The adsorption of Al on Pd(001) and of O and CO on an interfacial Al-alloyed Pd(001) surface

The adsorption of ultrathin Al films on Pd(001) and adsorption of oxygen and carbon monoxide on an interfacial Al-alloyed Pd(001) surface have been examined via low energy He+ ion scattering, low energy electron diffraction and work function change (ΔΦ) measurements. For low Al coverages at 325 K, interaction between Al and the Pd substrate is observed, resulting in the loss of near surface order by an Al coverage of 0.5 monolayer (ML). The adsorption of Al results in a work function decrease. Annealing Al films with initial coverages from 0.5 ML to larger than 1 ML at 750–950 K leads to interfacial alloying and a stable (2 × 2)p4g LEED pattern dominates the surface structure. This structure has been determined to be a clock rotated (001) Pd top layer above a mixed c(2 × 2) AlPd underlayer. Adsorption of oxygen on the (2 × 2)p4g surface at 325 K induces Al segregation and lifts the reconstruction. In contrast, the interaction of CO with the (2 × 2)p4g surface dose not lift the reconstruction. The implications of these results for relative stability of AlO bond strength are discussed.