Cheng, Hongbin
(2010)
FABRICATION OF ZINC OXIDE MICRO-NANOSTRUCTURES AND THEIR APPLICATIONS IN GAS SENSING AND NANOCOMPOSITES.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
To date, one-dimensional ZnO micro/nanostructures have been attracting much attention for wide potential applications due to their unique electrical, piezoelectric, optoelectronic, and photochemical properties. The overall objective of this dissertation is to grow various ZnO micro and nanostructures using a novel microwave thermal evaporation-deposition approach, to explore the application of ZnO nanostructures in gas sensing, and to fabricate and characterize multifunctional ZnO nanowires-polyimide nanocomposite. Therefore, three parts were included in this study: (1) A novel thermal evaporation-deposition method using microwave energy was investigated. Batch of ZnO structures including microtubes, microrods, nanotubes, nanowires and nanobelts have been successfully synthesized in the microwave system with a unique source materials-substrate configuration and a desirable temperature profile. These products are pure, structurally uniform, and single crystalline. The photoluminescence (PL) exhibits strong ultraviolet emission at room temperature, indicating potential applications for short-wave light-emitting photonic devices. (2) Piezoelectric crystal langasite bulk acoustic wave (LGS) resonator based high temperature gas sensor was fabricated. Ordered ZnO nanowire arrays were grown on the langasite resonator as the sensitive layer by two-step hydrothermal method at low temperature. The gas sensor coated with ZnO nanowire arrays exhibited good sensitivity to NO2 and NH3. The response of the sensor is fast due to the large surface area of ZnO nanowires. In addition, this work demonstrates that the combination of nanowire arrays with langasite thickness shear mode resonators could provide a promising high temperature gas sensing platform with both high sensitivity and enhanced response speed. (3) The nanocomposite with controlled alignment of ZnO nanowires in the polyimide matrix was achieved using self-alignment method and external electric field assisted method. For the the self-alignment process, the morphologies of the designed nanocomposites were dramatically influenced by the viscosity of the polymer and the geometrical structure of ZnO nanowires. For the nanocomposite prepared by the electric field assisted alignment, the density and the alignment degree of ordered ZnO nanowires significantly depended on the magnitude and the frequency of the applied ac electric field. The DC offset voltage had strong effect on the deposition sites of nanowires. The resultant nanocomposite devices exhibited great dielectric constant and conductivity enhancement at room temperature due to the interfacial effect between ZnO nanowires and the polymer matrix. These nanocomposites combining the superb properties of ZnO nanowires with the polyimide matrix provide a smart material candidate for multifunctional applications that require self-sensing and self-actuation capabilities. The self-alignment method and electric field assisted alignment method also provide a bright route to combine superb properties of nanomaterials with the lightweight, flexibility, and manufacturability of dielectric polymers for future generations of multifunctional materials.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
26 January 2010 |
| Date Type: |
Completion |
| Defense Date: |
25 August 2009 |
| Approval Date: |
26 January 2010 |
| Submission Date: |
25 November 2009 |
| Access Restriction: |
5 year -- Restrict access to University of Pittsburgh for a period of 5 years. |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Mechanical Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
gas sensor; nanocomposite; Zinc oxide nanostructrues |
| Other ID: |
http://etd.library.pitt.edu/ETD/available/etd-11252009-103510/, etd-11252009-103510 |
| Date Deposited: |
10 Nov 2011 20:06 |
| Last Modified: |
15 Nov 2016 13:52 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/9800 |
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