Surface Plasmons In Structures Research Articles

Enhancing the Extinction Efficiency and Plasmonic Response of Bimetallic Nanoparticles of Au-Ag in Robust Thin Film Sensing Platforms

The extinction efficiency of noble metal nanoparticles (NPs), namely gold (Au) and silver (Ag), are dependent on their size and surrounding dielectric. Exploiting the Localized Surface Plasmon Resonance (LSPR) phenomenon, the composition and structure of the NPs might be tailored to achieve a configuration that optimizes their response (sensitivity) to environmental changes. This can be done by preparing a bimetallic system, benefiting from the chemical stability of Au NPs and the higher scattering efficiency of Ag NPs. To enhance the LSPR sensing robustness, incorporating solid supports in the form of nanocomposite thin films is a suitable alternative. In this context, the NPs composed of gold (Au), silver (Ag), and their mixture in bimetallic Au-Ag NPs, were grown in a titanium dioxide (TiO2) matrix using reactive DC magnetron sputtering. Thermal treatment at different temperatures (up to 700 °C) tuned the LSPR response of the films and, consequently, their sensitivity. Notably, the bimetallic film with Au/Ag atomic ratio 1 exhibited the highest refractive index sensitivity (RIS), with a value of 181 nm/RIU, almost one order of magnitude higher than monometallic Au-TiO2. The nanostructural analysis revealed a wide NP size distribution of bimetallic NPs with an average size of 31 nm, covering about 20% of the overall surface area. These findings underscore the significant potential of bimetallic film systems, namely AuAg-TiO2, in LSPR sensing enhancement.

Enhanced broadband light absorption by WSe2 mono layers via surface plasmon structures

Enhanced broadband light absorption by WSe2 mono layers via surface plasmon structures

Low-loss high-confinement terahertz guided-wave propagation along a subwavelength gap between double-dielectric-ridge-integrated gratings

Dielectric grating-based spoof surface plasmonic (SSP) structures are among the recent low-loss and subwavelength field-concentrating solutions for realizing high-density terahertz (THz) and sub-THz integrated circuits. In this paper, we report on a novel waveguide structure capable of supporting highly confined SSP mode while exhibiting much lower propagation loss compared to other similar SSP structures. The proposed structure is composed of two perfectly aligned identical silica ridges placed on the inner faces of the metallic plates of a parallel plate waveguide with a proper plate distancing in order to leave an empty gap region between the ridges. Each of the ridges embodies a periodic arrangement of high-resistivity silicon blocks with the same height as their own, although with smaller widths compared to their width. By performing modal analysis on the 2D and 3D structures of the proposed waveguide, its propagation properties are studied. It is observed that if the gap region is properly designed, a waveguiding structure with a subwavelength cross-sectional size around λ0/3×λ0/3, where λ0 is the free-space wavelength at the maximum frequency of operation, capable of providing a high degree of field confinement over a wide frequency bandwidth of nearly two octaves and with a very low propagation loss factor compared to similar SSP structures is achieved. Moreover, the performance of the proposed waveguide for implementing a 90° waveguide bend of the radius λ0/3, and for obtaining a spectroscopy-based refractive-index sensor is addressed. The results of our assessments suggest that the proposed waveguide can bring the state-of-the-art SSP designs yet another step closer to realizing ideal waveguiding structures for various applications in THz and sub-THz regimes.

Reconfigurable Spoof Localized Surface Plasmonic for Frequency Detections

AbstractUnder the impetus of wireless communications, metamaterials have attracted considerable attention due to their superior merits of free manipulation of electromagnetic waves and easy integration. However, most efforts to date are mainly focused on the modulation of wave information or recognition of wave intensity, while the frequency detection is rarely explored. Here, a spoof localized surface plasmon (SLSP) structure is proposed to realize reconfigurable frequency detections. By switching the bias voltage applied to the varactor, the resonance frequency of SLSP can be controlled dynamically from 1.95 to 2.35 GHz. The SLSP‐based waveguide has a relatively high quality factor due to the strongly localized field confinement. Reconfigurable frequency detection is demonstrated experimentally by monitoring the output voltage of the introduced detector. The measured and simulated results are in good agreement. This work will hold promising applications in wireless communication and sensing systems.

Tuning magneto-electric coherent resonance with a deep-subwavelength localized spoof surface plasmonic structure.

