Laser shock imprinting of metallic nanostructures and shock processing of low-dimensional materials
Laser shock imprinting (LSI) is proposed and developed as a novel ultrafast room-temperature top-down technique for fabricating and tuning of plasmonic nanostructures, and processing of one-dimensional semiconductor nanowires and two-dimensional crystals. The technique utilizes a shock pressure generated by laser ablation of sacrificial materials. Compared with conventional technologies, LSI features ambient condition, good scalability, low cost and high efficiency. In this study, LSI is demonstrated as a top-down method for the fabrication of free-standing flexible nano-engineered metallic nanoarrays. Large-scale ordered structures with the capability of strong optical field enhancement, such as ultra-sharp 3D pyramids, 2D tips, and nanotrenches with 10-nm gaps, are nanoimprinted within nanoseconds and integrated with graphene. Polarized Raman spectroscopy of the suspended graphene veiled on shocked hybrid film reveals significantly enhanced and actively controlled light-matter interaction. By testing in reactive environment, elevated temperatures, and in the application of molecular sensing, the hybrid platform shows a significantly enhanced stability of light-matter interaction. In addition, LSI is applied to enable shock turning of an ordered metallic nanostructure and generate precise nanogap closing. It is found that the modification of nanoarray geometries is controlled by laser fluence and is nanoscale size dependent. A deformable transfer layer introduces a self-limiting effect with its collaborative superplastic flow with the target arrays, which forms a line-gap at sub-10 nm scale. Ultrafast opto-mechanical tuning of metallic nanoarrays with various designs is further demonstrated. Processed nanoantennas show red-shifts of their surface plasmon resonances and enhanced local fields, which significantly influence their performances in applications such as surface enhanced Raman scattering. Finally, laser shock processing of semiconductor nanowires and 2D crystals is presented. This study develops a CMOS-compatible top-down fabrication methodology with the aid of laser shock to achieve large scale nanoshaping of nanowires in parallel with tunable elastic strains. As a result of 3D straining, the inhomogeneous elastic strains in GeNWs result in notable Raman peak shifts and broadening, and enhancement of electronic properties. Ultrafine graphene-copper hybrid nanostructures is also achieved by LSI in one step. The presented nanoshaping opens a new avenue to manipulate nanomaterials with tunable electrical-optical properties and create many opportunities for nanoelectronics, nano-electrical-mechanical system, quantum devices.
Cheng, Purdue University.
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