Long-range metal-mediated interactions between S and CO on Cu(100)

The infrared study of carbon monoxide (CO) on presulfided Cu(100), combined with Auger electron spectroscopy and thermal desorption mass spectrometry, reveals that sulfur (S) introduces a long-range modification (Friedel oscillations) to the local density of states, which affects the bond strength of CO adsorbates. A local minimum of the LDOS is induced at the second nearest neighbor adsorption sites, suppressing CO adsorption, but a local maximum at the third nearest neighbor adsorption sites enhances the C-metal bond strength. For a low S coverage, where dipole-dipole coupling is still dominant, a coherent potential approximation treatment of dipole-dipole coupling by Persson and Ryberg is used to estimate the spatial extent (r{sub effective}) of S and CO metal-mediated interactions. r{sub effective} is found to be between 6-7 Angstroms.