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.
Metallic nanostructures possess many advantages for utilization in various applications including sensing applications.
However, achieving an easy to fabricate platform with high sensitivity performance is considered the main challenge in
designing such nanostructures. Two factors should be considered when designing a wavelength based nanostructured
sensor; the field distribution around the nanostructures, and the full width at half maximum (FWHM) of the sensor
spectral response. In this paper, we study suspended nanodisc structures as a candidate for enhancing the electric field
distribution in-plane and out of plane axes of the nanodiscs, and hence enhancing the probe depth of the nanosensor.
Another advantage of the suspended nanodisc structure is that it offers a 100% surface coverage. The Finite Difference
Time Domain (FDTD) method is used for the study of optical properties of the structure. The resonance location depends
on the dimensions of the nanodiscs as well as the polymer base. Higher order modes can also be supported by nanodiscs
with larger dimensions. The local electric field is enhanced as it is distributed in both perpendicular and horizontal planes
with respect to the plane of gold nanodiscs without altering the FWHM relative to the regular nanodisc structure. This is
considered as an advantage in sensing applications. Another advantage of this structure is that it can be readily fabricated
by nanoimprint lithography and gold deposition.
We present a study of gold nanopyramids and their optical properties. A comparison with the extinction properties of
gold nanorods and nanocubes is also undertaken. The Finite Difference Time Domain (FDTD) method is used for the
study of optical properties. The nanopyramids display a dual plasmon resonance when excited with a perpendicularly
polarized signal due to the excitation of dipole and quadrupole modes. The quadrupole modes are not strongly affected
by changing the height of the nanopyramids whereas the dipole mode is redshifted with increasing the height of the
nanopyramids. The quadrupole mode could be of interest in some applications where the shorter wavelength resonance is
desired. The quadrupole and dipole modes are located at 620 nm and 765 nm respectively. This band is used for both
intensity and wavelength modulated biosensors. Furthermore, the electric field is enhanced in the case of the
nanopyramids which is considered as another advantage in sensing and surface enhanced Raman scattering (SERS)
applications.
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