Photoelectron spectromicroscopy study of metal–insulator transition in Na WO3

Paul, Subrata; Ghosh, Anirudha; Dudin, Pavel; Barinov, A.; Chakraborty, Anirban; Ray, Sugata; Oishi, Shuji; Raj, Satyabrata

doi:10.1016/j.ssc.2013.05.008

Cited by 2 publications

(2 citation statements)

References 16 publications

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“…Throughout all experiments, low-energy electron diffraction (LEED) shows the persistent rutile (110) 1 × 1 pattern of the rutile single-crystal surface. With increasing cluster coverage, this pattern becomes blurred, but no indications for the formation of long-range ordered superstructures were found for the as-deposited material as well as for annealing at temperatures up to 880 K. In addition, based on the LEED and XPS results, we do not observe any signs of the formation of a mixed oxide at the surface. ,, In the literature, this is sometimes observed for the reaction with highly reduced transition-metal oxide thin films such as FeO or CuO. , We also point out that the deposition from the WO 3 powder that was handled under ambient conditions does not induce significant contamination (typical carbon content <0.7 atom % based on XPS). For more details, we refer to Figure S7 in the Supporting Information.…”

Section: Resultssupporting

confidence: 46%

“…In addition, based on the LEED and XPS results, we do not observe any signs of the formation of a mixed oxide at the surface. 37,66,67 In the literature, this is sometimes observed for the reaction with highly reduced transition-metal oxide thin films such as FeO or CuO. 37,38 We also point out that the deposition from the WO 3 powder that was handled under ambient conditions does not induce significant contamination (typical carbon content <0.7 atom % based on XPS).…”

Section: Resultsmentioning

confidence: 58%

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Electron Transfer in Oxide–Oxide Cocatalysts: Interaction of Tungsten Oxide Clusters with Ti³⁺ States in Rutile TiO₂

2020

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Heterogeneous (photo)catalysts are often complex mixtures of different nanostructured oxidic compounds. Chemical and electronic interactions within such combined materials may play a key role in improving the performance in technological applications but are difficult to investigate under technical conditions. This work presents a systematic study of the interactions between tungsten oxide clusters and the underlying rutile TiO2 (110) surface in special consideration of point defects such as Ti3+ interstitials. Using electron beam evaporation from WO3 powder, stoichiometric (WO3) n , and oxygen-deficient (WO3–x ) n , tungsten oxide clusters are produced simultaneously. Based on cluster coverage- and temperature-dependent X-ray photoelectron spectroscopy studies, the formation of a surface layer of stoichiometric and oxygen-deficient tungsten oxide clusters is shown, and the formation of mixed oxides can be excluded. For the first layer up to 7.1 WO3 nm–2, stoichiometric clusters are dominant at the TiO2 surface. The lack of W5+ indicates an electron transfer from the clusters toward the substrate under formation of Ti3+ interstitials. Furthermore, we found at elevated temperatures relevant for catalytic reactions that the tungsten oxide clusters are more stable on TiO2 surfaces than on other substrates such as the silicon oxide layer of Si wafers. Up to 900 K, only slight changes were observed on titania. We observed an accumulation of Ti3+ at the TiO2 surface between 500 and 800 K in the case of high bulk Ti3+ content in TiO2. As the Ti3+ accumulation is accompanied by significant changes of the W 4f signals, we suggest an interaction between these sites under a possible generation of surface fields or an anionic [(WO3) n ] z−-like cluster by electron transfer from Ti3+.

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