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

Thin tungsten oxide layers with thicknesses up to 250 nm have been formed on W surfaces by thermal oxidation following a parabolic growth rate. The reflectance of the layers in the IR range 2.5-16 mu m has been measured showing a decrease with the layer thickness especially at low wavelengths. Raman microscopy and x-ray diffraction show a nanocrystalline WO3 monoclinic structure. Low energy deuterium plasma exposure (11 eV/D+) has been performed inducing a phase transition, a change in the sample colour and the formation of tungsten bronze (DxWO3). Implantation modifies the whole layer suggesting a deep diffusion of deuterium inside the oxide. After exposure, a deuterium release due to the oxidation of DxWO3 under ambient conditions has been evidenced showing a reversible deuterium retention.