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In this paper, a metal–insulator–metal (MIM) array nanostructure consisting of a bowtie aperture and cylindrical holes is proposed as a field amplifier. This hybrid array consists of a grating film made of gold in which some cylindrical holes are replaced with a bowtie aperture, sapphire substrate, and finally a metal film. The array of cylindrical holes acting as a two-dimensional grating can effectively excite propagating surface plasmon polariton modes along a metal film, but the electric field enhancement inside it is relatively weak. On the other hand, the bowtie aperture, with its sharp corners and small gap, can provide a greater intensity enhancement factor within its gap. The combination of these two MIM nanostructures forms a strong coupling between the propagating and localized surface plasmons, leading to an improvement in field confinement in the bowtie aperture in the sub-diffraction limit and its magnitude increase of 115 times. This effective enhancement can be used in plasmonic sensors, lasers, SERS, etc., applications. [ABSTRACT FROM AUTHOR]

Plasmon-driven photocatalysis offers a unique means of leveraging nanoscale light–matter interactions to convert photon energy into chemical energy in a chemoselective and regioselective manner under mild reaction conditions. Plasmon-driven bond cleavage in molecular adsorbates represents a critical step in virtually all plasmon-mediated photocatalytic reactions and has been identified as the rate-determining step in many cases. This review article summarizes critical insights concerning plasmon-triggered bond-cleaving mechanisms gained through combined experimental and computational efforts over the past decade or so, elaborating on how the plasmon-derived physiochemical effects, metal–adsorbate interactions, and local chemical environments profoundly influence chemoselective bond-cleaving processes in a diverse set of molecular adsorbates ranging from small diatomic molecules to aliphatic and aromatic organic compounds. As demonstrated by several noteworthy examples, insights gained from fundamental mechanistic studies lay a critical knowledge foundation guiding rational design of nanoparticle–adsorbate systems with desired plasmonic molecule-scissoring functions for targeted applications, such as controlled release of molecular cargos, surface coating of solid-state materials, and selective bond activation for polymerization reactions. [ABSTRACT FROM AUTHOR]

Plasmonic nanostructures stand at the forefront of nanophotonics research, particularly in sensing and energy conversion applications. Their unique ability to confine light energy at the nanoscale makes them indispensable for a wide array of technological advancements. The study of these structures often makes use of different materials and, even more extensively, explores new shapes and configurations to extend our common repertoire of useful nanophotonics tools. Exploring the creation of bimetallic plasmonic nanostructures combines these two dimensions determining the space of possible plasmonic resonators and opens the possibility of tailoring systems with behavior unavailable to single-metal plasmonic structures. In this paper, we delve into the exploration of bimetallic systems employing plasmonic nanostars. These structures have demonstrated remarkable capabilities for surface-enhanced Raman scattering (SERS) spectroscopy and photochemistry, due to the strong plasmonic response of their peaks, whose disposition following a spherical symmetry makes them largely polarization- and orientation-insensitive. Herein, we report the colloidal synthesis of two different water-stable Au@Ag nanostars, explore their performance as photocatalysts and SERS substrates, and provide an in-depth account of their non-trivial physical response. [ABSTRACT FROM AUTHOR]

Using electrodynamical description of the average power absorbed by a conducting film, we present an expression for the electric-field intensity enhancement (FIE) due to epsilon-near-zero (ENZ) polariton modes. We show that FIE reaches a limit in ultrathin ENZ films inverse of second power of ENZ losses. This is illustrated in an exemplary series of aluminum-doped zinc oxide nanolayers grown by atomic layer deposition. Only in a case of unrealistic lossless ENZ films, FIE follows the inverse second power of film thickness predicted by S. Campione, et al. [Phys. Rev. B, vol. 91, no. 12, art. 121408, 2015]. We also predict that FIE could reach values of 100,000 in ultrathin polar semiconductor films. This work is important for establishing the limits of plasmonic field enhancement and the development of near zero refractive index photonics, nonlinear optics, thermal, and quantum optics in the ENZ regime.

