Growth Spirals on Carborundum Crystals

Abstract

THE observation of growth spirals on carborundum crystals has been reported earlier¹. These growth spirals can be divided into two classes: (1) those in which the step-height between the successive edges of the spiral is equal to the height of a unit cell; and (2) those in which the step-height is a multiple of it. The latter type of multi-stepped spiral will result from a dislocation the strength of which is a multiple of the repetition period, the Burger's vector being a multiple of the height of the unit cell. Such spirals have been found to originate at a large hole (see Fig. 2); they have a much higher optical visibility because of the relatively large step-height, being therefore easily observed with a microscope using bright-field illumination. Of the numerous spirals of this kind seen, two typical examples are shown here. The steps of these spirals can break up into their component steps under certain conditions. In Fig. 1, showing only one half of the spiral, the various components advance together in different directions for some twelve turns, after which they break up into five or six close branches. In Fig. 2 is illustrated a case where the dissociation takes place quite near the centre and growth can be regarded as taking place from the multiple dislocations.