The structure of graphene on graphene/C₆₀/Cu interfaces: a molecular dynamics study

Two experimental studies reported the spontaneous formation of amorphous and crystalline structures of C₆₀ molecules intercalated between graphene and a surface. The findings observed included interesting phenomena ranging from reaction between fullerene C₆₀s ('C₆₀s' stands for plural of C₆₀) under graphene to graphene sheets sagging between C₆₀s and control of strain in these sheets. Motivated by this work, we performed fully atomistic reactive molecular dynamics simulations to investigate the formation and thermal stability of graphene sheet wrinkles as well as graphene attachment to and detachment from a surface when the sheet is laid over a previously distributed array of C₆₀ molecules on a copper surface at different temperatures. As graphene compresses the C₆₀s against the surface, and graphene attachment to the surface in between C₆₀s depends on the height of the wrinkles in the graphene sheet, configurations with both frozen and non-frozen fullerenes were investigated in the simulations in order to examine the experimental result of stable, sagged graphene sheets when the distance between C₆₀s is about 4 nm and the height of the wrinkles in the sheet is about 0.8 nm. Below a distance of 4 nm between fullerenes, the graphene is predicted to become locally suspended and less strained. The simulations predict that this happens when the fullerenes can deform under the compressive action of the graphene sheet. If the fullerenes are kept frozen, spontaneous 'blanketing' of graphene is predicted only when the distance between neighbouring C₆₀s is equal to or great than about 7 nm. These predictions agree with a mechanical model relating the rigidity of a graphene sheet to the energy of graphene-surface adhesion. This work further reveals the structure of intercalated molecules and the role of stability and sheet wrinkling on the preferred configuration of graphene. This study thus might assist in the development of two-dimensional confined nanoreactors for chemical reactions.