Helium-atom-scattering measurements of surface-phonon dispersion curves of the C(111)-H(1x1) surface

The surface-phonon dispersion curves of the hydrogen-terminated diamond (111)-(1X1) surface have been measured by inelastic helium-atom scattering. By using a very high incident-beam energy of 80.5 meV, the Rayleigh-wave dispersion curve could be observed throughout the entire Brillouin zone. The measured zone-boundary energies at the (M) over bar point and (K) over bar point are 64.1 and 70.6 meV, respectively. The data lie about 5% above the Rayleigh-wave dispersion curve obtained from semiempirical total-energy calculations.