摘要：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 ***,the ultimate stretchability of Si nanostructure has not yet been demonstrated due to the difficulties in experimental ***,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)*** 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 *** 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.

摘要：A mechanical metamaterial that has a tailorable coefficient of thermal expansion(CTE)is promising for guaranteeing the reliability of electrical and optical instruments under thermal *** growing research on the design and manufacturing of metamaterials with extraordinary CTEs,it remains challenging to achieve a nearly isotropic tailorable CTE while ensuring a sufficient load bearing capacity for applications,such as mechanical supporting *** this research,we propose a type of bi-metallic lattice whose CTE is artificially programmed from positive(75 ppm/K)to negative(−45 ppm/K),and whose equivalent modulus can be as high as 80 *** bi-metallic lattice with a tailorable CTE in two orthogonal directions can be readily assembled without special modifications to construct large-scale planar structures with desired isotropic CTEs.A theoretical model that considers the actual configuration of the bi-metallic joint is developed;the model precisely captures the thermal deformations of lattice structures with varied geometries and material *** by our theoretical design method,planar metallic structures that were manufactured using Al,Ti,and Invar alloy were experimentally characterized;the structures exhibited outstanding performance when compared with typical engineering materials.