Graphene nanowrinkles found to generate flexoelectric polarization far stronger than bulk materials

Flexoelectricity describes polarization induced by a strain gradient, and it can occur even in materials that would otherwise show no polarization at all. In three-dimensional materials, competing electromechanical effects tend to mask it, but atomically thin two-dimensional materials offer a cleaner setting to isolate strain-driven polarization. In principle, bending a two-dimensional sheet tightly enough can perturb the out-of-plane orbitals that carry its electrons, generating a “quantum” flexoelectric response distinct from classical charge separation across a deformed membrane. Confirming this quantum contribution experimentally has been difficult, since most prior work accessed curvatures several orders of magnitude gentler than the atomic-scale bending needed to perturb individual orbitals.

Researchers at Rice University, together with collaborators from the University of Manchester, the University of Brighton, the South Dakota School of Mines and Technology, the University of Sussex, and Pennsylvania State University, have shown that sub-nanometer-scale wrinkles in graphene can generate a strong electrical polarization simply by bending, without any added chemistry or dopants. The effect, known as flexoelectricity, was predicted theoretically in graphene in 2008 but had not previously been directly measured at this scale.Flexoelectricity describes polarization induced by a strain gradient, and it can occur even in materials that would otherwise show no polarization at all. In three-dimensional materials, competing electromechanical effects tend to mask it, but atomically thin two-dimensional materials offer a cleaner setting to isolate strain-driven polarization. In principle, bending a two-dimensional sheet tightly enough can perturb the out-of-plane orbitals that carry its electrons, generating a “quantum” flexoelectric response distinct from classical charge separation across a deformed membrane. Confirming this quantum contribution experimentally has been difficult, since most prior work accessed curvatures several orders of magnitude gentler than the atomic-scale bending needed to perturb individual orbitals.

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