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 Au(x)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, DELTA-epsilon-ijk(Au), are small. This result supports the validity of the relation DELTA-epsilon-ijk(Au) congruent-to - DELTA-E(F)Au = E(F)Au - E(F)(x) [where E(F)Au and E(F)(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 charger 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, DELTA-xi(Au), as well as with analysis of DELTA-omega(Au), the valence-electron contribution to the Au XPS core binding energy; we predict that DELTA-xi congruent-to DELTA-omega for noble metals in general. This analysis yields the result that the dilute Au d-valence-electron occupations change congruent-to -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.