EELS study of the irradiation-induced compression of carbon onions and their transformation to diamond

The irradiation-induced self-compression of carbon onions and their transformation to diamond crystals are studied in situ by electron energy loss spectroscopy at high specimen temperature in a high-voltage electron microscope. Plasmon peaks in the low-loss region and the carbon K edge with the near-edge fine structure exhibit characteristic changes during irradiation. The spectra show the increasing electron density and the gradual change from sp(2) to sp(3) character of bonding during the self-compression of carbon onions. The spectra of the diamond cores correspond closely to those of cubic high-pressure diamonds. (C) 1998 Elsevier Science Ltd. All rights reserved.