Highly oriented tungsten trioxide thin films have been grown on (0 1 2) r-c
ut sapphire substrates using reactive rf magnetron sputtering of a tungsten
metal target in various oxygen/argon mixtures. Parameters for growth of st
oichiometric tungsten trioxide (WO3) films were determined by X-ray photoel
ectron spectroscopy (XPS). In situ four-point Van der Pauw conductivity mea
surements were performed on as grown films and after post-deposition anneal
ing to study changes in the oxygen vacancy population. Reflection high-ener
gy electron diffraction (RHEED) and X-ray diffraction (XRD) indicate that s
toichiometric WO3 films deposited at 450 degreesC are dominated by the tetr
agonal phase with (0 0 1) orientation along the growth direction, and films
deposited at 650 degreesC possess coexisting (0 0 2), (0 2 0), and (2 0 0)
in-plane orientations of the monoclinic phase. Tetragonal and monoclinic-p
hase WO3 films exhibit a change in conductivity of 0.1 Omega (-1) cm(-1) to
20 ppm H2S at 250 degreesC, but display different response kinetics. (C) 2
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