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Therefore, it is reasonable to define the effective permittivity in the TE SB 10 sb mode of rectangle waveguide as I i SB eff sb = I i SB I r i sb - ( I i /2 I w i ) SP 2 sp , such that the effective permittivity I i SB eff sb reflects the effective property of TE SB 10 sb mode in the rectangle waveguide. The waveguide effective plasmonics is realized by utilizing the structural dispersion of waveguide, and the effective negative permittivity can be obtained with non-dispersive and low-loss dielectrics with positive permittivity [[70]]. Keywords: localized surface plasmon; plasmonics; structural dispersion; surface plasmon polaritons; waveguide effective plasmonics EN localized surface plasmon plasmonics structural dispersion surface plasmon polaritons waveguide effective plasmonics 1659 1676 18 05/12/22 20220401 NES 220401 1 Introduction Since Mie and Ritchie first systematically described the fundamental physics on the interfaces between conductors and insulators for small particles and flat films, respectively [[1]], various researches on the surface electron oscillations have been widely conducted, including the propagating electromagnetic wave coupled to the conductor and dielectric interfaces, and the non-propagating resonance in the subwavelength nanostructure coupled to electromagnetic fields. In the work [[95]], waveguide effective SPP propagation is induced through two stacked half-mode SIWs (effective relative permittivities of filled dielectrics have opposite signs), achieving a sharp zero-transmission spectrum in waveguide response. The effective permittivity is corresponding to the propagating constant in the waveguide, and specifically, the effective permittivity is positive or negative when the waveguide is operating in propagating or below cut-off mode, respectively, and the effective permittivity equals zero when the waveguide is exactly at the cut-off frequency. [Extracted from the article]

Using the finite-difference time-domain (FDTD) method, we designed an ultra-thin Ge/GaAs/P3HT:PCBM hybrid solar cell (HSC), which showed good effects of ultra-wideband (300 nm–1200 nm), high absorption, and a short-circuit current density of 44.7 mA/cm2. By changing the thickness of the active layer P3HT:PCBM, we analyzed the capture of electron-hole pairs. We also studied the effect of Al2O3 on the absorption performance of the cell. Through adding metal Al nanoparticles (Al-NPs) and then analyzing the figures of absorption and electric field intensity, we found that surface plasma is the main cause of solar cell absorption enhancement, and we explain the mechanism. The results show that the broadband absorption of the solar cell is high, and it plays a great role in capturing sunlight, which will be of great significance in the field of solar cell research. [ABSTRACT FROM AUTHOR]

Owing to the intense carrier recombination and limited optical absorption, the as‐fabricated CsPbBr3 visible light photodetectors (PDs) are far from practical application. In this work, we have demonstrated performance‐improved metal‐semiconductor‐metal (MSM) structured CsPbBr3 visible light PDs realized by the decoration of sputtered Au nanoparticles (NPs). It showed that the Au NPs on the CsPbBr3 exhibited synergistic benefits including improving the photogenerated charge carriers' lifetime and enhancing the optical absorption of the CsPbBr3, both of which are fundamental factors for the performance‐improved PDs. Electrical characterizations showed that localized Schottky junctions formed at the Au NPs/CsPbBr3 interface. In addition, optical investigations showed that effective resonant coupling occurred between the localized surface plasmon resonance effects of Au NPs and excitons in the CsPbBr3. As a result, the on‐off switching of the Au‐decorated CsPbBr3 photodetector increased by 13 times compared with that of the pristine one. Meanwhile, the peak photo sensitivity of the CsPbBr3 photodetector was increased from 0.088 to 0.61 A W‐1 after the decoration of Au NPs. It is believed that the results shown in this work will provide pathways for fabricating high‐performance CsPbBr3 PDs and other similar devices in the future. [ABSTRACT FROM AUTHOR]

Localized plasmon resonance of a metal nanoantenna is determined by its size, shape and environment. Here, we diminish the size dependence by using multilayer metamaterials as epsilon-near-zero (ENZ) substrates. By means of the vanishing index of the substrate, we show that the spectral position of the plasmonic resonance becomes less sensitive to the characteristics of the plasmonic nanostructure and is controlled mostly by the substrate, and hence, it is pinned at a fixed narrow spectral range near the ENZ wavelength. Moreover, this plasmon wavelength can be adjusted by tuning the ENZ region of the substrate, for the same size nanodisk (ND) array. We also show that the difference in the phase of the scattered field by different size NDs at a certain distance is reduced when the substrate is changed to ENZ metamaterial. This provides effective control of the phase contribution of each nanostructure. Our results could be utilized to manipulate the resonance for advanced metasurfaces and plasmonic applications, especially when precise control of the plasmon resonance is required in flat optics designs. In addition, the pinning wavelength can be tuned optically, electrically and thermally by introducing active layers inside the hyperbolic metamaterial.

