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Characteristics of a Vertical Metal-Insulator-Metal Microring Cavity
摘要： We propose a vertical metal-insulator-metal (MIM) plasmonic cavity that comprises top Ag and bottom InGaAsP microring structures on an Ag substrate. A full vectorial numerical simulation was used to characterize the fundamental optical properties of the transverse-magnetic-like plasmonic whispering-gallery-modes (WGMs) excited in a variety of MIM plasmonic cavities. In addition, we exploit the controllability of far-field radiations using the single MIM microring cavity and successfully demonstrate strong directional and localized vertical radiations from the plasmonic WGMs by introducing a number of nanoscale disks along the circumference of the cavity. Our plasmonic cavity can be applied as a component of nanoscale photonic integrated circuits as well as spatially localized out-of-plane optical sensors.
关键词： Microring,Finite-difference time-domain simulations,Surface plasmon polaritons,Plasmonic cavities
更新于2025-09-10 09:29:36
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European Microscopy Congress 2016: Proceedings || Toroidal dipole plasmon resonance modes in upright split ring resonators
摘要： Nanoscale split ring resonators (SRRs) have been a popular topic of study due to their surface plasmon resonance (SPR) modes and their many interesting interactions with light. They can be used as components in metamaterials exhibiting, among other properties, a negative refractive index. The surface plasmon properties of these structures are strongly dependent on their size and spatial arrangement. Most studies so far have focussed on the horizontal SRR due to the ease of fabrication. However, there are some advantages to be gained in the design of materials using upright SRRs. We are studying a structure composed of four upright SRRs as shown in Figure 1. The coupling of these four upright SRRs produces a magnetic dipole moment and a toroidal dipole moment. The toroidal dipole moment, when compared to electric and magnetic dipole moments, shows a higher quality factor and lower gain threshold for a nanoscale laser analogue, the spaser (surface plasmon amplification by stimulated emission of radiation) [1]. The presence of a strong toroidal dipole moment isolated from magnetic and electric dipole moments makes the structure under study a promising candidate for a spaser for use in on-chip telecommunications. A similar structure was first realized experimentally in the microwave regime of the electromagnetic spectrum [2]. Scaling the geometry down to nanoscale dimensions has been shown by simulation to shift the toroidal dipole energies into the near infra-red regime [1]. In this work we demonstrate the experimental fabrication (Figure 2) and characterization of this structure using electron energy loss spectroscopy (EELS), with confirmation of the modes provided by finite element method (FEM) simulations. We have fabricated this structure using a double patterning process in electron beam lithography, with precise alignment of the second lithography layer to the first. The structures are made from gold deposited on a 50 nm thick silicon nitride membrane. We probe the plasmon modes using EELS on a monochromated scanning transmission electron microscope, collecting spectrum images with nanometer spatial resolution and 60 meV energy resolution. We extract site-specific spectra (Figure 3a) and energy-resolved maps of the SPR modes (Figure 3b, c). We apply the Richardson-Lucy algorithm to further increase the effective energy resolution and identify the magnetic and toroidal dipole modes at energies of 0.52 eV and 0.72 eV, with SPR maps as shown in Figure 3b and 3c, respectively. We are able to correlate our EELS results with COMSOL Multiphysics FEM simulations. The simulated SPR response is given in Figure 3a, d, and e, showing close agreement in the peaks with our experimental data. Simulations confirm the low energy magnetic dipole mode (0.56 eV) and reveal two closely spaced toroidal dipole modes (0.61 eV, 0.66 eV) which are not perfectly resolved in the EELS data. We are able to tune the energy and strength of the toroidal dipole moment through tuning of the fabrication parameters; with careful design this structure is a promising spaser design for a range of applications near telecommunications frequencies.
关键词： toroidal dipole,split ring resonator,EELS,Surface plasmon resonance
更新于2025-09-10 09:29:36
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Interband and intraband transition, dynamical polarization and screening of the monolayer and bilayer silicene in low-energy tight-binding model
摘要： We investigate the interband and intraband transitions of the monolayer and AB-stacked bilayer silicene in low-energy tight-binding model under the electric ?eld, where we focus on the dynamical polarization function, screening due to the charged impurity, and the plasmon dispersion. We obtain the logarithmically divergent polarization function within the random-phase-approximation, whose logarithmic singularities correspond to the discontinuities of the ?rst derivative at momentum q ? 2kF in static case and indicates the topological phase transition point between the gapless semimetal and the gapped band insulator. We also obtain the power-law-dependent Friedel oscillation which can be enhanced by increasing the Rashba coupling. The Friedel oscillation contributes to the screened potential of the charged impurity which scale as (cid:2) r(cid:3)1=2 in short distance from the impurity and scale as (cid:2) r(cid:3)1=3 in long distance from the impurity. In single-particle excitation regime with electron–hole continuum, the interband and intraband transitions happen, and the plasmon dispersion starts to damped into the electron–hole pairs due to the nonzero imaginary part of the polarization function. We also observe the linear (weakly damped) plasmon model for the classical bilayer silicene which is similar to the high-energy p-plasmon or the case of conducting substrate which with strong metallic screening. The density dependence of the plasmon dispersion is also clari?ed in this paper. Our results can also be applied to the other low-energy Dirac models or the topological insulators.
