Geometric structure and surface vibrational resonances: The bcc Fe(111) surface

Abstract
The influence of strong multiple interplanar forces is shown to give rise to a new class of surface vibrational resonances on metal surfaces as a result of higher-harmonic terms in the bulk-phonon dispersion relations. This effect is illustrated with the bcc Fe(111) surface where a surface resonance is observed at 21 meV by high-resolution electron-energy-loss spectroscopy, in excellent agreement with predictions by surface lattice-dynamics calculations.