Surface and in depth chemistry of polycrystalline WO/sub 3/ thin films studied by X-ray and soft X-ray photoemission spectroscopies

Abstract

The chemical composition of surface and underneath layers of WO 3 thin films, deposited by thermal evaporation and annealed in air at different temperatures, has been studied by means of soft X-ray and X-ray photoemission spectroscopies. Both the W 4f and valence band spectra have been analyzed. The analysis has been performed on samples as inserted and after an annealing process in an ultra high vacuum. The results have shown that the surface always presents a nonstoichiometric WO 3 compound, whose spectral components do not depend on the sample preparation. Instead, the study of the underneath layers has shown that the WO 3 films annealed in air at 500 C are highly stoichiometric and stable, while the samples heated in air at 300 C are much more sensitive to the vacuum thermal treatment showing the presence of reduced WO phases, whose intensity and chemical states change after the in vacuum annealing procedure.

Deposition of tungsten oxynitride nanowires through simple evaporation and subsequent annealing

“…5͑b͒, 5͑d͒, and 5͑f͒ were obtained from the WO 3 nanowires and tungsten oxynitride nanowires, respectively. 57 The XPS analysis indicates that the chemical binding states of WO 3 changed with nitrogen incorporation upon NH 3 annealing, which is consistent with the XRD results. 5͑a͒ and 5͑b͒.…”

Direct synthesis of W18O49nanorods from W2N film by thermal annealing

“…After annealing at 700 • C for 60 min in 5 Torr of Ar atmosphere, the binding energies were shifted toward higher values compared to the as-deposited W 2 N film. As shown in figure 3(b), the peaks positioned at 35.6 and 37.6 eV are assigned to the tungsten in the W-O bond configuration [35][36][37][38][39][40].…”

Synthesis and characterization of tungsten oxide nanorods from chemical vapor deposition-grown tungsten film by low-temperature thermal annealing

“…Figure 5(b) shows the W4f peaks positioned at 36 and 37.7 eV, which are assigned to the tungsten in W-O bond configuration, respectively. [52][53][54][55][56][57][58] The O1s core level spectra of the W film and the tungsten oxide nanorods are also compared in Figs. 5(c) and 5(d).…”

“…Both XPS spectra showed the same peak position at 530.6 eV, which is assigned to the oxygen in W-O bond configuration. [52][53][54][55][56][57] However, the atomic percentage was quite different. Although the atomic percentage of O in W film was below 9% before annealing, it increased to 67% after annealing.…”