PHASE-SHIFTING INTERFEROMETRY OF GROWTH-PATTERNS ON THE OCTAHEDRAL FACES OF NATURAL DIAMONDS

Phase shifting interferometry, a relatively new method for quantitative mapping of surface height profiles, has been applied to investigate the original growth patterns on the {111} faces of natural diamond. To avoid interference from post-growth etching phenomena, the specimen crystals were selected for the absence of dissolution features such as surface trigons and rounded edges between adjacent facets. Two types of growth features were encountered. The first were shallow growth hillocks, presumably related to dislocations. Below the growth surfaces, at a depth of a few micrometres, cathodoluminescence topography revealed trigonal patterns related to the hillocks. These patterns are a result of a difference in impurity uptake by growth steps of different orientations which advance at different velocities. Secondly, steep hillocks, emitting extended, trigonal step patterns were found. The (flat) summits of these elevations are characterized by a difference in surface morphology and impurity content, which is indicative of fluid-fluid-solid growth via a different phase on top of the hillocks. Finally, step bunching phenomena, leading to the formation of macro-steps are described.