Effect of Dose and Pressure on the Transformation from Neutron-Irradiated Graphite to Amorphous Diamond

We previously discovered a novel pathway for the transformation from highly orientated pyrolytic graphite foils irradiated with neutrons into amorphous diamond platelets. Here, we utilized graphite foils irradiated with a neutron dose of about a half of the previous study, and confirmed the pathway for the transformation. Raman spectrum of the irradiated graphite exhibits a broad amorphous one but still possessed weak G and D peaks, appearing in a less disordered state. The irradiated graphite foils were shock compressed at 46, 51 and 54 GPa. At 46 GPa, Raman spectra clearly show the G and D peaks but a weak photoluminescence appears. At 51 GPa, we can find transparent platelets with intense photoluminescence but no diamond Raman peak, implying the transformation to amorphous diamond. At 54 GPa, we obtained transparent platelets with intense photoluminescence and a small and broad diamond peak, suggesting the formation of nano-diamond.