Graphene growth and stability at nickel surfaces

The formation of single-layer graphene by exposure of a Ni(111) surface to ethylene at low pressure has been investigated. Two different growth regimes were found. At temperatures between 480 and 650 °C, graphene grows on a pure Ni(111) surface in the absence of a carbide. Below 480 °C, graphene growth competes with the formation of a surface Ni₂C carbide. This Ni₂C phase suppresses the nucleation of graphene. Destabilization of the surface carbide by the addition of Cu to the surface layer facilitates the nucleation and growth of graphene at temperatures below 480 °C. In addition to the growth of graphene on Ni substrates, the interaction between graphene and Ni was also studied. This was done both experimentally by Ni deposition on Ni-supported graphene and by density functional theory calculation of the work of adhesion between graphene and Ni. For graphene sandwiched between two Ni-layers, the work of adhesion between graphene and the Ni substrate was found to be four times as large as that for the Ni-supported graphene without a top layer. This stronger interaction may cause the destruction of graphene that is shown experimentally to occur at ∼200 °C when Ni is deposited on top of Ni-supported graphene. The destruction of graphene allows the Ni deposits to merge with the substrate Ni. After the completion of this process, the graphene sheet is re-formed on top of the Ni substrate, leaving no Ni at the surface.