Effect of annealing dependent surface free energy change of Cu foil during graphene growth on quality of monolayer continuous graphene

We report on the characteristics of graphene synthesized on 25 μm thin Cu foil by the chemical vapor deposition (CVD) technique with various surface free energy (SFE) conditions of the Cu foil by annealing. The SFE of Cu foil during graphene growth was changed depending on the pre-annealing time of Cu foil under H2 gas and was characterized by giving priority to its surface morphology. While the higher SFE of Cu foil during graphene growth is beneficial for the fabrication of continuous graphene film, a lower SFE is favorable for the formation of low-defect graphene (lower ID/IG ratio of Raman spectrum); however, a single layer and continuous graphene film does not form. Furthermore, the formation of monolayer graphene is also influenced by the average SFE of Cu foil during the graphene growth stage, resulting in higher I2D/IG ratio of 2.8422, confirming the existence of monolayer graphene. The graphene on high SFE Cu foil was better for optical transmittance due to the high monolayer coverage with moderate electrical properties. Furthermore, graphene with a high ID/IG ratio showed poor mechanical stability during the transfer process due to tearing and defects in the transferred graphene.