Sensitivity factor are dependent various factors, the well-known parameters include the intrinsic properties of the elements (cross section of different orbits of different elements), illumination condition and analyzer transmission (instrument geometry and analyzer setting), and the sample (surface) itself.
1) For non-spherical p- and d- orbital instrument geometry does matter, but their relative ratio does not change as much.
2) Sensitivity factor is directly related to the peak intensity and area measurement, so whatever influence them also influence the sensitivity factors, such as the spectral resolution (instrument and resolution dependent broadening), as well as baseline.
3) However, in the case of real surfaces, the biggest error on composition determination tends to come from the non-uniform depth distributions. Sensitivity factors yield quantitative information as such only for homogeneous, non-contaminated surfaces.
So, while surface compositions (calculated by area and sensitivity factor) does show relative changes and trends and are of great practical value, but one should take extreme cautions when use them as absolute quantification without experimentally proven information on surface distributions. Techniques which can provide such information include RBS, SIMS, and also possiblly by comparing XPS baseline changes.
A few references:
D. Briggs and M. P. Seah, Practical Surface Analysis (John Wiley & Sons, Chichester), Chapter 5, 2nd Edition (1996)
C. D. Wagner, Sensitivity factors for XPS Analysis of surface atoms, Journal of Electron Spectroscopy and Related Phenomena 328, 99-102 (1988)
R. F. Reilman, A. Msezane and S. T. Manson, Relative intensities in photoelectron spectroscopy of atoms and molecules, Journal of Electron Spectroscopy and Related Phenomena 8, 389-394 (1976)
S. Tougaard, Quantitative XPS: non-destructive analysis of surface nano-structure, Applied Surface Science 100-101, 1-10 (1996)
J. E. Castle, A. M. Salvi, Chemical state information from the near-peak region of the X-ray photoelectron background, Journal of Electron Spectroscopy and Related Phenomena 114-116, 1103-1113 (2001)
J. R. Shallenberger, Determination of chemistry and Microstructure in SiOx (0<0.8) films by x-ray photoelectron spectroscopy, J. Vac. Sci. Technol. A14(3), 693-698 (1996)
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