LASER INDUCED MICRO/NANO SHAPING OF 3D STRUCTURES ON DIFFICULT-TO-FORM MATERIALS

<p>The shock wave generated by confined laser-material interaction is a promising tool to process materials under ultrahigh strain rates. In 2014, the laser shock imprinting (LSI) technique was proposed as a novel micro/nano fabrication technique on membrane materials. The capability of large-scale, high-resolution and low-cost manufacturing makes LSI technique widely applied in electronics, photonics and plasmonics. The modulation of micro/nano structures by LSI technique was mainly applied in membrane materials in previous studies. Therefore, in this study, we designed different fabrication schemes to broaden the application of LSI technique in difficult-to-form materials, including metal organic frameworks (MOFs), bulk metals and 2D chiral-chain tellurium.</p> <p>MOFs crystal has unique physical and chemical properties due to its porous structures. However, MOF crystals usually exist as powdery materials. The scalable fabrication of monolithic and high-resolution patterns on MOF crystals is challenging. Here, we take the advantage of ultrafast strain rate and high pressure induced by laser shock, the formability of powdery MOFs is significantly enhanced. The nanosecond laser shock eliminates the voids among MOF crystals due to the surface amorphization effect, linking the MOF crystals to a dense film with designed micro/nano structures. Meanwhile, the mechanical strength of the MOF films is improved up to 100% compared with the powdery MOF crystals. The facile and low-cost method can be potentially used in devices, gas separation, and biochemical devices. Furthermore, we designed an electropulse-assisted laser shock imprinting (EPLSI) technique to improve the formability of bulk metals under ultrafast deformation. In daily life, metallic materials and metal parts re irreplaceable in many fields, which exists in bulk materials and parts. The previous LSI technique was able to fabricate high-resolution micro/nano structures on metallic membrane via a top-down imprinting process. In terms of bulk metals, the formability is limited due to strain burst, dislocation avalanches and size effect. Here, we designed a hybrid system, applying laser shock on the molds and introducing a high current pulse during the LSI processing. Hierarchical micro/nano structures are formed on bulk metals, and the aspect ratio of the nanostructures is doubled due to electroplasticity effects. The hydrophobicity of metal surfaces is significantly due to the surface structure change with improved aspect ratio. Finally, the deformation behavior of LSI processed 2D tellurium was investigated for strain engineering purposes. The introduction of a strain field effectively changes the band structure of 2D semiconductors. Symmetrical and asymmetrical strain field was introduced in 2D Te and the deformation mechanism was explored by transmission electron microscope, which provides theoretical guidance for strain engineering in chiral-chain 2D materials.</p>