Surface morphology of the {010} faces of potassium hydrogen phthalate crystals

Abstract

A detailed surface microtopographic study with the aid of highly sensitive differential interference and phase contrast microscopy has been carried out for the {010} faces of potassium hydrogen phthalate single crystals. Two types of growth hillocks could be identified: (i) macroscopic hillocks, emitting steps of considerable height (100–2500 A) from their centres, and (ii) shallow hillocks, being sources of growth steps of 14 A, which corresponds to one unit lattice translation. From a relationship between hillock centres and dislocation etchpits, the macroscopic hillocks were identified as a group of cooperating spirals, whereas the shallow hillocks are single spirals originating from single dislocations of unit height. Several properties of both spiral types are described, among which a relation between inclusion strings and the occurence of some of the macroscopic hillocks, the phenomenon of bunching of lower steps to higher steps, the formation of liquid inclusions via macrostep overhangs and the equivalence in advancement rates of steps of different heights.