The confinement of electrons in gold nanoparticles results in Surface Plasmon Resonance (SPR), which is characterized by electric field enhancement in the vicinity of these nanoparticles. This property has been extensively studied and applied in various fields. In our research, we conduct a detailed investigation of plasmonic coupling in spherical gold nanoparticles. Specifically, we use the Discrete Dipole Approximation (DDA) method implemented in DDSCAT to simulate the coupling of electric fields in a doublet of nanoparticles as a function of the distance between them. Our simulations show that the coupling of SPR between two nanoparticles occurs up to a separation of 12 nm. Moreover, we extend our simulations to study the coupling of nanoparticles in linear chains consisting of up to five nanoparticles and in clustered forms. Our results indicate that the SPR coupling in a linear chain occurs, and as the number of nanoparticles increases, the field enhancement also increases. However, we observe that this effect saturates after four nanoparticles in a line. Our study provides insights into the plasmonic coupling in gold nanoparticles, which can aid in the design and optimization of plasmonic devices for various applications.

Plasmonic nanoparticles have been intensely used in research because they possess powerful optical properties. Gold nanorods (Au NRs), in particular, feature the interesting ability to absorb and scatter light in the near-infrared region through their longitudinal localized surface plasmon resonance. This property is particularly interesting in biology because these wavelengths are associated with maximum tissue penetration. The interplay between plasmonic nanoparticles and fluorophores has also triggered exciting research. Specifically, illuminating the Au NRs produces an enhanced electromagnetic field in the vicinity of the particles. This allows nearby fluorophores to feature enhanced optical properties through a phenomenon known as surface-enhanced fluorescence. This effect, however, must be counterbalanced by potential quenching that can happen from the Au NRs to the fluorophore. Systems have been developed whereby a spacer layer insulates the Au NR from the fluorophore. Multiple studies have explored different materials to use as the spacer layer such as silica or polyelectrolyte multilayers. Many of these studies have also investigated the optimal spacer thickness for achieving maximum enhancement. This review summarizes and provides an outlook on important developments in this field that have been reported in the last 10 years. [ABSTRACT FROM AUTHOR]

In this paper, an analytical approach has been developed for electromagnetic field enhancement in fractal nanostructure under the quasi-static limit. A metallic fractal embedded in an unbounded, isotropic, and lossless chiral medium has been treated under this approach. In addition, the field enhancement is also noted by imposing surface plasmon resonance condition. To achieve the desired objective, Maxwell divergence equations are considered and written in an appropriate form by mean of fractional calculus. [ABSTRACT FROM AUTHOR]

The paper considers the problem of choosing the composition, structure, and size of spherical catalyst nanoparticles for carrying out plasmon-induced polymerization reactions. The concept of reducing the activation energy of the reaction in the presence of a catalyst and, accordingly, increasing the rate of a chemical reaction during heating due to the excitation of surface plasmon resonance is presented. Using the Drude model for the dielectric function, relationships were obtained for the frequency dependences of such characteristics as the real and imaginary parts of the polarizability, heating and the rate of chemical reactions when monometallic and bimetallic nanoparticles are used as catalysts, as well as the amplification of fields in their vicinity. The concepts developed in this work take into account the classical size dependence of the effective electron relaxation rate in monometallic and bimetallic nanoparticles under the assumption of diffuse scattering of electrons. Changes in the positions of the maxima of the imaginary part of the polarizability, heating, and reaction rate are analyzed with a change in the radii of monometallic and bimetallic nanoparticles. It is shown that the maxima of the dependences under study correspond to dipole surface plasmon resonances, and their number depends on the particle morphology. Changes in the amplification of electric fields in the vicinity of nanoparticles of different morphology have been studied. It has been found that the enhancement of the fields in all considered cases is maximum on the surface of the nanoparticle and decreases with distance from it. Practical recommendations are formulated regarding the size, composition and structure of nanoparticles for plasmon catalysis, which provide the highest rates of chemical reactions. Thus, all obtained frequency dependences have one maximum for monometallic and two maxima for bimetallic nanoparticles. [ABSTRACT FROM AUTHOR]

