In-plane and interlayer mechanical behaviors of diamane superlattice generated in twisted bilayer graphene

Diamane superlattice generated by the interlayer bonding of twisted bilayer graphene (IB-TBG) has attracted much attention thanks to its excellent properties inherited from bulk diamond, as well as the versatile modulation of physical and mechanical properties, which may open up novel electronic applications. In this work, we have systematically studied the in-plane and interlayer mechanical behaviors of IB-TBG through molecular dynamics simulations and theoretical analysis by considering different structural parameters, such as the twisted angle, stack pattern, and interlayer bonding density. It is found that interlayer bonding density plays a crucial role in determining the in-plane and interlayer shear mechanical properties of IB-TBG. Both the in-plane tensile modulus and strength follow the same linear attenuation relationship with interlayer bonding density for different twisted angles and stacked patterns, while the interlayer shear modulus increases with interlayer bonding density following the same power law, and the critical shear strain of failure linearly decreases with interlayer bonding density. Furthermore, two failure modes are observed under shear deformation, i.e., the failure of interlayer bonding (mode I) and fracture of graphene sheets (mode G). Then, theoretical prediction is carried out by considering the balance of in-plane tension and interlayer shear, which can identify the two failure modes well. The results presented herein yield useful insights for designing and tuning the mechanical properties of IB-TBG.