Interface morphology of the (100) face of zinc iris thiourea sulphate (ZTS) crystals, grown under different supersaturations, at 30 degrees C, was investigated using in situ atomic force microscopy (AFM). It comes out that the (100) face exhibits stepped surface characteristics. At lower supersaturations, nucleation easily occurred at the outcrops of edge dislocations which could act as persistent sources of monomolecular growth steps, and the edge dislocation sites appeared to exhibit a "memory function". At higher supersaturations, however, poly-nucleation becomes the primary growth mechanism. The rates of step advancement in the [010] and [001] directions of the two-dimensional nuclei were different, as it ensues from the symmetry anisotropy. The activation energy of the two-dimensional nuclei along with the step kinetic coefficients in the [010] and [001] directions, were calculated. We also found that microcrystals on the surface of the crystal could be better integrated into the crystal surface, or otherwise lead to the generation of pits by migration of the microcrystals. Pits could be gradually filled by elementary steps and thus no defect would be formed, or they might also be covered directly by macrosteps, which would result in liquid inclusions. (C) 2013 Elsevier B.V. All rights reserved.