Abstract Absorption enhancement based on interaction between the localized surface plasmon (LSP) and molecular exciton is one of the most important phenomena for the development of high-performance solar devices. In this study, hybrids of plasmonic metal nanoparticles and dye molecules have been developed, which exhibit enhanced absorption at precisely tuned wavelengths in a visible region. The hybrids consist of a porphyrin derivative, which has four absorption peaks (Q-bands) in a range of 500–700 nm, and triangular silver nanoprisms (AgPRs), which are developed by us to exhibit precisely tuned LSP resonance wavelengths. Absorption enhancement over the whole Q-band range is induced by the combined use of three kinds of AgPRs of different aspect ratios. Furthermore, the quantitative evaluation of absorption enhancement based on the LSP-based fluorescence enhancement phenomenon has demonstrated that efficient absorption enhancement can be effected at multiple wavelengths.

We report on a self-referenced refractive index optical sensor based on Au nanoislands. The device consists of a random distribution of Au nanoislands formed by dewetting on a planar SiO2/metal Fabry–Pérot cavity. Experimental and theoretical studies of the reflectance of this configuration reveal that its spectral response results from a combination of two resonances: a localized surface plasmon resonance (LSPR) associated to the Au nanoislands and the lowest-order anti-symmetric resonance of the Fabry–Pérot cavity. When the device is immersed in different fluids, the LSPR contribution provides high sensitivity to refractive index variations of the fluid, whereas those refractive index changes have little impact on the Fabry–Pérot resonance wavelength, allowing its use as a reference signal. The self-referenced sensor exhibits a spectral sensitivity of 212 nm/RIU (RIU: refractive index unit), which is larger than those of similar structures, and an intensity sensitivity of 4.9 RIU−1. The proposed chip-based architecture and the low cost and simplicity of the Au nanoisland synthesis procedure make the demonstrated sensor a promising self-referenced plasmonic sensor for compact biosensing optical platforms based on reflection mode operation.

Metallic nanowires have been utilized as a platform for propagating surface plasmon (SPs) fields. To be exploited for applications such as plasmonic circuits, manipulation of localized field propagating pattern is also important. In this study, we calculated the field distributions of localized surface plasmons (LSPs) on the specifically shaped nanostructures and explored the feasibility of manipulating LSP fields. Specifically, plasmonic fields were calculated at different wavelengths for a nanoscale rod array (I-shaped), an array connected with two nanoscale rods at right angles (T-shaped), and an array with three nanoscale rods at 120° to each other (Y-shaped). Three different types of nanostructures are suggested to manipulate the positions of LSP fields collaborating with adjustment of wavelength, polarization, and incident orientation of light source. The results of this study are important not only for the understanding of the wavelength-dependent surface plasmon field localization mechanism but also for the applicability of swept source-based plasmonic techniques or designing a plasmonic circuit. [ABSTRACT FROM AUTHOR]

A promising route to realize solar-to-chemical energy conversion resorts to water splitting using plasmon photocatalysis. However, the ultrafast carrier dynamics and underlying mechanism in such processes has seldom been investigated, especially when the single-atom catalyst is introduced. Here, from the perspective of quantum dynamics at the atomic length scale and femtosecond time scale, we probe the carrier and structural dynamics of plasmon-assisted water splitting on an Ag-alloyed Pt single-atom catalyst, represented by the Ag19Pt nanocluster. The substitution of an Ag atom by the Pt atom at the tip of the tetrahedron Ag20 enhances the interaction between water and the nanoparticle. The excitation of localized surface plasmons in the Ag19Pt cluster strengthens the charge separation and electron transfer upon illumination. These facts cooperatively turn on more than one charge transfer channels and give rise to enhanced charge transfer from the metal nanoparticle to the water molecule, resulting in rapid plasmon-induced water splitting. These results provide atomistic insights and guidelines for the design of efficient single-atom photocatalysts for plasmon-assisted water splitting.

Metamaterial perfect absorbers (MPAs) with dynamic thermal tuning features are able to control the absorption performance of the resonances, providing diverse applications spanning from optical switches and filters to modulators. In this paper, we propose an MPA with diverse functionalities enabled by vanadium dioxide (VO2) embedded in a metal-dielectric plasmonic structure. For the initial design purpose, a silicon (Si) nanograting on a silver (Ag) mirror is proposed to have multiple resonant responses in the near infrared (NIR) region. Then, the insertion of a thin VO2 layer at the right position enables the design to act as an on/off switch and resonance tuner. In the insulator phase of VO2, in which the permittivity data of VO2 is similar to that of Si, a double strong resonant behavior is achieved within the NIR region. By increasing the temperature, the state of VO2 transforms from insulator to metallic so that the absorption bands turn into three distinct resonant peaks with close spectral positions. Upon this transformation, a new resonance emerges and the existing resonance features experience blue/red shifts in the spectral domain. The superposition of these peaks makes the overall absorption bandwidth broad. Although Si has a small thermo-optic coefficient, owing to strong light confinement in the ultrasmall gaps, a substantial tuning can be achieved within the Si nanogratings. Therefore, the proposed hybrid design can provide multi-resonance tunable features to cover a broad range and can be a promising strategy for the design of linearly thermal-tunable and broadband MPAs. Owing to the proposed double tuning feature, the resonance wavelengths exhibits great sensitivity to temperature, covering a broad wavelength range. Overall, the proposed design strategy demonstrates diverse functionalities enabled by the integration of a thin VO2 layer with plasmonic absorbers. [ABSTRACT FROM AUTHOR]

