High-temperature formation of concentric fullerene-like structures within foam-like carbon: Experiment and molecular dynamics simulation

The formation mechanism of carbon onions is investigated. The microstructure of onions formed using pulsed-laser deposition is found to depend critically on the background gas pressure. Molecular dynamics simulations show that an optimal annealing temperature of 4000 K is required to form well-ordered onions (concentric fullerene-like spheres), in agreement with experiment. The onions form from the outer layer first, and a model is presented in which the background pressure must be sufficient to allow atoms to cluster, yet low enough to allow annealing into well-ordered onions.