13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- than that in the zigzag direction tension test when the strain is larger than 0.1. Smaller angle α can release stress which results in slower stress increase, which will enlarge the critical strain. Hence, the larger critical strain in zigzag direction tension than that in armchair direction tension can be understood. Figure 4 Young’s modulus as a function of the silicene nanoribbon’s width for uniaxial tension along the armchair and zigzag directions. To study the size and chirality effects on the mechanical properties of silicene nanoribbons, deformation-control uniaxial tensile tests are performed. The width of square-shaped silicene nanoribbons in armchair and zigzag directions varies from 0.8 to 20.7 nm. An NVT ensemble is used with 10.0 nm vacuum space on each side of the nanoribbon. The Yong’s modulus is calculated for armchair and zigzag directions using the above expression, / Y σ ε = in the elastic region. In Figure 4 we plot the variation of Young’s modulus as a function of the size of the silicene nanoribbon. It can be seen that Young’s modulus along zigzag and armchair directions increases with the width of the nanoribbon. This variation is similar to the size-dependent Young’s modulus of graphene nanoribbon [28]. For example, the size effect on Young’s modulus is negligible when the width of the silicene nanoribbon is over 15.0 nm. Furthermore, significant chirality effects are found in the Figure 4. For the nanoribbons with the same size, Young’s modulus is larger along the zigzag direction than along the armchair direction when the width of nanoribbon is smaller than 10.0 nm, which is consistent with the results for the graphene nanoribbon [28]. Figure 5 Snapshots of atomix configurations at various strains. As shown in Figure 2, as the strain increase to certain value, the bulk silicene starts to fracture, which is same for silicene nanoribbon under uniaxial tension. Figure 5 presents the fracture process of an armchair silicene nanoribbon with the width of 9.7 nm. The applied strain rate is 0.0005/ps.
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