Computer simulation of spherical crystal surfaces : Dislocation loops and dipoles in b.c.c. and f.c.c. crystals

Abstract

In a previous paper (Brandon and Perry 1967) the computer model of a field-evaporated crystal surface (Moore 1962) was extended to include the case of a dislocated b.c.c. crystal. The present paper describes a further extension to the case of a single dislocation loop or dipole in either f.c.c. or b.c.c. crystals. Image forces are neglected and classical isotropic elasticity theory is used throughout. Both the loop and the dipole are approximated by a pair of straight, parallel dislocations of opposite sign whose axis of symmetry passes through the centre of the spherical crystal. In general the computed images do not show the same degree of distortion as in field-ion images of loops (Fortes and Ralph 1966) and it is concluded that the experimentally observed distortion is associated with the ion trajectories of the imaging particles (Brandon 1967).