石墨烯对称晶界断裂动力学的分子模拟
Molecular Simulation of Fracture Dynamics of Symmetric Tilt Grain Boundaries in Graphene
摘要：
利用原子模拟方法获得了由各种嵌入式对称倾斜晶界（GB）组成的石墨烯片的拉伸过程的微观信息。与原始石墨烯相反，这些GBs在横向单轴拉伸下在所有但最大取向差角的情况下以非凡的模式断裂，其表现出间歇性裂纹扩展并在准机械失效后形成许多粘性残余连接。被称为单原子碳链（MACs）的弦，其重要性最近得到了强调，随着伸长的进行，逐渐延伸到几纳米的最大值。在扶手椅型和扶手椅型对称倾斜晶界中均观察到这些特征，这些特征对拉伸应力和应力-应变曲线的形状有重要影响。然而，存在显着差异的人口密度和MACC出现准机械故障后的可达长度，其中较高的面向GBs。此外，在最大错向角情况下，扶手椅型晶界的最大应力和极限应变均显著大于扶手椅型晶界，而在其他情况下，扶手椅型晶界的最大应力和极限应变均略小于扶手椅型晶界。对于扶手椅型和双晶型石墨烯，最大应力随取向差角的增大而增大，其范围在32~80 GPa之间，极限应变在0.06~0.11之间，其下限与多晶石墨烯的临界应变实验值吻合较好。
英文摘要：
Atomistic simulations were utilized to obtain microscopic information of the elongation process in graphene sheets consisting of various embedded symmetric tilt grain boundaries (GBs). In contrast to pristine graphene, these GBs fractured in an extraordinary pattern under transverse uniaxial elongation in all but the largest misorientation angle case, which exhibited intermittent crack propagation and formed many stringy residual connections after quasi mechanical failure. The strings known as monoatomic carbon chains (MACCs), whose importance was recently highlighted, gradually extended to a maximum of a few nanometers as the elongation proceeded. These features, which critically affect the tensile stress and the shape of stress-strain curve, were observed in both armchair and zigzag-oriented symmetric tilt GBs. However, there exist remarkable differences in the population density and the achievable length of MACCs appearing after quasi mechanical failure which were higher in the zigzag-oriented GBs. In addition, the maximum stress and ultimate strain for armchair-oriented GBs were significantly greater than those of zigzag-oriented GBs in case of the largest misorientation angle while they were slightly smaller in other cases. The maximum stress was larger as the misorientation angle increased for both armchair and zigzag-oriented GBs ranging between 32~80 GPa, and the ultimate strains were between 0.06~0.11, the lower limit of which agrees very well with the experimental value of threshold strain beyond which mechanical failure often occurred in polycrystalline graphene.
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