Control of the concentration of protons intercalated into tungsten oxide thin films during deposition

Tungsten oxide thin films with protons intercalated during deposition (HxWO3) were prepared using reactive direct-current magnetron sputtering in a gas mixture of argon, oxygen, and hydrogen. The as-deposited films were tungsten bronze. The concentration of intercalated protons, given by the x-values in HxWO3, was evaluated by electrochemically ejecting protons from the films. The x-value was proportional to the hydrogen flow ratio at the deposition. The dispersion of the extinction coefficient (κ) of the films was estimated by analyzing the experimental spectra measured with spectroscopic ellipsometry using the model composed of a homogeneous tungsten bronze layer with an additional surface roughness layer. As a result of this analysis, the κ-value increases strongly with intercalated protons, and a linear dependence existed between the x value and κ-value. Therefore, it is possible to evaluate the x-value of the HxWO3 films using this dependence without ejecting protons. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)