关键词： Friedel oscillation,Collective plasmon model,Silicene,Dynamical polarization,Screened potential
更新于2025-09-10 09:29:36
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[Springer Series in Optical Sciences] Fano Resonances in Optics and Microwaves Volume 219 (Physics and Applications) || Multiple-Resonance Interference in Metallic Nanohole Arrays
摘要： In metallic nanohole arrays, the surface plasmon polaritons on the metal surfaces and the waveguide modes in the nanoholes are combined to form multipole surface plasmons. If these surface bound modes appear in a narrow frequency range, interference between multiple resonances and yields various resonant peak-dip structures in transmission, reflection and absorption spectra. In this chapter, we discuss the theoretical details of the mechanism of the multiple-resonance interference in metallic nanohole array systems using spatial and temporal coupled mode methods.
关键词： Fano resonance,surface plasmon polaritons,metallic nanohole arrays,waveguide modes,multiple-resonance interference,EIT-like phenomena
更新于2025-09-10 09:29:36
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A novel protein binding strategy for energy-transfer-based photoelectrochemical detection of enzymatic activity of botulinum neurotoxin A
摘要： In this work, we propose a novel energy-transfer-based photoelectrochemical (PEC) platform for probing of protein-protein interaction, which associates intimately with zinc-dependent cleavage and substrate specificities in the enzymatic activities of botulinum neurotoxin (BoNT). Specifically, by using substrate protein SNAP-25 as the energy-transfer nanoprobe, an exciton-plasmon interaction (EPI) based strategy between CdS quantum dots (QDs) and Au nanoparticles (NPs) in a PEC system is constructed with the photocurrent declining. Interestingly, the EPI effect is then interrupted by the target botulinum neurotoxin serotype A light chain (BoNT-LCA) special cleavage of the probe SNAP-25, leading to the photocurrent recovery. Therefore, the enzymatic activity of BoNT-LCA could be sensitively detected with a detection limit of 1 pg/mL. Unlike conventional DNA-programable assembly, a protein probe is used to bridge the excitons and plasmons in this work, which provides a new route for the investigation of the EPI-based bioassay.
关键词： CdS QDs,Exciton–plasmon interaction,Energy transfer,Botulinum neurotoxin A,Photoelectrochemical detection
更新于2025-09-10 09:29:36
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Comparison and convergence of optical absorption spectra of noble metal nanoparticles computed using linear-response and real-time time-dependent density functional theories
摘要： The real-time time-dependent density functional theory (RT-TDDFT) is rapidly gaining prominence as an alternative approach to capture optical properties of molecular systems, which warrants the necessity to benchmark the traditional linear response (LR) method and the RT approach. We calculate the absorption spectra of noble metal nanoparticles with a variety of sizes and shapes to demonstrate the consistency of the two methods over a broad range of energy. The RT spectrum obtained using a grid-based basis set with pseudopotentials achieves results in good agreement with the LR spectrum obtained with large QZ4P atom-centered basis sets. Factors that lead to convergence of the spectra are considered. In addition, the real-time variation of the electron density is visualized to show the collective oscillation of electron density for the plasmon modes of noble metal nanoparticles. The RT approach is most useful when calculating wide absorption spectra of larger gold or silver nanoparticles.
关键词： optical absorption spectra,noble metal nanoparticles,RT-TDDFT,LR-TDDFT,plasmon modes
更新于2025-09-10 09:29:36
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Sensitive Bacterial Detection via Dielectrophoretic Enhanced Mass Transport Using Surface Plasmon Resonance Biosensors
摘要： The performance of surface plasmon resonance (SPR)-based bacterial biosensors is often compromised due to diffusion-limited mass transport of bacteria to the sensing surface. In this work, dually functional interdigitated electrodes (IDEs) were developed to sustain SPR, and increase bacterial mass transport through external application of dielectrophoresis (DEP). IDEs were defined into 50 nm thick Au films with fixed electrode gaps (EG = 5 μm) and varied electrode widths (EW = 10, 20, and 100 μm), and referred to as interdigitated SPR (iSPR) chips. The iSPR chips with EW = 100 μm can effectively support SPR, with comparable sensitivity to the conventional SPR chips. The surfaces of iSPR chips (EW = 100 μm) were modified with mannose to target the FimH adhesin of E. coli and increase cellular adhesion. An LOD of ~3.0 x 102 CFU/mL E. coli was achieved on mannosylated iSPR chips under pDEP condition, which is about five orders of magnitude improvement compared to the mannosylated conventional SPR chips without DEP. Furthermore, secondary antibody amplification enabled selective enhancement of dilute (103 CFU/mL), E. coli suspensions, while no amplification was observed for concentrated (108 CFU/mL), non-target (S. epidermidis) bacterial suspensions. The results presented here indicate a great potential of the incorporation of DEP into SPR biosensors for rapid, sensitive, and specific detection of bacteria with broad applications in the areas of biomedical diagnostics, environmental monitoring, food safety, and homeland security.