The confinement of electrons in gold nanoparticles results in Surface Plasmon Resonance (SPR), which is characterized by electric field enhancement in the vicinity of these nanoparticles. This property has been extensively studied and applied in various fields. In our research, we conduct a detailed investigation of plasmonic coupling in spherical gold nanoparticles. Specifically, we use the Discrete Dipole Approximation (DDA) method implemented in DDSCAT to simulate the coupling of electric fields in a doublet of nanoparticles as a function of the distance between them. Our simulations show that the coupling of SPR between two nanoparticles occurs up to a separation of 12 nm. Moreover, we extend our simulations to study the coupling of nanoparticles in linear chains consisting of up to five nanoparticles and in clustered forms. Our results indicate that the SPR coupling in a linear chain occurs, and as the number of nanoparticles increases, the field enhancement also increases. However, we observe that this effect saturates after four nanoparticles in a line. Our study provides insights into the plasmonic coupling in gold nanoparticles, which can aid in the design and optimization of plasmonic devices for various applications. [ABSTRACT FROM AUTHOR]

Researchers have paid great attention to pursuing metal‐free nanostructures as alternatives to metallic counterparts in the field of surface‐enhanced Raman scattering (SERS) for label‐free sensing. However, these metal‐free investigations are hindered by the tiny enhancement factor of the local near field. Here, the design of all‐dielectric SERS metasurfaces is proposed with quasi‐bound states in the continuum (Q‐BIC), inspired by transformer‐based deep learning. By manipulating the incident angle, the mechanism of strong coupling Q‐BIC is introduced with a large Rabi splitting of ≈105 meV, which opens a bandgap and forms an anti‐crossing behavior. Compared to conventional approaches, the strong coupling Q‐BIC scheme not only boosts an extraordinary SERS enhancement factor of ≈107 but also extends the field‐enhancing scale up to ten‐fold. The theoretical optimization implies overwhelming dominance versus the conventional metallic nanostructure design for SERS. The study denotes an approach to utilize the strong coupling effects of Q‐BIC in all‐dielectric SERS metasurfaces and will provide essential design guides for more powerful sensing applications based on SERS. [ABSTRACT FROM AUTHOR]

Resonant optical antennas (ROAs) are nanodevices that can enhance the electromagnetic field in their vicinity and scatter the light in the far field. The enhanced field is localized in subdiffraction-limited volume. Their ability to exhibit strong field enhancement in the gap makes them suitable for coupling with quantum emitters. This paper introduced two novel bimodal and triple-modal asymmetric cross-shaped optical nanoantenna designs. The performance of the reported nanoantennas is numerically studied via the finite element method (FEM). The electric field enhancements and optical cross-sections are calculated to characterize the performance of the designs. These nanoantennas are low-symmetry and polarization-sensitive devices. Furthermore, the reported plasmonic nanostructures exhibit two or three tunable resonances in the optical and near-infrared wavelength regions with ultra-high field enhancement. The reported coupled cross-shaped exhibits a field enhancement of 45.9 for the high-energy resonance and 149.4 for the low-energy resonance, respectively, on E TOT / E IN scale. [ABSTRACT FROM AUTHOR]

A giant electric field on a subwavelength scale is highly beneficial for boosting the light–matter interaction. In this paper, we investigated a hybrid structure consisting of a hemispheric dimer array and a gold film and realized resonant mode coupling of the surface lattice resonance (SLR) and surface plasmon polariton (SPP). Mode coupling is demonstrated by observing anti-crossing in reflection spectra, which corresponds to Rabi splitting. Although the resonance coupling does not enter the strong coupling regime, an improved quality factor (Q~350) and stronger electric field enhancement in the gap region of the dimer (i.e., hot spot) in our hybrid structure are obtained compared to those of the single dimer or dimer array only. Remarkably, the magnitude of electric field enhancement over 500 can be accessible. Such high field enhancement makes our hybridized structure a versatile platform for the realization of ultra-sensitive biosensing, low-threshold nanolasing, low-power nonlinear optical devices, etc. [ABSTRACT FROM AUTHOR]

Frequency‐modulated (FM) combs feature flat intensity spectra with a linear frequency chirp, useful for metrology and sensing applications. Generating FM combs in semiconductor lasers generally requires a fast saturable gain, usually limited by the intrinsic gain medium properties. Here, it is shown how a spatial modulation of the laser gain medium can enhance the gain saturation dynamics and nonlinearities to generate self‐starting FM combs. This is demonstrated with tapered planarized terahertz (THz) quantum cascade lasers (QCLs). While simple ridge THz QCLs typically generate combs presenting a mixture of amplitude and frequency modulation, the on‐chip field enhancement resulting from extreme spatial confinement leads to an ultrafast saturable gain regime, generating a pure FM comb with a flatter intensity spectrum and a clear linear frequency chirp. The observed linear frequency chirp is reproduced using a spatially inhomogeneous mean‐field theory model, which confirms the crucial role of field enhancement. In addition, the modified spatial temperature distribution within the waveguide results in an improved high‐temperature comb operation, up to a heat sink temperature of 115 K, with comb bandwidths of 600 GHz at 90 K. The spatial inhomogeneity leads as well to very intense radio frequency (RF) beatnotes up to ‐30 dBm and facilitates dynamic switching between various harmonic states in the same device. [ABSTRACT FROM AUTHOR]

