Surface phonon dispersion of platinum (111)

The dispersion of the vibrational modes of the Pt(111) surface has been measured by inelastic He scattering along the {Γ}{}-M{} and {Γ}{}-K{} azimuths of the two-dimensional Brillouin zone for the first time. Significant asymmetry between the two crystal directions is observed. A lattice-dynamical analysis gives good agreement with the data when the intralayer force constant of the Pt atoms in the first layer is reduced to forty percent of its value in the bulk.