Abstract
Graphene nucleation from crystalline Ni3C has been investigated using quantum chemical molecular dynamics (QM/MD) simulations based on the self-consistent-charge density-functional tight-binding (SCC-DFTB) method. It was observed that the lattice of Ni3C was quickly relaxed upon thermal annealing at high temperature, resulting in an amorphous Ni3C catalyst structure. With the aid of the mobile nickel atoms, inner layer carbon atoms precipitated rapidly out of the surface and then formed polyyne chains and Y-junctions. The frequent sinusoidal-like vibration of the branched carbon configurations led to the formation of nascent graphene precursors. In light of the rapid decomposition of the crystalline Ni3C, it is proposed that the crystalline Ni3C is unlikely to be a reaction intermediate in the CVD-growth of graphene at high temperatures. However, results present here indicate that Ni3C films can be employed as precursors in the synthesis of graphene with exciting possibility.
Highlights
Previous studies demonstrated that the following steps are involved in the graphene growth process on Ni-based catalysts: (1) gaseous hydrocarbons are adsorbed and decompose on nickel surfaces; (2) carbon adatoms dissolve into the subsurface or bulk nickel; (3) carbon atoms precipitate back to the nickel surface at low temperature and graphene is formed[12,13]
We present quantum chemical molecular dynamics (QM/MD) simulations of graphene nucleation from crystalline Ni3C phase
The results indicated that the lattice of Ni3C was quickly relaxed and damaged upon thermal annealing, resulting in a catalyst structure resembled an amorphous Ni3C phase
Summary
Previous studies demonstrated that the following steps are involved in the graphene growth process on Ni-based catalysts: (1) gaseous hydrocarbons are adsorbed and decompose on nickel surfaces; (2) carbon adatoms dissolve into the subsurface or bulk nickel; (3) carbon atoms precipitate back to the nickel surface at low temperature and graphene is formed[12,13]. It can be seen from Supplementary Movies S1 and S2 that subsurface carbon atoms precipitate out of the catalyst surface at the very beginning of the simulation. The rapid precipitation of subsurface carbon atoms and the subsequent formation of polyyne chains preceded the emergence of the “Y-junction” structure, consistent with the aforementioned mechanism.
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