Dynamics and structural transformations of carbon onion-like structures under high-velocity impacts

Abstract

Carbon nano-onions (CNO) are multilayered fullerenes. They exhibit good electrical conductivity and large surface area, being of interest for several optoelectronic applications. However, it is still an open question what synthesis routes can be used to convert them into diamonds. Here, we used fully atomistic reactive (ReaxFF) molecular dynamics simulations to study the dynamics and structural transformations of CNO structures under high-velocity impacts against a fixed and rigid substrate. The aim of this study is to propose a new synthesis route, based on the mechanical impact of CNO, that can be exploited in the conversion of onions to diamonds. Our results indicated three regimes formed after the CNO impact: slightly deformed CNO (quasi-elastic collision, below 2.0 km/s), collapsed CNO (inelastic collisions, between 3.0 and 5.0 km/s) forming a diamondoid-like core, and fragmented CNO yielding linear atomic carbon chains (above 5.0 km/s). We also discussed the dynamical reconfiguration of carbon-carbon bonds during the collision process. The impact of CNO yielded sp3-like bond types for all the used initial velocities. At intermediate velocities (between 3.0 and 5.0 km/s), the inelastic collision forms diamondoid-like cores by converting a substantial quantity of sp2-like bonds into sp3-like ones.