Two-dimensional nanomaterials for novel piezotronics and piezophototronics

Because of the novel properties owing to two-dimensional (2D) confinement, research on 2D nanomaterials has become one of the leading topics in condensed matter physics and materials science. From the viewpoint of crystallography, the 2D morphology embodies spontaneous breakdown of three-dimensional symmetry, which means that the inversion symmetry preserved in some bulk materials can be broken in their corresponding 2D ones, possibly resulting in intrinsic piezoelectric property. Such 2D materials in conjunction with their semiconductor properties are good candidates for novel ultrathin piezotronics and piezophototronics. In one hand, the 2D piezoelectric materials are easy to integrate with the state-of-the-art semiconductor process and conventional electronic technologies. On the other hand, the possible combination of piezoelectricity with other unusual properties in 2D materials such as ferromagnetism or topological insulator may give birth to new physics and innovative devices design for novel applications. Here, we present an overview of recent breakthroughs in 2D piezotronics and piezophototronics, covering from the fundamental principles to their vast applications in energy harvesting and adaptive electronics/optoelectronics. Considering the potential scientific and device developments, we conclude with an in-depth discussion of possible future directions in this active research field.