Surface Plasmon Coupling Research Articles

Tailorable Polarization‐Dependent Directional Coupling of Surface Plasmons

AbstractCoupling free‐space light into surface plasmons (SPs) has traditionally faced challenges in arbitrarily controlling the directionality of the SPs with respect to the incident polarization. Recently reported polarization‐dependent directional coupling of SPs using metasurfaces has attracted enormous attention for its promise in developing innovative and on‐demand plasmonic devices. However, further progress has been hampered by the limitation in designating the directional coupling with tailorable polarization‐dependent feature and compatible ability to incidence of complex polarization distribution. Here, a directional coupling strategy is introduced to overcome these limits. It is demonstrated that, by utilizing the interference between two pairs of slit resonators with different resonance responses, the directional SP coupling can be expanded to arbitrary group of polarized incidence by simply varying their relative distance, and the SP coupling direction will reverse under the corresponding orthogonally polarized incidence without affecting the efficiency. To exhibit the versatile design capability of the strategy, it is further utilized to construct several polarization‐dependent plasmonic devices for controlling SP propagations, including two SP metalenses and a plasmonic Airy beam launcher, in which it is shown that the device can even be designed to work for non‐uniformly polarized incidence. The strategy paves a reliable route towards many practical on‐chip applications.

Sensing absorptive fluids with backside illuminated grating coupled SPR sensor fabricated by nanoimprint technology

Grating coupled surface plasmon resonance (GC-SPR) sensors are widely used in analyzing gases, aqueous solutions, proteins and environmental pollutants. However, traditional GC-SPR sensors are difficult to detect absorptive fluids because the spectra of the light will be distorted after passing through the absorptive fluids. Here, we propose and experimentally demonstrate a backside illuminated GC-SPR (BIGC-SPR) sensor, where the light is incident from the transparent substrate side of the sensor chip. The grating chip is fabricated by a simple and cost-effective procedure. DVD-R disc is used as a template to imprint the grating structure onto a polydimethylsiloxane (PDMS) substrate, then a thin Au layer of 35 nm thickness is evaporated on it. By calibrating the sensor with glucose solutions, the sensitivity and refractive index resolution are measured to be 311.97 nm/RIU and 0.00043 RIU, respectively. Moreover, the BIGC-SPR sensor is demonstrated to monitor the concentration of blue engine coolant, green antirust cutting fluid and white antirust emulsified oil solutions. The designed sensor is able to detect colored or highly scattering solutions, and can be potentially used in the fields of medical diagnosis, environmental monitoring and biological protein detection.

Effect of surface plasmon coupling with radiating dipole on the polarization characteristics of AlGaN-based light-emitting diodes

The optical polarization characteristics of surface plasmon (SP) coupled AlGaN-based light emitting diodes (LEDs) are investigated theoretically by analyzing the radiation recombination process and scattering process respectively. For the Al0.5Ga0.5N/Al/Al2O3 slab structure, the relative intensity of TE-polarized and TM-polarized spontaneous emission (SE) rate into the SP mode obviously depends on the thickness of the Al layer. The calculation results show that TM dominated emission will be transformed into TE dominated emission with the decrease of the Al thickness, while the emission intensities of both TE/TM polarizations will decrease significantly. In addition, compared with TM polarized emission, TE polarized emission is easier to be extracted by SP coupling. For the Al0.5Ga0.5N/Al nano-particle structure, the ratio of transmittance for TE/TM polarized emission can reach ∼ 3.06, while for the Al free structure, it is only 1.2. Thus, the degree of polarization of SP coupled LED can be improved by the reasonable structural design.

Investigation on Light Extraction Behavior of Surface Plasmon-Coupled Deep-Ultraviolet LED in Different Emission Directions

The light extraction behavior of an AlGaN-based deep-ultraviolet LED covered with Al nanoparticles (NPs) is investigated by three-dimensional finite-difference time-domain simulation. For the transmission spectra of s- and p-polarizations in different emission directions, the position of maximum transmittance can be changed from (θ = 0°, λ = 273 nm) to (θ = 0°, λ = 286 nm) by increasing the diameter of Al NPs from 40 nm to 80 nm. In the direction that is greater than the critical angle, the transmittance of s-polarization is very small due to the strong absorption of Al NPs, while the transmittance spectrum of p-polarization can be observed obviously for the 80 nm Al NPs structure. For a ~284 nm AlGaN-based LED with surface plasmon (SP) coupling, although the luminous efficiency is significantly improved due to the improvement of the radiation recombination rate as compared with the conventional LED, the light extraction efficiency (LEE) is lower than 2.61% of the conventional LED without considering the lateral surface extraction and bottom reflection. The LEE is not greater than ~0.98% (~2.12%) for an SP coupling LED with 40 nm (80 nm) Al NPs. The lower LEE can be attributed to the strong absorption of Al NPs.

