An Atomistic Experimental Investigation of Fracture in Transitional Metal Dichalcogenides

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Transition metal dichalcogenides, a family of two-dimensional materials, have shown unique optical, electrical, and thermal properties that enable emergent applications in batteries, solar cells, electronics, and sensors. In all these applications, failure by fracture is a major concern. Under this project, the aim is to advance the fundamental knowledge of failure in transition metal dichalcogenides, and to establish robust experimental and computational protocols that are applicable to similar studies on other nanomaterials. In this regard, this project would pave the way to establishing methodologies for reliability and life prediction analyses. This project also presents excellent training opportunities for graduate students and postdoctoral fellows, offering exposure to cutting-edge instrumentation in a rapidly developing new field of science. The educational components of this project will leverage the Northwestern University International Institute of Nanotechnology research experience for undergraduate program to provide opportunities for minority students to gain exposure to an energizing research environment. Additionally, the students and postdocs participating in this project will create a YouTube channel to explain, to a wide audience, fundamental concepts of two-dimensional materials, in situ experimentation, and applications.By performing fracture testing using microsystem technology and in situ aberration-corrected transmission electron microscopy (TEM), the aim is to fill current gaps of scientific knowledge including quantification of the fracture toughness and the effect of atomistic defects (vacancies, dislocations, etc.) and phase transitions on transition metal dichalcogenides fracture behavior. The validity of current molecular dynamics simulations by comparing predicted atomistic configurations and mechanisms to measured ones will also be assessed. The atomistic studies will reveal whether defects such as vacancies, dislocations, and phase transitions nucleate around crack tips, and their role on toughness. Moreover, the ultrahigh resolution of transmission electron microscopy will enable the calculation of strain fields around the crack tip and therefore fracture toughness quantifications. The following fundamental questions will be answered: 1) What is the range of applicability of the Griffith fracture criterion? When are nonlinear effects important enough to call for the use of the J-integral fracture criterion? 2) Which types of atomic structures/defects emerge from crack tips? 3) How do defects (vacancies and dislocations) affect mechanistically and quantitatively the fracture behavior? 4) Do phase transformations predicted by density functional theory occur and if so, how do they affect the fracture process? By scientifically answering these questions, it is anticipated that this study will provide insights and quantitative information of value to the engineering community.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.