Bending, pulling, and cutting wrinkled two-dimensional materials
Two-dimensional materials (2DM) such as graphene, monolayer boron nitride, or monolayer molybdenum disulfide are crystalline layers only a few atoms thick. In this talk, we will examine the mechanical properties of these materials using newly developed techniques to pull, bend, twist, and cut them. We will see that the mechanics of 2DMs is drastically different from that of “conventional” bulk matter. It will be shown that inevitable out-of-plane crumpling modifies every mechanical property of 2DMs making their mechanical response more akin to that of biological membranes than of solid objects. For the case of a prototypical 2DM, graphene, it will be shown that out-of-plane crumpling renders the thermal expansion coefficient negative and substrate-dependent, decreases the Young’s modulus, increases the bending rigidity by several orders of magnitude, and changes the sign of the Poison’s ratio. We will discuss how these unusual mechanical properties can be used in developing new types of nanomechanical devices.