Two-dimensional (2D) materials, such as Graphene, hBN and MoS2, are promising candidates in a number of advanced functional and structural applications, owing to their exceptional electrical, thermal and mechanical properties. Understanding mechanical properties of 2D materials is critically important for their reliable integration into future electronic, composite and energy storage applications. However, it has been a significant challenge to quantitatively measure mechanical responses of 2D materials, due to technical difficulties in the nanomechanical testing of atomically thin membranes.
In this talk, we will report our recent effort to study fracture behaviours of 2D materials. Our combined experiment and modelling efforts verify the applicability of the classic Griffith theory of brittle fracture to graphene. Strategies on how to improve the fracture resistance in graphene, and the implications of the effects of defects on mechanical properties of other 2D atomic layers will be discussed. More interestingly, stable crack propagation in monolayer 2D h-BN is observed and the corresponding crack resistance curve is obtained for the first time in 2D crystals. Inspired by the asymmetric lattice structure of h-BN, an intrinsic toughening mechanism without loss of high strength is validated based on theoretical efforts. The crack deflection and branching occur repeatedly due to asymmetric edge elastic properties at the crack tip and edge swapping during crack propagation, which toughens h-BN tremendously and enables stable crack propagation not seen in graphene.
Jun Lou is a full professor and the associate chair of the Department of Materials Science and NanoEngineering at Rice University, and directs the Nanomaterials, Nanomechanics and Nanodevices Lab (N3L). He has extensive experience in the synthesis and design of 2D materials beyond Graphene and other nanomaterials; nanomechanical and multi-physics characterization, and fabrication of advanced material systems and devices. He has published more than 300 peer-reviewed papers, including ones published in high impact journals such as Nature, Science, Nature Materials, Nature Nanotechnology, etc., with more than 40,000 citations and a h-index of 94. Lou is a recipient of the AFOSR Young Investigator Award, the Brimacombe Medal from TMS and the Charles Duncan Award for Outstanding Academic Achievement from Rice. He is a fellow of the Royal Society of Chemistry (FRSC). He is the Editor-in-Chief of Materials Today, the Elsevier flagship journal covering original research and reviews in the broader materials science community. He currently serves as the site director for the NSF industry university collaborative research center (IUCRC) of Atomically Thin Multifunctional Coatings (ATOMIC), exploring potential applications of 2D materials in different industries with commercial partners.