The Auger parameter (α) can be a useful tool in assisting the correct identification of surface chemistry of a sample analysed by XPS. Often, while an electron core level of two states may be indistinguishable in terms of binding energy, the Auger transition may reveal distinct differences either in peak position or fingerprint shape (e.g. Copper).
Charles Wagner was the first to propose an Auger parameter, using the difference in kinetic energy between a core line and auger maxima to describe chemical states in XPS using equation 1.(1)
α = Ek(C1C2C3) – Ek(C) Equation 1
Where Ek(C1C2C3) is the energy of the Auger, and Ek(C) that of the core photoelectron peak.
This would come to be modified by Stephen Gaarenstroom and Nicolas Winograd(2) to use the binding energy of the core emission rather than the kinetic energy, and thus create a term independent of photon energy; the modified Auger parameter, α’ (equation 2).
α = Ek(C1C2C3) + EB(C) Equation 2
- Wagner, C. (1972). “Auger lines in x-ray photoelectron spectrometry.” Analytical Chemistry 44(6): 967-973. Read it online here.
- Gaarenstroom, S. and N. Winograd (1977). “Initial and final state effects in the ESCA spectra of cadmium and silver oxides.” The Journal of chemical physics 67(8): 3500-3506. Read it online here.