Nanocavity-in-Multiple Nanogap Plasmonic Coupling Effects from Vertical Sandwich-Like Au@Al2O3@Au Arrays for Surface-Enhanced Raman Scattering
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The development of ideal three-dimensional (3D) tailorable surface-enhanced Raman scattering (SERS) substrates with the properties of timesaving, large area, high throughput, single or few molecules detection, reproducibility, reusable ability, and high density of "hot spots" has been the mainstream challenge and the robust task. Here, we construct perpendicular sandwich-like Au@Al2O3@Au hybrid nanosheets (PSHNs) on the Al foil as a 3D flexible substrate for SERS. The design of 3D PSHNs incorporates several advantageous aspects for SERS to enhance the performance of plasmonic diamers via bifunctions of vertical Al2O3 nanosheets (NSs) including the nanoscaffold and nanobaffle plate effects. As a nanoscaffold, it increases the space utilization of Au-Au diamers, whereas as a nanobaffle, it forms densely homogeneous Au@Al2O3@Au nanojunctions by sub-4 nm thickness of Al2O3 NSs as the dielectric isolated layer for the double-sided exposure of slitlike surface plasmon resonance. The optimized PSHN substrate exhibits a fascinating SERS sensitivity with an experimental enhancement factor of 1012 and is able to detect rhodamine B at an extremely low concentration up to the limit of single or few molecules (10-18 M), as well as can be recycled without the loss of SERS enhancement via the simple impregnation process. These advantages will greatly facilitate the wider use of SERS in many fields.A plasmonic nanochannel structure consisting of periodic vertical Au/Si/Au nanochannels connected by U-shaped gold layers is demonstrated as a narrow-band plasmonic thermal emitter. Due to coupling of localized surface plasmons in the channels and propagating surface plasmons under the U-shaped gold layers, a narrow-band emission peak is observed.
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Abstract The Raman spectra of the nanotube (7,0) with point defects (monovacancy, divacancy, and Stone–Wales defect) were simulated in order to derive spectroscopic signatures of defective nanotubes. First, we calculated the electronic band structure and the phonon dispersion of the defective nanotubes using supercells within a non‐orthogonal tight‐binding model. We found that new optical transitions and Raman‐active phonons appeared in comparison with the perfect nanotube. Secondly, we calculated the resonance Raman excitation profile for all Raman‐active phonons of the defective nanotubes and simulated their Raman spectra at specific laser excitation energies. The predicted high‐intensity Raman lines can be used as spectroscopic signatures of the defective nanotubes.
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Surface enhanced Raman scattering (SERS) is studied from optically trapped dielectric spheres partially covered with silver colloids in a solution with SERS active molecules. The Raman scattering and Brownian motion of the sphere are simultaneously measured to reveal correlations between the enhancement of the Raman signal and average position of the sphere. The correlations are due to the momenta transfer of the emitted Raman photons from the probe molecules. The addition of a mechanical force measurement provides a different dimension to the study of Raman processes.
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We demonstrate an efficient nanoscale electrical detector for propagating surface plasmons, tightly confined to nanoscale silver wires. Our technique is based on the near-field coupling between guided plasmons and a nanowire field-effect transistor. We demonstrate that this near-field circuit can efficiently detect the plasmon emission from a single quantum dot that is directly coupled to the plasmonic waveguide.
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In Raman detection, the most popular solution for the samples is tri-distilled water. But the effect of aqueous solution is barely studied in Raman spectroscopy. In fact Raman spectroscopy of solid-state and liquid-state are obvious different. In addition, FWHM of Raman spectral peaks also change evidently. In this paper, several samples were selected for the experiment; including sodium nitrate, sodium nitrite, glucose and caffeine. By comparing the Raman spectroscopy of samples at different concentrations, it is found that the concentration of the sample can affect the strength of Raman spectroscopy, but it can hardly impact FWHM of Raman spectral peaks. By comparing the Raman spectroscopy of liquid-state with the Raman spectroscopy of solid-state, it is observed that the FWHM of some Raman spectral peaks varied obviously; that may be because when the sample was dissolved into the water, the crystal lattice structure was broken, and for some samples atom form became ion form in aqueous solution. Those structural variations caused the variation of the FWHM. The Raman spectroscopy of caffeine aqueous solution at very low concentration was also detected and analyzed. Compared with the Raman spectra of solid-state samples, it is found that some Raman spectral peaks disappeared when the sample was dissolved in water. It is possible that the low concentration of the sample result in the weakening of Raman signals and the disappearing of some weak Raman spectral peaks. Then Ag nanoparticles were added into the caffeine aqueous solution, the results suggest that surface enhanced Raman spectroscopy (SERS) not only can enhance the Raman spectral signal, but also can reduce the effect of aqueous solution. It is concluded that the concentration of sample only affects the strength of Raman spectroscopy; the aqueous solution can affect the FWHM of Raman spectral peaks; and SERS can reduce the effect of aqueous solution.
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Abstract Surface plasmons are collective oscillations of free electrons localized at surfaces of structures made of metals. Since the surface plasmons induce fluctuations of electric charge at surfaces, they are accompanied by electromagnetic oscillations. Electromagnetic fields associated with surface plasmons are localized at surfaces of metallic structures and significantly enhanced compared with the excitation field. These two characteristics are ingredients for making good use of surface plasmons in plasmonics . Plasmonics is a rapidly growing and well-established research field, which covers various aspects of surface plasmons towards realization of a variety of surface-plasmon-based devices. In this paper, after summarizing the fundamental aspects of surface plasmons propagating on planar metallic surfaces and localized at metallic nanoparticles, recent progress in plasmonic waveguides, plasmonic light-emitting devices and plasmonic solar cells is reviewed.
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