Quantum-size effects on chemisorption properties: CO on Cu ultrathin films

摘要

We address, by means of ab-initio calculations, the origin of the correlationthat has been observed experimentally between the chemisorption energy of CO onnanoscale Cu(001) supported films and quantum-size effects. The calculatedchemisorption energy shows systematic oscillations, as a function of filmthickness, with a periodicity corresponding to that of quantum-well states atthe surface-Brillouin-zone center crossing the Fermi energy. We explain thistrend based on the oscillations, with film thickness, of the decay length onthe vacuum side of the quantum-well states at the Fermi energy. Contrary toprevious suggestions, we find that the actual oscillations with film thicknessof the density of states per atom of the film at the Fermi energy cannotaccount for the observed trend in the chemisorption energy.