Crystal twinning occurs when two separate crystals symmetrically share the same lattice plane, the twin boundary (TB). In the extreme case, when 5 TBs are connected concurrently on a straight line parallel to their common axis [110], a five-fold twin will appear. In bulk metal samples, five-fold twins often form under severe plastic deformation or annealing conditions associated with grain growth. Five-fold twins are increasingly common in natural minerals and synthetic nanomaterials, especially in chemically synthesized face-centered cubic (fcc) metal nanoparticles. These unique five twins can significantly change the atomic/electronic structure, thereby changing the stress distribution in nanomaterials, providing a new way to adjust the physical, chemical and mechanical properties of nanomaterials. Therefore, compared with single-crystal nanomaterials, five-fold twin nanomaterials are often introduced into nanodevices for applications such as photonics, catalysis, sensing, and hydrogen storage. However, the intrinsic deformation behavior of quintuple twins under high shear stress conditions is not well understood.

Recently, the team of Wang Jiangwei, a researcher from the School of Materials Science and Engineering of Zhejiang University, used the high resolution and in-situ real-time advantages of in-situ electron microscopy technology to observe and study the internal deformation mechanism of five-fold twins. It is found that quintuple twins often undergo structural failure through coordinated TB deformation, resulting in the generation of reconstructed pentagonal regions at the pentapod core. The reconstructed core region is mainly caused by the coordinated migration (nucleation and growth) of TB along different directions, and is accelerated by TB slip (growth). These inherent deformation behaviors of the five-fold twin provide the possibility to control the morphology of five-fold twin nanomaterials with unique properties. The relevant research results were published in the international academic journal Nano Letters under the title of "Penta-Twin Destruction by Coordinated Twin BoundaryDeformation. Chen Yingbin, a doctoral student at Zhejiang University, is the first author of this paper.

Original Link: https://doi.org/10.1021/acs.nanolett.1c02970

Figure: Experimental Process

This experiment uses the PicoFemto of Zeyu Technology®The in-situ TEM-STM electrical measurement system builds a test platform in the transmission electron mirror, and the prepared gold wire is fixed on the fixed end and the moving end of the sample rod respectively. After entering the electron microscope, the in situ rod precisely butts the two gold wires at the nanoscale and completes the welding. After welding, shear force is applied to the sample and the denaturation mechanism of the five-fold twin crystal is observed in situ with high resolution.

Figure: High Resolution In-situ TEM Observation of Deformation Mechanism of Five Twins under Shear Force

Figure: Simulation and Simulation

Figure: zeyu Technology in-situ sample rod used in the experiment