Role of Impurity on Growth Hysteresis and Oscillatory Growth of Crystals

We proposed a simple physical model of growth hysteresis and oscillatory growth in a crystallization system with impurities. The model is based on two fundamental mechanisms: (i) removal of impurities adsorbed on the growing crystal surface by step advancement and (ii) retardation of step advancement by the adsorbed impurities (the pinning mechanism). We found that the coupling of these two mechanisms causes a cyclic feedback on the kinetics of impurity adsorption and step advancement. We revealed a growth hysteresis on the step velocity, namely, the history of the step velocity when the supersaturation is decreased is different from that when the supersaturation is increased. The critical supersaturation at which the growth hysteresis appears is given by definite physical parameters such as step free energy, number density of the adsorbed impurities, and time scale of impurity adsorption. The feedback loop also results in the oscillatory growth of crystals when the transportation of constituent molecules from the bulk environment to the crystal surface is inefficient.