Double-crystal diffractometric and topographic studies of (111) oriented synthetic diamonds

Synchrotron x-radiation in a double-crystal geometry has been used for topography and rocking-curve measurements to study imperfections in single-crystal HP/HT synthetic diamonds grown from (111) seeds by the reconstitution technique. The influence that clusters of small (1-5 mu m) opaque particles (sometimes called 'pin-point-like inclusions') have upon lattice parameter differences, as well as upon relative lattice tilts within each sample, was of particular interest in this study. Rocking curves measured with a large beam diameter (illuminating entire specimens) gave widths (FWHM) in the range 5-30 seconds of are in a non-dispersive Bragg-Bragg diffraction geometry in which good diamond crystals give 3 '' and for which the calculated theoretical minimum width is under 1 ''. Rocking curves were also recorded for small regions of each crystal, using a translatable pin-hole, and these showed that some diamonds had relatively narrow rocking curves in selected areas (of 100 mu m diameter). Epochs of crystal growth were recorded in series of x-ray topographs, taken at intervals of 2.5 seconds of are. Such series were taken for all four principal azimuths (chi = 0, 90, 180 and 270 degrees) of the incident beam by rotating the sample about the normal to the Bragg plane. This procedure yielded important information about lattice parameter distribution and lattice tilt across entire samples. For the samples heavily populated with pin-point-like inclusions it was concluded that there is a possible slight variation in lattice parameter values in some regions of the crystal but most of it falls below the adopted angular step resolution, although better accuracy can be achieved. Relative tilt measurements revealed that there are large misorientations of those parts of the crystal which are close to external outcrops of {111} boundaries. In this case of (111) oriented diamond samples, three separate regions with different tilts can be attributed to the three parts of the crystal close to optically visible {111} growth-sector boundaries.