A plasmonic flow reactor, consisting of thin Au film at exits of monolithic anodized aluminum oxide (AAO) membranes under LED illumination is demonstrated. The system shows over 200% quantum efficiency (QE) for peroxide activation and the ability to limit to single oxidation reaction by controlling residence time with flow rate and pore geometry. Periodic pore arrays (20–200 nm diameter) with 25 nm thick Au on AAO are modeled by finite‐difference time‐domain (FDTD) simulations and predicted largest E‐field enhancements for the larger 200 nm pore diameters. Peroxide activation, as measured by O2 generation is most efficient with a 200 nm pore diameter system under 523 nm LED illumination. The optimal wavelength falls near the absorption peak of Au@AAO with 200 nm pore diameter suggesting that hot electron generated from gold plasmonic response is the primary mechanism for activation of H2O2. QE for gold plasmonic flow system calculated from O2 generation experiments is as high as 250%, which indicates a mechanism of hot‐electron activation of peroxide that leaves a still energetic hot‐electron to catalytically activate multiple reactions. The formation of Au surface oxides that are catalytically active in dark is also observed and must be accounted for in Au plasmonic photochemical studies. [ABSTRACT FROM AUTHOR]

In this paper, a novel terahertz (THz) spectroscopy technique and a new graphene-based sensor is proposed. The proposed sensor consists of a graphene-based metasurface (MS) that operates in reflection mode over a broad range of frequency band (0.2 – 6 THz) and can detect relative permittivity of up to 4 with a resolution of 0.1 and a thickness ranging from 5 μm to 600 μm with a resolution of 0.5 μm. To the best of author’s knowledge, such a THz sensor with such capabilities has not been reported yet. Additionally, an equivalent circuit of the novel unit cell is derived and compared with two conventional grooved structures to showcase the superiority of the proposed unit cell. The proposed spectroscopy technique utilizes some unique spectral features of a broadband reflection wave including Accumulated Spectral power (ASP) and Averaged Group Delay (AGD), which are independent to resonance frequencies and can operate over a broad range of spectrum. ASP and AGD can be combined to analyse the magnitude and phase of the reflection diagram as a coherent technique for sensing purposes. This enables the capability to distinguish between different analytes with high precision which, to the best of author’s knowledge, has been accomplished for the first time. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermal dewetting technique is used to optimize the self-assembling of Ag NPs. • Integration of Ag nanoparticles in proximity to the InGaN/GaN-based nano-LEDs. • It exhibits LSP energy coupling efficiency (70 %) and fast decay lifetime (2.04 ns). • Nearly 130% and 290% enhancement in EL and CL compared with reference nanorod LEDs. • Numerical simulation is performed to correlate the degree of LSP coupling effect. Integration of metal nanoparticles (NPs) in proximity to the InGaN/GaN-based individual nanorod light-emitting diodes (nano-LEDs) can provide a platform to improve the emission efficiency through localized surface plasmon (LSP) coupling effect. This work evaluates an optimizing process for fabricating self-assembled Ag NPs on the surface of horizontally aligned individual nano-LEDs via thermal evaporation/dewetting techniques. The closely integrated Ag NPs on each nano-LED accelerate a strong LSP energy coupling efficiency of 70 % with a fast decay lifetime of 2.04 ns. The self-assembled Ag NPs/nano-LEDs exhibit nearly 130 % and 290 % enhancement in electroluminescent and cathodoluminescent performance compared with reference nanorod LEDs. Furthermore, numerical simulation is performed to correlate the degree of LSP coupling effect concerning changes in particle size and inter-particle distance between the Ag NPs. Thus, the realization of self-assembled Ag NPs/nano-LEDs can prove the concept of the idea to enhance emission efficiency suitable for next-generation display technology. [ABSTRACT FROM AUTHOR]

Traditional methods of polymers joining for industrial applications are limited to lasers, induction, or conduction heating. It is difficult to achieve precision and efficiency in large-scale applications simultaneously. In this paper, we report a precise microwave welding method induced by localized surface plasmons of metallic macro-gaps under microwave excitation. The proposed method uses energy from well-developed commercial microwaves and benefits from the precision of localized surface plasmons, an oscillating electron cloud excited by electromagnetic waves, which is currently under investigation only at the micro or nanoscales. This method is employed in plastic microwave welding, and the numerical analyses and experimental results reveal that, in comparison to traditional microwave heating methods, this process effectively focuses microwave energy to achieve precision area heating of a diameter of 4 mm or less; this results in a temperature increase at a rate of 333.8 °C/s, and the maximum tensile strength of the welded samples reaches as high as 668 N, which is comparable to that of the base material. The results demonstrate that the processing method is an environmentally friendly approach characterized by high quality, efficiency, and low energy consumption. [Display omitted] • Develop a novel plasmon local field enhancement assisted microwave welding method. • Achieve focused microwave energy and precise polymer heating. • Welded samples exhibit excellent mechanical properties. • Method offers high quality, efficiency, cleanliness, and low consumption advantages. [ABSTRACT FROM AUTHOR]

