In situ TEM observation of nucleation and growth of spherical graphitic clusters under ion implantation

Implantation with 100 keV C⁺ ions in a transmission electron microscope (TEM) was performed in copper at temperatures from 570 to 970 K to reveal the agglomeration process of implanted species immiscible in the substrates. Phase and strain contrast features with diameters of ∼5 nm appeared in Cu TEM samples at a fluence of 1 × 10¹⁷ C/cm², at which carbon concentration and radiation damage were roughly evaluated as 10 at% and four displacements per carbon atom, respectively. The features were determined as carbon onions due to their spherical morphology and concentric graphene shells with the interlayer distance of bulk graphite. The strain contrast around onions indicated that they were embedded in the substrate enhancing isotropic strain. We have further derived evidence on the location of onions, such as the interaction of onions with dislocations and with the sample edge, the latter of which was observed due to irradiation-enhanced evaporation of Cu. On the other hand, carbon nanocapsules (concentric graphitic spheres with cavities), typically observed in implanted polycrystalline Cu substrates, were formed through the graphitization at substrate grain boundaries and following emission of the encapsulated copper particles.