Electron energy loss studies of room-temperature co adsorption on Cu(100) induced by electron or ion irradiation

A custom-built multi-technique portable spectrometer was used to study the vibrational (and electronic) excitations associated with the “anomalous” CO adsorption recently observed on clean and oxidized Cu(100) surfaces at room temperature. Results from the electron energy loss (and thermal desorption) experiments have provided strong evidence for in-situ CO production induced by low-energy electron or ion irradiation of CO or C₂H₄ on Cu(100). In particular, the C-O vibrational stretch frequency for the room-temperature CO adsorption was found to be red-shifted by 9 meV from its nominal position (259 meV) and could be observed even at temperature as high as 420 K. Several plausible mechanisms involving coadsorbate interactions with CO on metal surfaces have been discussed. A direct interaction model involving partial bonding between CO, adsorbed on an atop site, and a coadsorbed O atom in a four-fold hollow site was found to be adequate in explaining the observed red shift and the apparent stabilization of CO on Cu(100) at room temperature.