High pressure transformation of single-crystal graphite to form molecular carbon–onions

Carbon onions were formed in graphite in the diamond anvil high pressure cell under axial pressure combined with shear deformation at room temperature. The onions were ranging in size from 1–2 nm to 1–2 µm and HREM studies have shown that the amount of their concentric shells tended to increase with pressure and deformation growth. Raman spectra were taken from large-size onions. Narrow bands found between 1400 and 1550 cm−1 correspond to fullerene-related carbon materials. The splitting of the pentagonal pinch mode 1446–1489 cm−1 is considered to be connected with the formation of heptagons.