I would like to ask all of you, which oxidation state peak appear at lower B.E? Co3+ or Co2+? (Attached)
Some paper fit 2p3/2 and 2p1/2 peaks to two peaks, one at lower B.E is correlated to Co3+ and the other one at higher B.E is for Co2+. but some papers did the reverse.
Could any one guide me for the correct one? and why?
but in Case of Fe, Cu or Ni the higher valence state peak is at higher BE.
for example https://www.researchgate.net/publication/279862419_Hierarchical_Cu2OCuOCo3O4_core-shell_nanowires_Synthesis_and_electrochemical_properties/figures?lo=1
https://www.researchgate.net/publication/273958386_In_situ_growth_of_hierarchical_mesoporous_NiCo2S4MnO2_arrays_on_nickel_foam_for_high-performance_supercapacitors/figures?lo=1
Article Hierarchical Cu2O/CuO/Co3O4 core-shell nanowires: Synthesis ...
Article In situ growth of hierarchical mesoporous NiCo2S4@MnO2 array...
I am confused by your question. Both articles that you reference (and the figures you show) have Co3+ fit at lower BE to Co2+.
Am I missing something?
Thanks, Prof. Weimer.
I missed the correct figure for the second case.
Herein I have attached the file in which Co3+ at higher BE
https://www.researchgate.net/publication/281409344_Synthesis_of_Porous_Ni-Co-Mn_Oxide_Nanoneedles_and_the_Temperature_Dependence_of_Their_Pseudocapacitive_Behavior
Article Synthesis of Porous Ni–Co–Mn Oxide Nanoneedles and the Tempe...
Ah! I see the problem. One or the other or all of the authors are wrong. Immediately, I cannot see that a +3 oxide peak is as narrow as defined in the second figure you show. I cannot see that a +2 oxide peak is as narrow as defined in the figure in the new reference you present. Finally, one author cannot assign the lowest peak to pure metal, another to +2, and another to +3.
I would spend time to reference the NIST database on Co XPS, Surface Science Spectra on XPS of Co, and XPS spectra information that is managed/published by BV. Crist to resolve the conflicts. I trust what is published in any one of these sources well over and above any thing that you have posted here as a first order reference to peak positions and shapes.
As a side note, reports on peak fitting to metal oxides is itself a mixed bag of trustworthy results to just total nonsense. In a nutshell, one cannot do proper justice to fitting XPS of metal oxides without careful consideration of the baseline and satellite structure and peak shapes as one coherent function during peak fitting. The extreme approach to throw a bunch of Gaussian peaks under a Shirley-type baseline is annoying if not downright disrespectful.
Clearly, reviewers who are allowing such conflicts if not outright mistakes to propagate have failed in their own due diligence.
I am glad that you have noted this! I would have thought that XPS analysis was well beyond the confusion some decades ago when I started in the field. Please report back what you learn in a follow-up.
I wholeheartedly agree with Jeffrey Weimer -- refer to the NIST database and other databases, and be very, very wary of trusting XPS peak fitting reported in journal articles. Peak fitting is not a trivial task, and it seems there are quite a few people who have access to peak fitting software that do not have enough background in the both experimental method employed (XPS or otherwise) and how to correctly use the software to do an appropriate and properly constrained fit to their data.
Thank you, Prof. Jeffrey Weimer and Prof. Lynette Kogler for your useful information.
In the second example the feature labelled as Co(III) is not correct. Please note that this is most likely Co(0) given its shape. The fitting of Co(II) and Co(III) as mentioned above is non-trivial due to the complex splitting pattern exhibited by many of the transition metals. One of the best approaches you can employ is considering the "so-called" satellite signal which when at approximately 790 eV should be largely indicative of Co3O4, while for CoO it is inherently much larger and appears well below this value (~786 eV). It could be argued that a more direct comparison can be made by calculating the integrated ratio between satellite and signal, which allows for you to identify samples with more Co(II). For a more comprehensive approach I suggest the publications of Biesigner et al. in "Applied Surface Science".
The following articles may help you
1. Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Cr, Mn, Fe, Co and Ni. Applied Surface Science 257 (2011) 2717–2730
2. INTERPRETATION OF THE X-RAY PHOTOEMISSION SPECTRA OF COBALT
OXIDES AND COBALT OXIDE SURFACES. Surface Science 59 (1976) 413-429
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