PolyU researchers unveil novel strategy to achieve both strength and toughness in 2D materials design, advancing applications in electronic and photonic devices

The mechanical strength and toughness of engineering materials are often mutually exclusive, posing challenges for material design and selection. To address this, a research team from The Hong Kong Polytechnic University (PolyU) has uncovered an innovative strategy: by simply twisting the layers of 2D materials, they can enhance toughness without compromising material’s strength.

Typical transition metal dichalcogenides (TMDs) is a class of 2D materials known for their unique electronic, optical and mechanical properties. While 2D materials often exhibit exceptional strength, they are extremely brittle.  Enhancing both the strength and toughness of bulk materials for engineering applications has remained a significant challenge.

To overcome these limitations, a research team led by Prof. ZHAO Jiong, Professor of the PolyU Department of Applied Physics and Member of the Research Institute for Advanced Manufacturing (RIAM), has pioneered a novel twisting engineering approach whereby twisted bilayer structures enable sequential fracture events, addressing the conflict between strength and toughness in 2D materials. By focusing on TMDs, such as molybdenum disulfide (MoS₂) and tungsten disulfide (WS₂), the team discovered a new fracture mechanism in twisted bilayers.  The finding was supported by nanoindentation and theoretical analysis.

Using in situ transmission electron microscopy, the team found that when cracks propagate in twisted bilayer structures, the lattice orientation mismatch between the upper and lower layers leads to the formation of interlocking crack paths. Following the initial fracture, the crack edges in both layers spontaneously form stable grain boundary structures through interlayer self-assembly.  This distinctive “crack self-healing” mechanism protects subsequent fracture tips from stress concentration, effectively preventing further crack propagation. Notably, this process consumes more energy than conventional fracture, and the degree of toughness enhancement can be tuned by adjusting the twist and twist angle.

This breakthrough facilitates the design of strong and tough new 2D materials, promoting their broader applications in photonic and electronic devices. The findings have been published in the international journal Nature Materials.

Press release: https://polyu.me/453uoBk

Online coverage:

Mirage News – https://polyu.me/4kBNFhX

Dot Dot News – https://polyu.me/4lYAysf (Chinese only)