J. Phys. Colloques
Volume 42, Numéro C6, Décembre 1981
International Conference on Phonon Physics
Page(s) C6-793 - C6-800
International Conference on Phonon Physics

J. Phys. Colloques 42 (1981) C6-793-C6-800

DOI: 10.1051/jphyscol:19816234


G. Benedek1, G. Brusdeylins2, R.B. Doak2 et J.P. Toennies2

1  Gruppo Nazionale di Struttura della Materia del Consiglio Nazionale delle Ricerche, Istituto di Fisica dell'Università, I-20133 Milano, Italy
2  Max-Planck-Institut für Strömungsforschung, Böttinger Str. 4-8, D-3400 Göttingen, F.R.G.

The recent great advance in the production of highly monochromatic atomic beams is opening new perspectives in surface physics, having made way to a full determination of the surface vibrational structure. After a short review of the earlier attempts to detect surface phonons from the angular distributions of scattered atoms, we report on the direct measurement of surface phonon dispersion curves, first achieved by Brusdeylins, Doak and Toennies in alkali halides, from time-of-flight (TOF) spectra of scattered He atoms. A comparison is made with the existing theories of surface phonons in ionic crystals. The state of the art in the theory of inelastic scattering processes is briefly illustrated in order to discuss the theoretical interpretation of TOF spectra. The one-phonon energy-loss spectra of He scattered from LiF (001) calculated for a hard corrugated surface model are found to be in good agreement with TOF spectra at all the incidence angles. Evidence is given that, in addition to Rayleigh waves, important contributions to the inelastic scattering come from the surface-projected density of bulk phonons. The possible observation of optical surface modes in KCl (001) is finally discussed.