Transformation of diamond nanoparticles into carbon onions under electron irradiation

The irradiation-induced transformation of diamond nanoparticles (DNP) to spherical onions and onion-like carbon was studied in situ by high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS). The process was observed in a transmission electron microscope operated at 200 kV without additional specimen heating. Estimated current density was in the range 20-40 A cm(-2). The onion-like particles formed from the diamonds were found to be quite stable to further electron irradiation. The changes in chemical bonding were also confirmed by EELS, revealing an increasing role of bonds with sp(2) hybridization in the irradiated material. The mechanism of structural transformation is discussed.