Theoretical study of CO and Pb adsorption on the Ni(111) and Ni_3Al(111) surfaces

摘要

Adsorption of CO molecules and Pb atoms on the Ni(111) and Ni_3Al(111) substrates is studied theoretically within an ab initio density-functional-theory approach. Stable adsorption sites and the corresponding adsorption energies are first determined for stoichiometric surfaces. The three-fold hollow sites (fcc for Pb and hep for CO) are found most favourable on both substrates. Next, the effect of surface alloying by a substitution of selected topmost substrate atoms by Pb or Ni atoms on the adsorption characteristics is investigated. When the surface Al atoms of the Ni_3Al(111) substrate are replaced by Ni atoms, the Pb and CO adsorption energies approach those for a pure Ni(111) substrate. The Pb alloying has a more substantial effect. On the Ni_3Al(111) substrate, it reduces considerably adsorption energy of CO. On the Ni(111) substrate, CO binding strengthens slightly upon the formation of the Ni(111)p(2 × 2)-Pb surface alloy, whereas it weakens drastically when the Ni(111)(3~(1/2) × 3~(1/2))R30°-Pb surface alloy is formed.