Electronic potential of a chemisorption interface

Abstract

7 pages, 4 figures.-- PACS nrs.: 73.20.-r. ; Chemisorption of atoms and molecules controls many interfacial phenomena such as charge transport and catalysis. The question of how the intrinsic properties of the interacting materials define the electronic structure of their interface remains one of the most important, yet intractable problems in surface physics. Through two-photon photoemission spectroscopy we determine a common binding energy of ~1.8–2.0 eV with respect to the vacuum for the unoccupied resonance of the ns valence electron of alkali atoms (Li-Cs) chemisorbed at low coverage (less than 0.1 monolayer) on noble metal [Cu(111) and Ag(111)] surfaces. We present a theoretical model based on the semiempirical potentials of the adsorbates and the substrates, their principal mode of interaction through the Coulomb interaction, and the ab initio adsorption structures. Our analysis reveals that atomic size and ionization potential independent interfacial electronic structure is a consequence of the Coulomb interaction among the ns electron, the alkali-atom ionic core, and the induced image charge in the substrate. We expect the same interactions to define the effective electronic potentials for a broad range of molecule/metal interfaces. ; This work was supported by the U.S. Department of Energy Grant No. DE-FG02-03ER15434. Some calculations were performed in the Environmental Molecular Sciences Laboratory, a user facility sponsored by the DOE Office of Biological and Environmental Research. N.P. thanks the Alexander von Humboldt Foundation for support. H.P. thanks Ikerbasque for the support of his stay at DIPC. The San Sebastián group acknowledges support by the Spanish MEC grant, the European FP6-NoE grant "Nanoquanta", the UPV/EHU and the projects "NANOMATERIALES" and "NANOTRON" of the Basque Government and the Diputación de Guipúzcoa. ; Peer reviewed