Resolving plasmonic hotspots by label-free super-resolution microscopy.

The plasmonic hotspot of metal nanostructures has small dimension far beyond the optical diffraction limit. When trying to locate the hotspot using fluorescent probes, the localization is significantly distorted due to the coupling of emission and surface plasmon. A label-free technique can solve the problem, which uses hotspot emission as the native probe. We demonstrate a super-resolution microscopy investigation based on this idea. By modulating hotspot emission of crossed silver nanowires, which have a pair of plasmonic hotspots approximately 100 nm apart at the intersection, we precisely locate and separate them with nanometer precision. This label-free technique could be applied for analyzing hotspot distribution with high efficiency and precision.

Label-free imaging and biomarker analysis of exosomes with plasmonic scattering microscopy.

Exosome analysis is a promising tool for clinical and biological research applications. However, detection and biomarker quantification of exosomes is technically challenging because they are small and highly heterogeneous. Here, we report an optical approach for imaging exosomes and quantifying their protein markers without labels using plasmonic scattering microscopy (PSM). PSM can provide improved spatial resolution and distortion-free image compared to conventional surface plasmon resonance (SPR) microscopy, with the signal-to-noise ratio similar to objective coupled surface plasmon resonance (SPR) microscopy, and millimeter-scale field of view as a prism-coupled SPR system, thus allowing exosome size distribution analysis with high throughput. In addition, PSM retains the high specificity and surface sensitivity of the SPR sensors and thus allows selection of exosomes from extracellular vesicles with antibody-modified sensor surfaces and in situ analyzing binding kinetics between antibody and the surface protein biomarkers on the captured exosomes. Finally, the PSM can be easily constructed on a popular prism-coupled SPR system with commercially available components. Thus, it may provide an economical and powerful tool for clinical exosome analysis and exploration of fundamental issues such as exosome biomarker binding properties.

Gold Nanorod Vertical Array-Based Electrochemiluminescence Polarization Assay for Triple-Negative Breast Cancer Detection.

In this work, a polarization-resolved electrochemiluminescence (ECL) sensor for microRNA-155 (miRNA-155) detection has been constructed based on the surface plasmon coupling effect. In the sensing system, nitrogen dots (N dots) were employed as ECL emitters. As a surface-enhanced structure, a gold nanorod vertical array was constructed on the electrode surface by the volatilization-induced self-assembly. The coupling of the adjacent gold nanorods in the array can generate significant local electromagnetic fields. Due to the anisotropy of gold nanorods and the hot spot effect of the vertical array, the ECL signal of N dots was greatly improved at a specific polarization angle. In addition, the catalytic hairpin self-assembly strategy was used to amplify the nucleic acid analyte signal. As a result, the polarization-resolved ECL sensor can detect miRNA-155 sensitively, which is related to triple-negative breast cancer.

Tunable and enhanced Goos–Hänchen shifts in a monolayer graphene-based metallic grating structure

The Goos–Hänchen (GH) effect, a lateral displacement of the reflection beam, enables rich applications in sensors and detectors. Metallic grating structures have gained great attention due to their unique properties, such as enhanced optical transmission and surface enhanced Raman scattering. Here, instead of using the dielectric grating, we demonstrate an enhanced GH shift in the structure with the metallic grating layer, monolayer graphene, dielectric spacer, and metallic substrate. We find that the amplitude of the GH shift is as high as 3616 times of the incident wavelength at the specific working frequency. This enhancement can be understood from the generation of the coupled surface plasmon polaritons between two surfaces of the dielectric space layer. Furthermore, we show efficient control of the GH shift by modulating the geometric parameters of the proposed structure and chemical potential of the monolayer graphene. Our result establishes an alternative metallic grating structure for tunable and enhanced GH shifts in graphene-based nanostructures.

