The effect of pressure and W-doping on the properties of ZnO thin films for NO2 gas sensing
Tesfamichael, Tuquabo, Cetin, Cadgas, Piloto, Carlo, Arita, Masashi, & Bell, John (2015) The effect of pressure and W-doping on the properties of ZnO thin films for NO2 gas sensing. Applied Surface Science, 357, pp. 728-734.
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Pure and W-doped ZnO thin films were obtained using magnetron sputtering at working pressures of 0.4 Pa and 1.33 Pa. The films were deposited on glass and alumina substrates at room temperature and subsequently annealed at 400oC for 1 hour in air. The effects of pressure and W-doping on the structure, chemical, optical and electronic properties of the ZnO films for gas sensing were examined. From AFM, the doped film deposited at higher pressure (1.33 Pa) has spiky morphology with much lower grain density and porosity compared to the doped film deposited at 0.4 Pa. The average gain size and roughness of the annealed films were estimated to be 65 nm and 2.2 nm, respectively with slightly larger grain size and roughness appeared in the doped films. From XPS the films deposited at 1.33 Pa favored the formation of adsorbed oxygen on the film surface and this has been more pronounced in the doped film which created active sites for OH adsorption. As a consequence the W-doped film deposited at 1.33 Pa was found to have lower oxidation state of W (35.1 eV) than the doped film deposited at 0.4 Pa (35.9 eV). Raman spectra indicated that doping modified the properties of the ZnO film and induced free-carrier defects. The transmittance of the samples also reveals an enhanced free-carrier density in the W-doped films. The refractive index of the pure film was also found to increase from 1.7 to 2.2 after W-doping whereas the optical band gap only slightly increased. The W-doped ZnO film deposited at 0.4 Pa appeared to have favorable properties for enhanced gas sensing. This film showed significantly higher sensing performance towards 5-10 ppm NO2 at lower operating temperature of 150oC most dominantly due to increased free-carrier defects achieved by W-doping.
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|Item Type:||Journal Article|
|Keywords:||Nanostructure, ZnO thin films, W-doping, sputtering pressure, NO2 gas sensors|
|Divisions:||Current > QUT Faculties and Divisions > Chancellery
Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > Institutes > Institute for Future Environments
Current > QUT Faculties and Divisions > Science & Engineering Faculty
|Facilities:||Science and Engineering Centre|
|Copyright Owner:||Copyright 2015 Elsevier B.V.|
|Copyright Statement:||This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/|
|Deposited On:||25 Apr 2016 23:13|
|Last Modified:||01 May 2016 05:49|
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