A comparison of growth Hillock structure and step dynamics on KDP {100} and {101} surfaces using force microscopy

We report the results of in situ and ex situ atomic force microscopy invest igations of hillock structure and step dynamics on the {100} face of KDP, a s well as the effects of Fe3+ ions on the generation and motion of both ele mentary and macrosteps. We compare these results to those obtained previous ly on the {101} face. We show that, in contrast to the {101} face, dislocat ion sources on the {100} face do not exhibit dislocation cores, even for la rge Burgers vectors. Thus, for simple dislocation sources, the measured hil lock slope depends on the Burgers vector and varies linearly with supersatu ration. We show that while growth hillocks on the {101} faces are character ized by elementary steps that exhibit step homogenization, even in highly p urified growth solutions, KDP {100} faces exhibit a tendency towards step b unching. We trace the evolution of this bunching with distance from the dis location source and compare it to theoretical models of impurity-induced bu nching. We also trace the evolution of step dynamics with supersaturation o n the {100} face. We show that well above the dead zone, elementary steps a nd macrosteps are straight and elementary steps move more rapidly than macr osteps. As the supersaturation is decreased, impurity pinning begins to slo w elementary step motion and the macrosteps begin to move faster than the e lementary steps. In the region just above the dead zone, elementary steps a re highly ramified and do not move while macrosteps continue to advance, sw eeping up the elementary steps at the leading edge and leaving them behind at the trailing edge. Thus, in this region, growth occurs exclusively by th e propagation of macrosteps. Finally, within the dead zone, both elementary and macrosteps cease to advance.