SURFACE PHONON MODES OF A MICROCRYSTAL SLAB

The frequencies of long-wavelength normal modes of a slab consisting of small spheres are calculated by using a dipole-dipole interaction Hamiltonian proposed by Clippe, Evrard and Lucas. Two optically active modes are found, one with a frequency lower than the Fröhlich mode frequency ωF and the other with a frequency higher than ωF. It is shown that for a thick enough slab the frequencies of the active modes coincide with those derived from the Maxwell-Garnett theory. This result indicates that the Maxwell-Garnett theory is reliable, even though it takes into account only approximately the dipole-dipole interaction. © 1979, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.