THE MIGRATION OF METAL ATOMS THROUGH CARBON ONIONS

Metallic nanocrystals such as cobalt or gold are encapsulated by spher ical graphitic shells under high-temperature electron irradiation. The irradiation promotes a heavy contraction of the carbon onions. The co ntraction forces the metal atoms to migrate outwards through the shell s, even without further irradiation. This leads to a gradual but compl ete displacement of the encapsulated crystals. In-situ observation in an electron microscope allows shrinkage of the encapsulated crystals a nd migration of the atoms through the shells to be monitored. The expe riment shows that spherically curved graphene layers are permeable to metal atoms. (C) 1998 Elsevier Science B.V. All rights reserved.