Abstract
Tungsten oxides show different stoichiometries, crystal lattices and morphologies. These characteristics are important mainly when they are used as photocatalysts. In this work tungsten oxide thin films were obtained by thermal evaporation on (100) silicon substrates covered with gold and heated at 350 and 600 oC, with different deposition times. The stoichiometry of the films, morphology, crystal structure and resistance to leaching were characterized through X-ray photoelectron spectroscopy, micro-Raman spectroscopy, scanning and transmission electron microscopy, X-ray diffractometry, Rutherford backscattering spectrometry and O16(α,α')O16 resonant nuclear reaction. Films obtained at higher temperatures show well-defined spherical nanometric structure; they are composed of WO3.1 and the presence of hydrated tungsten oxide was also observed. The major crystal structure observed is the hexagonal. Thin films obtained through thermal evaporation present resistance to leaching in aqueous media and excellent performance as photocatalysts, evaluated through the degradation of the methyl orange dye.
Highlights
The class of transition metal oxides drives attention of many researchers, when the preparation of photocatalyst devices is concerned
Surface area, lattice defects and morphology affect the electrochemical properties of this material and are important aspects in the development of technologies[7,8] with applications primarily in photocatalysis,[9] gas sensing[10,11] and electrochromic devices.[12]
Because the thin films were obtained on Au/Si, a Raman spectrum of the substrate was added to Figure 2 in order to identify the contribution originated from gold (298 cm-1)[36] and silicon (520 cm-1 and 948-980 cm-1).[37]
Summary
The class of transition metal oxides drives attention of many researchers, when the preparation of photocatalyst devices is concerned. Techniques for obtaining tungsten oxide films have an important role, mostly in structuring and modifying stoichiometry. The oxygen profiles under the film surface were obtained through O16(α,α')O16 resonant nuclear reaction analysis (NRA), using an α particle beam with energies of 3047, 3053 and 3077 keV to determine the oxygen content in the depths of 8, 30 and 120 nm, respectively.
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