X-ray photoemission and Auger energy shifts in some gold-palladium alloys

We report the results of x-ray photoemission (XPS) and Auger electron spectroscopies in the alloy Auₓ{Pd}_{1{{-}}x}$ for various concentrations. By comparing the predictions of the excited-atom version of the quasiatomic model with the dilute Au results, we show that charge-transfer corrections to the Au Auger kinetic-energy shift, {Δ}εᵢⱼₖAu, are small. This result supports the validity of the relation {Δ}εᵢⱼₖAu{}-{Δ}EFAu==EFAu-EF(x) [where EFAu and EF(x) are the Fermi energies in pure Au and the alloy, respectively] and permits determination of the order of magnitude of the charge transfer from Auger measurements alone (i.e., hundredths of electrons/atom). Such small charge transfer seems to hold also for the Ag and Cu atoms in Pd-Ag, Au-Ag, Pd-Cu, and Au-Cu. Furthermore, these results are consistent with interpretation of the Au Auger parameter shift, {Δ}ξAu, as well as with analysis of {Δ}ωAu, the valence-electron contribution to the Au XPS core binding energy; we predict that {Δ}{ξ}{}{Δ}{ω} for noble metals in general. This analysis yields the result that the dilute Au d-valence-electron occupations change {}-0.2 electrons/atom, approximately the negative of the sp change from isomer shifts. The Pd results are consistent with small charge transfer and a small gain of d electrons.