Onion-like graphitic particles produced from diamond

Onion-like particles composed of concentric spherical graphitic shells have been obtained by irradiating diamond crystals with 200 keV electrons. The onion-like structures were found to be producible only in intense electron beams with an irradiation flux density of about 107 electrons/nm2 s or greater. The genesis of this nanostructure of carbon was suggested to follow a three-step mechanism comprising displacements, migration, and aggregation. Electrical charging and electron-beam enhanced diffusion are proposed to be central to the high rate formation. The atomic evolution in diamond-graphite transformation is also discussed in connection with a recently reported model.