Clean and less defective transfer of monolayer graphene by floatation in hot water

Monolayer graphene grown by chemical vapor deposition has been intensively studied for applications such as transparent conductive films, electronic devices, sensors, molecular barriers, and electrodes. However, technology to transfer monolayer graphene from metal film must be improved through environmentally friendly and non-defective methods on arbitrary target substrates. Here, we report a clean and direct method for transferring monolayer graphene from Cu foil without defects and over a large area. In a water bath at 90–95 °C, we floated Cu foil with graphene on the water surface. After 5 h, a Cu₂O layer formed uniformly at the interface between the graphene and the Cu. Subsequently, the monolayer graphene on the Cu foil was delaminated from the thermal release tape, releasing the graphene to the target substrate (SiO₂/Si and PET). The Cu₂O formation and defect changes were monitored at each step via various characterization methods. The Cu₂O layer was uniformly established and no defects were generated after the transfer. Finally, we fabricated a graphene field effect transistor that exhibited an excellent electronic performance.