In this work, we present surface enhanced Raman scattering (SERS) based sensor chips for applications in nanomedicine. Finite Difference Time Domain (FDTD) simulations in visible, infrared and near-infrared regimes were done to model electric field enhancement in the vicinity of plasmonic nanostructures. Some of the plasmonic nanostructures simulated were present bowtie nanohole arrays and bridged-bowtie nanohole arrays in a gold thin film. Surface enhanced Raman scattering (SERS) substrates based on these nanostructures exhibit large electromagnetic enhancement of SERS. We employ numerical simulations based on the finite difference time domain (FDTD) method to determine the electric field enhancement factors (EFs) and therefore the electromagnetic SERS enhancement factor for these SERS substrates. It was observed that the resonance wavelength of these arrays of nanoholes can be tuned by altering the size of the nanoholes. It was also observed that bridged-bowtie nanohole arrays exhibit very high electric field enhancement factors (EF) for multiple wavelengths. It was observed that bridged-bowtie nanohole arrays exhibit a highest electromagnetic SERS enhancement factor (EF) of ~ 109, which is orders of magnitude higher than what has been previously reported for nanohole arrays as SERS substrates. Hence, these nanostructures can provide SERS enhancement suitable for a few-molecule detection.
We present nanostructured gold films ⎯ with complex plasmonic nanostructures present on the surface of the films ⎯ for enhanced SPR-based sensing and imaging of biomolecules attached to the surface of these films. We employed rigorous coupled wave analysis (RCWA) for simulating the nanostructured plasmonic gold films. In our simulations, surface plasmon polaritons were excited on the surface of the nanostructured gold films using the Kretschmann configuration. We observe that these nanostructured gold films show a significant enhancement in the sensitivity of SPR sensing and imaging of biomolecules as compared to planar gold films when optimal geometries and sizes of the plasmonic nanostructures (present on the surface of the gold film) are employed.
Bridged-bowtie nanohole arrays and cross bridged-bowtie nanohole arrays in a gold film are presented as surfaceenhanced Raman scattering (SERS) substrates. We employed the numerical FDTD method to calculate the maximum electromagnetic SERS enhancement factor (EF) as a function of wavelength. It is found that the proposed nanohole arrays do not only display an extremely large enhancement factor but also have the hotspot spread over a larger area compared to the various other nanopillar structures. The calculation of electromagnetic SERS enhancement factor reveals that the cross bridged-bowtie nanohole arrays exhibit the maximum electromagnetic SERS EF of ~ 109 spreading over an area of 100 nm2. In addition, the electromagnetic SERS EF of ~ 108 is spread over 500 nm2 area which is higher than hotspot area in case of nanopillar structures. The resonance wavelength of the nanohole array can be tuned by varying the size of the nanoholes. These nanohole arrays can be employed both in transmission as well as in reflection mode as effective SERS substrates. In addition, bridged-bowtie and cross bridged-bowtie nanohole arrays show the significantly high electromagnetic SERS EF at more than one wavelength and therefore are useful for application involving multiple wavelength SERS response. Furthermore, the cross bridged-bowtie nanohole array exhibit the spatial tunability of hotspot by rotating the direction of polarization of incident field.
We present a plasmonic switch based on a combination of plasmonic nanoantennas and a phase-change material such as vanadium dioxide (VO2) that exhibits great potential for switching the near-field around the nanoantenna at ultrafast time-scales. In order to characterize the switch, we employed the FDTD method to calculate the intensity switching ratio in the vicinity of the nanoantennas, i.e. the ratio of the electric-field intensity between the metallic state (On-state) and the semiconductor state (Off-state) of the VO2 material. The proposed switch exhibits an intensity switching ratio which is much higher as compared to those reported previously.
In this paper, we present a new design for an electro-optic modulator ⎯ operating at the telecomm wavelength of 1550 nm and having a very high extinction ratio ⎯ based on photonic crystal (PhC) slab waveguide and phase change material Germanium Selenide (GeSe) embedded in core silicon layer. The device is based on the shifting of the photonic bandgap of the PhC slab waveguide when the refractive index of the GeSe layer changes on application of electric field. Since GeSe changes from its phase crystalline to amorphous on application of an electric field, its refractive index also changes when this phase transition occurs. As a result of a large refractive index contrast between the two phases, the change in the effective refractive index in the PhC slab waveguide is also very high. With two self-sustainable states, the hybrid modulator shows broadband switching capability and an On/Off extinction ratio > 37 dB around a wavelength of 1550 nm.
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