XPS spectra of the Si2p core level usually show the spin-orbit splitting of this level (1/2 and 3/2). In the case of SiO_x, all spectra I have found show a particulary narrow component, which therefore cannot be fitted with a splitted component. Instead, this components are fitted with a singulette.
For example in https://www.researchgate.net/publication/230573687 and https://www.researchgate.net/publication/327308583).
What is the reason that the spin-orbit splitting is not visable in this components?
Manny thanks for all answers.
The splitting between the two is not that large, therefore it is difficult to fit it properly and people may consider it more convenient to use some sort of envelope curve for it despite not having covered all physics with that.
Of course, since the splitting is 0.5 eV we may debate controversially whether it makes sense in this case to use chemical components with distances smaller than that as especially done in the second reference you cited. Particulary the fitting of the neutral Si in fig. 3c does not fully convince me.
Jürgen Weippert You're absolutely right with not being convinced by the fits in Figure 3c) and also a), as they are simply wrong. There is no physcial reason for the Si2p1/2 to be larger than the Si2p3/2.
Otherwise you're right with your comments, people often neglect to differentiate two components because the splitting of the oxide peaks is small compared to their FWHM, although this is physically not correct.
Thank you very much for your answers!
You are absolutely right about the second reference.
My question refers to XPS spectra that I have measured and that I am currently analyzing. These spectra are from a SiC substrate with a graphene buffer layer and platinum. After annealing the sample, a new component appears that is shifted by 3.5 eV to higher binding energies compared to the Si 2p 3/2 component from the SiC. A component at this position could be Si4+. The oxide form this component could have moved from the deeper layers of the surface during annealing.
Unfortunately, this component is separated from the others and is so narrow that it cannot be fitted with a doublet. Of course, I looked for other possible causes for this component, but found none. As a singlet, the component can be fitted quite well, but then it must come from the carbon, the platinum, or some contamination. Other than oxygen, a contamination doesn't seem very likely since the survey spectra don't point to any other element.
Do you have any idea what could cause this extra component?
Could you attach the spectrum? What do you mean by "too narrow", is it narrower than the signal from the SiC? The Pt5s signal is in this region, however, it's usually quite broad.
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