Electron energy-loss spectroscopy of carbon onions

Carbon onions prepared by high-temperature annealing of nanocrystalline diamonds (nc-D) have been studied by electron energy-loss spectroscopy. It was found that the core-loss spectrum of spherical carbon onions was very similar to that of nc-D, although the low-loss spectrum and the high-resolution transmission electron microscopic observation suggest the formation of graphitic sp2 network. The core-loss spectrum indicates that spherical onions have a number of sp3 bonds. A possible explanation for these sp3 bonds is that there remains a tiny residual diamond particle in a spherical onion. Another explanation is that the spherical carbon onion has sp3 bonds as structural defects.