Coupling between nanoplasmonics and semiconducting materials can enhance and complement the efficiency of almost all semiconductor technologies. It has been demonstrated that such composites enhance the light coupling to nanowires, increase photocurrent in detectors, enable sub‐gap detection, allow DNA detection, and produce large non‐linearity. Nevertheless, the tailored fabrication using the conventional methods to produce such composites remains a formidable challenge. This work attempts to resolve that deficiency by deploying the immersion‐plating method to spontaneously grown gold clusters inside nano‐porous silicon (np‐Si). This method allows the fabrication of thin films of np‐Si with embedded gold nanoparticles (Au) and creates nanoplasmonic–semiconductor composites, np‐Si/Au, with fractional volume between 0.02 and 0.13 of the metallic component. Optical scattering measurements reveal a distinctive, 200 nm broad, localized surface plasmon (LSP) resonance, centered around 700 nm. Linear and non‐linear properties, and their time evolution are investigated by optically pumping the LSP resonance and probing the optical response with short wavelength infra‐red (2.5 μm) light. The ultrafast time‐resolved study demonstrates unambiguously that the non‐linear response is not only directly related to the LSP excitation, but strongly enhanced with respect to bare np‐Si, while its strength can be tuned by varying the metallic component. [ABSTRACT FROM AUTHOR]

We report a novel type of electromagnetically induced transparency (EIT) analogue based on metamaterials (MMs) with hybrid structures, in which spiral and cut-wire structures serve as bright-mode resonators with the spoof electric localized surface plasmons and electric dipole resonance. With the simulations and experiments, the EIT analogue generated by the frequency detuning and hybridization between the resonators is verified. The simulated surface charge density and electric and magnetic field distributions, together with the theoretical analysis based on the Lorentz oscillator model, reveal the principle of the EIT analogue. Moreover, the transmission window of the MM demonstrates linear dependence on the refractive index’s change of surrounding media, showing the potential as a tool for environmental detection. [ABSTRACT FROM AUTHOR]

Grating structures of the same grating period and similar ridge widths and heights are fabricated at the air interface of highly Ga‐doped ZnO (GaZnO) thin films of different thicknesses for studying the different resonance behaviors of induced surface plasmon (SP) polariton and localized SP in the near‐IR range. The wavelengths of those SP resonance modes obtained via the reflection and transmission measurements from the air and substrate sides are compared for observing the effects of the GaZnO/substrate interface on the behaviors of the SP resonances induced around the grating structures. With the refractive index of the sapphire substrate around 1.75, the resonance wavelengths of the SP modes induced in a sample of a smaller GaZnO film thickness generally become longer. This variation trend can be clearly observed in the reflection measurement from the sapphire side. Therefore, the SP resonance wavelengths of a GaZnO grating structure can be controlled by the refractive index of the used substrate as long as the GaZnO layer is not too thick (roughly thin than 200 nm). [ABSTRACT FROM AUTHOR]

Using the finite-difference time-domain (FDTD) method, we designed an ultra-thin Ge/GaAs/P3HT:PCBM hybrid solar cell (HSC), which showed good effects of ultra-wideband (300 nm–1200 nm), high absorption, and a short-circuit current density of 44.7 mA/cm2. By changing the thickness of the active layer P3HT:PCBM, we analyzed the capture of electron-hole pairs. We also studied the effect of Al2O3 on the absorption performance of the cell. Through adding metal Al nanoparticles (Al-NPs) and then analyzing the figures of absorption and electric field intensity, we found that surface plasma is the main cause of solar cell absorption enhancement, and we explain the mechanism. The results show that the broadband absorption of the solar cell is high, and it plays a great role in capturing sunlight, which will be of great significance in the field of solar cell research.

Abstract In order to enhance the refractive index sensing performance of simple particle arrays, a structure, consisting of Au/SiO2 triangle arrays layers and reflection Au substrate, with increasing size and lengthening tips of triangles, is studied. The triangle arrays are modeled after an experimentally realizable “imprint” of microsphere lithography. Numerical calculation was carried out to study its optical properties and spectral sensitivity. The calculation results show that a large local enhancement of electric field (61 times) and simultaneously high absorption is due to combination of the resonance absorption of Au triangle disks, plasmonic couplings between the Au triangle disks and the Au film, and the high-density packing of triangle disks. The absorption peaks were not detuned when the gap between neighboring tips of the triangles varied from 10 to 50 nm. When the thickness of SiO2 layer increased from 10 to 50 nm, the absorption peak shifted to longer wavelengths and the amplitude rises quickly signaling the dominance of the gap mode resonance between the two Au layers. As the thickness of the top Au layer varies from 10 to 50 nm, the absorption peak is also red shifted and the peak amplitude increases. The full width at half maximum of the peaks for high absorption (> 90%) is about 5 nm. When fixing the gap, the thicknesses of Au/SiO2 triangle layer, and increasing the surrounding refractive index from 1.33 to 1.36, the absorption peaks shifted quickly, with a refractive index sensitivity and figure of merit as high as 660 nm per refractive index unit and 132, respectively. Such arrays can be easily fabricated by using microsphere array as projection masks and find application in refractive index monitoring of liquid and identification of gas and liquid phases.

