Smoothing graphene by encapsulation

Nanomaterials Graphene is often depicted as a flat sheet, but in reality some surface roughness is present, especially for graphene placed on substrates, and this roughness scatters electrons and decreases carrier mobility. Thomsen et al. used diffraction-tilt measurements in a transmission electron microscope to determine the roughness of suspended graphene samples. The root-mean-square roughness of free-standing graphene was 114 pm, whereas it was 21 pm for graphene supported on hexagonal boron nitride (hBN) and only 12 pm for graphene encapsulated by hBN. First-principles calculations indicate that flexural acoustic phonon modes that roughen the graphene become localized mainly in hBN layers. Phys. Rev. B 10.1103/PhysRevB.96.014101 (2017).