Mass transport effect within the boundary layers in solution crystal growth: Holographic study of KTP and KDP crystal growth

Using holographic phase-contrast interferometric microphotography, we have carried out real-time investigations of the mass transport processes taking place during the high temperature solution growth of KTiOPO₄ (KTP) crystal and low-temperature solution growth of KH₂PO₄ (KDP) crystal. Our experiments demonstrate that a mere diffusion boundary layer is not existing. The mass transport process within the boundary layers is a result of the coupled effect of diffusion and convection actions, no matter whether it is high-temperature or low-temperature solution growth. Under free convection state, the influence of bulk supersaturation on the thickness of solute boundary layer exists in the two different regions. The solute concentration distribution within the layer is an exponential function of the position.