LATTICE-DYNAMICS OF ULTRATHIN LAYERS OF KBR GROWN EPITAXIALLY ON RBCL(001)

High-resolution helium-atom scattering experiments were performed on e pitaxially grown layers of KBr on a RbCl(001) substrate for films 1, 2 , and 3 ML thick. The layer-by-layer growth was monitored in situ by m easuring the intensity of the specularly scattered He beam versus cove rage. Measurements of the single-phonon inelastic scattering were carr ied out on each succeeding layer to determine the surface-phonon dispe rsion in both the <(Gamma M)over bar> and <(Gamma M)over bar> high-sym metry directions of the surface Brillouin zone. Shell-model potential parameters were determined in a consistent fashion for the four anion- cation constituents at the interface, which gave a good fit to the dis persion curve data from 1-, 2-, and 3-ML KBr/RbCl epitaxially grown sy stems as reported in this study and, in addition, the bulk and clean s urface dispersions of KBr, RbCl, KCl, and RbBr were fit by the same pa rameters.