SURFACE PHONONS OF LIBR/SI(100) EPITAXIAL LAYERS BY HIGH-RESOLUTION ELECTRON-ENERGY-LOSS SPECTROSCOPY

Surface and interface optical phonons (F-K mode) of LiBr epitaxial films with various thickness grown on Si(100) have been investigated by high resolution electron energy loss spectroscopy (HREELS). In addition to single excitations of surface and interface phonons, their multiple excitations and annihilations have also been observed. The dependence of surface phonon energy with film thickness are compared with dielectric theory calculations. It has been found that phonon energies deviate more than the predictions of dielectric approximation with the decrease in the film thickness down to few nm, indicating the necessity of microscopic treatment in this thickness range.