Surface phonon dispersion of ZrC(100)

The surface phonon dispersion on ZrC(100) has been measured in the T X and T M-direction by electron energy loss spectroscopy. We have observed the Ray-leigh wave, two resonance branches within the acoustical phonon band and several optical phonon branches. The experimental data are compared to a lattice dynamical calculation based on the screened shell model. Increasing the force constant between first layer zirconium and second layer carbon atoms and decreasing the force constant between first layer carbon and second layer zirconium atoms leads to a good agreement between experiment and theory. These force constant changes strongly suggest a rippled relaxation of the surface layer.