▎ 摘　　要

Density functional calculations were performed to investigate the role of Au in graphene growth on the Ni(111) step. It was shown that armchair (AC) and zigzag (ZZ) graphene edge growths have nucleation selectivity, depending on the curvature of the stepped surface. The AC and ZZ pristine graphene edges are energetically more favorable than the Ni-terminated one, and the stabilities of Au-passivated graphene edges strongly depend on the Au concentration. Au modification on the Ni terrace lowers the energy barrier of C incorporation onto the AC/ZZ graphene edge process, in agreement with the experimental observation that graphene can be produced at the low temperature of similar to 723 K with Au alloying. The growth rate of the AC graphene edge is always faster than the ZZ, leading to the ZZ edge's dominating the circumference of the growing graphene islands. With a decrease in the temperature, the increase in the AC graphene edge growth ratio greatly exceeds that of ZZ, driving the edges to incorporate a zigzag geometry. The overwhelming domination of ZZ edge rationalizes the experimental observation that Au modification can dramatically increase the quality of the graphene films at the lower temperature. On the basis of these results, we suggest that to obtain a high-quality graphene sheet on a Ni surface, the presence of a step should be necessary, and a promoter such as Au should be added to the Ni surface after graphene nucleation at the step edge site. Furthermore, this work not only provides implications on how to synthesize a high-quality graphene by a CVD approach but also guides inhibition of the undesirable graphene formation in some instances. This work represents the first attempt to investigate the graphene growth mechanism on a surface alloy by theoretical means, which will stimulate further experimental efforts to synthesize high-quality graphene by using a surface alloy as the substrate, especially the choice of an alloyed metal with low cost.