Ex situ and in situ observations of the surface morphology of the (010) face of potassium hydrogen phthalate (KAP) crystals

The surface morphology of the (010) face of potassium hydrogen phthalate (K AP) crystals grown from aqueous solution at low supersaturations (0.03 to 0 .05) has been investigated using ex situ optical and election microscopy in conjunction with a gold decoration technique. In situ atomic force microsc opy (AFM) has also been used to examine the growth of dislocation-free hill ocks. A variety of growth patterns was found: macroscopic hillocks, shallow hillocks, microscopic hillocks and numerous two-dimensional nuclei. The ma croscopic hillocks and smaller polygonal hillocks are formed by groups of c ooperating spirals or by single spirals. The density of observed shallow hi llocks is higher than the dislocation density. The results reveal that, at low supersaturations, growth of the (010) face occurs by combined spiral an d two-dimensional nucleation mechanisms. The influence of low concentration s of organic additives on the surface morphology of the (010) face of KAP h as also been studied. The additives stimulate two-dimensional nucleation bu t they also cause an increase in the spread velocity of steps. The growth p romoting effect of impurities is discussed in terms of the above data.