Direct observation of ultrafast carrier coupling dynamics in monolayer graphene/metal system

For promising graphene-based devices, graphene/metal contacts are inevitable. When they operate at high frequencies, it is essential to explore the ultrafast carrier dynamics between graphene and metal, which has been rarely studied. Owing to the special monolayer graphene/copper structure we designed, that is, the graphene is grown on copper, we have directly observed the ultrafast carrier dynamics between monolayer graphene and copper by using femtosecond laser pump-probe technique for the first time. The measured optical reflectivity changes of graphene/copper system are significantly different from that of bare copper, which is attributed to the ultrafast carrier dynamics between graphene and copper, and graphene optical properties. A model considering carriers coupling in graphene and copper, including electron and phonon, has been built and validated by the experiment. Present study provides direct observation of the ultrafast carrier dynamics between graphene and metal, which is of great significance for graphene-based device applications.