Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5426353 | Surface Science | 2006 | 6 Pages |
The vibrational properties of CO on Ni(1Â 0Â 0) were investigated by high resolution electron energy loss spectroscopy. Loss measurements were performed as a function of temperature and CO exposures. At room temperature, regardless of CO coverage, we found stretching energies at 250Â meV and 240Â meV, assigned to CO at atop and bridge sites, respectively. At low temperature and for CO exposures lower than 0.6Â L, the loss spectra showed a single stretching peak at 240Â meV which is assigned to CO at bridge sites. For higher doses, a new intense peak at 260Â meV appeared in the loss spectra. The rise of this new loss strongly influenced the intensity of the peak at 240Â meV suggesting the occurrence of dipole couplings between adjacent CO molecules. This unusual high stretching frequency leads us to assign the peak at 260Â meV to the stretching vibration of CO molecules which are weakly bonded to the Ni surface. We suggest that the formation of this phase is due to an electronic effect arising from a reduced back donation of electrons into the empty Ï orbital of CO.