Imaging fields around growing crystals

Crystal growth morphologies arise from the interplay between interface mechanisms 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 compare the observations with current growth theories for examples of two distinctly different types of crystal. The first example is NH4C1, a cubic crystal which grows dendritically from supersaturated aqueous solution, in which we have measured the two-dimensional concentration field by interference microscopy. The experiments allow determination of the anisotropies of both the surface tension and the kinetic growth admittance. As a result we have been able to explain the morphological transition observed in this crystal at high growth velocities. The second example is heavy ice (D₂O) growing from supercooled heavy water, in which we have investigated the three-dimensional temperature field by interference tomography. Ice crystals are very anisotropic and show peculiar growth modes. We illustrate the use of the temperature map in understanding the stability of asymmetrical morphologies which have been observed in ice and other crystals.