It has been recently shown that an ultrathin corrugated spiral metal strip can simultaneously support electric and magnetic localized spoof plasmonic modes at lower frequencies. In this Letter, we report a mirror quasi-symmetrical corrugated spiral metal disk which can support coherent resonance of an orthogonal electric dipole and a magnetic dipole to achieve azimuthally symmetric unidirectional scattering. By tuning the geometric dimensions, reconfigurable magneto-electric (ME) coherent resonance enhancement is realized. Excellent agreement between numerical simulations and experimental results verifies the tunable ME coherent resonance phenomenon. Our finding could anticipate future sensitive and versatile functional devices based on high-Q coherent resonance from the microwave to the terahertz bands.

Investigation of high-order resonant modes for aluminium nanoparticles (arrays) using the finite-difference time-domain method.

The optical properties of aluminum nanoparticles are simulated and calculated using the finite-difference time-domain (FDTD) method. Our research has given a comprehensive explanation of how the substrate's dielectric coefficients impact the surface plasmon resonance effect. Furthermore, it offers valuable insights into the role of substrate materials with different dielectric coefficients in modulating the surface plasmon resonance effect of aluminum nanoparticles. The simulation demonstrates the high sensitivity of the structure's surface plasmon resonance (SPR) to the particle size of aluminum nanoparticles. Primarily due to the short-wavelength resonance characteristics, as the particle size increases in the presence of a substrate, there is an overall red shift in the peak position compared to the case without a substrate. A non-metallic kind of substance, which is weakly coupled to the aluminum nanoparticles, has weak electric field enhancement; nevertheless the metal substrates confer significant electrically powered field enhancement to the system, and the height of the particles placed on the substrate also affects the SPR properties of the structure. For various specific needs or possible applications requiring different characteristic peaks, the SPR properties of the aluminum nanoparticle-substrate structure can be tuned by particle size and height.

A Mutual Coupling Theory for Arbitrarily Distributed Trimeric Localized Surface Plasmonic Particles

Coupled mode theory (CMT) is widely used to analyze the coupling relationship of plasmons and metasurfaces. However, some details involving coupled structures remain obscure. Herein, the coefficients in CMT are properly defined to solve the problems of inaccurate fitting from two particles to three or more. The proposed improved coupled mode theory (i‐CMT) can perfectly express both the amplitude and phase of transmission curve of dimeric and trimeric mutual coupled systems. A surface plasmonic structure containing multiple metallic spiral structures is fabricated to experimentally verify the accuracy of the i‐CMT. The experimental results are consistent with the theoretical and simulated values, proving the feasibility of using the i‐CMT to analyze and design asymmetric coupled devices. Moreover, the application of the i‐CMT confirms the presence of additional coupling terms in three or more coupled objects, making the calculation of eigenfrequency more accurate.

Propagation Characteristics of Surface Plasmon Polaritons Near Anisotropic 2D Materials Sandwiched by Chiral Media

AbstractA novel surface plasmonic waveguide structure composed of chiral medium and 2D material is proposed. The universal direction‐dependent dispersion relation is obtained, which covers the combinations between 2D materials with in‐plane isotropy or anisotropy and the surroundings with or without chirality. The tunability of the behavior of surface plasmon polaritons with the chirality of environment and the doping level are investigated. The averaging effect of chirality in both sides of 2D material is unveiled. Besides, the transverse spin of SPPs in the Chiral‐2D material structure is explored and the asymmetric distribution of the transverse spin depends mainly on the contribution from the magnetic spin instead of the electric spin. These features are advantageous for the manufacture of novel photonic devices and the development of sensors techniques for the chiral environment.

Antibacterial Pathways in Transition Metal-Based Nanocomposites: A Mechanistic Overview.

Across the planet, outbreaks of bacterial illnesses pose major health risks and raise concerns. Photodynamic,photothermal, and metal ion releaseeffects of transition metal-based nanocomposites (TMNs)were recently shown to be highly effective in reducing bacterial resistance and upsurges in outbreaks. Surface plasmonic resonance, photonics, crystal structures, and optical properties of TMNshave been used to regulate metal ion release, produce oxidative stress, and generate heat for bactericidal applications.The superior properties of TMNsprovide a chance to investigate and improve their antimicrobial actions, perhaps leading to therapeutic interventions. In this review, we discuss three alternative antibacterial strategies based on TMNs of photodynamic therapy,photothermal therapy, and metal ion release and their mechanistic actions. The scientific community has made significant efforts to address the safety, effectiveness, toxicity, and biocompatibility of these metallic nanostructures; significant achievements and trends have been highlighted in this review. The combination of therapies together has borne significant results to counter antimicrobial resistance (4-log reduction). These three antimicrobial pathways are separated into subcategories based on recent successes, highlighting potential needs and challenges in medical, environmental, and allied industries.

