Electronic structure of Ni and Pd alloys. III. Correlation effects in the Auger spectra of Ni alloys

Abstract

We have measured the Ni $L_3\mathrm{VV}$ Auger spectra of 27 Ni alloys. The line shape, including multiplets, is calculated with the use of a method based on an approximate solution developed by Cini for a filled $s$ band. For Ni metal and its alloys, we have determined the values of $U^A$, the shift of the main Auger peak with respect to the energy calculated for Auger final states in which the two final-state holes are uncorrelated. We find changes in $U^A$ to be less than 1.4 eV, despite changes in Ni $d$-band occupation and in the density of states at the Fermi level. An "excitonic" screening mechanism which explains these features is discussed. The Ni $L_3\mathrm{VV}$ feature sharpens considerably in alloys with, for instance, Al, La, and Th, so that the $d^8$ multiplet structure can be partially resolved. Two new mechanisms of line-shape broadening are found to dominate the Auger linewidths. The mechanisms are "hole-assisted dispersion," arising from the holes in the Ni $d$ bands, and "dissociational broadening," in which one of the valence-band holes left by the Auger process can move on to the partner-element site.