Optical studies on surface structures of diamond crystals

Abstract

Chapters I and II are introductory, surveying briefly the physical properties of diamond and the general principles of crystal growth. In Chapter III, the experimental techniques employed are explained. Chapter IV attempts to give a brief objective summary of the surface features of diamond crystals, as known from the studies of earlier workers. Chapters V to XI embody the results of the present investigation.Much new evidence (which we claim as incontrovertible) has been obtained to show that trigons are not etch-pits.It is shown that whereas an etch-pit grows from a point-pit to a large one, it is topographically impossible toconceive of a trigon altering its size. evidence is alsoobtained of growth occurring over a surface already containing trigons with the later growth layers partly covering up the trigons. Clear, conclusive evidence of the mechanism of growth on the octahedral face by layer deposition is obtained, there being no evidence at all of spiral growth.Earlier workers have studied the dodecahedral face with the face normal to the line of the microscope. In thepresent ivestigation, the crystal is so set as to see simultaneously the features on three faces viz. (110), (101) and (011). This has led to the discovery that the 'striations' which earlier workers have described as 'ruts' on the (110) faces are, in fact, edges of growth layers piled up one above the other. This seems to us a very significant result for it leads to the conclusion that the dodecahedral crystal could be formed by the transformation of a simple octahedral crystal by the piling up of layers on all its octahedral faces. That the mechanism proposed is correct, is verified by the observation of trigons in between layers. For the first time, the corners of 'cubes' have been studied and the very interesting result obtained that the corners are either truncated containing trigons or pyramidal, growing to a point top showing growth features similar to those on (111) faces. Also given are, some observations on twinning in diamond. The matching faces of a diamond crystal that cleaved by itself when being heated in boiling nitric acid have been studied. It is seen that the cleavage over large areas is cleaner than ordinarily obtained by a mechanical process.