Lesson plan
Surface core level shift
A surface core level shift (SCS) is a kind of core-level shift that often emerges in X-ray photoelectron spectroscopy spectra of surface atoms. Because surface atoms have different chemical environments from bulk atoms, small shifts of binding energies are observed by X-ray photoelectron spectroscopy. SCS is ascribed mainly to the lower coordination numbers of surface atoms than bulk atoms. Reduced coordination leads to narrower valence bandwidth. Such narrowing of the bandwidth increases the density of states, and if more than half of the valence band is filled, the band center is lower than bulk and the binding energy increases. In contrast, if less than half of the valence band is filled, the band center is higher than bulk, and the binding energy decreases. Because the binding energy in X-ray photoelectron spectroscopy is affected by the final state and other chemical environments, this simple explanation cannot always be applied to the interpretation of X-ray photoelectron spectra. In spite of such complexity, the SCS gives important information about the chemical nature of surface atoms.
Article summary
A surface core level shift (SCS) is a kind of core-level shift that often emerges in X-ray photoelectron spectroscopy spectra of surface atoms. Because surface atoms have different chemical environments from bulk atoms, small shifts of binding energies are observed by X-ray photoelectron spectroscopy. SCS is ascribed mainly to the lower coordination numbers of surface atoms than bulk atoms. Reduced coordination leads to narrower valence bandwidth. Such narrowing of the bandwidth increases the density of states, and if more than half of the valence band is filled, the band center is lower than bulk and the binding energy increases. In contrast, if less than half of the valence band is filled, the band center is higher than bulk, and the binding energy decreases. Because the binding energy in X-ray photoelectron spectroscopy is affected by the final state and other chemical environments, this simple explanation cannot always be applied to the interpretation of X-ray photoelectron spectra. In spite of such complexity, the SCS gives important information about the chemical nature of surface atoms.
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
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