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Abstract:

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. In this talk, we will report our efforts 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 [1]. 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 [2]. 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. Next, we will also review some of our more recent efforts in evaluating the mechanical properties of 2D covalent organic frameworks (COFs) [3, 4]. Finally, challenges and opportunities for fracture in 2D materials will be briefly discussed. 

References:
[1] P. Zhang, L. Ma, F. Fan, Z. Zeng, C. Peng, P.E. Loya, Z. Liu, Y. Gong, J. Zhang, X. Zhang, P.M. Ajayan, T. Zhu, and J. Lou, Fracture Toughness of Graphene, Nature Communications, Vol. 5, article number 3782, 2014. DOI: 10.1038/ncomms4782
[2] Y. Yang, Z. Song, G. Lu, Q. Zhang, B. Zhang, B. Ni, C. Wang, X. Li, L. Gu, X. Xie, H. Gao, J. Lou, Intrinsic Toughening and Stable Crack Propagation in Hexagonal Boron Nitride, Nature, Vol. 594(7861), 57-61, 2021. DOI: https://doi.org/10.1038/s41586-021-03488-1
[3] Q. Fang, C. Sui, C. Wang, T. Zhai, J. Zhang, J. Liang, H. Guo, E. Sandoz-Rosado, J. Lou, Strong and Flaw-insensitive Two-dimensional Covalent Organic Frameworks, Matter, Vol. 4(3), 1017-1028, 2021. DOI: https://doi.org/10.1016/j.matt.2021.01.001
[4] Q. Fang, Z. Pang, Q. Ai, Y. Liu, T. Zhai, D. Steinbach, G. Gao, Y. Zhu, T. Li, J. Lou, Superior Mechanical Properties of Multilayer Covalent-Organic Frameworks Enabled by Rationally Tuning Molecular Interlayer Interactions, Proceedings of the National Academy of Sciences (PNAS), Vol. 120, 15, e2208676120, 2023. DOI: https://doi.org/10.1073/pnas.2208676120