Flexoelectric effect in boron nitride-graphene heterostructures

Hexagonal boron nitride and graphene layers offer an attractive way to build 2D heterostructures as their lattices are well-matched as well as they are isostructural and isoelectronic. In this work, the flexoelectric coefficients of monolayer boron nitride-graphene heterostructures (BGHs) are determined using molecular dynamics simulations with a Tersoff potential force field. This is achieved by imposing the bending deformation to the pristine BN sheet (BNS) and BGHs. Three shapes of graphene domains are considered: triangular, trapezoidal and circular. Overall polarization of BGHs was enhanced when the graphene domain was surrounded by more N atoms than B atoms. This enhancement is attributed to higher dipole moments due to the C-N interface compared to the C-B interface. The flexoelectric response for BGHs with 5.6% of triangular and trapezoidal graphene domains was enhanced by 15.2% and 7.83%, respectively, and reduced by 25% for the circular graphene domain. We also studied the bending stiffness of pristine BNS and BGHs using the continuum-mechanics approach. Our results also reveal that the bending stiffness of BGHs increases compared to the pristine BNS. Moreover, the enhancement in the flexoelectric coefficient and bending stiffness was more significant when the graphene domain breaks the symmetry of BGHs. Our fundamental study highlights the possibility of using BGHs in nanoelectromechanical systems (NEMS) such as actuators, sensors and resonators.