Projection micro stereolithography (PμSL) has emerged as a powerful three-dimensional (3D) printing technique for manufacturing polymer structures with micron-scale high resolution at high printing speed, which enables the production of customized 3D microlattices with feature sizes down to several microns. However, the mechanical properties of as-printed polymers were not systemically studied at the relevant length scales, especially when the feature sizes step into micron/sub-micron level, limiting its reliable performance prediction in micro/nanolattice and other metamaterial applications. In this work, we demonstrate that PμSL-printed microfibers could become stronger and significantly more ductile with reduced size ranging from 20 μm to 60 μm, showing an obvious size-dependent mechanical behavior, in which the size decreases to 20 μm with a fracture strain up to ~100% and fracture strength up to ~100 MPa. Such size effect enables the tailoring of the material strength and stiffness of PμSL-printed microlattices over a broad range, allowing to fabricate the microlattice metamaterials with desired/tunable mechanical properties for various structural and functional applications.

Due to the enhanced ambient structural stability and excellent optoelectronic properties, all-inorganic metal halide perovskite nanowires have become one of the most attractive candidates for flexible electronics, photovoltaics and optoelectronics. Their elastic property and mechanical robustness become the key factors for device applications under realistic service conditions with various mechanical loadings. Here, we demonstrate that high tensile elastic strain (~ 4% to ~ 5.1%) can be achieved in vapor-liquid-solid-grown single-crystalline CsPbBr₃ nanowires through in situ scanning electron microscope (SEM) buckling experiments. Such high flexural elasticity can be attributed to the structural defect-scarce, smooth surface, single-crystallinity and nanomechanical size effect of CsPbBr₃ nanowires. The mechanical reliability of CsPbBr₃ nanowire- based flexible photodetectors was examined by cyclic bending tests, with no noticeable performance deterioration observed after 5, 000 cycles. The above results suggest great application potential for using all-inorganic perovskite nanowires in flexible electronics and energy harvesting systems.

Incorporating high-entropy alloys (HEAs) in composite microlattice structures yields superior mechanical performance and desirable functional properties compared to conventional metallic lattices. However, the modulus mismatch and relatively poor adhesion between the soft polymer core and stiff metallic film coating often results in film delamination and brittle strut fracture at relatively low strain levels (typically below 10%). In this work, we demonstrate that optimizing the HEA film thickness of a CoCrNiFe-coated microlattice completely suppresses delamination, significantly delays the onset of strut fracture (~100% increase in compressive strain), and increases the specific strength by up to 50%. This work presents an efficient strategy to improve the properties of metal-composite mechanical metamaterials for structural applications.

Comprehensive understanding of the structural/morphology stability of ultrathin (diameter < 10 nm) gold nanowires under real service conditions (such as under Joule heating) is a prerequisite for the reliable implementation of these emerging building blocks into functional nanoelectronics and mechatronics systems. Here, by using the in situ transmission electron microscopy (TEM) technique, we discovered that the Rayleigh instability phenomenon exists in ultrathin gold nanowires upon moderate heating. Through the controlled electron beam irradiation-induced heating mechanism (with < 100 ℃ temperature rise), we further quantified the effect of electron beam intensity and its dependence on Rayleigh instability in altering the geometry and morphology of the ultrathin gold nanowires. Moreover, in situ high-resolution TEM (HRTEM) observations revealed surface atomic diffusion process to be the dominating mechanism for the morphology evolution processes. Our results, with unprecedented details on the atomic-scale picture of Rayleigh instability and its underlying physics, provide critical insights on the thermal/structural stability of gold nanostructures down to a sub-10 nm level, which may pave the way for their interconnect applications in future ultralarge- scale integrated circuits.