Optical and interferometric studies of crystal growth from solution

Abstract

Crystal growth from solution has been studied optically and interferometrieally. The two dimensional diffusion phenomena for sodium chlorate crystal grown from aqueous solution has been studied using multiple beam white light fringes of equal chromatic order. The results are found to agree with the assumption of the existence of a quasi-stationary state theory. According to this theory, the radial gradient of concentration is analogous to a static potential field multiplied by a Gaussian cut off factor; the law relating the concentration at a point in the diffusion field to the distance of that point from the growing new phase is logarithmic near the crystal and exponential at larger distances. The growth in the light of the diffusion theory is briefly discussed. The more recent theory of dislocations, which accounts for growth properties of the crystal itself has been confirmed on chrysene crystals grown from solution. They were examined at high magnifications using optical techniques and spiral growth pictures in agreement with those predicted by the dislocation theory were observed. Measurements of step heights of the spirals were carried out using multiple beam inter-ferometric techniques. One origin of such dislocations has been investigated by studying the deformation of cadmium iodide crystals growing in thin plates from solution. They were subjected to a mechanical deformation by an indentation process, as a result of which the growth properties of the crystal have been altered. It is concluded from this experiment that the mechanical deformation is the vital factor for the growth effects here observed. Slip process leading to the creation of dislocations or increase of dislocations already present in the crystal may account for the spiral nature of the growth sometimes observed.