Structure of sodium chloride cleavage surfaces etched in vacuum at moderate temperature.

Abstract

The structure of NaCl cleavage surfaces subjected to evaporation in vacuum at temperatures between 100° to 300°C has been studied by examination of gold-decorated replicas in the electron microscope. The effect of bi-atomic step splitting and random formation of surface depressions is interpreted, assuming a vacancy cluster nucleation process. The phenomenon is correlated with the similar formation of impurity clusters observed by previous authors on the surface of thermally treated doped crystals. It is noted that, though split steps largely prevail on thermally etched surfaces, showing that monoatomic steps rarely exist, this fact does not signify that a/2 <011 > dislocation loops do not form in front of the crack. Such loops left behind by cleavage m ay change into half-loops. In these circumstances the electric forces associated with the surface emergence of the half-loops and the charged kinks existing along correlated steps com bine to restore electric equilibrium and annihilate the steps generated on the surface.