SURFACE PHONONS OF THE (100) SURFACE OF SOME COMPOUNDS WITH A ROCK-SALT CRYSTAL STRUCTURE

Abstract

The energy dispersion curves of surface phonons of the (100) surface of some compounds with a rock-salt crystal structure (TiC, ZrC, HfC, NbC, TaC, MgO, and NiO) have been investigated using electron energy loss spectroscopy. Drastic changes in force constants on all the carbide surfaces are correlated with a rippled structure. On the other hand, the surface phonons of insulating compounds, NiO and MgO (100), have showed dispersion curves agreeing with the predicted ones calculated on the basis of a shell model with bulk dynamical parameters. No changes in the parameters near the NiO and MgO (100) surfaces have been detected. The shielding effect of free electrons on the surface phonon for the transition metal carbide surfaces is discussed.