Plasmonic quantum nonlinear Hall effect in noncentrosymmetric two-dimensional materials

We investigate an interplay between quantum geometrical effects and surface plasmons through surface plasmonic structures, based on an electron hydrodynamic theory. First we demonstrate that the quantum nonlinear Hall effect can be dramatically enhanced over a very broad range of frequency by utilizing plasmonic resonances and near-field effects of grating gates. Under the resonant condition, the enhancement becomes several orders of magnitude larger than the case without the nanostructures, while the peaks of high-harmonic plasmons expand broadly and emerge under the off-resonant condition, leading to a remarkably broad spectrum. Furthermore, we clarify a universal relation between the photocurrent induced by the Berry curvature dipole and the optical absorption, which is essential for computational material design of long-wavelength photodetectors. Next we discuss a novel mechanism of geometrical photocurrent, which originates from an anomalous force induced by oscillating magnetic fields and is described by the dipole moment of orbital magnetic moments of Bloch electrons in the momentum space. Our theory is relevant to 2D quantum materials such as layered WTe${}_2$ and twisted bilayer graphene, thereby providing a promising route toward a novel type of highly sensitive, broadband terahertz photodetectors.

Monolithically integrated mid-infrared sensor with a millimeter-scale sensing range.

On-chip sensors based on quantum cascade laser technology are attracting broad attention because of their extreme compactness and abundant absorption fingerprints in the mid-infrared wavelength range. Recent continuous wave operation microcavity quantum cascade lasers are well suited for high-density optoelectronic integration because their volumes are small and thresholds are low. In this experimental work, we demonstrate a monolithically integrated sensor comprising a notched elliptical resonator as transmitter, a quantum cascade detector as receiver, and a surface plasmon structure as light-sensing waveguide. The sensor structure is designed to exploit the highly unidirectional lasing properties of the notched elliptical resonator to increase the optical absorption path length. Combined with the evanescent nature of the dielectric loaded surface plasmon polariton waveguides, the structure also ensures a strong light-matter interactions. The sensing transmission distance obtained is approximately 1.16 mm, which is about one order of magnitude improvement over the traditional Fabry-Perot waveguide. This sensor opens new opportunities for long-range and high-sensitivity on-chip gas sensing and spectroscopy.

Study on the absorption characteristics and refractive index sensitivity characteristics of the periodic structure of double nanorods

Metamaterial perfect absorber is very important in the study of refractive index sensor. The time domain finite difference method is used to simulate the surface plasmon structure. The double nanorod periodic structure is designed, and the parameters of the top layer structure are optimized according to the impedance matching principle, and the absorption rate of the structure to the light wave reaches 99.6% when the wavelength is about 12 mm. The absorption spectroscopy of the structure is studied with the change of the refractive index of the spatial medium around the structure, and the sensitivity of the double nanorod structure is 4,008 nm/RIU, which can be used to measure the refractive index of the gas.

A Multibeam and Surface Plasmonic Clothing With RF Energy-Localized Harvester for Powering Battery-Free Wireless Sensor

A wearable radio-frequency (RF) energy-localized harvester with multiple antennas and spoof surface plasmon (SSP) structure for multibeam radiation is presented to power the Bluetooth sensor module. The harvester contains four separate antennas connected by SSP waveguides, while the loop is applied to excite the structure to generate multibeam radiation and improve energy harvesting. The radiative waves will be harvested and converted into surface waves on the SSP waveguides, then, confined in a localized area of the structure through the evanescent field interactions between the current of SSP and the loop in a contactless way. More importantly, it is free of RF connectors and soldering works on the interface between the energy harvester and clothing. In addition, the wearable energy harvester is entirely made of flexible materials, such as conductive fabrics, polyimide, and nylon fabrics in a compact and low-profile structure. The loop can easily be integrated with the rectify circuit and power management unit (PMU) to provide direct-current (dc) power for different kinds of wireless sensor modules. In this design, the harvested power can support a battery-free Bluetooth temperature and humidity sensor with a power density of 2.75 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The complete system-level demonstration of RF energy harvesting shows the potential to power small electronic devices for wearable applications.

