Electronic structure of transition-metal-transition-metal interfaces: Pd on Nb(110)

With the use of a self-consistent tight-binding scheme, local electronic densities of states (LDOS) are calculated for commensurate (C) Pd* (110) and incommensurate (IC) Pd(111) layers on Nb(110). At low coverages ($\Theta <1\mathrm{}$) Pd induces a Pd-Nb resonance near the bottom of the Nb $d$ band. In agreement with the experimental results this resonance shifts to lower binding energy as the coverage is increased. Comparing detailed features of the LDOS with the photoemission data we predict a C-IC structural transformation for approximately one monolayer of Pd. This we also conclude from a simple interface energy calculation. The $d$-electron charge transfer across the interface and the LDOS of Pd at the Fermi energy ($E_F$) are small. The latter, however, increases with the Pd coverage. The LDOS of the top Pd layer is nearly the same for Pd(111) on Pd* (110)-Nb(110) or Pd(111)-Nb(110) interfaces and in all cases there is a significant decrease of Nb $d$ states near the $E_F$. This shows that the LDOS is mainly perturbed at the interface. Implications of these results for hydrogen uptake and work-function changes are discussed.