Surface Plasmon Coupling Research Articles

High-efficiency terahertz surface plasmon metacoupler empowered by bilayer bright–dark mode coupling

Conversion from free-space waves to surface plasmons has been well studied as a key aspect of plasmonics. In particular, efficient coupling and propagation of surface plasmons via phase gradient metasurfaces are of great current research interest. Hereby, we demonstrate a terahertz metacoupler based on a bilayer bright–dark mode coupling structure attaining near-perfect conversion efficiency (exceeding 95%) without considering absorption loss of the materials and maintaining a high conversion level even when the area of the excitation region changes. To validate our design, a fabricated metacoupler was assessed by scanning near-field terahertz microscopy. Our findings could pave the way for developing high-performance plasmonic devices encompassing ultra-thin and compact functional devices for a diverse range of applications, especially within the realm of high-speed terahertz communications.

EM metamaterials sensor based on close coupling of spoof localized surface plasmons

EM metamaterials sensor based on close coupling of spoof localized surface plasmons

Proximal High-Index Metamaterials based on a Superlattice of Gold Nanohexagons Targeting the Near-Infrared Band.

Plasmonic nanoparticles can be assembled into a superlattice, to form optical metamaterials, particularly targeting precise control of optical properties such as refractive index (RI). The superlattices exhibit enhanced near-field, given the sufficiently narrow gap between nanoparticles supporting multiple plasmonic resonance modes only realized in proximal environments. Herein, the planar superlattice of plasmonic Au nanohexagons (AuNHs) with precisely controlled geometries such as size, shape, and edge-gaps is reported. The proximal AuNHs superlattice realized over a large area with selective edge-to-edge assembly exhibited the highest-ever-recorded RI values in the near-infrared (NIR) band, surpassing the upper limit of the RI of the natural intrinsic materials (up to 10.04 at λ = 1.5µm). The exceptionally enhanced RI is derived from intensified in-plane surface plasmon coupling across the superlattices. Precise control of the edge-gap of neighboring AuNHs systematically tuned the RI as confirmed by numerical analysis based on the plasmonic percolation model. Furthermore, a 1D photonic crystal, composed of alternating layers of AuNHs superlattices and low-index polymers, is constructed to enhance the selectivity of the reflectivity operating in the NIR band. It is expected that the proximal AuNHs superlattices can be used as new optical metamaterials that can be extended to the NIR range.

Polarization-dependent near-field coupling and far-field harmonic modulation in a graphene-based plasmonic nanostructure

The interplay between light and matter has fostered innovative research in surface plasmons, specifically in graphene, due to its tunable Fermi energy and reduced losses in the infrared and terahertz spectra. This study explores the anisotropic coupling of nonlocalized surface plasmons in graphene with localized magnetic polaritons (MP) in a silicon carbide (SiC) array. By adjusting graphene’s Fermi energy and polarization angle, we successfully achieved hybrid coupling, giving rise to three clearly distinguishable hybridized states. Using the coupled oscillator model as a framework, we conducted an analysis of the intricate multimode coupling and accurately ascertained the weighting efficiencies of the individual modes comprising the hybrids. By integrating the design principles of space-time coding metasurfaces, we successfully broadened the scope of the application, extending its reach from the near-field to the far-field. These novel discoveries pave new paths for advancements in thermal emitters, photonic systems, energy conversion technologies, and the creation of cutting-edge plasmonic devices.

Coherent coupling of localized surface plasmons and surface plasmons in borophene-based metamaterial

The strong coherent coupling in different electromagnetic modes can control the light-matter interaction more conveniently. Here, we theoretically researched the hybridization between the borophene surface plasmon (BSP) mode and the borophene localized surface plasmon (BLSP) mode in borophene grating structure. This coupling effect leads to the emergence of multiple hybrid modes. The absorption spectra of the system are investigated through finite difference time domain (FDTD) simulation and coupled oscillator model (COM). Results show that the coherent coupling of BSP and BLSP can be achieved by adjusting the carrier density of the borophene gratings. A Rabi splitting effect with frequency of 21.6 THz can be observed. Furthermore, we investigated the effects of geometric structural parameters, incident angle, and relaxation time on the correlated coupling spectra. Our work may deepen the understanding of light–matter interactions and provide a reference for borophene-based active photonic devices in the near-infrared region.

