Multiscale Modeling of Defect Rearrangement and Removal in 2D Layered Crystals

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Two-dimensional (2D) crystals consist of a single layer or a few layers of atoms. Graphene and Molybdenum disulfide are respective examples. Adhesive tapes are used to peel layers off from bulk crystals. A large library of 2D crystals can be isolated and prepared, each with its unique character. It has been conceived to reassemble the isolated 2D crystals into 3D layered structures through layer-by-layer stacking. With rationally chosen atomic layers and stacking sequence, these vertically layered crystals can possess exceptional multifunctional properties for combined and coupled mechanical, optical, and electronic applications. However, defects within the atomic planes themselves and between the neighboring atomic planes can significantly degrade the materials performance. This award supports fundamental research on a new class of defects ubiquitous in layered crystals and their interactions with other atomic defects and impurities. Results from this research will provide insights into engineering processes dealing with defects and leading to the removal of defects from the layered crystals. This ultimately would lead to materials with enhanced reliability. The research is multidisciplinary in nature, interfacing mechanics with materials science and multiscale computational modeling. Graduate and undergraduate students trained under this project will be exposed to the multidisciplinary research environment. The software-sharing plan involves packaging the simulation models into user-friendly software and make these accessible to the broader research community. This effort will facilitate and stimulate collaborative research between mechanicians and materials scientists, physicists, and chemists in this new field of nanotechnology.Layered crystals support new classes of defects that are absent or unimportant in bulk crystals. A recent study has demonstrated that surface dislocations in layered crystals exhibit a rippling morphology in distinct comparison to conventional dislocations in bulk crystals. This defect is termed ripplocation. This line defect is straight, narrow, crystallographically oriented, and highly mobile. The team hypothesizes that as a ripplocation sweeps through the plane of the 2D crystals, it may cause rearrangement of intralayer defects and interlayer absorbates. It thus might function as defect collector and cleaner. To test this hypothesis, this project seeks to define a set of multiscale models for characterizing the interactions between ripplocations and the intralayer defects and interlayer absorbates. Research results will provide a fundamental guidance for ripplocation-mediated defect rearrangement and removal. The research project will initiate a new paradigm in the control of defects and the fundamentals for engineering of 3D layered heterostructures.