Surface Plasmon Coupling Research Articles

Wavelength-Dependent Surface Plasmon Coupling Electrochemiluminescence Biosensor Based on Sulfur-Doped Carbon Nitride Quantum Dots for K-RAS Gene Detection.

Although graphite phase carbon nitride quantum dots (GCN QDs) showed some advantages in the electrochemiluminescence (ECL) analytical research, the low ECL efficiency limited the potential sensing application. Herein, we synthesized sulfur-doped graphite phase carbon nitride quantum dots (S-GCN QDs) to fabricate a sandwich sensor based on amplified surface plasmon coupling ECL (SPC-ECL) mode. Sulfur doping can change the surface states of QDs effectively and produced new element vacancy. As a result, the ECL efficiency of S-GCN QDs was 2.5× over GCN QDs. Furthermore, compared with the big gap between the ECL peak of GCN QDs (620 nm) and the absorption peak of Au NPs, the doped sulfur elements in S-GCN QDs generated new ECL emission peaks at 555 nm, which was closed to the absorption peak of Au NPs at 530 nm. Due to the wavelength-dependent surface plasmon coupling effect, the ECL peak of S-GCN QDs at 555 nm had greater amplitude of enhancement in the sensing system. The proposed biosensor can quantify the K-RAS gene from 50 fM to 1 nM with a limit of detection (LOD) of 16 fM. We were the first to provide insight into the role of wavelength-dependent surface plasmon coupling in enhancing the sensitivity of ECL biosensor.

Doubly Resonant Plasmonic Hot Spot–Exciton Coupling Enhances Second Harmonic Generation from Au/ZnO Hybrid Porous Nanosponges

We introduce zinc oxide (ZnO) functionalized porous gold nanoparticles that exhibit strong second harmonic (SH) emission due to an efficient coupling of localized surface plasmons to ZnO excitons. ...

Highly-Conductive, Transparent Ga-Doped ZnO Nanoneedles for Improving the Efficiencies of GaN Light-Emitting Diode and Si Solar Cell

The growths of transparent, highly-conductive Ga-doped ZnO (GaZnO) nanoneedles (NNs) on the tops of GaN-based light-emitting diodes (LEDs) and Si solar cells for enhancing light extraction and reducing surface reflection, respectively, and hence increasing their efficiencies are demonstrated. The GaZnO NNs are grown based on the vapor-liquid-solid process by using surface Ag nanoparticles (NPs) as growth catalyst. In the application to LED, the residual Ag NPs can induce the surface plasmon (SP) coupling effect for increasing the LED emission efficiency. By combining the SP coupling effect, the light extraction effects of the GaZnO NNs and simultaneously deposited GaZnO thin film, and the current spreading effect of the thin film, the LED output intensity can be increased by 100%. In the solar cell application, the SP resonance of the residual Ag NPs can also enhance sunlight harvest and hence the energy conversion efficiency. By combining the effects of the residual Ag NPs, the GaZnO thin film, and the GaZnO NNs, the energy conversion efficiency of a Si solar cell can increase from 9.65 to 12.30%, corresponding to a relative enhancement of 27.5%.

Surface plasmon coupling electrochemiluminescence assay based on the use of AuNP@C3N4QD@mSiO2 for the determination of theShiga toxin-producing Escherichia coli (STEC) gene.

This work describes a surface plasmon coupling electrochemiluminescence (SPC-ECL) method for the determination of the Shiga toxin-producing Escherichia coli (STEC) gene. Firstly, gold nanoparticles (Au NPs) were encapsulated into a solid silica core (AuNP@SiO2). Secondly, graphite phase carbon nitride quantum dots (g-C3N4 QDs) were embedded in the mesoporous silica shell (mSiO2) to form nanospheres of type AuNP@C3N4QD@mSiO2. It is found that the surface plasmon coupling effect of the Au NPs in the solid silica core strongly enhances the ECL of the g-C3N4/K2S2O8 system. The mSiO2 carry much of the ECL luminophore (g-C3N4 QDs), and the co-reactant can readily pass the mesopores to react with QDs to give an ECL reaction. Because of these two features, the ECL is 3.8 times stronger compared to ECL sensing using g-C3N4 QDs only. Finally, AuNP@C3N4QD@mSiO2 was linked to the probe DNA to construct a competitive DNA sensor. When no target DNA is added, most of the capture DNA on the electrode is complementary to the probe DNA of AuNP@C3N4QD@mSiO2-probe DNA. At this time, the ECL signal is the strongest. When the target DNA is added, some of the capture DNA is paired with it and the remaining capture DNA is paired with the probe DNA. Consequently, less luminophore reaches the electrode and the signal is weaker. The method works in the 0.1 pM to 1nM concentration range and has a 9 fM detection limit. It was successfully applied to the ultrasensitive determination of the STEC gene in human serum. Graphical abstract Schematic illustration for the "egg-yolk puff" structured ECL sensor based on Au NPs, g-C3N4 QDs, and mesoporous silica shell.

