Low temperature elastic properties of chemically reduced and CVD-grown graphene thin films

We have measured internal friction and shear modulus of both reduced graphene oxide and chemical-vapor deposited graphene films measuring as thin as 5 nm. Graphene oxide films were deposited from solutions by spin-coating, and graphene films were synthesized by chemical-vapor deposition (CVD) on Ni thin films. In both cases, these films were transferred from their host substrate into a water bath, then re-deposited onto to a high-Q single crystal silicon mechanical double-paddle oscillator. A minimal thickness dependence of both internal friction and shear modulus was found within the experimental uncertainty for reduced graphene oxide films varying thickness from 5 to 90 nm. The internal friction of all films exhibits a temperature independent plateau below 10 K. The values of the plateaus are similar for both the reduced graphene oxide films and CVD graphene films, and they are as high as the universal “glassy range” where the tunneling states dominated internal friction of amorphous solids lies. This result shows that from a mechanical loss point of view, both graphene oxide and CVD graphene films have high and similar level of disorder. Raman measurements performed on the same samples show higher structure order in CVD graphene films than in graphene oxide films. Our results suggest that internal friction probes different sources of disorder from those by Raman, and the disorder is not directly related to the existence of C–O binding in the graphene oxide films. The shear modulus averages 53 GPa after subtracting Young's modulus component from the vibration mode used in experiments.