Author
Abstract
C60 fullerene and neutron-irradiated graphite have been reported to directly transform into “amorphous diamond” under shock compression, but the transformation mechanism is still not clear. Here, we report local fluctuations in the transformation to “amorphous diamond” from C60 fullerene and neutron- irradiated highly oriented pyrolytic graphite shock-compressed at 52 and 51 GPa respectively. For the platelets recovered from C60 fullerene film after the shock-compression, we observed a small Raman peak of diamond, of which peak shape changes depending on the area of platelets. Peak fitting revealed that the diamond Raman peak shifts to lower frequency with increasing the peak width and decreasing the peak intensity. This corresponds to the decrease of the crystalline size of nano-crystalline diamond and indicates the existence of amorphous diamond at an area where the intensity of diamond peak vanished. For the recovered sample of neutron-irradiated highly oriented pyrolytic graphite, on the other hand, we found an appearance of domain boundary between optically transparent and opaque areas, which respectively correspond to transformed and untransformed areas, thereby suggesting some novel transformation process originated in the initial disordered structure
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