Transformation of graphite into nanodiamond following extreme electronic excitations

Graphite targets have been irradiated at 90 K and 300 K with 850 MeV and 6 GeV lead ions and with 20-30 MeV fullerene cluster ions in a large range of fluences. Damage creation was studied both by transmission electron microscopy and Raman spectroscopy. The very strong energy density deposited in electronic processes generates a highly excited region around the projectile path. The relaxation of the deposited energy via hydrodynamic expansion and shock-wave propagation leads to the formation of small defective graphitic domains and of nanocrystalline diamond particles.