Department of Physics and Center of Integrated Nanomechanical Systems, University of California at Berkeley, Berkeley, California 94720, USA.
Nano Lett. 2012 Jan 11;12(1):293-7. doi: 10.1021/nl203547z. Epub 2011 Dec 15.
The understanding of crack formation due to applied stress is key to predicting the ultimate mechanical behavior of many solids. Here we present experimental and theoretical studies on cracks or tears in suspended monolayer graphene membranes. Using transmission electron microscopy, we investigate the crystallographic orientations of tears. Edges from mechanically induced ripping exhibit straight lines and are predominantly aligned in the armchair or zigzag directions of the graphene lattice. Electron-beam induced propagation of tears is also observed. Theoretical simulations account for the observed preferred tear directions, attributing the observed effect to an unusual nonmonotonic dependence of graphene edge energy on edge orientation with respect to the lattice. Furthermore, we study the behavior of tears in the vicinity of graphene grain boundaries, where tears surprisingly do not follow but cross grain boundaries. Our study provides significant insights into breakdown mechanisms of graphene in the presence of defective structures such as cracks and grain boundaries.
由于所施加的应力而导致的裂缝形成的理解是预测许多固体最终力学行为的关键。在这里，我们提出了关于悬浮单层石墨烯膜中裂缝或撕裂的实验和理论研究。使用透射电子显微镜，我们研究了撕裂的晶体取向。机械诱导撕裂的边缘呈现直线状，并且主要沿着石墨烯晶格的扶手椅或锯齿方向排列。还观察到电子束诱导撕裂的传播。理论模拟解释了观察到的优选撕裂方向，将观察到的效应归因于石墨烯边缘能对相对于晶格的边缘取向的非单调依赖性的不寻常现象。此外，我们研究了在石墨烯晶界附近的撕裂行为，令人惊讶的是，撕裂并没有遵循而是穿过晶界。我们的研究为在存在诸如裂缝和晶界等有缺陷结构的情况下石墨烯的失效机制提供了重要的见解。
