Numerical and experimental investigation of plasmonic properties of silver nanocrescent structures for sensing applications

A novel technique to fabricate metallic nanocrescents is presented. Their optical response is simulated using the finite difference time domain (FDTD) method and validated via experimental investigation and surface characterization. Nanocrescents support multiresonance extinction spectra, making them good candidates for sensing applications. In this work, silver nanocrescents are arrayed on a glass substrate. A silicon mold was used to imprint an array of polymer nanopillars that were coated using obliquely evaporated silver in order to introduce a wedge angle to the wall thickness around the pillars. The thin part of the silver wall and the inner pillars were then removed under a vertical hydrogen plasma shower and nanocrescents were formed. Scanning electron microscopy (SEM) was used to characterize the surface morphology, and the optical properties have been investigated by using spectroscopy. We then performed a FDTD analysis of the nanocrescent structures to investigate their plasmonic properties emphasizing the multiresonance behavior. A comparison between the measured and simulated extinction spectra for two different polarizations of the incident plane wave showed a slight redshift in the case of the simulated spectra in both polarization states. This slight discrepancy is attributed to the roughness of the fabricated nanostructures. The existence of multiple resonances was clearly seen in the case of measured spectra.