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

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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.