Magnetically responsive dynamic nanostructures

Date
2021-05-03
Authors
Luo, Zhiren
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Abstract

Inspired by natural nanostructures, magnetically responsive micro/nanoscale pillars have attracted significant research interest recently due to their dynamic properties. To overcome current fabrication challenges for better manipulation of micro/nanoscale objects and systems, and active tuning of visible light, I demonstrate active periodic nanostructures with high aspect ratio and pillar density. Having structure period of 2 μm, diameter of 600 nm, and high aspect ratio of up to 11, this structure can be magnetically actuated to form multiple movement modes with displacement of 200 nm and bending angle of 1.6°. This work can find potential applications in particle manipulation. Secondly, I demonstrate a new type of magnetically responsive nanostructure consisting of a polydimethylsiloxane (PDMS) nanopillar array with deposited nickel caps, that has successfully decoupled the mechanical compliance and magnetic susceptibility to enhance the actuation performance. The actuation results of nanopillars with 540 nm period and 1.3 μm height have been analyzed using image processing, leading to a displacement around 180 nm with a bending angle of up to 7.9°. Thirdly, I demonstrate a mechanism to achieve magnetically responsive dynamic iridescence, which is based on the tilting of periodic photonic nanostructures with large tilting angle of up to 30°. In this method, a periodic array of magnetic nanopillars serves as a template to guide the assembly of iron oxide nanoparticles when magnetized in a liquid environment. The local field gradient induced by the magnetic template anchors the assembled particle columns, allowing the structure to tilt about the base when the applied field direction is changed. This effect emulates a microscopic “Venetian blind” and results in dynamic iridescence that is tunable in real time. The reflectance spectra demonstrate the peak wavelength can shift from 528 nm to 720 nm. The magnetic actuation mechanism is reversible and has a fast response time around 0.3 s. This structure can be implemented on an arbitrary surface as dynamic camouflage, iridescent display, and tunable photonic elements, as well as in other applications such as active fluidic devices and particle manipulation

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