Advanced Quantification Combining Survey Scan and High Resolution Data

Using a combination of the results from survey scans and fitted high resolution data one can, using relatively simple math, develop a clear picture of the different species on a surface.  Recent work [1,2] highlights this and will be used as an example below.

A series of oxide films of Ni-Cr-Mo alloys (corrosion resistant alloys in both oxidizing and reducing environments) where analysed by XPS.  Survey scans (how to quantify here) and high resolution scans of the Ni 2p, Cr 2p, Mo 3d, O 1s and C 1s peaks were taken and the various chemical states determined and quantified using the curve-fitting procedures from [3-5] and [6].


Figure 1. XPS survey spectrum recorded on C22 after polarization at 0 V (+) in a pH = 7 solution.

Figure 2. Surface composition (normalized) obtained from the survey spectra of (a) C22 and (b) BC1 alloy after polarization at, 0 V and 0.5 V (positive scan) and 0 V and -0.4 V (negative scan) at pH = 7 solution. (The small amount of adventitious carbon has been factored out of these quantifications.)  

Carbon, which was mainly present as a small amount of adventitious carbon, has been simply factored out of the quantification in this case.  In cases where carbon plays a bigger role or is part of the species of interest one must include it in the calculations.  For example, if you want to calculate the contribution of carbonaceous oxygen in the O 1s spectrum you can use this calculator.


Figure 3. High-resolution deconvoluted XPS spectra for (a) O 1s, (b) Ni 2p, (c) Cr 2p and (d) Mo 3d collected on C22 at 0 V (+) and pH = 7.

These deconvoluted spectra will give us the percentage of each species as a function of each element. For example, 70% of the total Cr is present as Cr(OH)3, 20 % as Cr2O3 and 10 % as Cr metal.


Figure 4. Normalized relative film composition (%) of Ni, Cr and Mo and their relative metal, oxide, hydroxide components present in films polarized at specific potentials for (a) C22 and (b) BC1 alloy.

In Figure 4 the percentages of each oxide and metal species, from the high resolution data, has been combined with the amounts of each element in the survey scan data to give us a full picture of the amount of each species present at the surface of these films.

Caveat: Depth effects have not been accounted for here. Further work using Auger and/or XPS depth profiling, angle resolved analysis or QUASES analysis can help to further clarify the positions of various species. It is of course assumed here that the metal detected is from the underlying alloy.

References:
[1] Ebrahimi, Nafiseh, "The Influence of Alloying Elements on The Crevice Corrosion Behaviour of Ni-Cr-Mo Alloys" (2015). Electronic Thesis and Dissertation Repository. 3316.  http://ir.lib.uwo.ca/etd/3316
[2] N. Ebrahami, M.C. Biesinger,D.W. Shoesmith, J.J. Noel, The Influence of Chromium and Molybdenum on the Repassivationof Nickel-Chromium-Molybdenum Alloys in Saline Solutions, Surface and Interface Analysis, 49 (2017) 1359.
[3] M.C. Biesinger, B.P. Payne, A.P. Grosvenor, L.W. Lau, A.R. Gerson, R.St.C. Smart, Appl. Surf. Sci. 257 (2011) 2717.
[4] M.C. Biesinger, B.P. Payne, L.W. Lau, A.R. Gerson, R.St.C. Smart, Surf. Interface Anal. 41 (2009) 324.
[5] M.C. Biesinger, C. Brown, J.R. Mycroft, R.D. Davidson, N.S. McIntyre, Surf. Interface Anal. 36 (2004) 1550.
[6] P. Spevack, N.S. McIntyre, J. Phys. Chem. 96 (1992) 9029.