Helium diffraction and acoustic phonons of graphene grown on copper foil

We report helium diffraction from graphene grown by chemical vapour deposition (CVD) using copper foil. This method reveals acoustic phonons, which are physically important to thermal conductance as well as a sensitive probe of graphene's interactions with the underlying substrate. Helium diffraction is made possible by the high quality of graphene produced by a recently reported “peel-off method”. The graphene lattice parameter was found to remain constant in the temperature range between 110 and 500 K. The measured parabolic dispersion of the flexural mode along Γ¯M¯ allows determining the bending rigidity k = (1.30 ± 0.15) eV, and the graphene-Cu coupling strength g = (5.7 ± 0.4) × 1019  N/m3. Unlike analytics employing atomic resolution microscopy, we obtain information on the atomic-scale quality of the graphene over mm length scales, suggesting the potential for Helium atom scattering to become an important tool for controlling the quality of industrially produced graphene.