MORPHOLOGY OF CRYSTALS MADE OF HARD-SPHERES

The growth and morphology of crystals of hard colloidal spheres is mon itored by a special photographic technique. Crystals are observed to g row in size and increase in number density, initially. This is followe d by a decrease in size and an increase to saturation in the number de nsity. During the growth stage the crystals evidence irregular rectang ular shapes, and an internal substructure is evident within the larger crystals. The observed size decrease suggests a breakup of crystals t o a length scale of the internal structure. A simple model for surface roughening, which has been used to classify crystal morphology, is. e xamined for hard sphere crystals. Hard sphere crystals should be class ified as ''rough'' and subject to growth instabilities. The length sca le for simple planar and spherical instabilities is examined for hard sphere crystals and is found to be smaller than the observed length sc ales.