Optical hydrogen sensitivity of noble metal-tungsten oxide composite filmsprepared by sputtering deposition

Composite films composed of noble metals such as Pd, Pt and Au and tungsten oxide (WO3) for optical gas sensing were prepared by simultaneous rf and d e sputtering deposition, and the optical hydrogen sensitivities of these Pd -WO3, Pt-WO3 and Au-WO3 composite films were investigated together with the WO3 film without containing noble metals. At temperatures of 200-250 degre esC, no change in the visible-near IR absorption of the WO3 film without no ble metals could be detected by the presence of 1 vol.% H-2 in air. The com bination of Pd with WO3 film enhanced the detection of H-2 in air through a n increasing change of absorbance in the whole visible-near IR wavelength r egion centered at around lambda = 1000 nm. This increase of absorbance by H -2 Can be explained by the formation of tungsten bronze (HxWO3), which is e nhanced by the dissociation of H-2 On Pd. On the other hand, the combinatio n of Pt with WO3 did not make the film sensitive to H-2 In the case of the Au-WO3 composite film, the combination of Au made the film sensitive mainly at the plasmon absorption region around visible wavelengths, in addition t o the small sensitivity due to the formation of tungsten bronze around near IR wavelengths. The change of absorbance by H-2 in the plasmon absorption region, which include both an increasing change at wavelengths around 550 n m and a decreasing change of absorbance at wavelengths around 700 nm, might be because the absorbance by small Au particles in plasmon band was influe nced by the change in the dielectric constant of tungsten oxide which surro unded small Au particles. (C) 2001 Elsevier Science B.V. All rights reserve d.