Nanoscale growth of solids crystallising from multicomponent aqueous solutions

摘要

The effect of 'foreign' ions on the growth of pure crystals from aqueous solution is an important topic addressed by both crystal growth, mineral and surface sciences. However, many aspects of the role played by those ions remain unclear. Our atomic force microscope (AFM) observations of the propagation of monomolecular steps of crystals in solid solution-aqueous solution (SS-AS) systems show that step velocities are determined by the surface structure of the underlying layer, so that each new growth layer exerts a decisive influence on subsequent layers. Moreover, we show that our observations cannot be completely explained by present crystal growth models based on either the pinning of elementary step motion by impurities or changes in free energy by incorporation of different cations into the lattice. A 'surface strain relaxation' model is proposed to explain the experimental observations. Our results, apart from providing an alternative explanation for the development of "dead zones", can shed light on poorly understood phenomena such as the development of compositional zoning in crystals.