Molecular Sensing and Color Manipulation Based on Dimension-Controlled Plasmon-Enhanced Silicon Nanotube SERS Substrates

The system of suspended gold nanoring on silicon nanotube substrate with enhanced light harvesting and electromagnetic field enhancements was proposed in the present study. The effects of outer/inner diameter (<i>D</i>/<i>d</i>) ratio of the ring and tube on the plasmonic behavior were studied by systemic simulations and experiments. In simulations, the high order quadrupole–dipole mode was also excited in addition to the typical dipole–dipole mode, and the resonant configurations were characterized by both electric field profile and resonant surface charge distribution. Experimentally, both dark-field and Raman microscopies were conducted to examine the plasmonic behavior. The plasmon-enhanced scattering could be controlled by tailoring the <i>D</i>/<i>d</i> ratio, and the dark-field image colors could be manipulated covering the visible range. Raman spectra using two excitation wavelengths were also recorded and showed good agreement with calculated enhancement factor which, in turn, provided the evidence of the evolution of resonance mode and denoted our designed structure as a potential candidate for surface-enhanced Raman scattering applications

Giant Electric Field Enhancement and Localized Surface Plasmon Resonance by Optimizing Contour Bowtie Nanoantennas

The surface plasmon resonances of gold contour bowtie nanostructures were simulated in the present study. The local electromagnetic field enhancement and the resonance wavelength for different dimensions of contour bowtie antennas with various contour thicknesses were investigated to find the critical conditions to induce additional enhancement compared to the solid bowtie antenna. Both the phase of the electric field and the bound surface charge distribution on the surface of the contour bowtie were studied to characterize the coupled plasmon configurations of the contour bowtie antenna. Also, a model was proposed to explain the resonance and hybridization behavior in the contour bowtie nanoantenna, and it was verified by examining the phase of the electric field in the polarization direction

Self-Assembled Monolayer Immobilized Gold Nanoparticles for Plasmonic Effects in Small Molecule Organic Photovoltaic

The aim of this study was to investigate the effect of gold nanoparticle (Au NP)-induced surface plasmons on the performance of organic photovoltaics (OPVs) that consist of copper phthalocyanine and fullerene as the active materials. The photon absorption can be enhanced by immobilization of surfactant-stabilized Au NPs on a self-assembled monolayer-modified indium tin oxide (ITO) electrode, and thus, the photocurrent as well as the power conversion efficiency (PCE) of these OPVs can be improved. Varying the density of the immobilized Au NPs in the devices provided no significant variation in the charge mobility but it did enhance the photocurrent. In addition, device simulation results demonstrated that the improvement in photocurrent was due to the enhancement of light absorption and the increase in charge separation, which was facilitated by the Au NPs. Overall, we attributed the improvement in PCE of OPVs to a localized surface plasmon resonance effect generated by the Au NPs

3D Nanostructures of Silver Nanoparticle-Decorated Suspended Graphene for SERS Detection

The silver nanoparticle-decorated suspended graphene was proposed and fabricated to increase the efficiency of surface-enhanced Raman scattering (SERS) mainly by the enhanced electric field resulting from exciting the localized surface plasmon resonance. The morphology of cavity under the graphene was controlled by the thickness of catalyst and the etching time in the metal-assisted chemical etching process (MacEtch). The reflectance and ellipsometric spectra were examined to understand the optical behaviors of silver nanoparticle-decorated suspended graphene as functions of the etching time. For the samples treated with MacEtch, the Raman signals of graphene and <i>p</i>-mercaptoaniline were greatly enhanced due to the plasmonic cavity effect. Moreover, the graphene could increase the Raman intensity of the probed molecules by chemical enhancement. With the optimal etching time of 15 s, the SERS signals reached the maximum that was 13–15 times larger than those without etching. The electric field enhancement profiles and the SERS enhancement factor were simulated by finite-difference time-domain method to characterize the field distribution around the silver nanoparticles and to verify the enhanced SERS phenomenon observed in measurements

Effects of Gold Film Morphology on Surface Plasmon Resonance Using Periodic P3HT:PMMA/Au Nanostructures on Silicon Substrate for Surface-Enhanced Raman Scattering

We study the effects of the morphology of gold film on the unusual modulation of surface plasmon resonance (SPR) and surface-enhanced Raman scattering (SERS) using the periodic nanostructures of P3HT:PMMA/Au on the silicon substrate. The periodic structures of cylindrical holes with triangular lattice were fabricated first by e-beam lithography using a photoluminescent resist of P3HT:PMMA at a thickness of ∼100–200 nm, and the structures were then coated with gold of ∼20 nm thickness. The geometries and structures of the samples were studied by atomic force microscopy and scanning electron microscopy. The relationships between the geometry and the resonance were investigated by the extinction spectra and confocal Raman mapping. The results show that the resonance wavelength of the extinction peak is blue shifted, and its width becomes wider when the hole diameter of the structure increases or the lattice constant decreases. However, the extinction peak is red shifted when the thickness of the periodic nanostructures increases due to the surface plasmon resonance, localized surface plasmon resonances, and coupling between neighboring holes. The finite-difference time-domain (FDTD) method was adopted to simulate different nanostructures, and we found that the morphology and location of gold film on the periodic structure of P3HT:PMMA film played a vital role in the extinction spectra of the composite film of P3HT:PMMA/Au. A large enhancement of Raman scattering was observed when the SERS and SPR were correlated in the nanostructure at the exciting wavelength of 632.8 nm. This study provides a useful strategy to modulate the extinction spectra and enhance the intensity of Raman spectra by changing the nanostructures. The observed SERS will be useful for the design and fabrication of functional devices and sensors