Enhanced luminescence properties of Eu3+-doped high silica glass by Ag nanoparticles

Eu3+ and Ag nanoparticles (Ag-NPs) doped high silica glass (HSG) was synthesized by absorbing and sintering porous glass. The effect of localized surface plasmon resonance (LSPR) of Ag-NPs on absorbance, luminescence properties and decay curves was investigated. The results indicate that Ag-NPs are effectively doped into HSG. The surface plasmon coupling can be formed between the Eu3+ ions and the Ag-NPs surface because the broad absorption band of Ag-NPs overlaps with the excitation peaks of Eu3+. The profiles of the excitation and emission spectra were not affected by Ag-NPs. By optimizing the Ag concentration, the emission intensity and quantum yield (QY) of HSG-Eu3+-0.1%Ag are significantly higher than those of HSG-Eu3+. Plasmon-enhanced luminescence can occur through enhancement of local electromagnetic field and radiative decay rate.

Effects of Surface Plasmon Coupling on the Whispering-Gallery Resonance in a Hexagonal Nanowire Cavity Structure

The effects of surface plasmon (SP) coupling with the excitation radiating dipole on the behaviors of the whispering-gallery resonance (WGR) modes in a hexagonal GaN nanowire cavity structure, either suspended or supported by a substrate, are numerically investigated by placing an Ag nanoparticle (NP) on one of six facets of the hexagonal structure. Through the Purcell effect, the intrinsic resonance behavior of a WGR mode can affect the radiation behavior of the source dipole and hence influence the SP-coupling behavior, which eventually determines the effects of SP coupling on the WGR behavior. The SP coupling can produce two competing effects, including the enhanced stored energy within the resonance cavity and the increased light extraction from the cavity into the air. Both of them are related to the Purcell factor and quality- (Q-) factor of cavity resonance. When the former (latter) dominates, the resonance intensity of a WGR mode can be enhanced (suppressed). It is observed that the WGR becomes stronger, i.e., the radiated power is enhanced, through SP coupling when the intrinsic resonance is not strong. The resonance intensities of those WGR modes with strong intrinsic resonances or high Q-factors can be reduced.

Plasmonic enhanced mid-infrared InAs/GaSb superlattice photodetectors with the hybrid mode for wavelength-selective detection

Photodetectors with superlattice active regions suffered from relatively low infrared absorption and thus limited responsivity, which has greatly restricted the development of mid-infrared detection technology. In this work, we theoretically demonstrate a plasmonic enhanced mid-infrared InAs/GaSb superlattice photodetector, which employs the hybrid mode not only achieving the same infrared absorption as that of the reference device at the identical resonant wavelength, but also enhancing the optical absorption at the selective wavelength. In our proposed strategy, an effective coupling of surface plasmons into electromagnetic energy in the active layer was clearly shown. Moreover, our simulation results exhibited that wavelength-selective detection is achieved by the introduction of unique metal nanostructures within the devices, which shows potential applications in infrared detection and imaging.

Propagation of toroidal localized spoof surface plasmons using conductive coupling.

