Electronic structure of copper-rich copper-palladium alloys

In considering the electronic structure of (Cu-rich) $\mathrm{Cu}\mathrm{Pd}$ alloys, we present computations of complex-energy bands and average densities of states together with the angle-resolved photoemission spectra from the (100), (111), and (110) surfaces of ${\mathrm{Cu}}_{95}$ ${\mathrm{Pd}}_5$ and ${\mathrm{Cu}}_{85}$ ${\mathrm{Pd}}_{15}$ single crystals. The impurity spectrum in $\mathrm{Cu}\mathrm{Pd}$ is found to be dominated by two quite-well-separated Pd-derived impurity bands and differs sharply from the case of $\mathrm{Cu}\mathrm{Ni}$ or $\mathrm{Ag}\mathrm{Pd}$ systems, where only a single Ni- or Pd-related impurity structure appears in the alloy. Extensive comparisons between the theory and experiment are carried out with regard to the positions and halfwidths of the Pd-induced impurity structures, the level shifts and disorder smearings of the Cu-derived bands, and the shifts in the binding energies of the $\mathrm{Cu}2p$ and $\mathrm{Pd}3d$ core levels. A remarkably good agreement is found to exist in all cases. The (111) Shockley state is observed to lie at a binding energy of 0.2 eV (with respect to the Fermi energy) in ${\mathrm{Cu}}_{95}$ ${\mathrm{Pd}}_5$ and to possess an increased full width at half maximum (compared to Cu) of 60 meV. This state moves just above the Fermi energy in ${\mathrm{Cu}}_{85}$ ${\mathrm{Pd}}_{15}$. These effects can also be understood in terms of the changes in the bulk electronic spectrum of Cu upon alloying with Pd.