Novel Clarification of Surface Plasmon Coupling Reactions of Aromatic Alkynamine and Nitro Compounds

This work presents a theoretical and experimental approach for the coupling of 4-ethynylaniline (4-APA) and 4-ethynylnitrobenzene (4-NPA) in the theoretical application of density functional theory (DFT) and experimental monitoring of surface-enhanced Raman spectroscopy (SERS). The results support electromagnetic enhancement to drive the conversion of aromatic alkynamine and nitro compounds and regulation by the catalytic coupling reaction conditions. In addition, this work investigates the adsorption site effect of surface plasmon coupling reactions of 4-APA and 4-NPA molecules into alkynyl azo compounds. This study presents theoretical and experimental images used to analyze the plasmon-driven surface catalytic reaction system.

Surface Plasmon Coupling Electrochemiluminescence Immunosensor Based on Polymer Dots and AuNPs for Ultrasensitive Detection of Pancreatic Cancer Exosomes.

Polymer dots (Pdots) have become attractive electrochemiluminescence (ECL) luminophores due to their facile synthesis, easy modification, and stable electrochemical and optical properties. However, their ECL efficiency is not high enough for practical applications. In this work, we proposed an ECL immunosensor based on localized surface plasmon resonance (LSPR) between AuNPs and Pdots for the determination of pancreatic cancer exosomes. Based on the finite-difference time-domain simulations and the band energy of Pdots and AuNPs, we proposed the possible LSPR mechanism. The hot electrons of plasmonic AuNPs were photoexcited to surface plasmon states by ECL emission of Pdots, and then the excited hot electrons were transferred to the conduction band of Pdots, which significantly improved the ECL efficiency of Pdots. The ECL immunosensor displayed a wide calibration range of 1.0 × 103 to 1.0 × 106 particles/mL with a detection limit of 400 particles/mL. Cancer-related protein profiling revealed high selectivity toward different expressions of exosomal surface proteins from PANC-01, HeLa, MCF-7, and HPDE6-C7 cell lines. The proposed ECL system exhibits a promising prospect for protein biomarker profiling and early cancer-related diagnosis.

Simulation study on the enhancement of resonance energy transfer through surface plasmon coupling in a GaN porous structure

To understand the behavior of resonance energy transfer from a quantum well (donor) into a quantum dot (acceptor) located inside an oriented subsurface tubular void above the quantum well, the emission and energy transfer enhancements of the donor and acceptor dipoles are numerically studied. By reasonably assuming that the acceptor absorption efficiency is not influenced by the surface plasmon (SP) resonance of a nearby metal nanostructure, the acceptor absorption enhancement through SP coupling is proportional to the increase ratio of the donor-induced field intensity at the acceptor position. Therefore, the energy transfer enhancement can be obtained by multiplying this field intensity ratio with the radiated power ratio of the acceptor between the two cases under comparison. It is found that the emission and energy transfer enhancements are significantly higher when the orientations of the donor and acceptor dipoles are perpendicular to the void tube, in comparison with those in the case of parallel orientation. The differences in emission and energy transfer between the two dipole-orientation cases become larger when a surface Ag nanoparticle is applied to the sample for inducing SP coupling. The oriented subsurface tubular void can lead to a polarization-dependent energy transfer behavior.

Boosting Output Performance of Triboelectric Nanogenerator via Mutual Coupling Effects Enabled Photon-Carriers and Plasmon.

Boosting the output performance of triboelectric nanogenerators via some unique methods is always a meaningful way to speed up their commercialization. However, the available approach to boost performance is mainly restricted to one physics effect based and the basic research of boosting performance via mutual coupling effects is little research. Herein, a new strategy is creatively proposed based on charge traps from mutual coupling effects, generated from g‐C3N4/MXene‐Au composites, to further promote the output performance of triboelectric nanogenerator. It is found that photon‐generated carriers coupling surface plasmon effect enables composites filled into tribo‐material with visible light is an excellent value in boosting performance. The charge traps from mutual coupling effects for boosting performance are analyzed theoretically and verified by experiments. The output power of boosting‐triboelectric nanogenerator (TENG) achieves a sixfold enhancement (20 mW) of normal TENG with polydimethylsiloxane (PDMS) in ambient conditions. This work provides a profound understanding of the working mechanism of mutual coupling effects boosting the performance of TENG and an effective way for promoting TENG output.

Study on Localized Surface Plasmon Coupling with Many Radiators.