Here, on a platform of two split-ring resonator (SRR) disks in the microwave regime, we have numerically and experimentally investigated the coupling of toroidal localized spoof surface plasmons (LSSPs). The coupling effect is investigated both theoretically and experimentally. We observe that magnetic dipole coupling exists in the toroidal LSSPs coupling and causes a rearrangement of the toroidal LSSPs, which suppresses the propagation of toroidal LSSPs. To realize the propagation of toroidal LSSPs, we introduce conductive coupling into the SRR disks. The conductive coupling can correct magnetic dipole coupling and enhance toroidal LSSPs coupling. Both numerical simulations and experiments are in good agreement. The toroidal LSSPs can be effectively propagated, even in the three right-angle-bent SRR disks. This study paves the way toward a better understanding of toroidal LSSPs coupling and finds many applications in the transfer of electromagnetic energy using toroidal moments.

Tuning the period of femtosecond laser induced surface structures in steel: From angled incidence to quill writing

Exposure of metal surfaces to multiple ultrashort laser pulses under certain conditions leads to the formation of well-defined periodic surface structures. We show how the period of such structures in steel can be tuned over a wide range by controlling the complex interaction mechanisms triggered in the material. Amongst the different irradiation parameters that influence the properties of the induced structures, the angle of incidence of the laser beam occupies a prominent role. We present an experimental and theoretical investigation of this angle dependence in steel upon irradiation with laser pulses of 120 fs duration and 800 nm wavelength, while moving the sample at constant speed. Our findings can be grouped into two blocks. First, we observe the spatial coexistence of two different ripple periods at the steel surface, both featuring inverse scaling upon angle increase, which are related to forward and backward propagation of surface plasmon polaritons. To understand the underlying physical phenomena, we extend a recently developed model that takes into account quantitative properties of the surface roughness to the case of absorbing metals (large imaginary part of the dielectric function), and obtain an excellent match with the experimentally observed angle dependence. As second important finding, we observe a quill writing effect, also termed non-reciprocal writing, in form of a significant change of the ripple period upon reversing the sample movement direction. This remarkable phenomenon has been observed so far only inside dielectric materials and our work underlines its importance also in laser surface processing. We attribute the origin of symmetry breaking to the non-symmetric micro- and nanoscale roughness induced upon static multiple pulse irradiation, leading to non-symmetric modification of the wavevector of the coupled surface plasmon polariton.

Carrier densities of Sn-doped In2O3 nanoparticles and their effect on X-ray photoelectron emission

Sn-doped In2O3 (ITO) nanoparticles with various Sn doping concentrations were successfully fabricated using a liquid phase coprecipitation method. Similar to sputtered ITO thin films, Sn doping reaches a maximum carrier density (1.52×1021cm−3) at 10 at. % in ITO nanoparticles, which was estimated from the bulk plasmon energy based on a scanning ellipsometry (SE) simulation. Interestingly, the X-ray photoelectron emission spectra (XPS) of In 3d core levels show a clear asymmetric peak with a shoulder on the high-binding-energy side for degenerated ITO nanoparticles, which may be associated with the influence of the surface plasmon or plasmonic coupling. Our results suggest that combining the SE simulation and XPS measurements effectively provides a new way to understand the difference between bulk plasmons and surface plasmons for transparent conductive oxide nanoparticles.

Hybrid methods of surface plasmon resonance coupled to mass spectrometry for biomolecular interaction analysis.

Combining mass spectrometry (MS) with surface plasmon resonance (SPR) makes it possible to identify the chemical structures of the interacting molecules studied by SPR. Different approaches for coupling surface plasmon resonance sensors to mass spectrometry were developed. This article aims to summarize the established approaches and their applications to study biomolecular interactions. Three representative interactions were reviewed: protein-protein interactions, enzyme-substrate/inhibitor interactions, and protein-small molecule interactions.

Optimization Design of a Multi-slot Nanoantenna Based on Genetic Algorithm for Energy Harvesting

A new genetic algorithm (GA)-based multi-slot nanoantenna is proposed for energy harvesting, which consists of two element nanoantennas with rectangular shape and with double bowtie double ring (DBDR) slot. The DBDR slot structure can enhance the electric field to increase the absorptivity of nanoantennas; however, the larger parameter space of multi-slot is more hardly controlled. Therefore, we use GA to optimize the parameters of the DBDR slot nanoantenna and the Finite-Difference Time-Domain method to calculate the absorptivity. It is found that absorptivity of the optimized nanoantenna is over 77% in 400–1800 nm waveband. We attribute the better absorbing property of the nanoantenna to the synergistic effect of the localized surface plasmon resonance enhancement and coupling between slots.