Abstract Three kinds of typical structures, hemi-/spherical nanoparticles/nanoparticle dimers on the substrate and spherical nanoparticles/nanoparticle dimers half-buried into the substrate, are used for FDTD simulation to theoretically discuss the influence of the substrate to the localized surface plasmon (LSP) coupling when the metal nanoparticles/nanoparticle dimers are locating near a substrate. Simulated results show that the dependencies between the LSP coupling wavelength and the refractive index of the substrate for different structures are not the same, which can be attributed to the different polarization field distributions of LSPs. When light is incident from different directions, the LSP coupling strength are not the same as well and the ratios of the scattering peak intensities depend on the position of the metal nanoparticles or nanoparticle dimers. These phenomenon can be explained by the difference of the local driving electric field intensities which is modulated by the interface between the air and the substrate.

In this paper, we present a periodic nanostructure based on two types of silver plasmonic nanoantennas in order to enhance light absorption in graphene with a wavelength between 300 nm and 1800 nm. In this structure, a single graphene layer is located between two hexagonal boron nitride (hBN) layers, where this set is sandwiched between two layers of SiO2. The first nanoantenna type is a trapezoid inside SiO2, adjacent to the lower hBN, which focuses light within the graphene layer by intensifying the localized surface plasmons, triggering a significant increase in the absorption of the solar spectrum by graphene. The extent of this increase changes with varying bases of the trapezoid. The second nanoantenna type is in the same structure and contains two unequal trapezoids adjacent to each other. By adjusting the bases of these trapezoids, a relatively uniform broadband absorption spectrum is achieved which significantly enhances light absorption in the solar spectrum within 300–1800 nm, as compared to the first nanoantenna type. Both the first and second types of nanoantenna provide appropriate absorption at a communication window of 1550 nm as well as at 850 nm and 1300 nm, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we numerically investigated the emission characteristics of surface plasmon (SP)-enhanced deep ultraviolet light emitting diode (DUV-LED) by employing Al/Al2O3 core-shell nanoparticle(NP) structure on the p-GaN contact layer by utilizing finite-difference time-domain (FDTD) method. The results suggest that normalized dipole power of TE (TM) polarization is enhanced (inhibited) in the DUV range by coupling with in-plane substrate localized surface plasmon (LSP) mode from Al/Al2O3 core-shell nanoparticle (NP). It is found that normalized upward extraction power for both polarizations can also be significantly increased by scattering effect when photons and excitons coupling with in-plane air LSP mode induced on the NP; thus, the light extraction efficiency (LEE) can be substantially enhanced. The depth d between quantum well (QW) and NP and NP size have a remarkable influence on LSP resonance wavelength. Through careful regulation of NP size and depth d, the emission characteristics in DUV range (240–280 nm) exhibit a considerable amelioration. [ABSTRACT FROM AUTHOR]

Plasmonic photocatalysis represents the synergetic union of two active fields of research: plasmonic effects in illuminated metallic nanoparticles and catalytic effects in tailored metallic nanoparticles. Traditionally, metallic nanoparticles that excel for one application are limited for the other, but recent developments have shown that desirable catalytic behaviors, such as reduced activation barriers and improved product selectivity, derive from nonthermal behaviors uniquely produced by this synergy. After examining such findings, this review will address a specific debate that has recently surfaced: what is the relative degree of contributions of thermal and nonthermal effects in plasmonic photocatalysis? We demonstrate the importance of correctly accounting for thermal effects before characterizing nonthermal contributions. We show that another synergy occurs: these desirable nonthermal behaviors have a temperature dependence, and the resulting temperature-dependent reaction rates far exceed what can be explained from purely thermal effects alone. Thus, the synergy of plasmonic photocatalysis offers an exciting new contribution to the quest for efficient, selective, sustainable methods for chemical synthesis and energy conversion. [ABSTRACT FROM AUTHOR]

In this paper, we propose an ultra-broadband multi-slot cross bowtie (MSCB) nanoantenna for light absorption, whose elements compose of dual rectangles and cross bowtie and rectangular slots. The optical characteristics are analysis numerically by the three-dimensional finite-difference time-domain (FDTD) method. The results show that the average absorptivity of the nanostructure is over 90% in 400–1800-nm waveband, which covered the visible and near-infrared region. We attribute the better absorption property of the nanoantenna to the combining of plasmon coupling effects between slots, high-order modes, and surface plasmon resonance. Our work provides a promising method for the future developments of more advanced absorber for energy harvesting, thermoelectrics, and imaging. [ABSTRACT FROM AUTHOR]

