Low-temperature growth of carbon shells on gold and copper nanoparticles in transmission electron microscope

Abstract Assisted by electron beam irradiation in a transmission electron microscope chamber, carbon shells are grown on both gold (Au) and copper (Cu) nanoparticles at low temperatures. Using single-walled carbon nanotube film as support, it is observed that graphene shells can nucleate on Au nanoparticles at 350 °C and at a temperature as low as 150 °C on Cu nanoparticles. The low temperature carbon assembly is attributed to a truncated graphene formation pathway, low reaction barriers and exothermic reaction processes. The calculated energy barriers for graphene assembly from active carbon atoms on Au (111) and Cu (111) surfaces are 0.57 eV and 0.44 eV, respectively, which are roughly 1/3 of the barriers for carbon source dissociation. On the one hand, the decomposition of hydrocarbon molecules is entirely driven by the electron collision-induced radiolysis reaction and thus does not contribute to the graphene formation energetics. On the other hand, the feasible nucleation process ensures the synthesis of carbon shells at low temperature in view of both kinetics and thermodynamics. This work not only opens a new avenue for low temperature synthesis of graphitic shells, but also helps to understand the growth mechanisms of graphene encapsulated materials.