Imaging fields around growing crystals

Crystal growth morphologies arise from the interplay between interface mech anisms and temperature or concentration fields around the growing crystal. We shall describe experimental methods which we have developed in order to measure these fields in both two- and three dimensional environments. We co mpare the observations with current growth theories for examples of two dis tinctly different types of crystal. The first example is NH4Cl, a cubic cry stal which grows dendritically from supersaturated aqueous solution, in whi ch we have measured the two-dimensional concentration field by interference microscopy. The experiments allow determination of the anisotropies of bot h the surface tension and the kinetic growth admittance. As a result we hav e been able to explain the morphological transition observed in this crysta l at high growth velocities. The second example is heavy ice (D2O) growing from supercooled heavy water, in which we have investigated the three-dimen sional temperature field by interference tomography. Ice crystals are very anisotropic and show peculiar growth modes. We illustrate the use of the te mperature map in understanding the stability of asymmetrical morphologies w hich have been observed in ice and other crystals. (C) 1999 Elsevier Scienc e B.V. All rights reserved.