Absorption enhancement based on interaction between the localized surface plasmon (LSP) and molecular exciton is one of the most important phenomena for the development of high-performance solar devices. In this study, hybrids of plasmonic metal nanoparticles and dye molecules have been developed, which exhibit enhanced absorption at precisely tuned wavelengths in a visible region. The hybrids consist of a porphyrin derivative, which has four absorption peaks (Q-bands) in a range of 500–700 nm, and triangular silver nanoprisms (AgPRs), which are developed by us to exhibit precisely tuned LSP resonance wavelengths. Absorption enhancement over the whole Q-band range is induced by the combined use of three kinds of AgPRs of different aspect ratios. Furthermore, the quantitative evaluation of absorption enhancement based on the LSP-based fluorescence enhancement phenomenon has demonstrated that efficient absorption enhancement can be effected at multiple wavelengths. [ABSTRACT FROM AUTHOR]

Plasmonic nanofluids has been reported beneficial for enhancing absorption of the solar energy in a direct-absorption solar collector (DASC). In order to overcome the shortage of narrow absorption band associated with the localized surface plasmon, two strategies can be adopted. One is to blend nanoparticles with different absorption peaks, and the other is to develop nanoparticles capable of exhibiting multiple absorption peaks at different wavelengths. In this study, the latter strategy is explored systematically by investigating the absorption efficiency of metallic nanoparticles with sharp edges. The results show that the Ag nanoparticles with sharp edges can induce multiple absorption peaks due to both localized surface plasmon resonance and lightning rod effect. We also show that the sharper edges (i.e., with either smaller radius of curvature or smaller edge angle) can greatly enhance the lightning rod effect. In addition, the study of SiO 2 -core/Ag-shell suggests that the core/shell configuration is beneficial for further broadening the absorption band compared to the Ag nanoparticle. Further investigation shows that the solar-weighted absorption coefficient of a DASC using the four-edge nanoparticle is 35% and 20% point higher than the nanosphere and the nanorod respectively with a fixed volume fraction of 10 − 6 . • Ag nanoparticles with sharp edges can generate multiple absorption peaks. • Multiple peaks are due to the localized surface plasmon and the lightning rod effect. • More edges do not necessarily result in broader absorption. • Core/shell nanoparticles exhibit broader absorption band than the Ag nanoparticles. • Performance of a DASC with edged particles is much higher than smooth particles. [ABSTRACT FROM AUTHOR]

Most graphene electro-optic modulators based on the electro-refractive modulation are composed of Mach-Zehnder interferometer or microring resonator structures and have a relative compact size comparing with dielectric ones. To further shrink the footprint, we use the localized surface plasmon resonance of a chain of three metal disks to realize a submicron graphene modulator, whose length can be reduced to less than 1 μm. The proposed graphene modulator has an extinction ratio of 5.5 dB with a length of only 740 nm. And the insertion loss, 3-dB bandwidth, and power consumption of the modulator are 1.9 dB, 83.4 GHz, and 8.55 fJ/bit respectively. [ABSTRACT FROM AUTHOR]

A new colorimetric method that can be used to rapidly detect toxic ricin is demonstrated. Lactosylated cysteine-functionalized gold nanoparticles (Au@LACY NPs) were prepared by a one-pot reaction and employed as optical probes for determination of ricin B chain. It is found that the Au@LACY NPs undergo aggregation in the presence of ricin B chain. This leads to surface plasmon coupling effects of the particles and a color change from red to blue, with absorption maxima at 519 and 670 nm, respectively. The feasibility of using the current approach for quantitative analysis of ricin B chain is also demonstrated. The calibration plot is generated by plotting the ratio of the absorbance at the wavelength of 634 to 518 nm versus the concentration of the ricin B chain. The spectrophotometric method has a ~29 pM (~ 0.91 ng·mL−1) detection limit, and the sample with the concentration of ~ 400 pM (~ 13 ng·mL−1) can be detected visually. [ABSTRACT FROM AUTHOR]

We have designed a metal-dielectric-metal (MDM) nanoantenna array that can support both localized surface plasmon (LSP) modes and magnetic plasmon polariton (MPP) modes. Due to the differences in environmental response among the modes, the array achieves a wide refractive index detection within range of 1.00–1.60. Its sensitivity reaches 522.76 nm/RIU. In addition, we also proposed a universal computing model for sensing under certain disturbances, indicating that the excessive emphasis on the stability of reference signal is unnecessary in self-reference sensing. Benefiting from the quasi-invariant property of magnetic plasmon resonance, the chip has been verified to maintain a significant detection accuracy even under certain perturbations. This work has potential applications in environmental sensing with integrated optics, as well as in the fields of biomedical research and diagnosis. • In this work, a metasurface achieves refractive index detection within a wide range is proposed. • MPP has been introduced to improve sensing stability. • Self-referencing sensing is implemented and optimized. [ABSTRACT FROM AUTHOR]

• Quantum tunneling effect reduces PERS intensity at separation distance below 0.4 nm. • Nonlocal dielectric response can further quench fluorescence intensity at the narrowing gap. • Raman and fluorescence enhancement factors reach at 13 and 6 orders of magnitude by optimizing the system. We investigate the influence of quantum tunneling on the plasmon-enhanced electric field and photoluminescence spectroscopy in the subnanometer nanogap between two adjacent Ag nanoparticles using the quantum-corrected method. We analyze the contribution of nonlocal dielectric response at different separation distances to plasmon-enhanced fluorescence using the D-parameters method. Our results demonstrate the high sensitivity of the quantum-induced effect and nonlocal dielectric response to the separation distance. In cases of shorter separation distances, the localized fields start to decrease due to tunneling current short circuit, resulting in a substantial reduction in Raman enhancement. Additionally, the lower quantum yield caused by loss of electron-hole pairs further quenches the fluorescence intensity in the narrowing gaps. We achieve calculated Raman and fluorescence enhancement factors of 13 and 6 orders of magnitude. Under excitation wavelengths of 660 nm, we achieve spatial resolutions of 1.5 nm and 2.2 nm for Raman and fluorescence spectroscopy. [ABSTRACT FROM AUTHOR]

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.

