Hello, I am currently doing my master thesis and my subject is: "determination of Fe2+/Fe3+ ratio in multicoponent slags". So thank you for sharing your research, it will be of great help.
I saw that a lot of studies were done on XANES and XPS to determine the Fe2+/Fe3+ ratio, but no studies have been done with the Auger Electron Spectroscopy and I am currious to know why is this the case.
Lenaïg Meignan
AES is highly surface-sensitive, analyzing only the top nanometers, while Fe²⁺/Fe³⁺ analysis often requires deeper measurement. Techniques like Mössbauer spectroscopy or XANES, which penetrate further, are more suitable.
There are several reasons:
(1) In Auger transitions several electronic levels are involved (e.g. Fe(LVV), Fe(MVV)) show variation in peak position and shape with chemical state) but it's harder to understand than the peak shift in XPS.
(2) In XPS one can achieve a high spectral resolution using monochromatic X-rays and a high resolution spectrometer, in AES the peak width is the natural one (with 3 levels involved) and historically a lot of work had been done using low resolution spectrometers. Nowadays you could investigate X-ray excited Auger electrons using a high resolution spectrometer, but 3 levels will be involved.
(3) Extracting the different bonding states remains difficult, chemical information is mostly extracted by "fingerprints" (comparing spectra of known compounds by peak fitting). The deconvolution of spectra of MVV-peaks was studied in the 1980ies (Fourier analysis, van Cittert) using the available computers (PDP-11, Sinclair ZX), but the results never reached the XPS results. For a recent try see here:
https://www.researchgate.net/publication/378027390_Application_of_the_Van_Cittert_Algorithm_for_Deconvolving_Loss_Features_in_X-ray_Photoelectron_Spectroscopy_Spectra
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