Localized surface plasmon (LSP) coupling with many radiators are investigated. The LSP is generated by excitation of laser or electron beam on the random Ag nano particles (NPs) and arrayed ones embedded in the p-GaN of green LEDs. They couple with the excitons or radiative recombination in the quantum well (QW) and electron beam, which enhance or suppress the luminescence of the radiators. The photoluminescence (PL) intensity of periodic Ag NPs can get as much as 4.5 times higher than that of bare LED. In addition to the periodic structure, the morphology of Ag NPs also affects the localized SP (LSP) resonance intensity and light scattering efficiency. In the finite difference time domain (FDTD) simulation, five x-polarized dipoles are approximated to five quantum wells. Considering the interaction between the five dipoles and their feedback effect on LSP, the enhancement effect of SP dipole coupling with Ag NPs is amplified and the energy dissipation is reduced. The enhancement of cathodoluminescence (CL) was also found in green LEDs with Ag NPs. The three-body model composed of two orthogonal dipoles and an Ag NP is used for 3D FDTD simulation. The LSP-QWs coupling effect is separated from the electron beam (e-beam)-LSP-QW system by linear approximation. Under the excitation of electron beam, the introduction of z-dipole greatly reduces the energy dissipation. In the cross-sectional sample, z-polarized dipoles in QWs show more coupling strength to the dipole and quadrupole modes of LSP. The perturbation theory is used to separate the LSP coupling effects to x-dipole and z-dipole. At last, the resonator and the antenna effects are discussed for LSP coupling at different positions to the Ag NP.

Structure-selected graphene/metallic surface plasmon coupling regime and infrared modulation application

Here we present a graphene-based long-wavelength infrared modulator characteristic of extra-high contrast, where the frequency detuning degree of magnetic and electric surface plasmons (SPs) is controllable by the gated graphene Fermi energy. If the device is designed to work in a strong SP-coupling regime by selecting an appropriate low-lossy gate dielectric thickness, a modulation depth (MD) up to ∼100% but insertion loss (IL) as low as ∼−0.37 dB is achievable. Moreover, a compromised MD > 90% with IL < −1.0 dB is still retainable in two broadband ranges. The disclosed underlying mechanism to the device working state in the strong, electromagnetic-induced transparency (EIT), or weak SP-coupling regime, indicates the coupling regime shows a strong dependence on the dielectric thickness, which is related to the magnetic-SP mode volume, while the working wavelength can be selected in a broader spectral range by scaling the device geometry. These findings are helpful to construct those optoelectronics for infrared absorption enhancement, EIT, and strong coupling spectral characteristic itself.

MoS2-based multiple surface plasmonic coupling for enhanced surface-enhanced Raman scattering and photoelectrocatalytic performance utilizing the size effect.

MoS2-based heterostructures have received increasing attention for not only surface-enhanced Raman scattering (SERS) but also for enhanced photoelectrocatalytic (PEC) performance. This study presents a hydrothermal method for preparing vertical MoS2 nanosheets composed of in situ grown AuNPs with small size and chemically reduced AgNPs with large size to achieve the synergistic enhancement of SERS and PEC properties owing to the size effect of the plasmonic structure. Compared with pristine MoS2 nanosheets and unitary AuNPs or AgNPs composited with MoS2 nanosheets, the ternary heterostructure exhibited the strongest electromagnetic field and surface plasmon coupling, which was confirmed by finite-difference time-domain (FDTD) simulation and absorption spectra. In addition, the experimental results confirmed the outstanding SERS enhancement with an EF of 1.1×109, and the most efficient hydrogen evolution reaction (HER) activity with a sensitive photocurrent response, attributing to the multiple surface plasmonic coupling effects of the Au-Ag bimetal and efficient charge-transfer process between MoS2 and the bimetal. That is, it provides a robust method for developing multi-size bimetal-semiconductor complex nanocomposites for high-performance SERS sensors and PEC applications.