Emission Wavelength Control Based on Coupling of Surface Plasmon and Microcavity Mode in Organic Light-Emitting Diodes with Metal/Dielectric/Metal Anodes

Emission Wavelength Control Based on Coupling of Surface Plasmon and Microcavity Mode in Organic Light-Emitting Diodes with Metal/Dielectric/Metal Anodes

Phase-Controllable Spoof Surface Plasmon Coupling From Bull's Eye Aperture to Planar Silicon Waveguide in the Terahertz Band

Phase-Controllable Spoof Surface Plasmon Coupling From Bull's Eye Aperture to Planar Silicon Waveguide in the Terahertz Band

Cu NCs@MXene-luminescent Faraday cage and Cu Nanocone/Bi NPs array-based saliva exosome assay for asthma evaluation

In this work, a novel nano-sensing system with luminescent Faraday cage mode has been developed to detect miRNA-221-5p in clinic saliva exosomes to evaluate asthma. Firstly, copper nanoclusters (Cu NCs) were synthesized in situ on the defects in Ti3CN nanosheets based on the nanoconfinement effect. Due to the Electronic metal-support interactions (EMSI) between MXene and the anchored Cu NCs, Cu NCs@MXene displayed the strong luminescence performance, high electrochemical activity and good stability properties. Furthermore, MXene nanosheets with good conductivity and flexibility was used to expand the outer Helmholtz plane and improve the sensing ability. Meanwhile, Cu nanocone/Bi nanoparticles (NPs) arrays were constructed by step-by-step electrodeposition. Due to the surface plasmon coupling effect, the Cu nanocone/Bi NPs arrays can convert the electrochemiluminescence (ECL) signal of Cu NCs@MXene-Faraday cage into the directional emission with 13.4-fold enhancement. Finally, a thin phospholipid film and capture DNA were modified on the surface of the Cu nanocone/Bi NPs array as the sensing interface to detect miRNA-221-5p in saliva exosomes. The designed nano-sensing system had a detection range was 1.0 × 10-16 ∼ 1.0 × 10-8 mol/L with the detection limit of 34 aM. Finally, the biosensor has been successfully employed to evaluate asthma in the clinical analysis.

Surface Plasmon-Coupled Directional Emission Enhanced Raman Scattering Based on Waveguide Coupling Surface Plasmon Resonance Configuration

Surface Plasmon-Coupled Directional Emission Enhanced Raman Scattering Based on Waveguide Coupling Surface Plasmon Resonance Configuration

Large-Area Near-Infrared Emission Enhancement on Single Upconversion Nanoparticles by Metal Nanohole Array.

Single lanthanide (Ln) ion doped upconversion nanoparticles (UCNPs) exhibit great potential for biomolecule sensing and counting. Plasmonic structures can improve the emission efficiency of single UCNPs by modulating the energy transferring process. Yet, achieving robust and large-area single UCNP emission modulation remains a challenge, which obstructs investigation and application of single UCNPs. Here, we present a strategy using metal nanohole arrays (NHAs) to achieve energy-transfer modulation on single UCNPs simultaneously within large-area plasmonic structures. By coupling surface plasmon polaritons (SPPs) with higher-intermediate state (1D2 → 3F3, 1D2 → 3H4) transitions, we achieved a remarkable up to 10-fold enhancement in 800 nm emission, surpassing the conventional approach of coupling SPPs with an intermediate ground state (3H4 → 3H6). We numerically simulate the electrical field distribution and reveal that luminescent enhancement is robust and insensitive to the exact location of particles. It is anticipated that the strategy provides a platform for widely exploring applications in single-particle quantitative biosensing.

Harmonic Generation up to Fifth Order from Al/Au/CuS Nanoparticle Films.

Dual heterostructures integrating noble-metal and copper chalcogenide nanoparticles have attracted a great deal of attention in nonlinear optics, because coupling of their localized surface plasmon resonances (LSPRs) substantially enhances light-matter interactions through local-field effects. Previously, enhanced cascaded third-harmonic generation was demonstrated in Au/CuS heterostructures mediated by harmonically coupled surface plasmon resonances. This suggests a promising approach for extending nonlinear enhancement to higher harmonics by adding an additional nanoparticulate material with higher-frequency harmonic resonances to the hybrid films. Here we report the first observation of enhanced cascaded fourth- and fifth-harmonic generation in Al/Au/CuS driven by coupled LSPRs at the fundamental (1050 nm), second harmonic (525 nm), and third harmonic (350 nm) of the pump frequency. An analytical model based on incoherent dipole-dipole interactions among plasmonic nanoparticles accounts for the observed enhancements. The results suggest a novel design for efficiently generating higher harmonics in resonant plasmonic structures by means of multiple sum-frequency cascades.

