On the surface diffusion during growth of a crystal on a substrate

Some of the possibilities of the method of investigating the growth kinetics of crystals from the vapour phase are discussed. The diffusion problem for the growth of non-singular cylindrical crystal surface is investigated, considering as example a cylindrical crystal model lying on a foreign substrate and taking into account the direct impact of molecules from the vapour as well as diffusion along the surface of the substrate. An expression is derived for the growth rate at the edge of the crystal face in contact with the substrate. It is established that for small crystals the growth rate does not depend on their size. In this case it is possible to measure from the experimental data the product of the kinetic coefficient and the concentration of the molecules in the adsorption layer at the surface of the crystal. The author's experimental estimate in the case of growth of diphenyl from the vapour phase shows that such measurements can be performed with crystals smaller than about 30 microns.