Electronic structure of aluminum and aluminum-noble-metal alloys studied by soft-x-ray and x-ray photoelectron spectroscopies

Abstract

X-ray photoelectron spectra (XPS) and $\mathrm{Al} K$ and $\mathrm{Al} {L}_{2,3}$ soft-x-ray spectra (SXS) of valence bands for aluminum-noble-metal alloys are rationalized on the basis that SXS spectra are dominated by dipole selection rules while XPS spectra chiefly reflect the noble-metal $d$ bands. We find, in agreement with theory, that the main peaks in the $\mathrm{Al} 3s$ partial densities of states are at higher binding energy than those for the noble metal $d$ states. Peaks in the $\mathrm{Al} 3p$ partial densities of states approximately coincide with the higher-energy peaks in the partial densities of noble-metal $d$ states. The remarkable large chemical shifts of core levels in these alloys are noted and the $\mathrm{Au} {N}_{6,7}$ SXS emission from aluminum-noble-metal alloys also discussed. The Auger spectra from Al-Ag and Al-Cu alloys provide strong additional evidence that single-atom effects dominate in the Auger processes for these alloys.