Normally I have nanocomposite which rich with sulphide and Thiocyanate groups, Its shown S 2P 3/2 and S 2P 1/2 but the middle of that there is the strange peak. I am thinking S of Sulphides- S 2P 1/2 and Thiocyanates's S2P 3/2 peaks are overlapped. Is this Possible?
(S2-) S2P 1/2 + (SCN-) S2P 3/2 is this one is possible
The state of the art in XPS analysis is further advanced than shown in the spectrum. I would personally be reluctant as a reviewer to accept the results shown thus far in a publication.
The accurate approach is to fit the spectrum with a doublet function for each oxidation state of the S. Constrain the area ratio (not height ratio) of the 3/2 to 1/2 to be 2:1. Constrain the separation distance of the p3/2 to p1/2 to be fixed as demanded by theory. Finally, constrain the half-widths to always be the same for both peaks in the doublet. This will end with three doublet functions, one for the S2-, one for the SCN, and one for the S (oxidizing) according to your labels. The peak fitting will vary the heights and half-widths of each doublet function. I routinely programmed and used this approach nearly two decades ago to fit doublet spectra in XPS. Therefore, by now, the proper approach with fixed doublets cannot be dismissed as too esoteric or advanced as to be ignored.
The spectrum shown also has a perfectly flat baseline. I find this odd. Has a baseline already been removed? If so, what was the shape? A Shirley baseline is preferably.
Any other approach to peak fitting is by now only an approximation. Finding a 10% variation after using an approximate method to peak fit an XPS spectrum is what I call an acceptable "first guess". I would however encourage a revision of the analysis prior to publication to take in to account the considerations that I have noted.
Show the spectrum - we need to see the peaks and their eV's. XPS only looks at the top 5 - 10 atomic layers. Have you Ar+ etched your sample?
Dear Sir,
Actually some publications says S in metal sulfides shown at 161.5 eV and some other publications says S in 2p 3/2 in SCN group shown at 163 eV....
I made an nano-composite which rich Covellite and -SCN in equal ratio...so I think 2p 3/2 of S in -SCN group and 2p1/2 of S in S2- group were overlapped and produce new peak with high intensity....(mentioned in the picture)
is there any possibility to happen this by some peak which has deficiencies with the metal ion?
It would be great If you can check and let me know whether my guessing is correct or incorrect.
Thanks
Dear Sir,
please note that your analysis should meet the constraint of a 2:1 intensity ratio for p3/2 and p1/2 contributions. According o the labels you used in the figure, the intensity of the peak caused by the overlap, i.e, "(S2-) S2p1/2 + (-SCN) S2p3/2", is expected to be 2x the intensity of the peak labelled "(-SCN) S2p1/2" + 0.5 x the intensity of the peak labelled "(S2-) S2p3/2". However, when looking at the figure with a graphic tool, the intensity of the "(S2-) S2p1/2 + (-SCN) S2p3/2" peak is about 20% larger than the expected value.
Quite siimilar, the intensity ratio of about 1.5 for the "S(Oxidizing)" peaks is much smaller than the expected ratio of 2.
Sincerely, FM
dear Dr Frank,
does this analysis must give the sharp ratio of 2:1 in p3/2 : p1/2? after calculate, according to you mentioned in your comment, I have calculated and the difference is around 10 %. if the difference is in that range did I able to prove my argument through this explanation in the figure?
The state of the art in XPS analysis is further advanced than shown in the spectrum. I would personally be reluctant as a reviewer to accept the results shown thus far in a publication.
The accurate approach is to fit the spectrum with a doublet function for each oxidation state of the S. Constrain the area ratio (not height ratio) of the 3/2 to 1/2 to be 2:1. Constrain the separation distance of the p3/2 to p1/2 to be fixed as demanded by theory. Finally, constrain the half-widths to always be the same for both peaks in the doublet. This will end with three doublet functions, one for the S2-, one for the SCN, and one for the S (oxidizing) according to your labels. The peak fitting will vary the heights and half-widths of each doublet function. I routinely programmed and used this approach nearly two decades ago to fit doublet spectra in XPS. Therefore, by now, the proper approach with fixed doublets cannot be dismissed as too esoteric or advanced as to be ignored.
The spectrum shown also has a perfectly flat baseline. I find this odd. Has a baseline already been removed? If so, what was the shape? A Shirley baseline is preferably.
Any other approach to peak fitting is by now only an approximation. Finding a 10% variation after using an approximate method to peak fit an XPS spectrum is what I call an acceptable "first guess". I would however encourage a revision of the analysis prior to publication to take in to account the considerations that I have noted.
Dear Sir,
your latest question that was adressed to me was perfectly answered by J.J. Weimer.
The 2:1 intensity ratio for photoemission from p-orbitals result from the general rule that the intensity ratio of a doublet is given by (L+1):L with L describing the angular momentum of the orbital (i.e. L = 0,1,2,3 for s,p,d,f orbitals).
The reason is as follows: when emitting a photoelectron from an L orbital the total angular momentum J, i.e. when coupling the angular momentum L with the spin S=1/2 of the photoelectron, is either J+ = L+S = L +1/2 or J- = L-S = L-1/2. The number of Eigenstates for the total angular momentum J is given by 2J+1.
Therefore the ratio J+ : J- is [2(L+1/2)+1] : [2(L-1/2)+1] = [2L+2] : [2L] = [L+1] : L. For p orbitas, i.e.L=1, the ratio p3/2 : p1/2 is therefore 2 : 1.
Sincerely, FM
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