Moire Patterns and the Mechanics of Defects and Interfaces in 2D Materials

石墨烯和其他原子级薄的二维层状材料可用作表面添加剂，以定制材料的机械性能，尽管它们非常薄。例如，用单层石墨烯涂覆金属表面可以有效地增强和强化底层材料，并实现不寻常的摩擦和磨损性能。石墨烯层在另一个表面上有组织地堆叠，每个表面具有不同的原子排列，导致所谓的异质结构。 由于层中对齐和未对齐的原子堆叠的周期性布置，形成莫尔图案。这些莫尔条纹是叠层材料的电学和力学性质改变的标志，也是新的异质结构行为的起源。这项研究将通过创建新的理论和实验工具来推进二维材料科学：在原子尺度上探索莫尔图案的力学，发现新的有用材料行为，并揭示在更大尺度上利用这些特性的策略。该项目的成功将通过促进具有上级性能的先进材料的设计和制造来促进国家的健康、繁荣和福利。作为该项目的一部分，将通过与艺术+设计学院的广泛合作，为初中和高中女生创建一个关于莫尔艺术的科学、技术、工程、艺术和数学（STEAM）活动。这将是一个年度夏令营，通过将艺术和设计与材料力学联系起来，激发和激励女性学生对工程的兴趣。二维材料的异质结构是工程设计的独特空间，无论是发现新的涌现现象还是开发新的设备。这项研究的目的是探索在垂直或堆叠的二维材料及其缺陷之间的界面中观察到的莫尔图案的力学。 这项研究是由假设驱动的，即堆叠的2D材料中的缺陷赋予异质结构不寻常的机械和电子特性。一个巨正则最小跳跃（GCMH）的计算方法将被应用在LAMMPS分子动力学框架内，以解决二维材料层及其异质结构中的缺陷结构和运动。机械原子力显微镜（AFM）技术将用于测量各种晶体衬底上石墨烯的莫尔图案的力学。使用校准的多频和横向力AFM观察莫尔条纹将提供关于弹性、塑性和摩擦特性的局部调制的信息。这些补充性研究将用于揭示二维材料特有的部分位错重建、缺陷相互作用以及与面外变形的耦合的能量学。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Graphene and other atomically thin, two-dimensional layered materials can be used as surface additives to tailor the mechanical properties of materials, despite their extreme thinness. For example, coating the surface of a metal with single layer of graphene can effectively stiffen and strengthen the underlying material, as well as enable unusual friction and wear properties. The organized stacking of a graphene layer on another surface, each having different atomic arrangements, results in what is called a heterostructure. Moire patterns form as a result of periodic arrangements of aligned and misaligned atomic stacking in the layers. These Moire patterns are the signature of modifications of the electric and mechanical properties of the stacked materials, and the origin of new heterostructure behavior. This study will advance the science of two-dimensional materials by creating new theoretical and experimental tools to: probe the mechanics of the Moire patterns at the atomic scale, discover new useful material behavior, and reveal strategies to leverage these properties at larger scales. The success of the project will advance the national health, prosperity, and welfare by facilitating design and fabrication of advanced materials with superior properties. As part of the project, a Science, Technology, Engineering, Art and Math (STEAM) activity on the Art of Moire will be created for middle and high school girls through an extensive collaboration with the School of Arts+Design. This will be an annual summer camps to excite and motivate female students about engineering by connecting art and design to the mechanics of materials.Heterostructures of 2D materials are a unique space for engineering design, both for discovering new emergent phenomena and for developing novel devices. The objective of the study is to explore the mechanics of Moire patterns observed in vertical, or stacked, interfaces between 2D materials and their defects. The study is driven by the hypothesis that defects in stacked 2D materials endow heterostructures with unusual mechanical and electronic properties. A grand-canonical minimum hopping (GCMH) computational method will be applied within the LAMMPS molecular dynamics framework to resolve defect structure and motion in 2D material layers and their heterostructures. Mechanical Atomic Force Microscopy (AFM) techniques will be used to measure the mechanics of the Moire patterns of graphene on various crystalline substrates. The use of calibrated multi-frequency and lateral force AFM to observe the Moire will give information on the local modulation of elastic, plastic, and frictional properties. These complementary studies will be used to uncover the energetics of partial dislocation reconstructions unique to 2D materials, defect interactions, and coupling to out-of-plane deformation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.