Phonon dynamics and structure of the deuterated diamond ( 111 ) − ( 1 × 1 ) surface: Experiment and theory

Surface-phonon dispersion curves for deuterium-terminated C(111)-(1{times}1) have been measured out to the surface Brillouin zone boundary in both the [10{bar 1}] and [1{bar 2}1] high-symmetry directions by helium-atom scattering (HAS). The experimental results are compared with calculated surface-phonon dispersion curves obtained within a semiempirical total-energy scheme and with previous HAS measurements on the hydrogen-terminated C(111)-(1{times}1) surface. The experimental and theoretical results are in very good agreement and they clearly reveal a distinctive isotope shift of the Rayleigh mode energies along the boundaries of the surface Brillouin zone when the H adatoms are replaced by D. The comparison provides evidence for a single hydrogen/deuterium atom terminating each substrate C-atom site. {copyright} {ital 1998} {ital The American Physical Society}