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 AuₗPd₁-ₗ 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, ₈₉₊^Au, are small. This result supports the validity of the relation ₈₉₊^Au-E₅^Au==E₅^Au-E₅ (x) where E₅^Au and E₅ (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, ^Au, as well as with analysis of ^Au, the valence-electron contribution to the Au XPS core binding energy; we predict that 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.