Raman scattering from microcrystals

This review discusses the size effects on Raman scattering from microcrystals. For ionic microcrystals, the existence of surface phonon modes is predicted from electromagnetic theories. It is shown that Raman spectroscopy is very effective to detect the surface phonon modes. The size effects on nonpolar phonons in covalent microcrystals can also be studied by Raman spectroscopy. However, the relaxation of the wave-vector selection rule or the phonon confinement explains only some of the experimental data. Development of lattice dynamical theories of Raman scattering from microcrystals including surface effects is highly required. Enhancement of Raman intensities arising from the excitation of electromagnetic normal modes of microcrystals is also discussed.