Observation of Structure-Induced Surface Vibrational Resonances on Metal Surfaces

A new kind of dipole-active surface vibrational resonance has been observed on (110) surfaces of Cu and Ni by electron-energy-loss spectroscopy. An analysis based on lattice dynamics suggests that such resonances should be observable on surfaces where a single bulk-phonon dispersion relation has a pseudo band gap in the probed phonon density of states. In the [110] direction of facecentered-cubic metals this gap is due to the particular geometric structure in that direction.