Enhanced laser-induced fluorescence and Raman spectroscopy with gold nanoparticles for the diagnosis of oral squamous cell carcinoma

BackgroundThe incidence, mortality, and recurrence rates of oral cancer are high worldwide. It is a common and aggressive type of tumor. Owing to the challenges associated with early illness diagnosis, squamous cell carcinoma, a kind that is prevalent of oral cancer, has an unacceptably high fatality rate. The management of the condition and the prevention of cancer, on the other hand, depend greatly on early detection. Therefore, alternative methods for the treatment and early diagnosis are essential for oral cancer. The detection of tongue squamous cell carcinoma is aided by coupled surface plasmon resonance, which can occur in gold nanoparticles (AuNPs). Compared to the currently utilized imaging contrast chemicals, AuNPs are more biocompatible and capable of targeting specific surface molecules. In the current study, AuNPs were synthesized in one step via citrate reduction and applied to tongue samples of a Caucasian man's Homo sapiens (Squamous cell carcinoma from ATCC cell-lines) in order to improve early detection using and laser-induced fluorescence and Raman spectroscopy.ResultsUV–visible spectroscopy, Zeta potential, TEM, and FTIR spectroscopic technique were used to characterize the synthesized nanoparticles. The synthesized AuNPs measured 13 ± 3 nm with uniform size distribution and high stability. Results demonstrate the significance of AuNPs in improving the identification of tongue squamous cell carcinoma.ConclusionObtained results revealed that the use of AuNPs modifies the emitted spectra in the two employed spectroscopic techniques and provides more significant receiver operating characteristic curve parameters, hence a higher detection rate of cancer.

Manipulation of plasmon dephasing time via the coupling between localized surface plasmon resonance and waveguide modes

Manipulation of plasmon dephasing time of the hybrid modes has gained much attention in recent years, which plays critical roles in many important applications of plasmonics. Here, we manipulate the dephasing time of plasmonic field resulting from coupling of the localized surface plasmon (LSP) of the nanosphere array and the waveguide mode supported by the indium tin oxide film with quasi-normal mode-assisted harmonic oscillator model method. It results in the formation of two distinct modes, transverse electric (TE) and transverse magnetic (TM) modes. Such coupling can significantly modify the dynamics of the original plasmonic modes. The dephasing time of the hybrid plasmon modes, encompassing both TE and TM modes, can be extended from 1.25fs to 4.95fs, which is about 2–7 times compared to that of a single localized surface plasmon resonant mode. More importantly, by changing the structural parameters, we can flexibly manipulate either the dephasing time with a fixed wavelength or the resonant wavelength with a fixed dephasing time.

Magnetoplasmonic Metasurface-Modulated Electrochemiluminescence Strategy for Extracellular Vesicle Detection.

Due to the ideal optical manipulation ability, the metasurface has broad prospects in the development of novel optical research. In particular, an active metasurface can control optical response through external stimulus, which has attracted great research interest. However, achieving effective modulation of the optical response is a significant challenge. In this work, we have developed a novel electrochemiluminescence (ECL) signal modulation strategy by an active magnetoplasmonic metasurface under an external magnetic field. The magnetoplasmonic metasurface was assembled based on yolk-shell Fe3O4@Au nanoparticles (Fe3O4@Au YS-NPs). On the one hand, the yolk-shell structure of Fe3O4@Au YS-NPs possessed the surface plasmon coupling effect and cavity-based Purcell effect, which provided high-intensity electromagnetic hot spots in the magnetoplasmonic metasurface. On the other hand, due to the strong magnetic response of the Fe3O4 core, the local magnetic field was induced by the external magnetic field, which further generated Lorentz force acting on the free electrons of Au nanoshells with strong optical anisotropy. The plasmon frequency of the metasurface can be effectively modulated by the Lorentz force effect. As a result, the ECL signal of nitrogen dots (N dots) was dynamically modulated and significantly enhanced at a specific polarization angle by the magnetoplasmonic metasurface under the variable external magnetic field. Based on the luminescence modulation ability and structure feature, the magnetoplasmonic metasurface was further established successfully as a sensing interface for gastric cancer (GC) extracellular vesicle (EV) detection. This study illustrated that the electromagnetic response of the active metasurface can effectively improve the optical modulation ability and luminescence sensing performance.

Efficiency enhancement of micro-light-emitting diode with shrinking size by localized surface plasmons coupling

Efficiency enhancement of micro-light-emitting diode with shrinking size by localized surface plasmons coupling

Small attenuation negative group delay of spoof surface plasmon polaritons

Spoof surface plasmon polariton (SSPP) waveguides can be used to effectively construct on-chip microwave systems due to the single-side conductor structure. SSPP waveguides usually exhibit normal dispersion, which can introduce large group delays to transmission signal and impair waveform shapes. However, the negative group velocity (NGV) effect may occur in the split modes of coupled surface plasmon polariton waveguides. In this regard, the synthesis wave model of forward and backward transmission waves is applied, which generates a quadrupole vortex wave transmission. In this paper, the SSPP unit structure with folded multi-split rings is proposed to achieve anomalous dispersion with NGV feature in the fundamental mode. The SSPP unit can be equivalent to an epsilon-negative medium, and a maximum negative group delay (NGD) can be reached at the frequency where the NGV begins to appear. For the corresponding SSPP waveguide, a NGD band with lower attenuation can be achieved at the stopband edge. While the SSPP unit structures are loaded as dispersive materials in a microstip line, the similar NGD performance can be obtained. Clearly, the SSPP NGD with lower attenuation provides a new delay equalization method for ultra reliable and low latency communications (URLLC), and can also be used as an effective dispersion compensation means.

