Achieving ultra-large tensile strain in nanoscale Si mechanical metamaterials

Compared with the inherent brittleness of bulk silicon (Si) at ambient temperature, the nanosized Si materials with very high strength, plasticity, and anelasticity due to size effect, are all well-documented. However, the ultimate stretchability of Si nanostructure has not yet been demonstrated due to the difficulties in experimental design. Herein, directly performing in-situ tensile tests in a scanning electron microscope after developing a protocol for sample transfer, shaping and straining, we report the customized nanosized Si mechanical metamaterial which overcomes brittle limitations and achieves an ultra-large tensile strain of up to 95% using the maskless focused ion beam (FIB) technology. The unprecedented characteristic is achieved synergistically through FIB-induced size-softening effect and engineering modification of mechanical metamaterials, revealed through analyses of finite element analysis, atomic-scale transmission electron microscope characterization and molecular dynamics simulations. This work is not only instructive for tailoring the strength and deformation behavior of nanosized Si mechanical metamaterials or other bulk materials, but also of practical relevance to the application of Si nanomaterials in nanoelectromechanical system and nanoscale strain engineering.