Surface Chemical Reactivity of Ultrathin Pd(111) Films on Ru(0001): Importance of Orbital Symmetry in the Application of the d-Band Model

摘要

The chemical bonding of adsorbate molecules on transition-metal surfaces isstrongly influenced by the hybridization between the molecular orbitals and themetal d-band. The strength of this interaction is often correlated with thelocation of the metal d-band center relative to the Fermi level. Here, weexploit finite size effects in the electronic structure of ultrathin Pd(111)films grown on Ru(0001) to tune their reactivity by changing the film thicknessone atom layer at a time, while keeping all other variables unchanged.Interestingly, while bulk Pd(111) is reactive towards oxygen, Pd(111) filmsbelow five monolayers are surprisingly inert. This observation is fully in linewith the d-band model prediction when applied to the orbitals involved in thebonding. The shift of the d-band center with film thickness is primarilyattributed to shifts in the partial density of states associated with the 4dxzand 4dyz orbitals. This study gives an in-depth look into the orbital specificcontributions to the surface chemical reactivity, providing new insights thatcould be useful in surface catalysis.