In situ core‐level and valence‐band photoelectron spectroscopy of reactively sputtered tungsten oxide films

Abstract

In this paper, we study tungsten oxides deposited by reactive magnetron sputtering. The total working pressure during deposition was varied in order to obtain different morphology. The effects on the electronic properties and chemical composition were studied by XPS and UPS. It was observed that, for the same argon to oxygen ratio in the gas feed, the decrease in total working pressure implies a decrease of the oxygen content in the film. In the nearly stoichiometric WO 3 films, W 4f 5/2 and W 4f 7/2 form a distinct doublet peak. In sub-stoichiometric films, the films do not exhibit a well-resolved doublet and suggest multiple oxidation states of tungsten.The valence-band spectra of the sub-stoichiometric samples present an additional feature below the Fermi edge (~0.5 eV). This peak is assigned to W 5d 1 because of the presence of W 5+. It is consistent with the changes on the corelevel spectra. XPS results, UPS features, and visual aspect are in agreement and suggest that the total working pressure has a strong influence on the oxygen content and therefore on the oxidation state of tungsten in the films.

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“…All four samples show well‐resolved doublet peaks at binding energies of ≈35 and ≈37 eV, ascribed to W 4f 7/2 and W 4f 5/2 , respectively. These doublets are representative peaks of +6 oxidation state of W in WO 3 . The small peak in all four samples at a higher binding energy of ≈41 eV is attributed to W 5p 3/2 ; however, the contribution from this peak is extremely negligible.…”

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“…The XPS W4fc ore level spectrum ( Figure 3d) of the ternary M-W-rGO composite shows the doublet peaks at binding energies of 35.8 and 37.9 eV corresponding to W4f 7/2 and W4f 5/2 ,r espectively.T hese peaks are characteristics peaks of Ww ith + 6o xidations tate in hexa-WO 3 . [54] Similarly,F igure S5 a-b (in the Supporting Information) shows that there is also no significant shifts of the W4fp eaks for both W-rGO and M-W-rGO composites. In the XPS O1ss pectrum (Figure 3e), the peak at the bindinge nergy of 531.5 eV confirms the presence of metallic oxygen in hexa-WO 3 .…”

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“…Innovative approaches for switchable optical coatings, such as novel nanocomposite electrochromic transition metal oxide layers combined with new solid ion conductors and chiral liquid crystals, open new perspectives for more durable smart glazing with faster optical response (Fig.12). The objectives currently pursued within this project are the development of novel nanostructured materials for switchable windows, their characterization and the prediction of their performances [16]. The new glass for smart "window" -At Lawrence Berkeley National Laboratory in Berkeley, California, a team of researchers led by Delia Milliron, has developed a new technology that allows to obtain a particular type of glass that can work dynamically controlling the flow of heat and light which passes through it, modulating it according to different weather conditions, through the transparency.…”