Deposition mechanism of graphene flakes directly from graphite particles in the kinetic spray process studied using molecular dynamics simulation

Deposition of graphene flakes in a kinetic spray process is a relatively new topic of research. The present work provides insight into the formation of graphene flakes from bulk graphite particles using molecular dynamics (MD) simulations due to the advantage of the short MD simulation timescales. The deposition of nano-scale graphite particles onto a copper (Cu) substrate was studied as a function of various particle sizes (4 nm, 6 nm, 8 nm and 10 nm) and impact velocities. For each particle, there is a critical impact velocity in which graphene flakes (single or few-layer) were separated from bulk graphite particles, and the separated graphene flakes were attached to a Cu substrate to form deposited layers. The critical impact velocity required for layer separation decreased gradually with increasing particle size. The deposition behavior was observed over the whole simulation period for each particle with different impact velocities, where the deposition mechanism at the critical impact velocity involves interlayer separation of graphite particles due to the high impact velocity. Particles deformed plastically during deposition, and Cu substrates deformed elastically/plastically for the deposition of various graphene flake structures, which are strongly dependent on impact velocities. The surface temperature of the Cu substrate increased at the impact zone due to the kinetic energy of the impacted graphite particles. Moreover, the number of deposited layers increased with increasing impact velocities beyond the critical impact velocity for the separation of graphene layers. Apart from these, there is a critical impact velocity for each particle, where excess impaction causes disordering of atoms/etching of the Cu substrate at the impact zone, and the disorder of atoms increased violently beyond this critical impact velocity. The simulation results also revealed a deposition window for graphene flake deposition in the kinetic spray process, where the impact velocity of nano-scale graphite particles plays a crucial role in successful graphene flake deposition.