Investigation of optical absorption enhancement of plasmonic configuration by graphene on LiNbO3-SiO2 structure

A novel plasmonic structure is demonstrated by combining graphene with a planar LiNbO3 thin layer, which is simple and easy to fabricate compared to the complex design of general graphene surface plasmons devices. Graphene from the chemical vapor deposition is investigated and characterized to be a continuous and uniform monolayer or fewlayer. LiNbO3 capped by graphene layer show an extraordinary absorption enhancement in an attenuated total reflection (ATR) measurement at a wide bandwidth of 500–4000 cm−1, which can be explained by resonance absorption resulting from the coupling of graphene surface plasmons with optical modes of LiNbO3-SiO2 Fabry–Perot cavity and LiNbO3 planar waveguide. The simulation results are generally consistent with the ATR experimental results. The absorption spectra versus temperature of this plasmonic configuration is also investigated, which show that increasing the testing temperature not only highlights the atomic vibrational peaks of graphene, but also enhances the absorption at several characteristic absorption frequencies due to the enhanced coupling between the surface plamons excitations and the optical modes.

Improved efficiency of green GaN LEDs via exciton–surface plasmon coupling by Au nanoclusters embedded in a micro-hole patterned p-GaN layer

We report green light emitting diodes (LEDs) with Au nanoclusters in a micro-hole patterned p-GaN layer (ANCs-MHPP) to improve the light emission efficiency. Low-temperature photoluminescence (PL) and time-resolved PL showed that green LEDs with ANCs-MHPP demonstrated higher internal quantum efficiencies and faster decay times compared to conventional green LEDs. In addition, the opto-electronic performance of green LEDs with ANCs-MHPP was remarkable. These results can be attributed to the exciton–surface plasmon coupling between excitons in multi-quantum wells and surface plasmons of Au nanoclusters and the surface texturing effect caused by the geometrical shape of the micro-hole patterned p-GaN layer.

Temperature-dependent surface plasmon enhanced photoluminescence in CsPbBr3 thin film

In this paper, we report CsPbBr3/SiO2/Ag hybrid thin films structure to realize the metal surface plasmon enhanced photoluminescence. The photoluminescence of CsPbBr3 can be enhanced when the CsPbBr3 excitons interact with surface plasmon from Ag thin film. The numerical simulation demonstrates the localized electric field induced by surface plasmon is the strongest when SiO2 interlayer has the thickness of 5 nm. If taking account of the energy transfer from CsPbBr3 excitons to Ag layer, the experimental maximum photoluminescence enhancement factor actually occurs when the SiO2 thin film has a thickness of 20 nm. The temperature-dependent photoluminescence demonstrates that metal surface plasmon enhanced photoluminescence has higher enhancement factor at lower temperature, which is attributed to the stronger surface plasmon coupling efficiency at low temperature. The time-resolved photoluminescence further proves that the surface plasmon coupling can enhance the spontaneous emission rate at low temperature.

Optimized Colossal Near-Field Thermal Radiation Enabled by Manipulating Coupled Plasmon Polariton Geometry.

Collective optoelectronic phenomena such as plasmons and phonon polaritons can drive processes in many branches of nanoscale science. Classical physics predicts that a perfect thermal emitter operates at the black body limit. Numerous experiments have shown that surface phonon polaritons allow emission two orders of magnitude above the limit at a gap distance of ≈50nm. This work shows that a supported multilayer graphene structure improves the state of the art by around one order of magnitude with a ≈1129-fold-enhancement at a gap distance of ≈55nm. Coupled surface plasmon polaritons at mid- and far-infrared frequencies allow for near-unity photon tunneling across a broad swath of k-space enabling the improved result. Electric tuning of the Fermi-level allows for the detailed characterization and optimization of the colossal nanoscale heat transfer.

(Invited) Measure Single Protein Size and Binding Kinetics with Plasmonic Scattering Imaging

Measuring individual protein properties is the most critical and challenging tasks for protein analysis. We show that it is possible to quantify single protein size and binding kinetics by plasmonic scattering imaging (PSM). The interference between the protein scattered light and the background light scattered by the rough substrate significantly enhances the signal intensity and contrast, which allows PSM to image single proteins, measure their sizes, and identify them based on their specific binding to antibodies. In addition, PSM can quantify protein binding kinetics by counting the binding of individual molecules, providing a digital method to measure binding kinetics and analyze heterogeneity of protein behavior. Furthermore, PSM can distinct specific and nonspecific binding processes by quantifying the mass and binding dynamics of individual bound analyte molecules, thus allowing the binding kinetic analysis in complex media such as serum. PSM can be implemented on top of an objective or a prism coupled surface plasmon resonance system, providing a convenient solution to realize high sensitivity single molecule imaging. We anticipate that PSM will become an important tool for single protein analysis, especially for low volume samples, such as single cells.