Chiroptical response of aluminum nano-crescents at ultraviolet wavelengths
Matthew S. Davis, Wenqi Zhu, Jared H. Strait, Jay K. Lee, Henri J. Lezec, Steve Blair, Amit K. Agrawal
Manipulation of plasmon modes at ultraviolet wavelengths using engineered nanophotonic devices allows for the development of high-sensitivity chiroptical spectroscopy systems. We present here a framework for the fabrication and characterization of Al based crescent shaped nanostructures that exhibit a strong chiroptical response at ultraviolet wavelengths. Through utilization of higher-order plasmon modes in wavelength scale nanostructures, we address the inherent fabrication challenges in scaling the response of these structures to higher frequencies such as the ultraviolet. Additionally, the distinct far-field spectral features of the various response types are analyzed within a coupled-oscillator model framework. We find two competing chiroptical response types that contribute towards potential ambiguity in the interpretation of the resultant circular dichroism spectra. The first, optical activity, originates from the interaction between hybridized eigenmodes while the second manifests as a response superficially similar to optical activity but originating instead from differential near-field absorption modes. The theoretical and experimental framework for the design, measurement and interpretation of the chiroptical response from nanoplasmonic devices presented here is expected to aid the development and implementation of next-generation chiroptical spectroscopy systems.