The effect of final state screening changes on alloy energy shifts

The effect of screening of the final state in Auger and photoemission has been the subject of various studies. In particular, investigations of energetics have yielded consider-able insight into the screening process, as, for example, in studies of the Auger parameter in the 3d, 4d and 5d series of transition and noble metals. It is clear that changes in the nature of the screening electrons from d- to sp-type reduces the efficacy of the screening, which affects the Auger parameter significantly. Extension of these results to analysis of XPS and Auger energy shifts in alloys produces some important differences from the form of the conventional expression, which supposes that the energy shift is linear in the ground state d- and sp-electron occupation changes (delta n(d) and delta n(s), respectively). Basically, the form of the conventional expression is correct for alloys in which the nature of the screening electrons does not change during the screening of the final state. When, however, the screening electrons' nature changes from d- to sp-type during the screening, the corresponding energy shift remains linear in delta n(s), but comes quadratic in delta n(d) and is sensitive to the number of ground state d-band holes. This situation holds for the Auger shift in Ni, Pd and Pt and the XPS shift in Cu, Ag and Au. Since it is now recognized that the determination of alloy occupation changes requires measurement of both Auger and XPS shifts, we examine the consequences of these new expressions for the shifts of a number of alloys, especially AuPd. The results are consistent with those derived independently from the transitivity of noble metal Auger shifts. In all the complete solid solutions we examine the charge transfer is on the order of 0.01 electrons/atom. Furthermore, we reexamine some alloy results from the literature, those of AuZn and AuMg.