Measurements were made by x-ray photoelectron spectroscopy of the 4f level energies in Au and the 3d level energies in Ag with these elements in several forms: pure metals, Au-Ag alloys, AuA12, and AuGa2. Only very small core-level energy shifts are seen, even though existing Mossbauer isomer-shift data for Au show that there are differences in s charge at Au sites such that one would anticipate substantial level shifts. These two sets of observations are interpreted within the framework of band theory to mean that when Au is alloyed with Ag, Al, or Ga, the flow of s charge onto Au sites is accompanied by a compensating depletion of d charge. The problems associated with relating chemical shifts in alloys to charge flow are considered in some detail. 't is concluded that the ratio of d depletion to conduction electron gain is 0. 6+ 0. 2 in the case of Auo 5 Ago &, and similar behavior is encountered in other Au alloys.

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The (initial state) core-level shifts of transition metals in bulk alloys and for bimetallic adlayer systems are calculated and analyzed in terms of extra-and (l-decomposed) intra-atomic contributions. Both the trends and magnitudes of the calculated shifts are consistent with experimental data where they exist. Core-level shifts of the same sign for both constituents are common in both alloy and adlayer systems. The commonly used "charge transfer" model for interpreting core-level shifts is shown to be grossly inadequate, especially for describing the adlayer shifts; for bulk alloys, however, there is a correlation between the shifts and the changes in the d electron count. The results support the view that the bonding in bulk alloys and adlayers is fundaxnentally the same; in particular, there is no evidence for any anomalous charge transfer in adlayer systems. The extraatomic contributions to the adlayer shifts are found to dominate the total shifts for Cu/Rh(001), Cu/Ta(110), and Pd/Ta (110), with the intra-atomic contributions often having the opposite sign compared to the total shift. For the substrate, however, the intra-atomic contributions are relatively more important, suggesting that substrate core-level shifts may provide a better measure of the local chemical e6'ects than adlayer shifts. The relationship of core-level shifts to other physical properties is also discussed.

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