Interface between graphene and liquid Cu from molecular dynamics simulations

Abstract

Controllable synthesis of defect-free graphene is crucial for applications since the properties of graphene are highly sensitive to any deviations from the crystalline lattice. We focus here on the emerging use of liquid Cu catalysts, which has high potential for fast and efficient industrial-scale production of high-quality graphene. The interface between graphene and liquid Cu is studied using force field and ab initio molecular dynamics, revealing a complete or partial embedding of finite-sized flakes. By analyzing flakes of different sizes we find that the size-dependence of the embedding can be rationalized based on the energy cost of embedding versus bending the graphene flake. The embedding itself is driven by the formation of covalent bonds between the under-coordinated edge C atoms and the liquid Cu surface, which is accompanied by a significant charge transfer. In contrast, the central flake atoms are located around or slightly above 3 Å from the liquid Cu surface and exhibit weak vdW-bonding and much lower charge transfer. The structural and electronic properties of the embedded state revealed in our work provides the atomicscale information needed to develop effective models to explain the special growth observed in experiments where various interesting phenomena such as flake self-assembly and rotational alignment, high growth speeds and low defect densities in the final graphene product have been observed.

Real-Time Multiscale Monitoring and Tailoring of Graphene Growth on Liquid Copper

“…In situ XRR measurements (Figure A) provide the out-of-plane electron density profile (Figure B), from which we confirm the formation of SLG, and we deduce low values of 1.2 Å for both Cu and graphene roughness, as well as 2 ± 0.1 Å for the Cu–C average separation distance when using the same definition of the distance as given above for the MD simulations. The latter simulations model a perfect graphene layer without defects and a pure liquid copper surface and give rise to a somewhat larger separation value of 2.89 Å . An explanation for the discrepancy between theory and experiment could be inaccuracies in the Cu–C interaction curve predicted by the employed force field and the presence of defects in the experiment.…”

“…The latter simulations model a perfect graphene layer without defects and a pure liquid copper surface and give rise to a somewhat larger separation value of 2.89 Å. 51 An explanation for the discrepancy between theory and experiment could be inaccuracies in the Cu−C interaction curve predicted by the employed force field and the presence of defects in the experiment. During CVD growth, graphene undergoes continuous defect formation (e.g., H 2 attack) and self-healing.…”

Ab Initio Thermodynamics of Hydrocarbons Relevant to Graphene Growth at Solid and Liquid Cu Surfaces

“…For a liquid Cu surface, on the other hand, the dynamic state of the Cu atoms might allow for flat defectfree clusters that achieve Cu-coordination of the edge C atoms by slightly sinking down into the liquid. 44 Such defect-free geometries could possibly stabilize the pure carbon clusters to the extent where their stability would become similar or even greater than the clusters with hydrogenated edges. Less defects in the pure carbon clusters formed during graphene growth on liquid Cu, as compared to on solid Cu, could also be one of the factors explaining the higher structural quality of graphene flakes grown on liquid Cu.…”

In Situ Investigation of the Motion Behavior of Graphene on Liquid Copper

“…At stage 1, the building blocks with small size were in random distribution (Figure 4b), they would spontaneously converge and arrange on the liquid surface to reach a well‐arranged configuration, which was attributed to the minimum surface energy principle. [ 33–35 ] The building blocks within the dotted hexagonal line indicated the uniform distribution (Figure 4c). Then, the as‐arranged graphene flakes continued to grow at stage 2, the gap between the adjacent graphene decreased with the size increasing, and the relative position between graphene slightly changed owing to the interaction between adjacent graphene (Figure 4d).…”