Measurements of diamond lattice displacement by platelet defects with electron microscopic moiré patterns

Abstract

Among the diverse lattice defects occurring in natural diamonds, none has engendered so much controversy as the ‘platelets’, those planar defects which lie on {100} planes of the diamond matrix and whose diameters commonly lie in the range 10–100 nm. For many years, the only evidence for the existence of platelets was indirect, residing in the reported anomalous ‘spike’ diffuse X-ray reflections¹, but it was eventually accepted that these diffuse reflections could not be due to thermal vibrations but arose from static lattice disorder². Guinier³ and Frank⁴ independently pointed out that the defects responsible for the ‘spike’ reflections must be plate-like, lying in {100}. Direct proof of the existence of platelets came with the transmission electron microscope (TEM) observations of Evans and Phaal⁵, and it has been shown that the platelet structure is extrinsic, that is, that it forces apart the diamond matrix on either side of the platelet⁶. We now report a new and more reliable way of measuring the magnitude of matrix displacement produced by platelets.