Chiral metamaterials fabricated by dynamic shadowing growth
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Metamaterials have demonstrated unusual electromagnetic properties, which enable various novel applications, such as sub-wavelength imaging and optical filters. Now it has come to the time to realize these applications with metamaterial based devices. One of the greatest challenges of the metamaterial applications is the fabrication of large-area metamaterials. In this dissertation, we describe a simple and scalable fabrication technique for chiral metamaterial, which is an important branch of metamaterials with a great capability of manipulating polarizations of light. Our fabrication technique is based on dynamic shadowing growth on self-assembled colloidal monolayers, which mainly employs the shadowing effect of regular colloidal nanospheres during physical vapor depositions to produce ordered arrays of chiral nanostructures. Using this fabrication technique, two strategies for preparing chiral nanostructures have been demonstrated. The first strategy is to create a single layer of quasi-three-dimensional nanostructure films with chiral shape on nanospheres in one plasmonic material, such as silver. A systematic study reveals that various nanostructures can be created using this method by simply tuning the monolayer orientations with respect to the incident vapor. Fan-shaped chiral nanostructures obtained at a particular monolayer orientation exhibit giant chiral optical response with fabrication conditions optimized. The second strategy is to create three-dimensional multiple layers of chiral nanostructures with one plasmonic material, such as silver, and one dielectric material, such as silicon dioxide. The plasmonic or dielectric layers are helically stacked forming two helices twisted together. Two different chiral structures have been realized by this method, helically stacked plasmonic layers, and Swiss roll nanostructures. Finally, we demonstrate that this dynamic shadowing growth fabrication method can be used for developing chiral optical devices. The fan-shaped chiral nanostructures are fabricated on a monocrystalline monolayer on 1 cm2 substrate, which can be potentially developed as a narrow-band circular polarizer after annealing. Active chiral optical device can be obtained by transferring such large-area chiral metamaterial into a flexible polymer substrate, whose optical property can be tuned by mechanical deformations. The fabricated chiral metamaterial can also be used as a localized surface plasmon resonance based sensor for refractive index sensing, with an enhanced sensitivity.