Masahito Niibe

Abstract Using neutron-irradiated highly oriented pyrolytic graphite (n-HOPG) as a starting material, we have synthesized nano-layered diamonds for the first time by high-pressure and high-temperature treatment at 15 GPa and 2070 °C. Furthermore, analysis of the in situ angle-dispersive X-ray diffraction patterns of n-irradiated and unirradiated HOPGs showed cubic diamond (cDIA) formation was not observed for n-HOPG below approximately 1400 °C, but was for unirradiated HOPG at approximately 1000 °C. In contrast, transmission electron microscopy observation of the recovered specimens revealed that nano-layered cDIAs oriented in the [111] direction were formed in both n-irradiated and unirradiated HOPGs. Still the thickness of the individual nano-layered cDIAs was larger in n-HOPG than in unirradiated HOPG. These results were discussed in terms of the recovery of irradiation-induced defects with increasing temperature under high pressure in n-HOPG and the nucleation and growth of diamond.