Adsorbate Effects on a Mixed-Valence Compound: Carbon Monoxide Chemisorption on CeIr2

摘要

We have studied the effects of stoichiometry change and CO chemisorption on the surface electronic structure of the mixed-valence compound CeIr22. We show that the surface iridium to cerium ratio can be varied by changing sample temperature while sputtering. Carbon monoxide is found to adsorb 80% molecularly on the surface and cause a mild surface oxidation which induces a shift of electron density into available cerium f orbitals. Peaks due to the 4 sigma, 1 pi, and 5 sigma CO molecular orbitals appear at different binding energies than those due to molecular CO on the pure iridium surface. This binding-energy shift as well as the high percentage of molecular CO on the surface (CO adsorption on pure cerium is completely dissociative) points toward a surface which has lost much of the elemental character of its two constituents upon compound formation. Keywords: Cerium, Iridium, Reprints. (MJM)