Showing posts with label Sulphur. Show all posts
Showing posts with label Sulphur. Show all posts

Sulphur

Table 1. S 2p3/2 binding energies compiled from the NIST database [1] and other sources.



Notes: 2p3/2 - 2p1/2 doublet separation = 1.18eV, peaks constrained to a 2:1 area ratio (2p3/2 : 2p1/2), generally one sets both peaks to an equal FWHM for ease of use although in pure samples this may not be the case.

Smart et al. [9] and Pratt et al. [10] give an excellent overview of binding energy ranges for the study of mineral surfaces. These ranges can be used with other sulphur containing systems as well. Of particular interest is the assignment for polysulphides eg. (S4)2- = 162.0-163.0 eV, (S5)2- = 161.9 - 163.2 eV, (Sx)2-) = 163.7 eV. Surface species can also play a role in XPS, especially for in-situ fractured sulphide mineral species [11].

[a] Nesbitt et al. [12] give a value of 162.2 eV for the disulphide in arsenopyrite.
[b] A more detailed look at organic sulphur species can be found here.

In a recent paper from Sarah Harmer's group at Flinders University, synchrotron XPS is used to convincingly elucidate surface 3-coordinate, bulk and surface 4-coordinate and bulk 5-coordinate sulfur in the chalcogenide (Fe,Ni)9S8.  This work shows that sulfide coordination changes can be seen by XPS [13].

A Na2S2O3.5H2O (sodium thiosulphite cooled to -130C during analysis) reference sample gave S 2p3/2 peak positions of 162.1 eV and 168.1 eV for S*SO3 and SS*O3 moieties, respectively.

There is a lot of confusion in the literature when presenting the data for sulphur. Some papers mention S 2p when they really mean S 2p3/2, these are not interchangeable! Please remember to be specific about the exact peak you are referring to.  

A recent paper from Clark et al. [14] highlights how widespread the issue of erroneous peak fitting of S 2p is.  Section B within this paper is worth a look as it highlights some of the common errors that should be avoided, these include:
1) Lack of spin–orbit splitting. Doublets (2p3/2 and 2p1/2 peaks) in their appropriate 2:1 ratios, respectively, should be used to represent each chemical state in the material.
2) Inconsistent and widely varying peak widths/full widths at half maximum (FWHMs).
3) Questionable assignments of the peaks to chemical species or oxidation states.
4) Backgrounds that cut through and then extend above the data on the high and low binding energy sides of the peak envelopes. 
5) Relatively large range of peak binding energy positions or fit components that are assigned as the same chemical states and should have well defined positions.
6) Noisy spectra, insufficient S/N.

References:
[1] C.D. Wagner, A.V. Naumkin, A. Kraut-Vass, J.W. Allison, C.J. Powell, J.R.Jr. Rumble, NIST Standard Reference Database 20, Version 3.4 (web version) (http:/srdata.nist.gov/xps/) 2003.
[2] Z.E. Pettifer, J.S. Quinton, S.L. Harmer, Minerals Engineering, 184 (2022) 107666.
[3] A.N. Buckley, W.M. Skinner, S.L. Harmer, A. Pring, L-J. Fan, Geochimica et Cosmochimica Acta, 73 (2009) 4452-4467.
[4] A.N. Buckley, W.M. Skinner, S.L. Harmer, A. Pring, R.N. Lamb, L.J. Fan, Y. Yang, Canadian Journal of Chemistry, 85 (2007) 767- 781.
[5] S.L. Harmer, A.R. Pratt, H.W. Nesbitt, M.E. Fleet, Canadian Mineralogist, 43 (5) (2005) 1619-1630.
[6] M.E. Fleet, X. Liu, S.L. Harmer, H.W. Nesbitt, Surface Science, 584 (2005) 133-145.
[7] V.P. Zakaznova-Iakovleva, S.L. Harmer, H.W. Nesbitt, G.M. Bancroft, A.R. Pratt, R. Flemming, Surface Science, 600(2) (2006) 348-356.
[8] A.R. Pratt, H.W. Nesbitt, American Mineralogist, 85 (2000) 619-622.
[9] R.St.C. Smart, W.M. Skinner and A.R. Gerson, Surface and Interface Analysis, 28 (1999) 101-105.
[10] A.R. Pratt, I.J. Muir and H.W. Nesbitt, Geochimica et Cosmochimica Acta, 58 (2) (1994) 827-841.
[11] H.W. Nesbitt, M. Scaini, H. Hochst, G.M. Bancroft, A.G. Schaufuss and R. Szargan, American Mineralogist, 85 (2000) 850-857.
[12] H.W. Nesbitt, I.J. Muir, A.R. Pratt, Geochimica et Cosmochimica Acta, 59 (9) (1995) 1773-1786.
[13] Z.E. Pettifer, J.S. Quinton, W.M. Skinner, S.L. Harmer, Applied Surface Science, 504 (2020) 144458. 
[14] B.M. Clark, G.H. Major, J.W. Pinder, D.E. Austin, D.R. Baer, M.C. Biesinger, C.D. Easton, S.L. Harmer, A. Herrera-Gomez, A.E. Hughes, W.M. Skinner, M.R. Linford, Journal of Vacuum Science and Technology A, 42 (2024) 063213.
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Organic Sulphur

