High-frequency phonon modes on stepped and kinked Cu surfaces: Experiments and theory

Using electron energy loss spectroscopy, we have found step-localized vibrational modes with frequencieshigher than those of the bulk phonons on Cu(532) and Cu(211). From structural and lattice dynamical calcu-lations based on many-body interaction potentials, we trace the origin of these modes to local effects involvingsurface relaxations and resulting stiffening of force constants between the step (or kink-site) atom and its‘‘bulk’’ nearest neighbor. Such modes are not observed on Cu(511) and Cu(17,1,1), although they are pre-dicted in the theoretical calculations. We discuss the impact of these results on systems with bond-length–bond-order correlation.