Park Yeonggu, Choi Jin Sik, Choi Taekjib, Lee Mi Jung, Jia Quanxi, Park Minwoo, Lee Hoonkyung, Park Bae Ho
Division of Quantum Phases &devices, Department of Physics, Konkuk University, Seoul, 143-701, Korea.
Creative Research Center for Graphene Electronics, Electronics and Telecommunications Research Institute (ETRI), Daejeon 305-700, Korea.
Sci Rep. 2015 Mar 24;5:9390. doi: 10.1038/srep09390.
Ripples in graphene are extensively investigated because they ensure the mechanical stability of two-dimensional graphene and affect its electronic properties. They arise from spontaneous symmetry breaking and are usually manifested in the form of domains with long-range order. It is expected that topological defects accompany a material exhibiting long-range order, whose functionality depends on characteristics of domains and topological defects. However, there remains a lack of understanding regarding ripple domains and their topological defects formed on monolayer graphene. Here we explore configuration of ripple domains and their topological defects in exfoliated monolayer graphenes on SiO2/Si substrates using transverse shear microscope. We observe three-color domains with three different ripple directions, which meet at a core. Furthermore, the closed domain is surrounded by an even number of cores connected together by domain boundaries, similar to topological vortex and anti-vortex pairs. In addition, we have found that axisymmetric three-color domains can be induced around nanoparticles underneath the graphene. This fascinating configuration of ripple domains may result from the intrinsic hexagonal symmetry of two-dimensional graphene, which is supported by theoretical simulation using molecular dynamics. Our findings are expected to play a key role in understanding of ripple physics in graphene and other two-dimensional materials.
石墨烯中的波纹受到广泛研究，因为它们确保了二维石墨烯的机械稳定性并影响其电子特性。它们源于自发对称性破缺，通常以具有长程有序的畴的形式表现出来。预计拓扑缺陷会伴随具有长程有序的材料出现，其功能取决于畴和拓扑缺陷的特性。然而，对于在单层石墨烯上形成的波纹畴及其拓扑缺陷，人们仍然缺乏了解。在这里，我们使用横向剪切显微镜探索了在SiO2/Si衬底上的剥离单层石墨烯中波纹畴及其拓扑缺陷的构型。我们观察到具有三种不同波纹方向的三色畴，它们在一个核心处相交。此外，封闭畴被偶数个通过畴边界连接在一起的核心所包围，类似于拓扑涡旋和反涡旋对。此外，我们发现可以在石墨烯下方的纳米颗粒周围诱导出轴对称三色畴。这种迷人的波纹畴构型可能源于二维石墨烯固有的六边形对称性，分子动力学理论模拟支持了这一点。我们的发现有望在理解石墨烯和其他二维材料中的波纹物理方面发挥关键作用。
