Remarkable plasticity and softness of polymorphic InSe van der Waals crystals

Indium selenide (InSe) crystals are reported to show exceptional plasticity, a new property to two-dimensional van der Waals (2D vdW) semiconductors. However, the correlation between plasticity and specific prototypes is unclear, and the understanding of detailed plastic deformation mechanisms is inadequate. Here three prototypes of InSe are predicted to be plastically deformable by calculation, and the plasticity of polymorphic crystals is verified by experiment. Moreover, distinct nanoindentation behaviors are seen on the cleavage and cross-section surfaces. The modulus and hardness of InSe are the lowest ones among a large variety of materials. The plastic deformation is further perceived from chemical interactions during the slip process. Particularly for the cross-layer slip, the initial In-Se bonds break while new In-In and Se-Se bonds are newly formed, maintaining a decent interaction strength. The remarkable plasticity and softness alongside the novel physical properties, endow InSe great promise for application in deformable and flexible electronics.