Auxeticity of monolayer, few-layer, vdW heterostructure and ribbon penta-graphene.

Using molecular statics simulations, we specifically focus on investigating the negative Poisson's ratio of the monolayer, few-layer, van der Waals, and ribbon penta-graphene. As a result, we provide evidence to show that the Poisson's ratio is the combination of bond stretching and angle rotating mechanism. The auxeticity of monolayer penta-graphene is due to the dominance of bond stretching. However, the significant effect of the angle rotating mechanism causes the enhancement of the in-plane Poisson's ratio of few-layer penta-graphene. Furthermore, the elongation of interlayer bonds results in a negative out-of-plane Poisson's ratio in few-layer penta-graphene. The strong dependence of Poisson's ratio on stacking configuration and number of layers was found. We also show that the van der Waals interaction slightly enhances the auxeticity of heterostructure penta-graphene. Finally, we discuss the significant effects of warped edges on the auxeticity of penta-graphene ribbons.

Negative out-of-plane Poisson's ratio of bilayer graphane.

With its excellent mechanical and thermal properties, bilayer graphane is a promising material for realizing future nanoelectromechanical systems. In this study, we focus on the auxetic behavior of bilayer graphane under external loading along various directions through atomistic simulations. We numerically and theoretically reveal the mechanism of the auxeticity in terms of intrinsic interactions between carbon atoms by constructing bilayer graphane. Given that the origin of the auxeticity is intrinsic rather than extrinsic, the work provides a novel technique to control the dimensions of nanoscale bilayer graphane by simply changing the external conditions without the requirement of complex structural design of the material.

Complex three-dimensional graphene structures driven by surface functionalization.

The origami technique can provide inspiration for fabrication of novel three-dimensional (3D) structures with unique material properties from two-dimensional sheets. In particular, transformation of graphene sheets into complex 3D graphene structures is promising for functional nano-devices. However, practical realization of such structures is a great challenge. Here, we introduce a self-folding approach inspired by the origami technique to form complex 3D structures from graphene sheets using surface functionalization. A broad set of examples (Miura-ori, water-bomb, helix, flapping bird, dachshund dog, and saddle structure) is achieved via molecular dynamics simulations and density functional theory calculations. To illustrate the potential of the origami approach, we show that the graphene Miura-ori structure combines super-compliance, super-flexibility (both in tension and compression), and negative Poisson's ratio behavior.