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Tungsten oxide thin films

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Tungsten oxide thin films

Formation of thin tungsten oxide layers : characterisation and exposure to deuterium

Y. Addab et al. Physica Scripta T167 014036 (2016)

Thin tungsten oxide films have been formed on W surfaces by thermal oxidation (thicknesses up to 250 nm) following a parabolic growth law. Raman microscopy and X-ray diffraction show that the film structure is that of nanocrystalline monoclinic WO3. Their reflectance (2.5 - 16 µm) has been measured and shows a decrease when their thickness increases, especially at low wavelength.

Low energy deuterium plasma exposure (11 eV/D+) has been performed leading to a change in the sample colour from blue to yellow, a phase transition from monoclinic to hexagonal, and the formation of a tungsten bronze (DxWO3). These observations are consistent with an electrochromic effect due to D+ implantation followed by diffusion throughout the layer and leading to color center formation. Such electrochromic effect is here observed for the first time under plasma irradiation. Reversibility has been observed after exposure under ambient conditions.


The figure shows the Raman spectra, before and after irradiation, in the WO stretching vibrational mode region. The shift of the bands peaked at ∼ 700 and ∼ 800 cm-1 proves the monoclinic hexagonal transition. The band at ∼ 900 cm-1 is attributed to defects such as terminal W=O bonds (WO network breaking). Its increase could be related to O-D bonding at this type of defects.