Electronic structure of Au and Ag overlayers on Ru(001): The behavior of the noble-metal d bands

The metal d bands of Au and Ag individually adsorbed on Ru(001) have been observed with photoemission as have the core 4f levels of Au. The adlayer d bands display shifts in their centroids as well as band narrowing due to having fewer noble-metal nearest neighbors relative to bulk metals. The narrowing may be monitored by measuring the doublet nature of these valence-band densities of states or by sampling the overall d-band width with the former not susceptible to instrumental broadening problems. These widths receive contributions from spin-orbit splitting ${\mathrm{\Delta }}_{\mathrm{s}.\mathrm{o}.\mathrm{}}$ and intrinsic d-band effects ${\mathrm{\Delta }}_{\mathrm{band}}$. These have been separated and the inferred ${\mathrm{\Delta }}_{\mathrm{band}}$ for a Au monolayer suggests that the substrate is contributing measurably to the Au bandwidth while having little or no effect on Ag. Providing that the Au adlayer 4f-level shifts are measured with respect to the surface of Au rather than the bulk, a consistent picture of d-band and core-level chemical shifts emerges that, granted the lower number of unlike nearest-neighbor atoms, is compatible with what has been previously observed for bulk noble-metal alloys.