Simulation study on light color conversion enhancement through surface plasmon coupling.

A theoretical model together with a numerical algorithm of surface plasmon (SP) coupling are built for simulating SP-enhanced light color conversion from a shorter-wavelength radiating dipole (representing a quantum well - QW) into a longer-wavelength one (representing a quantum dot - QD) through QD absorption at the shorter wavelength. An Ag nanoparticle (NP) located between the two dipoles is designed for producing strong SP couplings simultaneously at the two wavelengths. At the QW emission wavelength, SP couplings with the QW and QD dipoles lead to the energy transfer from the QW into the QD and hence the absorption enhancement of the QD. At the QD emission wavelength, SP coupling with the excited QD dipole results in the enhancement of QD emission efficiency. The combination of the SP-induced effects at the two wavelengths leads to the increase of overall color conversion efficiency. The color conversion efficiencies in using Ag NPs of different geometries or SP resonance behaviors for producing different QD absorption and emission enhancement levels are compared.

The coupling effects of surface plasmons and Fermi arc plasmons in Weyl semimetals

We study the effects of coupling between surface plasmon and Fermi arc plasmon modes on a planar surface of the Weyl semimetal. A model Hamiltonian is proposed in the second quantization representation for the system of coupled surface plasmon and Fermi arc plasmon modes. We obtain the dispersion relations of coupled modes using the Bogoliubov transformation technique. We identify the upper coupled mode as the renormalized surface plasmon and the lower coupled mode as the renormalized Fermi arc plasmon. It is shown how the magnitude of the coupling depends on both the bare mode dispersions and their dampings. We also demonstrate that coupling increases the surface plasmon mode lifetime. Obtained results for the surface plasmon mode are qualitatively consistent with the recent experimental data of Weyl semimetals.

Polarization controlled couplings of surface plasmon with asymmetrical nanoslit pairs

Light-driven surface plasmons offer an opportunity to ultrafast information processing combining the compactness of electric circuits with the bandwidth of photonic networks. For practical applications, the efficient and controllable conversion from signal light to surface plasmons is essential. This leads to the recent developments in the polarization controlled couplings of surface plasmons. Currently, most works only tailor the orientation and arrangement of nanoslits to control the launching of surface plasmons. In this paper, we consider both the orientation and size of each slit in a one-dimensional array of nanoslit dimers. We first realize the unidirectional propagation of surface plasmons with designed wavefronts. Next, the unidirectional coupling and bi-directional coupling of surface plasmons are realized for a pair of orthogonal polarizations, respectively. This is quite different from the conventional opposite propagating surface plasmons excited by two orthogonal polarizations. The manipulation of both orientation and size of nanoslits allows additional freedom in the photon-plasmon conversions.

Emission Enhancement from CdSe/ZnS Quantum Dots Induced by Strong Localized Surface Plasmonic Resonances without Damping.

A high-performance exciton-localized surface plasmon (LSP) coupling system consisting of well-designed plasmonic nanostructures and CdSe/ZnS quantum dots (QDs)was fabricated by first introducing a Ta2O5 layer as both an adhesive coating and coupling medium. It is shown that a larger emission enhancement factor of 6 from CdSe/ZnSQDs can be obtained from the strong coupling effect between QDs and triprism Au nanoarrays and the high scattering efficiency of LSPs without damping. This can be attributed to the matching conditions and a low extinction coefficient with little damping absorption of the Ta2O5 layer in the system. The radiative scattering rate of ΓLSPs can make a contribution to the spontaneous emission rate Γ and thus improve the internal quantum yield of the QDs. This strategy could be promising for practical application of metal-modified fluorescence enhancement.

Theoretical investigation of size, shape, and aspect ratio effect on the LSPR sensitivity of hollow-gold nanoshells.

