Collaborative Research: Friction in Flatland - Contact, Adhesion, and Friction of 2D Materials

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Two-dimensional materials are layered materials having atomic- to nano-scale thickness. They are increasingly being explored and used for a multitude of applications that take advantage of the materials' layered structure. However, the properties of the interfaces between the layers are still poorly understood, due in part to challenges associated with direct measurement of such properties at very small length scales. The goal of this project is to obtain a fundamental understanding of the effect of material properties, including composition, phase, and crystallinity, on the critical properties of interfacial contact, adhesion, and friction. This will have broad technological impact, since investigation of layered materials is needed to optimize and transform their use in applications that rely on these critical properties to function effectively. The focus of this research is on layered materials that are relevant to current and emerging applications, including those in the automotive, aerospace, and electronics industries, thereby promoting the progress of science; advancing the national health, prosperity, and welfare; and securing the national defense. The research objectives of this project will be complemented by activities focused on providing opportunities for students from underrepresented groups, including involving the large Hispanic population at University of California Merced and leveraging successful outreach programs at University of Pennsylvania. The team will also engage with pre-college audiences, building on the PIs' track records of public and youth engagement.This project will focus on the nanoscale interfacial contact, adhesion, and friction behavior of transition metal dichalcogenides, including molybdenum disulfide. Research on these materials will be carried out through optimally-matched atomic force microscopy and accelerated molecular dynamics simulations, taking advantage of the unique capabilities of the PIs. Optimal matching allows simulations to be validated by experiments, and experimental findings to be fully explored in atomically-resolved detail by simulations. Availability of probe tips and substrates coated with well-defined, ultrathin transition metal dichalcogenides using recently developed techniques will enable isolation of the effects of composition, phase, and crystallinity for both self-mated and heterostructure interfaces. This novel approach will yield fundamental insights into the mechanical properties of transition metal dichalcogenide interfaces that are needed for rational and predictive design of materials, devices, and systems composed of these materials.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.