Inelastic atom scattering from layers of atoms and molecules on Cu(110)

The vibrational properties of adsorbed layers have been studied using inelastic He atom scattering. The substrate was Cu(110) viewed along the [001] and [11̄0] azimuth. The adsorbates included, Kr, Xe, CH₄, CD₄, C₂H₆, CO, CO₂ and O₂ and covered the region of both physisorption and chemisorption. Despite a range of binding energies and mass ratios the vibrational frequencies showed no dependence on the momentum change, i.e. scattering was dispersionless, although intensity changes occurred in the inelastic peaks. There seemed to be no dependence of the adsorbate spectra on coverage below a monolayer. The peaks of CH₄ and C₂H₆ appeared broader than those of Kr and Xe suggesting molecular motions. Further, CH₄ and C₂H₆ gave very similar spectra. Both energy gain and loss events were observed in the inelastic spectrum. For those adsorbates which gave multilayer adsorption (Xe, C₂H₆) changes in the spectra were observed as the second layer developed. In the latter category also, mixed layers (Xe on C₂H₆, Xe on CO and C₂H₆ on Xe) were studied.