In this paper, we present the theoretical modeling of gold nanostar for localized surface plasmon resonance-based sensor application and SERS over red to NIR region. Au nanostars exhibiting LSPR peak over 1400 nm were considered in isolated and multimer configuration. The refractive index sensitivity for all configurations was measured, and nanostars exhibit the RIS factor up to 1175 nm/RIU. The effect of interacting nanostars on LSPR and field enhancement was studied by considering multimer configuration forming quadrumer, rhombus, crown, and closed loop nanostructure. The quadrumer, rhombus, and crown pattern points exhibit the highest near-field intensity. In general, the near-field energy localization and plasmon resonance wavelengths of the structure can be considerably influenced by the configuration of nanostars. [ABSTRACT FROM AUTHOR]

Nanoslits have various applications, including localized surface plasmon resonance (LSPR)-based nanodevices, optical biosensors, superfocusing, high-efficiency refractive index sensors and chip-based protein detection. In this study, the effect of substrates on the optical properties of gold nanoslits placed in free space is discussed; for this purpose, glass BK7 and Al 2 O 3 are used as substrates and the wavelength of incident light is supposed to be 650 nm. The optical properties, power flow and electric field enhancement for gold nanoslits are investigated by using the finite element method (FEM) in COMSOL Multiphysics software. The effect of polarization of an incident electromagnetic wave as it propagates from a gold nanoslit is also analyzed. As special case, the effect of glass and alumina substrate on magnetic field, power flow and electric field enhancement is discussed. The goal of this research is to investigate the phenomenon of power flow and electric field enhancement. The study of power flow in gold nanoslits provides valuable insights into the behavior of light at the nanoscale and offers opportunities for developing novel applications in the field of nanophotonics and plasmonics. The consequences of this study show the significance of gold nanoslits as optical nanosensors. [ABSTRACT FROM AUTHOR]

Harvesting low grade hydrodynamic energy is attracting growing interest. Droplet generators have recently emerged as promising harvesting devices. However, toward practical utilization, their power density and energy conversion efficiency still warrant further improvement. In addition, the performance of droplet generators typically degrades when in contact with ambient water, significantly limiting their applications considering that they, by definition, are constantly exposed to water. This work reports a field‐enhanced droplet electricity generator (FE‐DEG) that significantly address these challenges. Using the field effect induced by a bias voltage to store high volumetric charge in the dielectric layer, the amount of charge that transfers during droplet impinging is significantly increased, which simultaneously improves the instantaneous power density and energy conversion efficiency. In addition, the performance of the generator can be reliably set by the external bias and remains stable after repeated immersion in bulk water, and even in some harsh chemical conditions. It is expected that this work may also inspire other robust energy harvesting devices. [ABSTRACT FROM AUTHOR]

L-shaped resonant optical antennas (ROAs) are low-symmetry plasmonic nanostructures with the unique ability to show two tunable resonances in the optical and near-infrared wavelength regions. The plasmon length of the so-called longitudinal dipolar fundamental plasmon mode of these asymmetric L-shaped ROAs can be used as plasmon resonance building blocks to design polarization-sensitive devices. This paper introduces and numerically analyzes a novel design of asymmetric L-shape ROAs. The reported design offers two resonance modes, i.e., bimodal longitudinal antenna resonance behavior with a high enhancement factor. These two resonances can be selectively excited by changing the linear polarization angle. It is found that the coupled L-shaped ROA with a very small 2 nm gap width exhibits field enhancements 40 and 147.3 on scale E TOT / E IN for the high energy and low energy resonance, respectively. The obtained results and the analysis open a new route for multiple plasmon resonance devices with ultra-high field enhancement that can be easily integrated with future nano-optical circuits with multiple operational frequencies. [ABSTRACT FROM AUTHOR]