Metallic nanowires have been utilized as a platform for propagating surface plasmon (SPs) fields. To be exploited for applications such as plasmonic circuits, manipulation of localized field propagating pattern is also important. In this study, we calculated the field distributions of localized surface plasmons (LSPs) on the specifically shaped nanostructures and explored the feasibility of manipulating LSP fields. Specifically, plasmonic fields were calculated at different wavelengths for a nanoscale rod array (I-shaped), an array connected with two nanoscale rods at right angles (T-shaped), and an array with three nanoscale rods at 120° to each other (Y-shaped). Three different types of nanostructures are suggested to manipulate the positions of LSP fields collaborating with adjustment of wavelength, polarization, and incident orientation of light source. The results of this study are important not only for the understanding of the wavelength-dependent surface plasmon field localization mechanism but also for the applicability of swept source-based plasmonic techniques or designing a plasmonic circuit.

We demonstrate the enhancement of fluorescence emitted from dye molecules coupled with two surface plasmons, i.e., silver nanoparticles (AgNPs)-induced localized surface plasmons (LSP) and thin silver (Ag) film supported surface plasmons. Excitation light is illuminated to a SiO2 layer that contains both rhodamine 110 molecules and AgNPs. AgNPs enhances excitation rates of dye molecules in their close proximity due to LSP-induced enhancement of local electromagnetic fields at dye excitation wavelengths. Moreover, the SiO2 layer on one surface of which a 50 nm-thick Ag film is coated for metal cladding (air on the other surface), acts as a waveguide core at the dye emission wavelengths. The Ag film induces the surface plasmons which couple with the waveguide modes, resulting in a waveguide-modulated version of surface plasmon coupled emission (SPCE) for different SiO2 thicknesses in a reverse Kretschmann configuration. We find that varying the SiO2 thickness modulates the fluorescent signal of SPCE, its modulation behavior being in agreement with the theoretical simulation of thickness dependent properties of the coupled plasmon waveguide resonance. This enables optimization engineering of the waveguide structure for enhancement of fluorescent signals. The combination of LSP enhanced dye excitation and the waveguide-modulated version of SPCE may offer chances of enhancing fluorescent signals for a highly sensitive fluorescent assay of biomedical and chemical substances.

Qingwen Zhang,1,2,* Lin Wu,3,* Ten It Wong,4 Jinling Zhang,5 Xiaohu Liu,5 Xiaodong Zhou,4 Ping Bai,3 Bo Liedberg,5 Yi Wang1,2,5 1School of Ophthalmology and Optometry, Eye Hospital, School of Biomedical Engineering, Wenzhou Medical University, 2Wenzhou Institute of Biomaterials and Engineering, Chinese Academy of Sciences, Wenzhou, People’s Republic of China; 3Electronics and Photonics Department, Institute of High Performance Computing, 4Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), 5Centre for Biomimetic Sensor Science, School of Materials Science and Engineering, Nanyang Technological University, Singapore *These authors contributed equally to this work Abstract: Localized surface plasmon (LSP) has been widely applied for the enhancement of fluorescence emission for biosensing owing to its potential for strong field enhancement. However, due to its small penetration depth, LSP offers limited fluorescence enhancement over a whole sensor chip and, therefore, insufficient sensitivity for the detection of biomolecules, especially large molecules. We demonstrate the simultaneous excitation of LSP and propagating surface plasmon (PSP) on an Au nanohole array under Kretschmann configuration for the detection of prostate-specific antigen with a sandwich immunoassay. The proposed method combines the advantages of high field enhancement by LSP and large surface area probed by PSP field. The simulated results indicated that a maximum enhancement of electric field intensity up to 1,600 times can be achieved under the simultaneous excitation of LSP and PSP modes. The sandwich assay of PSA carried out on gold nanohole array substrate showed a limit of detection of 140 fM supporting coexcitation of LSP and PSP modes. The limit of detection was approximately sevenfold lower than that when only LSP was resonantly excited on the same substrate. The results of this study demonstrate high fluorescence enhancement through the coexcitation of LSP and PSP modes and pave a way for its implementation as a highly sensitive bioassay. Keywords: gold nanohole array, localized surface plasmon, propagating surface plasmon, fluorescence enhancement, prostate-specific antigen

High spectra response of metal-semiconductor-metal (MSM) ultraviolet photodetectors (UV PDs) based on GaN epitaxial wafers with different diameters of Al nanodots on the surface were realized on free-standing GaN substrates. The UV PDs exhibit low dark current and high spectral response both at room temperature and 150 °C, demonstrating the thermal stability of the fabricated devices. The peak responsivities for the PDs with Al nanodot diameters of 60, 80, and 120 nm are 1.079, 2.420, and 3.096 A/W, showing an enhancement ratio of 32%, 196%, and 280%, respectively, compared to the referential PD without Al nanodots. Numerical investigations reveal that the significant enhancement performance is due to the localized surface plasmon effect, which enhances the localized electric field and produces more electron-hole pairs in the optoelectronic devices, leading to a higher responsivity. The results presented in this paper can promote the development and application for high performance GaN UV PDs.

