The migration of metal atoms through carbon onions

Metallic nanocrystals such as cobalt or gold are encapsulated by spherical graphitic shells under high-temperature electron irradiation. The irradiation promotes a heavy contraction of the carbon onions. The contraction forces the metal atoms to migrate outwards through the shells, even without further irradiation. This leads to a gradual but complete displacement of the encapsulated crystals. In-situ observation in an electron microscope allows shrinkage of the encapsulated crystals and migration of the atoms through the shells to be monitored. The experiment shows that spherically curved graphene layers are permeable to metal atoms.