The chiroptical activity of metal nanostructures has attracted attention because of the potential to induce chiral plasmons through the sculpting of electric and magnetic fields based on structural design. Much research activity has focused on elucidating the design rules for chiroptical plasmonic responses, with most materials systems focused on bottom-up nanoparticle assembly or top-down fabricated chiral structures. Nanosphere template lithography (NTL) is a simple, versatile fabrication method for preparing plasmonic nanoparticles with controlled structural properties. When extendting NTL to aluminum, the rather robust native oxide layer poses a challenge for the typical Ar ion milling step, thus limiting the scope of shape control. In order to overcome this challenge, we introduced a sacrificial copper layer into the NTL fabrication process, ultimately eliminating the need for a milling step. Using this fabrication process, symmetric and asymmetric dimer aluminum nanocrescents were fabricated. In studying these structures, we observed large circular dichroism (CD) responses over broad wavelength ranges. We compared the chiroptical response of the aluminum structures to more simple gold structures. Both sets of nanocrescents exhibit chiroptical activity with a strong orientation-dependent handedness. Orientation chiroptical response dependencies are observed relative to in-plane as well as out-of-plane rotation. Optical responses are compared between symmetric nanocrescents and asymmetric dimer nanocrescents (i.e., nominally achiral and chiral nanostructures). These responses potentially represent a simple approach in controlling desired handedness in chiral nanomaterials, irrespective of the inherent structural handedness.

Chiroptical activity of symmetric and asymmetric aluminum nanocrescents

2019 Fall National Meeting

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