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

We have measured the Ni L3VV 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 UA, 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 UA 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 L3VV feature sharpens considerably in alloys with, for instance, Al, La, and Th, so that the d8 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.