The structure and mechanism of formation of platelets in natural type Ia diamond

Abstract

Observations have been made on medium- and large-sized platelets in a natural type Ia diamond. Attempts have been made to detect any regularity in the structure of the platelets by means of electron diffraction, but none was found. The displacement associated with the platelets has been determined to be extrinsic, normal to the plane of the platelet and of magnitude 0.4 ‹010›. This value has led to the proposal of a model for the platelet structure in which the platelet consists of an interstitial layer of carbon atoms pentagonally bonded to the surrounding diamond matrix. The way in which the detailed bonding may be varied, while complete tetrahedral bonding is maintained, can lead to irregular structures consistent with the diffraction evidence. Possible mechanisms for producing interstitial carbon atoms are considered and the role of nitrogen in this context and in providing possible nuclei for platelet growth is discussed.

Detailed microscopic analysis of self-interstitial aggregation in silicon. I. Direct molecular dynamics simulations of aggregation

“…25,[27][28][29][30][31]56 The ͕100͖ planar defects ͓Fig. 1͑g͔͒ are also in structural agreement with literature models, 31,38 although as noted earlier, ͕100͖ defects are not typically observed in implanted silicon samples.…”

“…Finally, we mention briefly ͕100͖-oriented planar defects. 31,38 These defects are comprised of ͕100͖ planar arrays of the well-known Humble/Arai [38][39][40][41] four-interstitial cluster structure. They are generally not observed in silicon although have been extensively studied in diamond 38 and germanium.…”

“…31,38 These defects are comprised of ͕100͖ planar arrays of the well-known Humble/Arai [38][39][40][41] four-interstitial cluster structure. They are generally not observed in silicon although have been extensively studied in diamond 38 and germanium. 42 Some evidence for their presence in silicon has been gathered following high-dose boron implantation 43 but it is thought that the boron may play an important role in this case and that the observed ͕100͖ defects are examples of boron-interstitial clusters, or BICs.…”

Transmission Electron Microscopy of Carbon: A Brief History

“…Improvements in TEM technology during the 1980s and 1990s meant that lattice imaging of the diamond structure became a practical possibility, and this helped to resolve the nitrogen-in-platelets issue. In 1995, Fallon, Brown, Barry, and Bruley, using a combination of EELS and high-resolution TEM [67], showed that the nitrogen concentration differed from platelet to platelet and concluded that the most likely structure for the platelets was a variation of a model that had been proposed by Humble in 1982 [68]. In this model, the platelets consist of an interstitial layer of carbon atoms pentagonally bonded to the surrounding diamond matrix.…”

Electron nanodiffraction

“…The observed patterns were then compared with patterns computed using many-beam dynamical diffraction programs based on the various models that had been proposed for the defect. Moderate agreement was found for the model that had been proposed by Humble (1982) and that, unlike the other proposed models, was not based on the assumption that the defect contained nitrogen impurity atoms.…”