Wideband Filtering Antenna Fed Through Hybrid Substrate Integrated Waveguide and Spoof Localized Surface Plasmon Structure

In this communication, we propose a novel feeding scheme to design a wideband filtering patch antenna. The antenna is composed of two substrates: the feeding and the radiating ones. Two circular patches are etched on the top surface of the radiating substrate as the radiators and a hybrid substrate integrated waveguide (SIW) and spoof localized surface plasmon (SLSP) structure is used as the feeding scheme. Due to abundant resonant modes and filtering feature of the hybrid SIW-SLSP structure, the antenna can radiate under the triple-mode resonance with high filtering performance. Moreover, the proposed filtering antenna has an independently adjustable capability of both low-band and high-band radiation nulls. The presented antenna is designed, fabricated, and measured. The measured results reveal that the operating bandwidth reaches up to 11.3%, ranging from 7.44 to 8.33 GHz. The peak gain of 10 dBi is obtained in passband with 10 dB gain suppression out of the band. This approach provides a simple way to design wideband filtering patch antenna, which can be easily integrated with planar circuit.

Efficient Radiative Enhancement in Perovskite Light-Emitting Devices through Involving a Novel Sandwich Localized Surface Plasmon Structure.

In recent years, CsPbX3 (X = Cl, Br, I) perovskite quantum dots (QDs) have been considered as the most promising materials for light-emitting diodes (LEDs). However, the advances of CsPbX3 quantum dot-based light emitting diodes (QLEDs) still lagged behind inorganic III-V LEDs and other organic LEDs. Herein, a strategy to improve the performances of perovskite QLEDs is reported by utilizing the localized surface plasmon resonance (LSPR) effects of Au nanospheres (NSs). It is accomplished by introducing a Au NS layer into the electron transport layer of Ca2+ -CsPbBr3 QLEDs, where the diameter and spacing of Au NSs and the interaction distance between the Ca2+ -CsPbBr3 QD and Au NS layers are modulated, according to the theoretical simulation of Finite-difference time-domain. As a result, the photoluminescence quantum yield of Ca2+ -CsPbBr3 QD layer is improved from 31.5% to 73.3%. Finally, the luminance of Ca2+ -CsPbBr3 QLEDs is improved from 16824 to 63931cd m-2 and external quantum efficiency (EQE) is improved from 4.2% to 10.5%. The radiative transition rate can be remarkably modulated from 0.7 × 107 to 6.6 × 107 s-1 . The enhancement in luminance and EQE are the best values in the LSPR modified perovskite QLEDs and the strategy offered in this work fits with other LEDs and optoelectrical devices.

Surface Plasmonic Lasing in Micro-Nanostructures of Silicon Excited by using Pulsed Infrared Lasers

Surface plasmon is a possible candidate to break the diffraction limit and open the door for developing nanolasers on silicon chips. A new step in this development involves the choice of the structures and compositions for better surface plasmonic emission. The micro-nanostructures were fabricated by using a nanosecond pulsed laser on silicon surface, in which the surface plasmonic emission is stronger. The group of emission peaks with multiple-longitudinal-mode occurs in the optical gain curve. Interestingly, the quantum energy of surface plasmon with 140[Formula: see text]meV has been measured at first, which is related to the peak interval (about 62[Formula: see text]nm) of longitudinal modes in the surface plasmonic lasing spectra. The surface plasmonic lasing near 865[Formula: see text]nm was observed in the Purcell cavity with Si–Cr–Si layers excited by using pulsed lasers at 1064[Formula: see text]nm. Surface plasmonic structure induced with photons was observed by using the reflection Talbot effect image, in which the mechanism of the surface plasmonic lasing can be explored. The physical model of the surface plasmonic laser has been built on the energy levels of the micro-nanostructures of Si.

