含缺陷双层石墨烯的纳米压痕模拟研究

石墨烯具有独特的力学、电学性能，被誉为是具有战略意义的新材料，具有广泛的应用前景. 目前生产的石墨烯含有各种缺陷，相较于完美石墨烯，其仍有较大应用价值. 因此有必要研究和掌握缺陷对石墨烯性能的影响，以便在目前的生产技术下，推动其工业化应用. 采用Tersoffff 势来模拟C—C 共价键的相互作用，Lernnard-Jones 势来模拟非成键碳原子之间相互作用力，基于分子动力学模拟了金刚石压头压入含缺陷双层石墨烯的纳米压痕过程，讨论了Lernnard-Jones 势函数的截断半径最佳值以及得到了典型的载荷-位移曲线. 重点探讨了Stone-Thrower-Wales、空位(包括单空位和双空位缺陷) 以及圆孔缺陷当位置不同和数目不同时对石墨烯力学性能的影响. 得出结论:薄膜中心存在缺陷时，破坏强度下降幅度特别明显. 空位缺陷在压头半径范围内存在时，临界载荷与缺陷与薄膜中心的距离成线性关系；缺陷数目越多，其杨氏模量、破坏强度等就越低. 圆孔缺陷数目在压头范围外达到一定浓度后会使石墨烯的力学性质显著降低. 本文结论也说明石墨烯结构稳定，对小缺陷不敏感，缺陷石墨烯仍具有较好的性能和使用价值. 

NUMERICAL STUDY ON NANOINDENTATION OF DEFECTIVE BILAYER GRAPHENE

Comparing with pristine graphene, graphene with various defects produced by the current technology still has a certain application value. Therefore it is necessary to investigate the influence of defects on graphene properties. In this paper, interaction between carbon atoms that forms the covalent bonds of graphene is modeled with Tersoff potential, the long range interactions of carbon atoms are characterized by Lennard-Jones potential. The nanoindentation of spherical diamond indenter into defective bilayer graphene is studied by molecular dynamics simulations. The Lernnard-Jones potential function optimal value of cut-off radius is discussed and typical load-depth curves are obtained. The effects including Stone-Thrower-Wales (STW) defect, vacancy (single and double vacancy defects) and hole defect in different positions and numbers on the mechanical properties of graphene are studied. The results show that when defect is in the film’s center, it makes intensity decrease significantly;when vacancy defect is in the region covered by indenter, the critical load increases linearly with the increase of distance which is from the defect to the film’s center;The more vacancy defect, the lower Young’s modulus and intensity. The number of hole defects reaching a certain concentration outside the region covered by indenter radius which makes the mechanical properties of graphene decrease apparently. It is concluded that graphene with the stable structure is not sensitive to small defects and defective graphene still has good performance and practical value.