Surface phonons ofp(2×2) structures: The effect bond-stretching interactions

Abstract

We present here lattice-dynamical calculations of the dispersion of the surface phonons of p(2×2) structures of oxygen on Pt(111) and Ni(100) to illustrate the importance of bond-stretching interactions between the adsorbate atom and nearest-neighbor substrate atoms. We show that only with the inclusion of such an interaction can we explain the observed gap in the Rayleigh wave frequency at the reduced-Brillouin-zone boundary and the presence of several modes along the Γ¯-M¯ direction for the oxygen overlayer on Pt(111). In the case of the same overlayer on Ni(100), this interaction is essential in reproducing the observed dispersion of the adsorbate modes along the Γ¯-X¯ direction and in understanding the origin of the low-lying resonance modes in the spectrum.