Recently, I have recorded an XPS spectra of an electrode for supercapacitor application at different states of charge. I have observed a shift in the peak position toward a higher binding energy and the peak intensity also changes. please I need a possible reason for these
Dear Mustapha,
The peak shift in XPS is most of time related to a change of oxidation state of the element your a looking at. Here, higher binding energies mean also higher oxidation states. This is known as chemical shift. A good starting point for a literature research for the peak shifts of your material is the XPS database of NIST: https://srdata.nist.gov/xps/
The intensity of your peaks mainly changes because of two reason: Firstly, the intensity is directly linked to the number of atoms with the respective oxidation state. It is directly proportional to atoms on the respective chemical state.
A second cause for a change of intensity can be diffusive processes, because the intensity depends also on the depth distribution of your atoms. Here, the sum of the intensity of all peaks of one core level changes. If your atoms diffuse towards the surface, you will see an increase in intensity, even if they are the same in numbers. And of course, the intensity will decrease, if the atoms diffuse towards the bulk.
A good place to start to refresh one’s memory about the basic principles of XPS is the wikipedia article: https://en.wikipedia.org/wiki/X-ray_photoelectron_spectroscopy
If you need further help, please post one or more of your spectra.
Best regards,
Martin
https://en.wikipedia.org/wiki/X-ray_photoelectron_spectroscopy
https://srdata.nist.gov/xps/
If I am guessing correctly, then you are applying a bias to your samples while you are recording XPS spectra. If indeed you are applying a bias during analysis, then you might cause "voltage induced differential charging" which helps to understand the different chemistry hiding in your sample, but it is challenging to understand.
If you are not applying a bias, then it is likely that you have accidental differential charging which can occur if you are using a Mg non-monochromatic source or you might be using a Al monochromatic source but your flood gun is not properly aligned or the voltage from your flood gun needs to be larger.
In case of electrochemical processes, you may also observe so called "electrochemical" peak shifts - see e.g. the works of Kolb and others (e.g. Z. Phys. Chem. NF 154 (1987) 179, Surf. Sci. 165 (1986) 268, J. Electron Spectrosc. Related Phenom. 46 (1988) 155, Electrochim. Acta. 43 (1998) 2957). This may also be the case in your samples and would explain why the XPS peaks shift to larger binding energies upon negative charging, and vice versa.
Keep us updated about your analysis and interpretation, good luck, Dirk
The shifts in the XPS peak is related to its oxidation state and higher shift in binding energy corresponds to higher oxidation state. Some times more shift with noise peak is related to the satellite peak or shake up and it is a case for only some metal or its oxide for example Ni or NiO.
Before analyzing XPS peak, first you must do charging correction by taking the reference binding energy of C1s (284.8 eV), otherwise it will difficult to identify the multiple oxidation state.
The shift in peak position is either by the charging effect or coz of change in the surrounding of an element so that we observe a change in binding energy.
The charging effect is explained by this guy in this video is easy to understand -
https://www.youtube.com/watch?v=AJ-T8uAGsMk
The intensity of a peak is dependent on the concentration of that specie in that sample and the sensibility of that specie which is more or less a constant.
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