Vibrations in superlattices

This is a comprehensive survey, both theoretical and experimental, of the vibrational modes in periodic multilayered structures. The phonon modes are particularly detailed in the case of superlattices but the vibrational properties of other superperiodic structures such as SiC polytypes and graphite intercalation compounds are also briefly introduced. onon propagation is treated either by considering the superlattice layers as elastic continuum media or by using atomic linear chain models. Different kinds of modes can be encountered in superlattice systems: bulk optical or acoustical modes which are propagative or confined in the layers, interface modes mainly localized at the boundaries between the constitutive layers, and surface modes whose frequencies lie in the bulk mode energy gaps. Emphasis is given to the folding process and to phonon propagation along the direction of growth of the superlattice layers. l experimental techniques can be used to probe the vibrational modes like light scattering, electron energy loss spectroscopy, phonon spectroscopy and phonon imaging techniques. The Raman and Brillouin scattering experiments are particularly reviewed as they constitute an ideal tool of investigation of the phonon modes, of the optical and acoustical properties of the materials and of the superlattice structure and quality.