prepared using a simple thermal decomposition of a sheet-like hydrozincite, whereas the nanorods and nanowires were grown byhydrothermal and chemical vapor deposition methods, respectively. Themorphology and crystal structure of the synthesized materials were charac-terized by field-emission scanning electron microscopy and x-ray diffraction.Ethanol gas-sensing characteristics were systematically studied at differenttemperatures. Our findings show that for ethanol gas-sensing applications,ZnO porous nanoparticles exhibited the best sensitivity, followed by thenanowires and nanorods. Gas-sensing properties were also examined withrespect to the role of crystal growth orientation, crystal size, and porosity.

Keyword
ZnO, porous nanoparticles, nanorods, nanowires, gas sensors
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:uu:diva-320148 (URN)10.1007/s11664-016-5270-2 (DOI)000400560400019 ()
Available from: 2017-04-16 Created: 2017-04-16 Last updated: 2017-06-14Bibliographically approved
5. Influence of annealing temperature on the performance of on-chip hydrothermally grown ZnO nanorod gas sensor toward NO2
Open this publication in new window or tab >>Influence of annealing temperature on the performance of on-chip hydrothermally grown ZnO nanorod gas sensor toward NO2
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Nanorod-based gas sensors synthesized at low temperature should generally be annealed before usage. However, the influence of annealing on the sensing performance of these nanorods is rarely reported. In this study, we first fabricated gas sensors based on ZnO nanorods grown on-chip on glass substrate using hydrothermal method. Subsequently, these sensors were annealed at either 400 °C, 500 °C, or 600 °C in air for 4 h. The gas-sensing performance of the ZnO nanorods toward NO2 was tested before and after annealing. The sensitivity of the gas sensors to NO2 decreased, but the stability increased with the increase in annealing temperature. Photoluminescence spectroscopy and X-ray diffraction were used to investigate the material structure of ZnO nanorods. Results revealed that the oxygen-atom-related defects in the ZnO lattice in the region close to the surface influenced by annealing process were the most significant factors on the sensing properties and stability of ZnO nanorods.

Keyword
zinc oxide; gas sensor; defects in nanorods; annealing; hydrothermal
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:uu:diva-320155 (URN)
Available from: 2017-04-16 Created: 2017-04-16 Last updated: 2017-04-24
6. On-chip growth of patterned ZnO nanorod sensors with PdO decoration for enhancement of hydrogen-sensing performance
Open this publication in new window or tab >>On-chip growth of patterned ZnO nanorod sensors with PdO decoration for enhancement of hydrogen-sensing performance
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In this study, we used a low-temperature hydrothermal technique to fabricate arrays of sensors with ZnO nanorods grown on-chip. The sensors on the glass substrate then were sputter decorated with Pd at thicknesses of 2, 4, and 8 nm and annealed at 650 °C in air for an hour. Scanning electron microscopy, high resolution transmission microscopy, X-ray diffraction, and surface analysis by X-ray photoelectron spectroscopy characterization demonstrated that decoration of homogenous PdO nanoparticles on the surface of ZnO nanorods had been achieved. The sensors were tested against three reducing gases, namely hydrogen, ethanol, and ammonia, at 350, 400, and 450 °C. The ZnO nanorods decorated with PdO particles from the 2 and 4 nm layers showed the highest responses to H2 at 450 and 350 °C, respectively. These samples also generally exhibited better selectivity for hydrogen than for ethanol and ammonia at the same concentrations and at all tested temperatures. However, the ZnO nanorods decorated with PdO particles from the 8 nm layer showed a reverse sensing behaviour compared with the first two. The sensing mechanism behind these phenomena is discussed in the light of the spillover effect of hydrogen in contact with the PdO particles as well as the negative competition of the PdO thin film formed between the sensor electrodes during sputter decoration, Pd-Zn heterojunction that forms at high temperature and thus influences the conductivity of the ZnO nanorods.

Keyword
Hydrogen-sensing at high temperature; On-chip hydrothermal growth; ZnO nanorods; Sputter-decoration; PdO nanoparticles
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:uu:diva-320156 (URN)
Available from: 2017-04-16 Created: 2017-04-16 Last updated: 2017-04-24

Open Access in DiVA

fulltext(3529 kB)96 downloads
File information
File name FULLTEXT01.pdfFile size 3529 kBChecksum SHA-512
5c46548be2a241cdba496a40cf6d8163eebfbdd4b56a1ea9efee20668135f38eb80c211106c808808c413d28cca07d3dcc7b4c9e22c0be423625530fe7b64fef
Type fulltextMimetype application/pdf
Buy this publication >>

Search in DiVA

By author/editor
Jiao, Mingzhi
By organisation
Microsystems Technology
Other Materials Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 96 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 669 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf