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Title: Optical studies on some crystal surfaces : cleavage and etch
Author: Pandya, N. S.
Awarding Body: University of London
Current Institution: Royal Holloway, University of London
Date of Award: 1954
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Abstract:
The results of optical studies on some crystal surfaces - cleavage and etched, with special reference to diamonds are reported in the thesis. It is divided into four parts. In the part I, a brief historical review of the studies on crystal growth is given as a general introduction. The existing information on diamond is also described. All the experimental techniques used in the course of this work are given in part II. The techniques used were (1) Multiple beam interferometry (2) Phase contrast microscopy (3) Light profile microscopy (4) Optical goniometry in part III is given a description of the optical studies of cleavage surfaces of topaz, calcite, mica and diamonds type I and type II. Both the surfaces obtained on cleaving a crystal were examined and the counter parts were matched for comparison. In the case of topaz, calcite and mica the matching was exact within limits of interferometric measurements, where as in the case of diamonds there were marked differences. The cleavage surface of type I diamond is very rough compared to that of type II diamond which is a strong difference in the cleavage. In the case of one pair of type II diamond triangular depressions were noticed. An explanation for these is offered. In the last part the evolution of etch phenomena on natural octahedron faces, cleavage (111) face, polished dodecahedron faces and polished cube faces, produced by immersion in hot potassium nitrate in temperatures ranging from 500° to 700°C is reported. In the case of natural (111) faces the etching process though a continuous one, is divided into three stages. The first stage begins with preferential attack on any surface flaws and then develops into random distribution of small etch pits. The concentration of these pits is less within growth trigons than elsewhere. In the second stage relatively small number of etch pits grow steadily and devour their smaller members. The corners become rounded and flat bottomed pits are frequent. In this stage, growth trigons tend to become hexagonal in outline and this mechanism is unfolded. In the third stage the whole of the original face has been eaten away. Triangular pyramidal depression begins to grow deeper and ultimately striking block formation results. The pile of blocks has plane surfaces which are mainly (221), (212), (122) and less prominent (331), (313), (133) which tend to become (334) but then rounding sets in. In the case of etching of cleavage (111), polished dodecahedron and polished cube faces, the etch pits observed are triangular for (111), boat-shaped for (110) and square for (100). Some of these are evaluated and discussed. Appearance of strongly marked rectilinear pattern proves each of the diamond to have laminated structure.(111) face is crossed with lines parallel to (111) edges, the (110) face is filled with beautifully regular set of concentric hexagons with sides parallel to (111) edges and the cube face reveals an equally striking set of concentric rectangles filling most of the face. The etch patterns reveal a sectional history of the growth of diamond. The observations can be accounted for by postulating increased resistance to etching at the on-set (or end) of each layer. The proposed growth by sheet layers is in conformity with the failure to find growth spirals on natural octahedron diamond faces.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.703722  DOI: Not available
Keywords: Optics
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