Motivated by the recent progress in the nanofabrication field and the increasing demand for cost-effective, portable, and easy-to-use point-of-care platforms, localized surface plasmon resonance (LSPR) biosensors have been subjected to a great scientific interest in the last few years. The progress observed in the research of this nanoplasmonic technology is remarkable not only from a nanostructure fabrication point of view but also in the complete development and integration of operative devices and their application. The potential benefits that LSPR biosensors can offer, such as sensor miniaturization, multiplexing opportunities, and enhanced performances, have quickly positioned them as an interesting candidate in the design of lab-on-a-chip (LOC) optical biosensor platforms. This review covers specifically the most significant achievements that occurred in recent years towards the integration of this technology in compact devices, with views of obtaining LOC devices. We also discuss the most relevant examples of the use of the nanoplasmonic biosensors for real bioanalytical and clinical applications from assay development and validation to the identification of the implications, requirements, and challenges to be surpassed to achieve fully operative devices.

Ultracompact chiral plasmonic nanostructures with unique chiral light-matter interactions are vital for future photonic technologies. However, previous studies are limited to reporting their steady-state performance, presenting a fundamental obstacle to the development of high-speed optical devices with polarization sensitivity. Here, a comprehensive analysis of ultrafast chiroptical response of chiral gold nano-oligomers using time-resolved polarimetric measurements is provided. Significant differences are observed in terms of the absorption intensity, thus hot electron generation, and hot carrier decay time upon polarized photopumping, which are explained by a phenomenological model of the helicity-resolved optical transitions. Moreover, the chiroptical signal is switchable by reversing the direction of the pump pulse, demonstrating the versatile modulation of polarization selection in a single device. The results offer fundamental insights into the helicity-resolved optical transitions in photoexcited chiral plasmonics and can facilitate the development of high-speed polarization-sensitive flat optics with potential applications in nanophotonics and quantum optics., (© 2023 Wiley-VCH GmbH.)

Optical nanoantennas possess broad applications in the fields of photodetection, environmental science, biosensing and nonlinear optics, owing to their remarkable ability to enhance and confine the optical field at the nanoscale. In this article, we present a theoretical investigation of surface-enhanced photoluminescence spectroscopy for single molecules confined within novel Au bowtie nanoantenna, covering a wavelength range from the visible to near-infrared spectral regions. We employ the finite element method to quantitatively study the optical enhancement properties of the plasmonic field, quantum yield, Raman scattering and fluorescence. Additionally, we systematically examine the contribution of nonlocal dielectric response in the gap mode to the quantum yield, aiming to gain a better understanding of the fluorescence enhancement mechanism. Our results demonstrate that altering the configuration of the nanoantenna has a significant impact on plasmonic sensitivity. The nonlocal dielectric response plays a crucial role in reducing the quantum yield and corresponding fluorescence intensity when the gap distance is less than 3 nm. However, a substantial excitation field can effectively overcome fluorescence quenching and enhance the fluorescence intensity. By optimizing nanoantenna configuration, the maximum enhancement of surface-enhanced Raman can be turned to 9 and 10 magnitude orders in the visible and near-infrared regions, and 3 and 4 magnitude orders for fluorescence enhancement, respectively. The maximum spatial resolutions of 0.8 nm and 1.5 nm for Raman and fluorescence are also achieved, respectively. Our calculated results not only provide theoretical guidance for the design and application of new nanoantennas, but also contribute to expanding the range of surface-enhanced Raman and fluorescence technology from the visible to the near-infrared region., (© 2024 IOP Publishing Ltd.)

As a promising way to reduce the temperature for conventional thermolysis, plasmon-induced photocatalysis has been utilized for the dehydrogenation of methane. Here we probe the microscopic dynamic mechanism for plasmon-induced methane dissociation over a tetrahedral Ag 20 nanoparticle with molecular orbital insights using time-dependent density functional theory. We ingeniously built the relationship between the chemical bonds and molecular orbitals via Hellmann-Feynman forces. The time- and energy-resolved photocarrier analysis shows that the indirect hot hole transfer from the Ag nanoparticle to methane dominates the photoreaction at low laser intensity, due to the strong hybridization of the Ag nanoparticle and CH 4 orbitals, while indirect and direct charge transfer coexist to facilitate methane dissociation in intense laser fields. Our findings can be used to design novel methane photocatalysts and highlight the broad prospects of the molecular orbital approach for adsorbate-substrate systems.