HIGH RESOLUTION DIFFUSE X-RAY SCATTERING STUDY OF POINT DEFECT CLUSTERS IN NATURAL DIAMOND CRYSTALS. R. R. Ramanan, Krishan Lal, National Physical Laboratory, New Delhi-11012, India

Point defect clusters in natural diamond crystals of type I and type II variety have been investigated by measuring and analysing distribution of diffuse X-ray scattering around 1 1 1 and 2 2 0 reciprocal lattice points. A multicrystal X-ray diffractometer with three plane-silicon crystal monochromators crystals oriented in (+,-,-) configuration which yield a highly collimated and monochromated MoK[[alpha]]₁ beam was employed in these measurements. Specimen crystals were natural { 111 } diamond platelets. IR absorption measurements were used to identify type I and type II specimens. High resolution X-ray diffractometry and topography has been employed to monitor the crystalline perfection. Also, absolute values of integrated intensities were determined. We had selected specimen crystals having varying degree of crystalline perfection. The experiments were performed in symmetrical Bragg geometry. Half widths of difraction curves were in the range: ~ 20 arc sec to ~ 300 arc sec. Diffuse X-ray scattering measurements were made around both the reciprocal lattice points in four diffrent directions. The DXS intensities versus K* plots show regions with slope of -2 (Huang region) and -4 (Stokes-Wilson region), as also observed in silicon crystals [e.g. Ramanan, Bhagavannarayana and Lal, JCG, 156, 377 (1995)]. An analysis of these results showed the presence of submicron size platelets of interstitial type due nitrogen Some vacancy clusters have also been observed. Shapes and sizes of clusters have been analysed. Interesting differences in defects structures have been observed between crystals of type I and type II variety. An attempt has been made to co-relate defect details with the gross perfection of these crystals and with nitrogen concentration