Nucleation and growth of carbon onions synthesized by ion-implantation:: a transmission electron microscopy study

Carbon onions were synthesized by 120 keV carbon ion-implantation into silver substrates heated at high temperature (> 400 degreesC). Their nucleation and growth mechanisms are discussed from plane view and cross-sectional transmission electron microscope (TEM) characterizations of implanted samples. Implanted carbon atoms precipitate inside the bulk of the silver substrate, allowing the formation of spherical carbon nanostructures distributed in the silver matrix. A progressive transformation of these precipitates into onion-like structures as well as the growth of the carbon nanostructures occurred in the bulk of the substrates when the fluence increased. Furthermore, the correlation between the size of the carbon onions and the carbon concentration into the silver matrix is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.