Chromium

Chromium • Transition Metal

Primary XPS region: Cr2p
Overlapping regions: Te3d, Zn LMM
Binding energies of common chemical states:

Experimental information

• Cr2p overlaps strongly with Zn LMM Auger peaks, e.g., in steel samples.
  • Use weaker Cr3p peak instead if chromium concentration is high enough to give good Cr3p signal.

Interpretation of XPS spectra

• In the presence of high concentrations of zinc, it may be difficult to assign chromium chemistry using the Cr2p region, due to strong overlap with the Zn LMM Auger region.
  • The secondary chromium peak, Cr3p, shows reasonably large chemical shifts and may be easier to peak fit in this situation.
  • Binding energies Cr3p peak : metal = 42.4eV, Cr₂O₃ = 43.0eV, CrO₃ = 48.3eV
• Cr2p peak has significantly split spin-orbit components (Δ_metal=9.3eV)
• Direct overlap between Te3d and Cr2p peaks.
  • Although Te3d/Cr2p peaks have strong overlap, Te3d spin-orbit components have a 3:2 intensity ratio compared to a 2:1 ratio for Cr2p.
  • Check for the weaker Te3p peaks, if tellurium concentration is high enough.
• Method for chemical analysis of Cr(III) oxide [1, 2].
  • A satellite feature of the Cr2p_3/2 peak overlaps the Cr2p_1/2 component in Cr₂O₃.
  • Fit only the Cr2p_3/2 component.
  • Cr2p for Cr(III) oxide has many multiplet-split components.
  • Correct fitting of multiplet split structure prevents false identification of other chemical states.

• Native oxide on Cr metal may be a mix of Cr(III) oxide and Cr(III) hydroxide.
  • Cr2p for Cr(III) hydroxide can be fit with a single Cr2p_3/2 component.
  • Cr(III) oxide fit with multiplet as shown above and fit Cr metal with asymmetric peak.
• Air-exposed crocoites (PbCrO₄) has been peak fit using a modified version of the Cr₂O₃ fitting method, with an additional component for the Cr(VI) state.

References

• [1] MC Biesinger et al. / Applied Surface Science 257 (2011) 2717-2730.
• [2] M Aronniemi et al. / Surface Science 578 (2005) 108-123.