Graphitic onions as reaction cells on the nanoscale

Multishell fullerene clusters (carbon onions) encapsulating iron crystals of a few nanometers in size are subjected to intense electron irradiation at high temperature in an electron microscope. A reaction between graphite and iron, leading to the formation of iron carbide (cementite) in the core of the clusters, is observed in situ. The reaction in these spherical nanoencapsulates is explained by the occurrence of high pressure, mobile carbon interstitial atoms, and the irradiation-induced lowering of the kinetic barrier. Thus, carbon onions can be used as high-pressure cells for inducing a chemical reaction in nanometer-sized particles.