Controlled growth of WO{sub 3} films
- Laboratory for Surface Science and Technology, University of Maine, Orono, Maine 04469-5764 (United States)
We have used reactive rf magnetron sputtering of a tungsten target in Ar/O{sub 2} mixtures and direct electron-beam evaporation of WO{sub 3} pellets with and without the presence of an electron cyclotron resonance (ECR) oxygen plasma to grow WO{sub 3} films on {alpha}-Al{sub 2}O{sub 3}(10{bar 1}2) single-crystal substrates (r-cut sapphire). The WO{sub 3} films exhibit a range of microstructures depending on deposition conditions. Using any of the deposition methods, the films are amorphous when grown at room temperature. Postdeposition annealing in O{sub 2} induces the formation of a random polycrystalline microstructure and an increased surface roughness. Growth of crystalline WO{sub 3} films can be achieved at deposition temperatures above 200{degree}C. During electron-beam evaporation of WO{sub 3} at 600{degree}C, reflection high-energy electron diffraction observations indicate that a tetragonal phase of WO{sub 3} grows epitaxially on r-cut sapphire with the (100) tetragonal plane coincident with the rectangular mesh of the r-cut sapphire substrate. Deposition of WO{sub 3} using plasma species generated by either a rf magnetron or ECR source promotes the formation of some nuclei of an orthorhombic and/or monoclinic phase coexisting with the tetragonal phase; the nearly identical lattice parameters make the orthorhombic and monoclinic phases difficult to distinguish. Compared to the polycrystalline films, the epitaxial films exhibit both a higher base-line conductivity and a larger conductivity change upon exposure to H{sub 2}S gas. {copyright} {ital 1997 American Vacuum Society.}
- DOE Contract Number:
- FC02-93ER75945
- OSTI ID:
- 545270
- Report Number(s):
- CONF-961002--
- Journal Information:
- Journal of Vacuum Science and Technology, A, Journal Name: Journal of Vacuum Science and Technology, A Journal Issue: 3 Vol. 15; ISSN 0734-2101; ISSN JVTAD6
- Country of Publication:
- United States
- Language:
- English
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