First Direct Measurement Of The Energy Spectra Of Individual Auger Cascade Steps In Solid MnO, Ag And Pd

We present the first direct measurements of energy spectra of electrons emitted in the later steps of the Auger cascade processes in solids. Measurements were carried out for the L-->MV-->VVV and L-->MM-->MVV-->VVVV Auger cascades in MnO and L-->MM-->MVV, M-->NV-->VVV Auger cascades in Ag and M-->NV-->VVV Auger cascade for Pd. The spectra associated with the later steps in the cascade were separated from overlapping spectral contribution from other decay processes by acquiring the cascade induced spectra in time coincidence with Auger electrons emitted in the prior cascade step. The Auger spectra associated with the decay of core holes created via, Auger cascade processes are significantly wider than spectra associated with Auger decays in directly following the photo-ionization of the core hole. A new theoretical model was developed to allow for the inclusion of processes in which holes generated in the valence band in a prior cascade step change to a different energy in the valence band during the next cascade step. A comparison of the measured spectra with model calculation enabled an estimation of the valence-valence, core-core, and core-valence correlation energies. The success of the model in accounting for the increased width observed in the spectra of Auger electrons emitted in the later steps of the Auger cascade provides strong evidence that valence holes left from the previous cascade step participate in the subsequent Auger transitions in the case of transitions involving the outer cores.