2, Paul-Drude-Institute fur Festkörperelektronik, Berlin, , Germany
Due to its centrosymmetric crystal structure, graphene is intrinsically non-piezoelectric. However, piezoelectricity can be engineered into graphene through symmetry-breaking strategies. Here, we will report on the piezoelectric contrast, measured with piezoresponse force microscopy (PFM), between regions with different graphene layer numbers on 6H-SiC (0001). Additional experiments on oxygen-intercalated, freestanding graphene and on tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) doped graphene on SiC, indicate that the observed piezoelectric contrast arises from the interfacial dipole moment across the van der Waals (vdW)-bonded graphene and the partially -bonded zerolayer graphene. The interfacial dipole moment is due to the spontaneous polarization of the bulk SiC substrate, which breaks the crystal symmetry in the out-of-plane direction. Our findings demonstrate a new way to turn graphene into a piezoelectric material by manipulating the graphene-substrate interface, which opens new potentials for graphene in piezoelectric material-related applications.