Iron

Iron • Transition Metal

Primary XPS region: Fe2p
Overlapping regions: Cu LMM, Ni LMM
Binding energies of common chemical states:

Experimental information

• Fe2p overlaps strongly with Ni LMM Auger peaks, e.g., in some steel samples.
  • Can use weaker Fe3p or Fe3s peaks instead for quantification.
• Some compounds/alloys of iron are magnetic.
  • Degauss samples if possible before analysis.
• Iron oxides are readily reduced by argon monomer sputtering.
  • Use lowest possible ion beam energy when attempting to clean oxide sample surface or during depth profiling.
    • Minimizes (but does not completely prevent) reduction effect.

Interpretation of XPS spectra

• Fe2p region has significantly split spin-orbit components (Δ_metal=13.1eV).
• Fe2p peaks have asymmetric shape for metal.
  • A well resolved Fe2p_3/2 spectrum for metal shows multiplet splitting.
  • Second component (shifted by 0.9eV from main peak) can be neglected when fitting typical mixed oxide/metal spectra.

• Fe oxide peaks are significantly shifted to higher binding energy than the metal.
  • Fe compounds can be reduced by Ar ion sputtering, even at relatively low ion energies.
• Iron compounds may be described as high-spin or low-spin (as defined by crystal field theory).
  • Fe(III) compounds are always high-spin, leading to complex multiplet-split Fe2p spectra^[1].
  • Fe(II) compounds may be high or low-spin [1].
    • Fe2p spectra of high-spin compounds (e.g., FeO or FeCl₂) exhibit complex multiplet splitting and have satellite features.
    • Spectra from low-spin compounds (e.g., FeS₂) do not show multiplet splitting or satellite features.
  • It is possible to distinguish Fe oxidation states using satellite features of Fe2p.