Graphene Is Thin, but Not Infinitely So

We live in a 3D world, yet 2D materials are one of the hottest topics in physics right now. Graphene (Fig. 1) is perhaps the most famous example. Quite simply, the material “looks” 2D because it is only one atom thick. But does it act 2D? In terms of electronic properties, the answer is yes, as graphene has an electronic band structure that is different from its 3D counterpart, graphite. Similarly, graphene’s thermal expansion exhibits telltale 2D characteristics. But what about graphene’s mechanical properties? Yiwei Sun of Queen Mary University of London and colleagues have addressed this question by subjecting this prototypical 2D material to a traditional 3D experiment [1]. The team compressed flakes of graphene to a pressure of 12 GPa (120,000 times greater than atmospheric pressure) and showed that the resulting energy shift of graphene’s vibrations (phonons) is consistent with a 3D material rather than a 2D one. The finding may have implications for applications of graphene and other 2D materials as mechanical sensors and structural reinforcements.