Observations of the influence of stress fields on the shape of growth and dissolution spirals

Abstract

Examples are presented which show the influence of stress fields around screw dislocations upon the shape of growth and dissolution spirals. When a growth spiral originates from an independent single screw dislocation with a large Burgers vector, the spiral step shows a change of curvature from negative to positive as it escapes from the centre of the spiral. The degree of change of curvature varies depending on the type of stress field. In case of a strong stress field a stable hollow core is formed in the spiral centre, whose diameter depends on the stress field. When a composite spiral is formed from a group of screw dislocations, a depressed area may occur in the spiral centre due to stress. In the case of dissolution spirals, although a hollow core appears, a change of curvature is not observed. The relation between the hollow cores thus formed and the outcrops of the hollow tubes in crystals observed in SiC or YIG crystals is also discussed.