LIGHT-SCATTERING IN CRYSTAL-GROWTH

Dynamic light scattering techniques (Rayleigh scattering) can be used to study the dynamics of crystal growth. This technique is able to provide information about dynamic processes, which take place at the surface of a growing crystal or in the vicinity of such a surface. Light scattering has several advantages in comparison to optical imaging techniques or to neutron scattering: No diffraction limits exist for scattering experiments and only very small scattering volumes are necessary. Therefore light scattering experiments can be performed at almost any setup where crystallization processes are studied. Light scattering techniques can be used to study surface structures at growing crystals in situ during crystal growth, e.g. the velocity of growth steps and the distance between growth steps can be determined from the frequency and intensity distributions of the scattered light. Light scattering gives evidence for a layer of preordered material in front of growing crystals. Continuous density fluctuations are observed in this interface layer. The correlation length of these density fluctuations is of the order of magnitude of the wave-length of visible light. The thickness of the interface layer can be several μm. The fluctuations in the interface layer have a decay rate, which is by a factor of 106 slower as the decay rate of density fluctuations in bulk liquid. The crystal grows into the mesophase and therefore the dynamics of crystal growth are determined by the dynamics in the interface layer. © 1990.