Crystal surfaces and crystal growth mechanisms: application to crystals having the NaCl structure and especially silver halide crystals

Abstract

Results of computer simulation studies of crystal surfaces and related crystal growth mechanisms as well as statistical mechanical roughening transition theories of these surfaces are reviewed. The implications of these theories for crystal growth mechanisms, such as the spiral growth mechanism and the substep mechanism, recently described by Ming and co-workers, are treated briefly. Relations between roughening theories and recent developments in the crystallographic morphological theory of Hartman and Perdok are introduced. It is shown how this integrated theory can be applied to crystals having an NaCl structure, such as AgBr and AgCl crystals. The most stable faces are the {100} and {111} faces respectively. The {111} faces will be stable only if the high dipole moment can be removed by reconstruction or interaction with the solvent. Supersaturation is the key parameter that determines the growth morphology. At low supersaturations, only {100} faces are present. At higher supersaturations, {111} faces will become dominant. On these faces, formation of twins will occur at even higher supersaturations, leading, as a result of the substep mechanism, to tabular and needle-like crystals. The detailed understanding of all kinds of tabular and needle-like AgBr and AgCl crystals will be the subject of a subsequent paper.

Keywords:

• crystal surfaces
• crystal growth mechanisms
• NaCl structure
• silver halide crystals