Dr. Jun Lou
Department of Materials Science and NanoEngineering,
Rice University, Houston, Texas 77005, USA
« Defect and Strain Engineering of Two Dimensional Materials »
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. Additionally, actively tuning functional properties of 2D materials by stress/strain is a very attractive approach for engineering these atomically thin components in practical applications. In this talk, we will discuss our recent effort to determine the engineering relevant fracture toughness of graphene with pre-existing defects, rather than the intrinsic strength that governs the uniform breaking of atomic bonds in perfect graphene. Our combined experiment and modeling verify the applicability of the classic Griffith theory of brittle fracture to graphene. Strategies on how to improve the fracture resistance in graphene will be discussed. Also in this talk, we report the atomic structure and morphology of the grains and their boundaries in the CVD grown polycrystalline molybdenum disulfide atomic layers. The implications of the effects of defects such as grain boundaries on mechanical and electrical properties of two-dimensional atomic layers will be discussed. In another example, we systematically characterize chemical vapour deposition-grown MoS2 by photoluminescence spectroscopy and mapping and demonstrate non-uniform strain in single-crystalline monolayer MoS2 and strain-induced bandgap engineering. By evaluating the effective strain transferred from polymer substrates to MoS2 using three-dimensional finite element analysis, we demonstrate how strain concentration propagates in a triangular MoS2 monolayer crystal and propose substrates’ Young’s modulus as dominating mechanisms of strain loss.
Short Bio :
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