Spectator vacancy contributions to the L(2,3)M(4,5)M(4,5) Auger spectra of Pd and Rh: Satellites as images of the main spectrum

Interpretation of the satellites of the Cu L(2,3)M(4,5)M(4,5) has involved considerable controversy in recent years. Reaching unambiguous conclusions is impeded by the contribution of L(2)L(3)M(4,5) and L(1)L(2)M(4,5) Coster-Kronig (CK) transitions, so that considerable experimental investigation is required before clarifying the relative roles of shake-up and CK processes in this case. The L(2,3)M(4,5)M(4,5) spectra of Ag, Pd and Rh excited by bremsstrahlung also have satellite features. For Ag, we have shown that the experimental measurements are consistent with an interpretation in which the satellites arise from valence band spectator vacancies in L(2,3)N(4,5) --> M(4,5)M(4,5)N(4,5) and L(2,3)M(4,5)N(4,5) --> M(4,5)M(4,5)N(4,5)N(4,5) processes. The Pd and Rh spectra we report here manifest similar experimental systematics: (A) both the L(3) and L(2) losses are displaced the same amount relative to their respective main peaks; (B) the ratio of the L(3) and L(2) intensities is very close to the statistical ratio, suggesting little CK contribution; (C) the shapes of both satellite structures are approximately the same and cannot arise from multiplet splitting of the final states with the spectator vacancies; (D) the satellite to main peak intensity ratios are very similar for both the L(3) and L(2) spectra; (E) comparison with spectra from PdAg alloys indicate the intrinsic nature of the losses; and (F) energy loss spectra present lineshape variations inconsistent with the satellite measurements. We demonstrate that the Pd and Rh satellite relative positions and lineshapes are consistent with the spectator vacancy interpretation. In particular, the satellite lineshapes appear to correspond basically to broadened, displaced ''images'' of the corresponding main spectra. It would seem, therefore, that the bremsstrahlung excited Pd and Rh L(2,3)M(4,5)M(4,5) satellites are almost entirely caused by intra-atomic shake-up processes; the ''image'' nature of their lineshapes resembles that of extrinsic losses such as plasmons in other metals.