RAYLEIGH-WAVE DISPERSION ON AG(100) ALONG THE (100) DIRECTION

Electron-energy-loss-spectroscopy measurements of Rayleigh phonon dispersion are reported for the -M direction of the Ag(100) surface. The data are compared to lattice-dynamical calculations performed within a nearest-neighbor model. The comparison shows that a slight increase of the force constant between the first and second layer with respect to the bulk value is needed in order to fit the data. The force-constant change is, however, less than the accuracy with which one can reproduce the bulk phonon spectrum with this model and is therefore not physically significant. More sophisticated models are, on the other hand, shown to give wrong predictions for the surface spectrum. We conclude therefore that the Ag(100) surface exhibits smaller effects of surface relaxation, if indeed there are any effects, than the same surfaces of Cu and Ni. © 1990 The American Physical Society.