Controlling the Nucleation and Growth Orientation of Nanocrystalline Carbon Films during Plasma-Assisted Deposition: A Reactive Molecular Dynamics/Monte Carlo Study

摘要

Nanocrystalline carbon films containing preferentially oriented graphene-based nanocrystals within an amorphous carbon matrix have attracted significant theoretical and experimental interest due to their favorable chemical and physical properties. At present, there are intense efforts to study the grain size and growth orientation of the graphene-based nanocrystals to achieve a controllable growth of nanocrystalline carbon films. However, despite the frequent use of plasma-assisted deposition techniques, the atomistic-scale mechanisms, including the effects of plasma density and energy on the nucleation process and growth orientation of the graphene-based nanocrystals, as well as associated dynamic processes involved in deposition processes, have not yet been thoroughly studied. In this paper, the plasma-assisted growth of nanocrystalline carbon thin films with preferentially oriented nanocrystals was systematically studied by hybrid molecular dynamics—Monte Carlo simulations using a recently developed force field, the charge-implicit ReaxFF. By combining the experimental data with the atomistic simulations, we reveal that plasma ion bombardments, in suitable ranges of energies and densities, allow the highest nucleation density in the nanocrystalline carbon films. Theoretically optimum windows of the plasma energy and density are first presented in the form of crystallization phase diagrams. Furthermore, to investigate the relationship between the growth orientation and the plasma ion energy, simulations of graphene irradiated with Ar ions from different incident angles were also performed. On the basis of the mechanism of "survival of the fittest", we proposed using the critical energy of generating the Stone—Thrower—Wales defects to design the growth orientation of graphite-like nanocrystals by controlling the plasma ion energy.