One-pot synthesized Au@Pt nanostars-based lateral flow immunoassay for colorimetric and photothermal dual-mode detection of SARS-CoV-2 nucleocapsid antibody

In addition to confirming virus infection, quantitative identification of the antibodies to severe acute respiratory syndrome coronavirus 2(SARS-CoV-2) also evaluates persons immunity to guide personal protection. However, portable assays for fast and accurate quantification of SARS-CoV-2 antibodies remain challenging. In this work, we synthesized Au@Pt star-like nanoparticles (NPs) quickly and easily by a one-pot wet-chemical approach, allowing the stellate Au core to be partially decorated by Pt nanoshells. The nanoparticles were used as probe in a lateral flow immunoassay (LFIA) that operated in both colorimetric and photothermal dual modes, which could detect the antibodies to the SARS-CoV-2 nucleocapsid (N) protein with high sensitivity. Due to the sharp tips on the external region of nanostars and surface plasmon coupling effect between the Au core and Pt shell, the NIR absorption capacity and photothermal performance of these NPs were exceptional. Under optimal conditions, the colorimetric mode's detection limit for SARS-CoV-2 N protein antibody was 1 ng mL−1, which is significantly lower by 2-order of magnitude compared to commercially available colloidal gold strips. And the detection limit for the photothermal mode was as low as 24.91 pg mL−1, which was approximately 40-fold more sensitive than colorimetric detection. Moreover, the method demonstrated favorable specificity, reproducibility and stability. Finally, the approach was employed for the successful identification of actual serum samples. Therefore, the dual-mode LFIA can be applied for screening and tracking the early immunological reaction to SARS-CoV-2, and it has great promise for clinical application.

Near-Perfect Infrared Transmission Based on Metallic Hole and Disk Coupling Array for Mid-Infrared Refractive Index Sensing

Nanostructured color filters, particularly those generated by the extraordinary optical transmission (EOT) resonance of metal–dielectric nanostructures, have been intensively studied over the past few decades. In this work, we propose a hybrid array composed of a hole array and a disk array with the same working period within the 3–14 μm mid-infrared band. Through numerical simulations, near-perfect transmission (more than 99%) and a narrower linewidth at some resonance wavelengths were achieved, which is vital for highly sensitive sensing applications. This superior performance is attributed to the surface plasmon coupling resonance between the hole and disk arrays. A high tunability of the near-perfect transmission peak with varying structural parameters, characteristics of sensitivity to the background refractive index, and angle independence were observed. We expect that this metallic hole and disk coupling array is promising for use in various applications, such as in plasmon biosensors for the high-sensitivity detection of biochemical substances.

Surface plasmon coupling between wide-field SPR microscopy and gold nanoparticles

The coupling behavior of the wide field surface plasmon microscopy (WF-SPRM) with single-, two-, and multiple-gold nanoparticles (AuNPs) with different AuNPs sizes is investigated using theoretical, simulation, and experimental approaches. The signal intensity of a single AuNP increases from 208 a.u. to 583 a.u. as particle size increases from 40 to 80 nm, which evidences the signal-building mechanism of Rayleigh scattering theory. A discrete particle model of SPR is used to understand the interaction between an Au-layer and a single AuNP. The calculated intensity profile of the single AuNP from the discrete particle model is accepted with the experimental data. In addition, the superposition between 2-AuNPs surface plasmon waves is studied using the finite element method as well as experimental data from WF-SPRM. The surface plasmon waves around the two particles generate an interference pattern. Finally, it is demonstrated that plasmonic multiple particles scattering can be represented by an effective media, which is described by Maxwell-Garnet equations.

Improving optical coherence of light-emitting diodes by surface plasmons via shallow-etched conic pit array.

We propose the coupling of multiple quantum wells and surface plasmons can improve coherence of light emitted from LED wafers, as evidenced herein by a shallow-etched conic pit array with evaporated Ag (V-Ag) on a GaN-based LED wafer. The improvement in spatial coherence is critically verified by angle-resolved spectra. The temporal coherence length of the V-Ag wafer is 1.4 times larger than that of the plain wafer. The coherence-enhanced wafer achieves anisotropic and deflective emission in micro area and at far field by diffraction. This research provides a novel perspective on research of plasmonic LEDs and a new straightforward architecture to acquire partially coherent light from LEDs.