Computer simulation of spherical crystal surfaces: Stacking faults and partial dislocation in f.c.c. crystals

Previous calculations (Brandon and Perry 1967, Perry and Brandon 1968) have now been extended to cover the case of a single ribbon of stacking fault separating two parallel Shockley partial dislocations in a hemispherical f.c.c. crystal. Image forces are neglected and classical isotropic elasticity theory is used throughout. It is shown that the splitting of a perfect dislocation into two partials may make inapplicable the g · b rule for predicting dislocation contrast in the field-ion microscope. It is also demonstrated that dissociation into partials need not necessarily be visible in the field-ion image. A time-of-flight technique was used to determine the energy spectrum of atoms ejected by ion bombardment from a metal target. The ion beam was pulsed in synchronism with a magnetically suspended rotor, spinning at speeds up to 3000 rev. sec−1. The flight path of 50 cm between target and rotor was sufficient to obtain a dispersed deposit of atoms on the rim of the rotor for all atom energies up to about 10 kev. The deposit was detected with auto-radiography by means of its radioactivity, the Cu or Au targets having been previously activated by irradiation with thermal neutrons.