XXXV. The growth of cadmium iodide crystals : II—A study of the heights of growth steps on cadmium iodide

Summary Several methods for measuring step-heights on crystal surfaces are described. The measurements of small growth steps (<500 a high) on cadmium iodide, by an internal interference method, show that the theory of formation of large screw dislocation groups, based on a ‘buckle, followed by slip’ hypothesis, is probably correct. Dislocation groups having Burgers' vectors equal to any integral number of minimal sandwich layer thicknesses can be expected, but even values occur with much greater frequency. It has been shown that the occurrence of ‘odd” dislocation groups indicates polytypism in cadmium iodide crystals.