THE GROWTH AND PERFECTION OF ORGANIC NONLINEAR-OPTICAL CRYSTALS - N-METHYL UREA (NMU) FROM METHANOL SOLUTION .1. KINETICS AND GROWTH ANISOTROPY

As a preliminary to the preparation of large single crystals of N-meth yl urea (NMU) for evaluation and use as a non-linear optical material, we have examined the growth characteristics of this material from sol ution in methanol using an interferometric technique. NMU shows high g rowth anisotropy which cannot be linked to the interaction of the solv ent with the rowing surfaces. We find no experimental evidence to sugg est that the methanol molecules have either a blocking or decelerating effect on step movement on all crystal faces. The principal limitatio n to growth is volume diffusion. This influence and its variation from face to face is shown to increase with the kinetic coefficient of the crystal face and probably represents the dominant cause of the growth anisotropy.