Achieving ultra-large tensile strain in nanoscale Si mechanical metamaterials

可实现超大拉伸应变的纳米尺寸硅机械超材料

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.

不同于体硅材料在室温下的固有脆性特征,纳米尺寸硅材料因尺寸效应表现出更高的强度、塑性和滞弹性.然而,由于实验条件严苛,硅纳米结构的超大拉伸性能尚未得到证实.本研究通过对纳米尺寸硅样品进行转移、加工和测试等实验设计,在扫描电子显微镜中实现了纳米尺寸硅机械超材料原位拉伸测试,观察到高达95%超大拉伸应变.有限元仿真、原子级透射电子显微镜表征和分子动力学模拟表明,硅机械超材料的变形能力是聚焦离子束诱导尺寸软化和机械超材料几何结构力学改性共同作用的结果.本工作不仅有助于纳米材料、结构的强度、变形行为机理研究,也为硅纳米材料在纳机电系统和纳米应变工程中的潜在应用提供指导.