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Thin film deposition and characterization of pure and iron-doped electron-beam evaporated tungsten oxide for gas sensors |
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| Authors: | Tuquabo Tesfamichael Masashi Arita John Bell |
| Affiliation: | a Faculty of Built Environment and Engineering, School of Engineering Systems, Queensland University of Technology, 2 George Street, Brisbane, QLD 4000, Australia b Graduate School of Information Science and Technology, Hokkaido University, Kita-14, Nishi-9, Kita-ku, Sapporo, 060-0814, Japan c Faculty of Science and Technology, School of Physical and Chemical Sciences, Queensland University of Technology, 2 George Street, Brisbane, QLD 4000, Australia d Centre for Built Environment and Engineering Research, Queensland University of Technology, 2 George Street, Brisbane, QLD 4000, Australia |
| Abstract: | Pure tungsten oxide (WO3) and iron-doped (10 at.%) tungsten oxide (WO3:Fe) nanostructured thin films were prepared using a dual crucible Electron Beam Evaporation (EBE) technique. The films were deposited at room temperature under high vacuum onto glass as well as alumina substrates and post-heat treated at 300 °C for 1 h. Using Raman spectroscopy the as-deposited WO3 and WO3:Fe films were found to be amorphous, however their crystallinity increased after annealing. The estimated surface roughness of the films was similar (of the order of 3 nm) to that determined using Atomic Force Microscopy (AFM). As observed by AFM, the WO3:Fe film appeared to have a more compact surface as compared to the more porous WO3 film. X-ray photoelectron spectroscopy analysis showed that the elemental stoichiometry of the tungsten oxide films was consistent with WO3. A slight difference in optical band gap energies was found between the as-deposited WO3 (3.22 eV) and WO3:Fe (3.12 eV) films. The differences in the band gap energies of the annealed films were significantly higher, having values of 3.12 eV and 2.61 eV for the WO3 and WO3:Fe films respectively. The heat treated films were investigated for gas sensing applications using noise spectroscopy. It was found that doping of Fe to WO3 produced gas selectivity but a reduced gas sensitivity as compared to the WO3 sensor. |
| Keywords: | Tungsten oxide Electron beam evaporation Co-evaporated thin films Surface morphology Optical properties Surface characterization X-ray photoelectron spectroscopy Atomic force microscopy |
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