Table 1. S 2p3/2 binding energies for organic sulphur compounds [1,2,3,4,5].  Note data from [2] has been corrected to C-C/C-H set to 284.8 eV (original work is corrected to 285.0 eV).

There is a lot of confusion in the literature when presenting the data for sulphur. Some papers mention S 2p when they really mean S 2p3/2, these are not interchangeable! Please remember to be specific about the exact peak you are referring to.  

Other Notes:
S 2p3/2 - S 2p1/2 splitting is 1.18 eV.
For thiol compounds attached to Au nanoparticles:
Au-S-C S 2p3/2 was found at 162.6 eV [3], 162.9 eV [4] and 162.8 eV [5]. 

References:
[1] C.D. Wagner, A.V. Naumkin, A. Kraut-Vass, J.W. Allison, C.J. Powell, J.R.Jr. Rumble, NIST Standard Reference Database 20, Version 3.4 (web version) (http:/srdata.nist.gov/xps/) 2003.
[2] G. Beamson, D. Briggs, High Resolution XPS of Organic Polymers - The Scienta ESCA300 Database Wiley Interscience, 1992.
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Copper Sulphides, Cu2S and CuS


Table 1. Cu 2p3/2 binding energies, Cu 2p3/2 - Cu LMM modified Auger parameters and S 2p3/2 binding energies for copper sulphides (Cu2S and CuS)[1].

CuS does not show shakeup peaks like CuO. CuS is weakly paramagnetic and behaves like a more metallic like species.

Further values for Cu2S (in vacuum cleaved chalcocite)[2].
Cu 2p3/2 = 932.5 eV
S 2p3/2 = 161.8 eV

CuInSe2 Auger Parameter: 1849.4 eV - 1849.6 eV [3]

References:
[1] C.D. Wagner, A.V. Naumkin, A. Kraut-Vass, J.W. Allison, C.J. Powell, J.R.Jr. Rumble, NIST Standard Reference Database 20, Version 3.4 (web version) (http:/srdata.nist.gov/xps/) 2003.
[2] M.C. Biesinger, B.R. Hart, R. Polack, B.A. Kobe, R.St.C. Smart, Miner. Eng. 20 (2007) 152.
[3] D. Cahen, P.J. Ireland, L.L. Kazmerski, F.A. Thiel, J. Appl. Phys. 57 (1985) 4761.
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Selenium and Sulphur

Quantification of sulphur in the presence of selenium by XPS is difficult from survey scan data due to the overlap of the S 2p peak with the Se 3p3/2 and Se 3p1/2 peaks and the S 2s peak with the Se 3s peak. It is possible, in some cases, to quantify the amounts of Se and S present using a high-resolution scan of the S 2p and Se 3p region (use a B.E. window of 174 - 154 eV). Using a Se 3p3/2 - 3p1/2 doublet separation of 5.8 eV (+/- 0.2 eV) (Se metal was found here to have a separation of 5.75 eV) and constraining the 3p3/2 - 3p1/2 peaks to a 2:1 ratio (constraint factor of A*0.5), the remaining structure may then be attributed to the S 2p peak(s). Of course this analysis will also give you information on the sulphur species present. Then, by using the correct R.S.F. values, a Se:S ratio can be obtained using a components quantification.

If the survey spectrum is collected at the same time, the survey scan data and high-resolution data can be combined using a "Regions and Comps" calculation (under the Report Spec. / Quantification Parameters window in CasaXPS) to give full quantification of all the elements present. Remember to set the R.S.F. to 0 for the Regions window of the high-resolution spectrum.

A closer look at the Se 3p spectrum shows that the Se 3p3/2-3p1/2 ratio may be closer to 7:3, or an area constraint factor of A*0.43. This may be due to some overlap of the Auger structure with the 3p peaks. A example of the final fit of the S 2p and Se 3p can be found here.

R.S.F. Values
S 2p3/2 = 0.4453
Se 3p3/2 = 0.84933
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