AFM Study of the Behaviour of Growth Steps on the (100) Faces of KDP Crystals and the Tapering Phenomenon

The experimental results of an investigation of the surface morphology of the as-grown (100) faces of KDP single crystals grown on seeds from aqueous solutions containing different concentrations of Fe3+ and Cr3+ impurities are described and discussed. It was found that the behaviour of steps in terms of their mutual spacing and height does not depend on the presence of an impurity in the growth medium, and that the association of elementary steps to form bunched steps on the growing surface is a statistical process. The bunching of steps and the formation of tapered faces are related phenomena. Step bunching on a face and its tapering are not related with the presence of an impurity in the medium but impurities favour these processes. Our analysis of the evolution of the spacing of elementary steps indicates that the Schwoebel effect is responsible for step bunching and face tapering.