关键词： bacterial detection,dielectrophoresis,surface plasmon resonance,mass transport,biosensors
更新于2025-09-10 09:29:36
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Precise Control of Localized Surface Plasmon Wavelengths Is Needed for Effective Enhancement of Triplet-Triplet Annihilation-Based Upconversion Emission
摘要： In this study, we demonstrate that the localized surface plasmon (LSP) resonance of metal nanoparticles, depending strictly on the generating wavelength of LSP resonance, can have both beneficial enhancement and harmful quenching effects on a triplet-triplet annihilation-based upconversion (TTA-UC) emission. When the LSP resonance band of anisotropic silver nanoprisms spectrally overlapped with the photoexcitation wavelength of a sensitizer and the fluorescence of an emitter, an increase in the photoexcitation efficiency and an acceleration of the radiative decay rate were respectively induced, resulting in an effective enhancement in the TTA-UC emission. Furthermore, the overlapping with the photoexcitation wavelength led to a significant decrease (93%) in the threshold light excitation intensity, which greatly enhances the figure-of-merit in TTA-UC systems. However, when the LSP resonance band overlapped with the phosphorescence band of the sensitizer, the TTA-UC emission was extremely quenched, accompanied by the enhanced phosphorescence and the decreased phosphorescence lifetime. These results suggest that the decrease in the TTA-UC emission is a result of the competition between the triplet-triplet energy transfer to the emitter and the LSP-induced nonradiative energy transfer to the silver nanoprisms from the triplet-excited sensitizer. This discovery of the conflicting effects of LSP resonance provides an important guideline: a precise adjustment of LSP resonance wavelengths is needed for the efficient enhancement of TTA-UC emission. This requirement is different from those of other fluorescence systems such as single downconverted fluorophores and lanthanide-based upconversion nanoparticles.
关键词： solid state,fluorescence,phosphorescence,silver nanoprisms,localized surface plasmon resonance,triplet-triplet annihilation,photon upconversion
更新于2025-09-10 09:29:36
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Plasmon-Polariton Properties in Metallic Nanosphere Chains
摘要： The propagation of collective wave type plasmonic excitations along in?nite chains of metallic nanospheres has been analyzed, including near-, medium- and far-?eld contributions to the plasmon dipole interaction with all retardation effects taken into account. It is proven that there exist weakly-damped self-modes of plasmon-polaritons in the chain for which the propagation range is limited by relatively small Ohmic losses only. In this regime, the Lorentz friction irradiation losses on each nanosphere in the chain are ideally compensated by the energy income from the rest of the chain. The completely undamped collective waves were identi?ed in the case of the presence of persistent external excitation of some fragment of the chain. The obtained characteristics of these excitations ?t the experimental observations well.
关键词： radiative undamped propagation,Lorentz friction,plasmon-polariton,metallic nano-chain,plasmons
更新于2025-09-10 09:29:36
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Highly sensitive detection of photo-thermal transient stress by a sub-nanosecond pump probe with surface plasmon resonance
摘要： Photoacoustic microscopy (PAM) has attracted increasing attention for non-invasive functional imaging in biomedicine and biomedical studies. The surface plasmon resonance (SPR) sensor is a potential acoustical detector with high sensitivity and wide bandwidth for use in high-resolution 3D PAM. In this study, we investigated a simple Kretschmann SPR sensor, demonstrating highly sensitive stress detection in the sub-nanosecond timescale by directly inducing photo-thermal transient stress. To do this, we designed and used a sub-nanosecond pump probe system. The SPR sensor clearly detected the transient response from the thermal elastic effect, while a simple pump-probe sensor without SPR did not detect it. Our experimental results demonstrate a simple SPR sensor that can detect stress with high sensitivity and sub-nanosecond time resolution. This technique could be used in high-resolution 3D PAM by mounting a small biomedical sample on the sensor.
关键词： photoacoustic microscopy,sub-nanosecond pump probe,surface plasmon resonance,photo-thermal transient stress,high-resolution 3D imaging
更新于2025-09-10 09:29:36