MEASUREMENT OF THE LATTICE DISPLACEMENT ACROSS (100)PLATELETS IN DIAMOND BY LARGE-ANGLE CONVERGENT-BEAM ELECTRON-DIFFRACTION

Large-angle convergent-beam electron diffraction is used to measure th e displacement across {100} [R00] platelets in an Argyle brown diamond . By examining the intersection of a series of two-beam diffraction co ntours g with an inclined platelet, it is shown that integral and frac tional components of g.R can be separately determined. The integral pa rt of g.R is determined by applying standard Cherns-Preston rules to t he image of the bounding partial dislocation. The fractional part f of g.R is determined by comparing the rocking curve in the faulted regio n with two-beam dynamical simulations. It is shown that the rocking-cu rve asymmetry at small deviation parameters provides a simple measurem ent of f which is relatively unaffected by background inelastic scatte ring and a finite probe size. Higher-order reflections are used to imp rove sensitivity, giving R = 0.40 +/- 0.01. This result is compared wi th measurements obtained by other techniques and its significance for understanding the structure of diamond platelets is discussed.