| AVS 64th International Symposium & Exhibition | |
| Applied Surface Science Division | Tuesday Sessions |
| Session AS+MI+SS-TuM |
| Session: | Quantitative Surface Analysis: Effective Quantitation Strategies |
| Presenter: | B. Vincent Crist, XPS International LLC |
| Authors: | B.V, Crist, XPS International LLC C.R. Brundle, C. R. Brundle and Associates |
| Correspondent: | Click to Email |
It is common, in the practical world, to use the most intense XPS peaks from survey spectra, in combination with instrument software RSF’s, for atom percent quantitation. The advantage is obvious: time saved. Occasionally, peak overlaps force the use of a secondary peak plus a ratio of RSF’s. The origin of that ratio is usually based on theoretical cross-sections, σ (1), corrected for transmission function, T, and escape depth, λ.
Using clean elemental surfaces the validity of using relative σ’s for peaks in the spectrum was tested. Some large discrepancies were found. The same occurred for some crystal materials and bulk polymers. Two possible causes are errors in σ’s, or variations in intensity losses to satellites, invalidating the use of main peak intensities plus σ values (σ includes intensity from all final states). σ values should be good to better than 10% error (1). Intensity losses can vary with core level, but there are examples here where this does not seem to be the problem.
Suppliers’ RSF’s come either from theoretical σ’s (1), or from empirical standards (2) where only main peaks are included. Except for 1st row elements there are significant discrepancies (>30%) between the approaches. We discuss possible reasons and note:
(a) the suppliers’ empirical standard based RSF’s all seem to be derived from the data of Wagner, et al. (2). That Herculean study included results from other studies on a range of poorly characterized instruments and samples whose surface compositions might be suspect.
(b) The discrepancies cannot be explained by the lack of inclusion of satellite intensities for the standards approach, as any correction generally worsens agreement.
We conclude it is time for a reexamination of the standards approach with modern instruments and better controlled samples. It is now possible to theoretically estimate the fraction of total intensity lost to satellites (3) and so to establish what fraction of σ should be used when relying on main peak intensities.
1 J. H. Scofield, J. Elec. Spec. 8, 129 (1976)
2 C. D. Wagner, et al, Surface Interface Analysis, 3, 211, (1981)
3 P. S. Baguset al., J. Chem. Phys., in press (2017).