Direct measurement of tensile mechanical properties of few-layer hexagonal boron nitride (h-BN)

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Abstract
Hexagonal boron nitride (h-BN) has excellent thermal conductivity and dielectric properties, which shows great potential for low-dimensional devices. However, mechanical properties of h-BN have not been comprehensively investigated through experiments. In this work, we conduct in situ direct tensile tests on freestanding single-crystal few-layer h-BN nanosheets with various layer numbers from 3 to 8, with an elaborate sample transfer and characterization protocol. Young's modulus of 573.8 ± 101.4 GPa and a tensile fracture strain up to 3.2% are revealed, which are comparable to its monolayer counterpart. Moreover, we find a tough-to-brittle transition in few-layer h-BN with the increase in layer number, which is attributed the interplay between the van der Waals interaction and in-plane covalent bonding. These findings could open up new possibilities in mechanical research of van der Waals materials and provide guidance for the design of h-BN-based devices and composites.
Funding Information
  • Research Grants Council, University Grants Committee (N_HKU159/22)
  • Shenzhen Science and Technology Innovation Program (Type C, SGDX2020110309300301)
  • Research Grants Council, University Grants Committee (RFS2021-1S05)

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