Chromium • Transition Metal

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

Chemical stateBinding energy Cr2p3/2
Cr metal574.3 eV
Cr(III) oxide~576 eV
Cr(VI) oxide~580 eV

 

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 (Δmetal=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 Cr2p3/2 peak overlaps the Cr2p1/2 component in Cr2O3.
    • Fit only the Cr2p3/2 component.
    • Cr2p for Cr(III) oxide has many multiplet-split components.
    • Correct fitting of multiplet split structure prevents false identification of other chemical states.
Cr2p Spectrum Native Oxide Cr Metal
  • 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 Cr2p3/2 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.

 

Chromium • Transition Metal
Element Crystal Cub

About this element

Symbol: Cr
Date of discovery: 1797
Name origin: Greek chrôma
Appearance: gray
Discoverer: Louis Vauquelin
Obtained from: chromite

Melting point: 2180 K
Boiling point: 2944 K
Density[kg/m3]: 7140
Molar volume: 7.23 × 10-6 m3/mol
Protons/Electrons: 24
Neutrons: 28
Shell structure: 2,8,13,1
Electron configuration: [Ar]3d54s1
Oxidation state: 6,4,3,2
Crystal structure: cubic

Chromium is a malleable hard metal best known for its attractive luster when polished. Chromium gets its name from the Greek word for color due to the many colorful compounds that can be made from it. During the 1800s, chromium was used mainly as a component in paints and tanning salts for leather. Today, 85% of its use is in metallic alloys, such as stainless steel and anodized aluminum. Traces of chromium can be found in gemstones, such as ruby and emerald. Chromium is a common element and is used in producing synthetic gems.

 


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