Knowledge Base

Doublet Separations

• Co 2p: 14.99 eV
• Co 3p: 1.1 eV

The Energies Listed are Binding Energies!

• Co 2p: 780 eV
• Co 2s: 927 eV
• Co 3s 101 eV
• Co 3p: 60 eV

The Energies Listed are Binding Energies!

Co is primarily analyzed via the 2p orbital

• U 4d3/2 (781 eV)
• Ba 3d5/2 (781 eV)
• Fe LMM (Al source) (786 eV)
• Pr MNN (Al source) (788 eV)
• Ba 3d3/2 (796 eV)
• Hg 4s (800 eV)

Energies listed are Kinetic Energies!

Co LMM: ~ 780 eV

Analysis of Cobalt by XPS is typically performed on the intense 2p region, however as with most first row TMs, significant multiplet splitting renders deconvolution of Co complexes and compounds difficult (Figure 1). Co(II) and high spin Co(III) contain unpaired d-electrons and therefore the resultant spectra of these metal cations will possess complex structure.⁽¹⁾

The only photoemission which is likely to cause issues with overlapping is Ba 3d, however Fe LMM, Pr MNN and even Co LMM augers (Al ka X-rays – 1486.7 eV) may overlap, though the Co LMM auger is only a minor overlap.

Co 2p peaks are separated by a sizable doublet separation (14.99 eV).

Work from Grosvenor et al determined that cobalt metal consists of one asymmetric photoemission and 2 plasmons (surface and bulk) at +3 and +5 eV above the photoemission (Figure 2).⁽²⁾

Cobalt compounds displaying multiplet splitting pose a much steeper challenge as far as data interpretation is concerned. As can be seen in figure 3, broad combinations of overlapping features render deconvolution of multiple compounds exceptionally challenging, whilst even deconvolution of metal and oxide/hydroxide requires non-standard modifications to the application of a background due to overlaps between metal 2p_1/2 and oxide 2p_3/2 satellites.^(1,4)

The unique lineshapes do afford the possibility of fingerprint analysis however, either through utilising the theoretically derived fits of Biesinger⁽¹⁾ or using reference spectra of standard materials.

Cobalt oxides reduced by Ar⁺ sputtering, use low energy for profiling or cleaning.

Cobalt 3s spectra, whilst relatively weak (and overlapping with some notable emissions such as Si 2p and Ce 4d) may also offer unique insights into the cobalt speciation since 3s region splitting (figure 4) of TMs may be sensitive to the metal spin state and ligand-metal charge transfer.⁽⁷⁾

Spin-induced Co 3s multiplet splittings for some common species may be found in table 2. Note that the splitting may not always be strongly observable, for example in Co metal it is present as a shoulder and often recorded as no splitting. Cobalt (III) oxide, as with the 2p region, exhibit negligible multiplet splitting compared with Co (II) species.