Two-dimensional layered van der Waals materials exhibit great application potential in next-generation semiconductor and flexible electronic devices due to their excellent and tunable electrical properties. However, such materials generally face severe bottlenecks in mechanical properties. The strong in-plane covalent or ionic bonds and the weak interlayer van der Waals interactions lead to significant mechanical brittleness, making them highly prone to sudden fracture and even catastrophic failure during practical service. At present, bulk layered materials with room-temperature plasticity are extremely scarce, and their deformation mechanisms are mainly limited to conventional interlayer and intralayer slip accompanied by dislocation motion, resulting in macroscopic tensile elongation typically below 12%, which greatly hinders their practical integration into deformable and flexible devices.

Although twisted moiré superlattices can break the original crystal symmetry of materials and regulate novel quantum effects and physical properties at the microscale, how to introduce moiré twist angles into bulk materials to regulate mechanical properties remains a key unexplored challenge. Traditionally, moiré twist angles are mostly considered to exist in micro/nanoscale two-dimensional heterostructures. In macroscopic bulk van der Waals crystals, it is not only difficult to uniformly introduce a controllable twist-angle distribution, but whether they can serve as dislocation-like stress dissipation channels to achieve large plastic deformation without destroying in-plane electron transport also lacks systematic theoretical support and deformation-mechanism guidance. Therefore, exploring a universal and facile preparation method to construct tunable moiré twist angles in bulk layered semiconductors and break the trade-off between plasticity and mobility is a major issue that urgently needs to be overcome in the current field.

To address the above issues, a joint team composed of the Shanghai Institute of Ceramics, Zhejiang University, and others conducted in-depth research using ZEPTOOLS' in situ TEM measurement system. The team proposed a new mechanism for controllably introducing interlayer moiré twist angles in bulk van der Waals semiconductors through off-axis pre-compression, successfully achieving a significant increase in macroscopic tensile plasticity of up to 360% while fully maintaining excellent room-temperature electrical properties.

Title: Tuning moiré twist angles enhances tensile plasticity in bulk van der Waals crystals 
Journal: Nature Materials 
URL:https://doi.org/10.1038/s41563-026-02731-2

This study first focuses on the challenge of macroscopic tensile brittleness and plasticity regulation in bulk layered van der Waals materials, and innovatively proposes and verifies a deformation strategy for engineering-induced interlayer moiré twist angles via off-axis pre-compression. Using the ternary layered semiconductor GaGeTe crystal as a typical model system, the researchers applied off-axis bias treatment with a small tilt angle of about 5°, effectively utilizing non-uniform stress fields and shear torque to excite a large-range interlayer twist-angle distribution inside the bulk material. Tensile mechanical property test results show that the GaGeTe crystal after 10% optimized off-axis pre-compression treatment exhibits a room-temperature macroscopic tensile strain greatly increased from 8.3% in the pristine sample to 30.0%, achieving a tensile plasticity leap as high as 360%. This mechanical modification strategy was further successfully extended to various binary and ternary bulk van der Waals systems such as InSe, GaS, GaSe, CrSiTe₃, InSiTe₃, and SnBi₂Te₄, fully demonstrating that moiré twist-angle regulation of mechanical behavior has broad material universality in enhancing the ductility of layered crystals.

In order to precisely elucidate the microscopic evolution mechanism of moiré twist-angle-induced high tensile plasticity, the research team carried out systematic room-temperature in situ and quasi-in situ transmission electron microscopy analysis. During the microscopic tracking of mechanical behavior, the research team used ZEPTOOLS' in situ tensile sample holder to apply quantitative uniaxial tensile loading to the electron-beam-transparent thin region under displacement-controlled mode, capturing in real time the in situ dynamic information of moiré superlattice evolution during crystal deformation under stress. Microstructural characterization combined with fast Fourier transform and diffraction analysis clearly showed that the non-pre-compressed sample could only excite small-angle moiré fringes of less than 6.0° when stretched, whereas the off-axis compressed sample pre-introduced a wide-range moiré structure spanning 1.5° to 21.4°. During the subsequent tensile deformation process, the microscopic twist angles inside the sample gradually reorganized and evolved continuously toward large angles such as 13.1° and 21.4°, confirming that the gradual increase and reconstruction of interlayer twist angles are the core microscopic processes for releasing macroscopic mechanical energy and coordinating large deformation.

On the basis of microscopic experimental observations, the research team further explored the physical origin and energy dissipation mechanism by which interlayer moiré twist angles reduce the slip energy barrier. First-principles calculations based on density functional theory and generalized stacking fault energy surfaces show that directly constructing large-angle moiré structures in pristine untwisted crystals requires overcoming a relatively high formation energy, but once the initial moiré configuration is formed, the energy change required for subsequent evolution to higher twist angles is significantly reduced by more than an order of magnitude. At the same time, due to the existence of moiré twisting, the interlayer Te-Te and Ga-Te interactions are significantly weakened, causing the interlayer slip energy barrier to drop sharply by about two orders of magnitude, while the cleavage energy of the material remains basically constant, thereby increasing the ratio of cleavage energy to slip energy barrier by about two orders of magnitude. This extremely low slip resistance enables individual layers to undergo large-scale relative sliding and twist reorganization under very small shear stress during tension, effectively suppressing stress concentration and catastrophic propagation of microcracks, and fundamentally explaining the coexistence mechanism of high fracture resistance and excellent tensile ductility.

This study ultimately aims to solve the long-standing trade-off bottleneck between mechanical plasticity and electrical transport performance in flexible electronic materials, and evaluates the influence of twist-induced plastic deformation on electronic band structure and carrier mobility. Electrical property tests and band calculations show that p-type GaGeTe single crystal has a room-temperature hole mobility as high as 587 cm²·V⁻¹·s⁻¹, and its interlayer moiré twist deformation is completely confined within the van der Waals gap, while the strong in-plane chemical bonding network and band-edge electronic states are not destroyed. Therefore, after off-axis compression and repeated bending deformation, the material's Hall mobility and carrier concentration remain highly stable, with the mobility change rate after 200 bending cycles being less than 1%. This achievement successfully breaks the dilemma that traditional layered semiconductors find it difficult to simultaneously achieve plasticity and mobility, establishes a design paradigm for simultaneously obtaining high macroscopic ductility and excellent electrical transport stability through controllable van der Waals moiré engineering, and provides a solid theoretical foundation and technical path for developing high-performance, highly reliable next-generation flexible and deformable semiconductor devices.

As a high-end precision instrument company based in China, ZEPTOOLS is a first-class supplier of in situ electron microscopy characterization solutions. Its launched PicoFemto series of in situ transmission electron microscopy characterization solutions have successively provided technical support for important research achievements by users at home and abroad. The figure below shows the ZEPTOOLS in situ TEM sample holder product used in this research: