AVS 52nd International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM3
Freidel Oscillations: S and CO Metal Mediated Interactions

Tuesday, November 1, 2005, 9:00 am, Room 202

Session: Vibrational Spectroscopy of Surfaces
Presenter: C.J. Hirschmugl, University of Wisconsin-Milwaukee
Authors: X.F. Hu, University of Wisconsin-Milwaukee
C.J. Hirschmugl, University of Wisconsin-Milwaukee
Correspondent: Click to Email
The coadsorption of CO and S on Cu(100) is examined to gain a deeper understanding of metal-mediated interactions between co-adsorbates. Using a combination of IRAS, Auger Electron Spectroscopy (AES) and TDMS, we find that CO adsorbates do not occupy the first and second nearest-neighbor adsorption sites of S adatoms, but are strongly bound to third-nearest neighbor sites. Simple site-blocking can explain the absence of CO adsorption at first-nearest neighbor sites. However, we attribute the second- and third-nearest neighbor results to S-induced changes in the LDOS. A local minimum is induced at second-nearest sites, suppressing CO adsorption, but a local maximum at third-nearest sites enhances the C-metal bonding strength. Bonding to these sites is stronger than even on the clean Cu(100) surface. Furthermore, the C-O stretch frequency and the dipole-dipole coupling are affected by the S coverage. For a low S coverage, where dipole-dipole coupling is still dominant, a Coherent Potential Approximation (CPA) treatment of dipole-dipole coupling is used to estimate the spatial extent reffective of S and CO substrate-mediated interactions. reffective is found to be between 6 ~ 7 Å. This work shows that S affects the CO adsorption in three ways: making adsorption sites electronically unfavorable, affecting the interface bonding between CO and Cu, and reducing the CO intermolecular interaction.