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

TL;DR

This study uses ab-initio calculations to reveal how quantum-size effects cause oscillations in CO chemisorption energy on Cu ultrathin films, linking electronic structure changes to surface chemistry.

Contribution

It demonstrates that quantum-well state decay length oscillations, not density of states, explain chemisorption energy variations with film thickness.

Findings

Chemisorption energy oscillates with film thickness.

Oscillations are linked to quantum-well states crossing the Fermi level.

Density of states does not account for the chemisorption trend.

Abstract

We address, by means of ab-initio calculations, the origin of the correlation that has been observed experimentally between the chemisorption energy of CO on nanoscale Cu(001) supported films and quantum-size effects. The calculated chemisorption energy shows systematic oscillations, as a function of film thickness, with a periodicity corresponding to that of quantum-well states at the surface-Brillouin-zone center crossing the Fermi energy. We explain this trend based on the oscillations, with film thickness, of the decay length on the vacuum side of the quantum-well states at the Fermi energy. Contrary to previous suggestions, we find that the actual oscillations with film thickness of the density of states per atom of the film at the Fermi energy cannot account for the observed trend in the chemisorption energy.