INFLUENCE OF AN ELECTRIC-FIELD ON THE RELATIVE ABUNDANCE OF DISLOCATION LAMELLAE IN SODIUM-CHLORIDE

Lamellae of atomic steps generated during evaporation at points of emergence of dislocations are investigated relative to the presence of an externally imposed (non-contacting) inhomogeneous electric field. The nature of these steps were not affected by the field. However, specific features were found to develop when evaporation is carried out in the presence of a field. These include the formation of concentric loops (edge dislocation related) in the centre of what originally was a spiral (screw dislocation) pattern. The relative abundance of types of lamellae (edge as opposed to screw) was investigated relative to the location of the field probe. Regardless of field polarity, the relative abundance of edge dislocation-generated concentric loops was found to increase with increase in field strength. When the field polarity was positive, a maximum increase in the relative number of these loops occurred at a field strength of 0.5 MV m(-1). The imposition of higher field strengths resulted in a subsequent decrease in the relative number. These observations are explained in terms of motion of dislocations in the presence of the field.