The change in refractive index around plasmonic nanoparticles upon binding to biomolecules is routinely used in localized surface plasmon resonance (LSPR)-based biosensors and in biosensing platforms. In this study, the plasmon sensitivity of hollow gold (Au) nanoshells is studied using theoretical modeling where the influence of shape, size, shell thickness, and aspect ratio is addressed. Different shapes of hollow Au nanoshells are studied that include sphere, disk, triangular prism, rod, ellipsoid, and rectangular block. Multilayered Mie theory and discrete dipole approximation were used to determine the LSPR peak position and LSPR sensitivity as a function of size, shell thickness, shape, and aspect ratio. The change in LSPR peak wavelength per unit refractive index is defined as the sensitivity, and interesting results were obtained from the analysis. The rectangular block and rod-shaped Au nanoshells have shown maximum LSPR sensitivity when compared to other shaped Au nanoshells. In addition, increased sensitivity was observed for higher aspect ratio as well as for smaller shell thicknesses. The results are rationalized based on the inner and outer surface plasmonic coupling.

Enhancement of Light Extraction Efficiency for InGaN/GaN Light-Emitting Diodes Using Silver Nanoparticle Embedded ZnO Thin Films.

In this study, we propose a liquid-phase-deposited silver nanoparticle embedded ZnO (LPD-Ag NP/ZnO) thin film at room temperature to improve the light extraction efficiency (LEE) for InGaN/GaN light-emitting diodes (LEDs). The treatment solution for the deposition of the LPD-Ag/NP ZnO thin film comprised a ZnO-powder-saturated HCl and a silver nitrate (AgNO3) aqueous solution. The enhanced LEE of an InGaN/GaN LED with the LPD-Ag NP/ZnO window layer can be attributed to the surface texture and localized surface plasmon (LSP) coupling effect. The surface texture of the LPD-Ag/NP ZnO window layer relies on the AgNO3 concentration, which decides the root-mean-square (RMS) roughness of the thin film. The LSP resonance or extinction wavelength also depends on the concentration of AgNO3, which determines the Ag NP size and content of Ag atoms in the LPD-Ag NP/ZnO thin film. The AgNO3 concentration for the optimal LEE of an InGaN/GaN LED with an LPD-Ag NP/ZnO window layer occurs at 0.05 M, which demonstrates an increased light output intensity that is approximately 1.52 times that of a conventional InGaN/GaN LED under a 20-mA driving current.

Single-Particle Spectroscopy of Supported Silver Clusters on Silicon: Substrate Effects on Localized Surface Plasmons

The presence of a surrounding medium strongly affects the spectral properties of localized surface plasmons at metallic nanoparticles. Vice versa, plasmonic resonances have large impact on the electric polarization in a surrounding or supporting material. For applications, e.g., in light-converting devices, the coupling of localized surface plasmons with polarizations in semiconducting substrates is of particular importance. Using photoemission electron microscopy with tunable laser excitation, we perform single-particle spectroscopy of silver nanoclusters directly grown on Si(100). Two distinct localized surface plasmon modes are observed as resonances in the two-photon photoemission signals from individual silver clusters. The strengths of these resonances strongly depend on the polarization of the exciting electric field, which allows us to assign them to plasmon modes with polarizations parallel and perpendicular, respectively, to the supporting silicon substrate. Our mode assignment is supported by simulations which provide insight into the mutual interaction of charge oscillations at the particle surface with electric polarizations at the silver/silicon interface.

Highly sensitive biosensor with graphene-MoS2 heterostructure based on photonic spin Hall effect

Abstract We propose a new optical biosensor based on photonic spin Hall effect (PSHE) for detection of DNA hybridization. This device consists of BK7 prism, Ag, SiO2, Au and graphene-MoS2 heterostructure which produces waveguide coupled surface plasmon resonance (WCSPR) effect to enormously enhance PSHE. The adsorption of graphene-MoS2 heterostructure to biomolecules changes the refractive index of the sensing medium, thereby affecting spin-dependent splitting in PSHE. The 2 × 2 transfer matrix method is applied to calculate the generalized Fresnel reflection and we deduce the reflected light shifts in PSHE. We study the correlation between spin-dependent displacements and the refractive index variations of sensed solution to obtain the highest sensitivity in the proposed sensor. However, the PSHE exists in the proposed biosensor is extremely weak, so a signal enhancement technology called weak measurement is adopted to amplify the PSHE shift. Thus, the proposed biosensor can successfully detect the hybridization of probe DNA with target DNA. These results may provide practical applications for PSHE in biological monitoring, medical diagnosis, and food safety.