Optical properties of tungsten oxide thin films with protons intercalated during sputtering

• 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 fabricated under suitable conditions were colored due to the formation of tungsten bronze. The concentration of intercalated protons, given by the x values in HxWO(3), was evaluated by ejecting protons electrochemically from the films. The x value of the films prepared at a constant working pressure was found to be proportional to the hydrogen flow ratio during deposition. On the other hand, the x value of the films prepared at a constant hydrogen flow ratio decreased sharply with increasing working pressure during deposition. The dispersion of the extinction coefficient (kappa) of the films was estimated by analyzing the experimental spectra of psi and Delta 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 kappa value was found to increase sharply with the number of intercalated protons. There was a linear dependence between the kappa value and the x value for x 0.2, while for x 0.3, the absorption saturated. This indicates that it is possible to evaluate the x value of HxWO3 films using spectroscopic ellipsometry.

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electrochemistry

electrolytes

extinction coefficients

sputter deposition

surface roughness

thin films

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