Scientists in France and Italy have successfully transformed graphite into nanodiamond by irradiating the graphite with energetic heavy ions or clusters. The nanodiamond is produced by inducing damage in the graphite, which was observed using transmission electron microscopy.

Nanodiamond

When energetic projectiles slow down in a target they lose energy and induce ionisation of the target atoms lying near the projectile path.A large number of electrons are emitted at the same time. These processes are called "electronic excitations" and can result in strong local temperature increases and generate radial pressure waves.

Team member Annie Dunlop of the Laboratoire des Solides Irradies, France, says that such high temperatures and pressures are essential for producing diamond from graphite: "The fact that we obtained this phase is important because it gives us a precise idea of the minimum temperature increase and intensity of the outgoing pressure wave that is generated."

The researchers obtained their results by firing 6 GeV lead ions and fullerene cluster ions with energies of 20 and 30MeV at nanosized fragments of graphite. The lead ions were fired at temperatures of 90 K and the fullerene clusters at room temperature. The researchers performed their experiments at the tandem accelerator at the University of Orsay, near Paris, and the GANIL facility in Caen, France.

Using transmission electron microscopy and Raman spectroscopy, the team observed that a large number of nanoclusters were ejected. These were found lying on the sample surface. Raman spectroscopy also revealed that some of these clusters could only be small diamond crystallites.According to the scientists, diamond seems to be the more stable phase at these very small particle sizes.

The results were published in Physical Review B.

For further information, contact: Annie Dunlop, Laboratoire des Solides Irradies, France; E-mail: boizot@hp1sesi.polytechnique.fr; Internet: www.lsi.polytechnique.fr