Evidence of flexoelectricity in graphene nanobubbles created by tip induced electric field

Strain engineering in graphene nanobubbles (GNB) has made significant progress in recent years opening new possibilities to observe quantum phenomena such as Newton's ring oscillation and generation of pseudomagnetic field. Here, we demonstrated that controlled formation of graphene nanobubbles is possible on transferred graphene on standard SiO2/Si substrate by the application of external electric field through the tip of piezoelectric force microscope (PFM). We manipulated their dimensional attributes (height, area and volume) by varying tip ramp voltage and tip distance. Prominent out-of-plane piezo-response (flexoelectricity) was observed using PFM in the newly created nanobubbles due to the presence of non-uniform strain gradients in the nanobubbles. Moreover, we found quadratic dependence of the effective piezoelectric coefficient proportional to the increasing bubble creation ramp voltage. Our work motivates the exploration of flexoelectric properties and related applications with 2D nanobubbles on different substrates. [Display omitted]