The Thermal Etching of Single Crystals of Cadmium

Abstract

The heating of single crystal wires of cadmium in circumstances that permit free evaporation produces a development of crystalline planes. When the basal plane makes a small angle with the axis of the wire there is a characteristic formation of hexagonal pits, the bottoms of which are mirror-like basal planes: when the basal planes make larger angles, characteristic elliptical traces appear, reminiscent of those formed by mechanical extension. The thermal etching reveals, by the formation of steps, thin laminae existing in the unstrained wire: the thickness of these, of the order of 1 μ, is the same as the spacing of the glide planes revealed by mechanical extension. The etched figures, in general, indicate that the substructure revealed by straining is already present in the unstrained crystal. The secondary pyramidal faces revealed agree with the calculations of Stranski, Kaischew and Krastanov. The mirror-like basal planes are sufficiently large to permit the application of an optical method to reveal a scatter in their inclination to the axis. This method shows that there is a variation, round about 20 minutes, of orientation among the basal planes about the direction of growth of the crystals, which were grown by the method of Andrade and Roscoe and showed good single crystal properties by the usual criteria.