Driven by the increasing demand for micro-/nano-technologies, stimuli-responsive shape memory materials at nanoscale have recently attracted great research interests. However, by reducing the size of conventional shape memory materials down to approximately nanometre range, the shape memory effect diminishes. Here, using density functional theory calculations, we report the discovery of a shape memory effect in a two-dimensional atomically thin graphene oxide crystal with ordered epoxy groups, namely C8O. A maximum recoverable strain of 14.5% is achieved as a result of reversible phase transition between two intrinsically stable phases. Our calculations conclude co-existence of the two stable phases in a coherent crystal lattice, giving rise to the possibility of constructing multiple temporary shapes in a single material, thus, enabling highly desirable programmability. With an atomic thickness, excellent shape memory mechanical properties and electric field stimulus, the discovery of a two-dimensional shape memory graphene oxide opens a path for the development of exceptional micro-/nano-electromechanical devices.

The superior mechanical flexibility, mechanical strength, electrical conductivity, high specific surface area, and a special two-dimensional crystalline structure make graphene a very promising building block material for flexible electromechanical actuators. However, graphene papers have exhibited limited electromechanical actuation strain in aqueous electrolyte solution. In this paper, we show an easy approach to significantly improve the electromechanical actuation of reduced graphene oxide (rGO) papers via fine tuning the oxygen functional groups in rGO sheets, which was achieved by careful control of quantity of the reduction agent used in the chemical reduction process of graphene oxide.The actuation strains are enhanced up to 0.2% at an applied voltage of À1 V, which is more than a 2 fold increase compared to the regular pristine rGO paper. Further theoretical and experimental analyses reveal that the change of the capacitance and the stiffness of the rGO papers are two key factors responsible for the observed improvement.

Using density functional theory (DFT) calculations, two stable phases were found for several graphene oxide (GO) crystals with linearly aligned epoxy groups. Upon electron injection, they exhibit two-way actuation behavior. This two-way actuation is named by the observations that one piece of monolayer GO crystal is able to expand or contract upon electron injection, namely, contraction of the stable phase, and expansion of the meta-stable phase. The obtained maximum in-plane strains are as high as 8% and −5%. Such large deformation in opposite directions obtained from a single piece GO material offers unique opportunities in designing highly tunable and integrated actuators for microelectromechanical or nanoelectromechanical systems.