Hello,
I am interested in understanding the relationship between binding energy (B.E.) and ions' oxidation state (O.S.) in XPS spectra.
Per example
The core-level XPS of Mn2P in MnxNy can be deconvoluted into the following peaks, attached Fig.1
The B.E. of the respective peaks can be matched (NIST XPS database) and assigned to Mn2+ and Mn3+(presence in MnO and Mn2O3) because no information is available on the XPS analysis of the Manganese nitride compound.
Is the Binding energy of (Mn+n) oxidation states are same, irrespective of the compounds?
More specifically, is the B.E. for Mn2+in MnO, MnCl2, Mn(NO3)2, and Mn4N the same?
Best Regards.
The assignment of an "oxidation" state is of course only an approximation to reality, but in many cases it's a very good one.
For some salts like e.g. chlorides in which the anion keeps its electrons mostly to itself (check out the Pearson HSAB principle and the spectrochemical series https://en.wikipedia.org/wiki/Spectrochemical_series), an oxidation state can be assigned really clearly - it's just what is needed to compensate for the negative charge of the anion. As soon as the anion starts sharing more electron density and/or the covalent share of the bond becomes enhanced, assigning a clear oxidation state becomes succesively harder and a spread opens.
Therefore, if you have several compounds present in the same oxidation state but with different counteranions there may be a spread of the cation binding energies.
Having said that, the assignments in the spectrum you posted don't really match the NIST values. There Mn3+ is already found at 642 eV and that's your blue "Mn2+" peak, not the violet peak which may as well be a baseline subtraction effect. However, in that case you would have to see that also in the 2p1/2 signal for which you find Mn3+ at 653.5eV in NIST.
Thermo Fisher actually recommends the Mn3s peak for oxidation state analysis:
https://www.thermofisher.com/de/de/home/materials-science/learning-center/periodic-table/transition-metal/manganese.html
Another addition: Every component you add in the 2p_3/2 peak should also be added to the 2p_1/2 peak due to spin-orbit splitting, with an intensity of 0.5. In your case you have 3 components for the 2p_3/2 peak, but only 2 components in the 2p_1/2 peak with the wrong area ratios as well.
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