  The healing of graphene grown from a metallic substrate is investigated using
tight-binding Monte Carlo simulations. At temperatures (ranging from 1000 to
2500 K), an isolated graphene sheet can anneal a large number of defects
suggesting that their healing are thermally activated. We show that in presence
of a nickel substrate we obtain a perfect graphene layer. The nickel-carbon
chemical bonds keep breaking and reforming around defected carbon zones,
providing a direct interaction, necessary for the healing. Thus, the action of
Ni atoms is found to play a key role in the reconstruction of the graphene
sheet by annealing defects.