Infrared Photodetectors Based on 2D Materials and Nanophotonics

Abstract2D materials, such as graphene, transition metal dichalcogenides, black phosphorus, and tellurium, have been demonstrated to be promising building blocks for the fabrication of next‐generation high‐performance infrared (IR) photodetectors with diverse device architectures and impressive device performance. Integrating IR photodetectors with nanophotonic structures, such as surface plasmon structures, optical waveguides, and optical cavities, has proven to be a promising strategy to maximize the light absorption of 2D absorbers, thus enhancing the detector performance. In this review, the state‐of‐the‐art progress of IR photodetectors is comprehensively summarized based on 2D materials and nanophotonic structures. First, the advantages of using 2D materials for IR photodetectors are discussed. Following that, 2D material‐based IR detectors are classified based on their composition, and their detection mechanisms, key figures‐of‐merit, and the principle of absorption enhancement are discussed using nanophotonic approaches. Then, recent advances in 2D material‐based IR photodetectors are reviewed, categorized by device architecture, i.e., photoconductors, van der Waals heterojunctions, and hybrid systems consisting of 2D materials and nanophotonic structures. The review is concluded by providing perspectives on the challenges and future directions of this field.

Nanoscale Visualization of a Photoinduced Plasmonic Near-Field in a Single Nanowire by Free Electrons.

Swift electrons can undergo inelastic interactions not only with electrons but also with near-fields, which may result in an energy loss or gain. Developments in photon-induced near-field electron microscopy (PINEM) enable direct imaging of the plasmon near-field distribution with nanometer resolution. Here, we report an analysis of the surface plasmonic near-field structure based on PINEM observations of silver nanowires. Single-photon order-selected electron images revealed the wavelike and banded structure of electric equipotential regions for a confined near-field integral associated with typical absorption of photon quanta (nℏω). Multimodal plasmon oscillations and second-harmonic generation were simultaneously observed, and the polarization dependence of plasmon wavelength and symmetry properties were analyzed. Based on advanced imaging techniques, our work has implications for future studies of the localized-field structures at interfaces and visualization of novel phenomena in nanostructures, nanosensors, and plasmonic devices.

Multiple Fano resonances based on clockwork spring-shaped resonator for refractive index sensing

A surface plasmon polarized structure consisting of two metal-insulator-metal (MIM) waveguide coupled with clockwork spring-shaped resonators are constructed in this paper, and its geometric parameters are controlled within a few hundred nanometers. The finite element method (FEM) and multimode interference coupled mode theory (MICMT) are used to simulate and theoretically calculate the optical response of the designed structure. By modifying the structural parameters of the system, the influence on the asymmetry of the Fano resonance line is studied. The changes of the transmission spectra at different refractive indexes are also investigated. Based on this asymmetric resonant line, the sensitivity and FOM* (figure of merit) value of the cavity with different parameters are measured. The sensitivity and FOM* under the best parameters are 1200 nm RIU−1 and 191.6, respectively. The surface plasmon structure proposed and the results in this paper are promising for applications in the field of high-performance sensing and micro-nano optical devices.

Broadband and wide-angle metamaterial absorber based on the hybrid of spoof surface plasmonic polariton structure and resistive metasurface.

Electromagnetic (EM) wave absorber with broad and robust absorption performance over wide incident angle range is persistently desired in specific applications. In this work, we propose and demonstrate a broadband and wide-angle metamaterial absorber (MA) based on a hybrid of stereo spoof surface plasmonic polariton (SSPP) structure and planar resistive metasurface. At first, we design a broadband SSPP absorber by adjusting the dispersion and loss of the artificial plasmonic structure (PS) simultaneously. Furthermore, owing to utilize its spatial phase manipulation ability, we integrate a resistive metasurface on top of the PS to construct a modified circuit analog (CA) absorber with a dispersive metamaterial spacer. The absorption mechanism of the hybrid structure is analyzed theoretically. The results indicate that the hybrid MA is equipped with broad and robust absorption performance over a wide incident angle range due to the synergistic absorption of the PS and metasurface. Finally, a prototype of the hybrid MA is fabricated by silk-printing technic and its absorption performances are measured. The experimental results can verify the theoretic ones and indicate that proposed hybrid MA can achieve 90% absorptivity from 3.9 GHz to 10.6 GHz with thickness of 7.0 mm, which is only 106% times of the ultimate thickness corresponding to the absorption performance of MA. In general, the concept and design offer a distinct approach of utilizing SSPP to design absorbers with excellent performances from radio frequency to optic band, which are promising for extensive applications.