Reversible phase transformation in graphene nano-ribbons: Lattice shearing based mechanism

When armchair graphene nano-ribbons (GNRs) are subjected to uniaxial tensile loading along the width direction, molecular dynamics studies reveal a hexagonal-to-orthorhombic phase transformation via lattice shearing, resulting in a terrace in the stress–strain curve. Upon unloading, the original hexagonal lattice can be reverted back, even at a uniaxial strain of up to 35%, which is different from the brittle fracture or plastic behavior usually observed from sp2 hybridized carbon materials. The larger bending stiffness of GNRs suppresses the out-of-plane movement of atoms and enhances in-plane lattice shearing when the resolved shear stress along the closely packed directions reaches a critical value. Since the shear strain is still in the elastic limit and there is no energy barrier, the phase transformation is reversible. Hence, the electronic properties of the armchair GNRs may be changed reversibly via simple uniaxial tensile loading and unloading, which is expected in graphene-based nano-electromechanical systems.