Synchrotron spike topography of natural Type IA diamond

Abstract

Natural Type Ia diamond contains impurity platelet precipitates of only a few atoms thick and of diameters typically 10–100 nm, lying on {100} planes. Such platelets produce 〈100〉 spikes in diffraction associated with some reciprocal lattice points. They are very weak and long exposures are needed to record them. Hitherto, X-ray topographic studies of reciprocal lattice spikes in diamond have concentrated upon the strong 111 reflexion, which is surrounded by six spikes; but here we have studied with powerful synchrotron radiation the two spikes emanating from the weaker 331 reflexion. This has the advantage that only one spike at a time, rather than three, is intersected by the Ewald sphere; and consequently, only one image is recorded, rather than three (possibly overlapping) ones. We have discovered that the intensity of these spikes follows an inverse 3 2 power law with distance from the 331 reciprocal lattice point, whereas an inverse square law had been expected. Associated with platelets are voidites. These are {111} faceted defects of low electron density; and in certain diamonds, sheets of voidites replace platelets. Spikes in the 〈111〉 directions from the 111 reciprocal lattice point appear to arise from voidite sheets, and we have observed weak 〈111〉 spikes emanating from the 331 reciprocal lattice point.