Laser-Shock-Induced Nanoscale Kink-Bands in WSe₂ 2D Crystals.

Abstract

The response of materials to high stress and strain rates in nature has been a long-term scientific interest. The formation of kinks is a common deformation feature under high pressure and strain rates among foliated structures, such as rock-forming minerals. Although deformation of foliated rock layers in geology has been investigated for a century, the deformation behavior of their nanoscale counterparts, such as two-dimensional (2D) layered materials, under high stress and strain rates has not been investigated. 2D transition metal dichalcogenides have very strong in-plane rigidity, whereas the interlayer shear modulus is 3 orders of magnitude lower than their in-plane Young's modulus. Here, we study the structure and property changes in multilayer WSe₂ 2D layers during a 3D nanoshaping process where laser-shock pressure at the GPa level is applied to imprint the 2D multilayers into a designed nanomold, forming a large local bending strain of 5-6%. The microstructure of the 2D multilayers after laser shock is observed to be a nanoscale kink-band, similar to that of strained geological layered crystals, due to the high-pressure-induced bending and shearing. The deformed kink-band structure is investigated experimentally by high-resolution transmission electron microscopy and atomic force microscopy and validated by molecular dynamics simulations. The changes in the resulting electronic band structure are investigated by first-principles calculations. The laser-shock straining technology to induce kink-band structures can enrich the understanding and facilitate the applications of many 2D materials.