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Abstract Plasmonic effects that enhance electric fields and amplify optical signals are crucial for improving the resolution of optical imaging systems. In this paper, a metal-based plasmonic nanostructure (MPN) is designed to increase the resolution of an optical imaging system by amplifying a specific signal while producing a plasmonic effect via a dipole nanoantenna (DN) and grating nanostructure (GN), which couple the electric field to be focused at the center of the unit cell. We confirmed that the MPN enhances electric fields 15 times more than the DN and GN, enabling the acquisition of finely resolved optical signals. The experiments confirmed that compared with the initial laser intensity, the MPN, which was fabricated by nanoimprint lithography, enhanced the optical signal of the laser by 2.24 times. Moreover, when the MPN was applied in two optical imaging systems, an indistinguishable signal that was similar to noise in original was distinguished by amplifying the optical signal as 106 times in functional near-infrared spectroscopy(fNIRS), and a specific wavelength was enhanced in fluorescence image. Thus, the incorporation of this nanostructure increased the utility of the collected data and could enhance optical signals in optics, bioimaging, and biology applications.

This paper presents a new bi-rhombic aperture arrays structure (BAAs) that exhibits high transmission and extraordinary field enhancement. Through numerical simulation and theoretical analysis, the surface plasmon resonance mode and a quasi-FP resonance mode within the structure are approved to enhance the optical transmittance effectively. The transmission spectrum and the charge distribution of the resonance mode shows that the gap size and the bi-rhombic aperture short axis have a significant effect on shiftting of the spectrum without damping the transmission peak of the wave, enabling the achievement of both high transmission and high field enhancement. The optimized structure achieved a transmittance of 85% and a maximum enhancement factor of 18000. Besides that, an ultra-wide spectrum transmission in the near to mid-infrared was attained by adjusting the aperture structure. At wavelengths larger than mid-infrared, the transmittance can avoid damping, and the adjusted device is primarily sensitive to the lattice constant in one- direction. These results suggest that the proposed BAAs has significant potential for various applications in nanophononics, infrared sensing, and biomedical imaging.

Moving the polarization of the incident wave along a meridian of the Poincaré sphere, experimentally we show that the coupling with the fundamental Bloch's surface waves of the mode, provide a spatially coherent, macroscopic spinmomentum locked propagation along the symmetry axes of the PhCM. This novel mechanism of light-spin manipulation enables a versatile implementation of spin-optical structures that may pave the way to novel strategies for light spin technology and photonic multiplatform implementations.

Transition metal dichalcogenides (TMD) heterostructure is widely applied for second harmonic generation (SHG) and holds great promises for laser source, nonlinear switch, and optical logic gate. However, for atomically thin TMD heterostructures, low SHG conversion efficiency would occur due to reduction of light—matter interaction length and lack of phase matching. Herein, we demonstrated a facile directional SHG amplifier formed by MoS2/WS2 monolayer heterostructures suspended on a holey SiO2/Si substrate. The SHG enhancement factor reaches more than two orders of magnitude in a wide spectral range from 355 to 470 nm, and the radiation angle is reduced from 38° to 19° indicating higher coherence and better emission directionality. The giant SHG enhancement and directional emission are attributed to the great excitation and emission field concentration induced by a self-formed vertical Fabry—Pérot microcavity. Our discovery gives helpful insights for the development of two-dimensional (2D) nonlinear optical devices. [ABSTRACT FROM AUTHOR]

The ever-growing demand for sensitive and reliable detection of hazardous material in the food chain and trace detection of chemical entities in a variety of field attracted advanced Surface Enhanced Raman Spectroscopy (SERS) active materials such as graphene-based hybrid SERS. The graphene silver nanostructures (AgNS) based hybrid SERS substrates are explored to understand the critical role of pristine graphene grown by chemical vapor deposition (CVD) on SERS signal and its possible mechanism. A lithography-free fabrication process has been developed for growth of uniform array of AgNS with varying both particle sizes and inter-particle gaps. The optimal AgNS with average feature size ∼40 nm and average inter-particle spacing of ∼13 nm demonstrated the maximum SERS enhancement with rhodamine 6G (R6G). The single-layer graphene (SLG) grown by CVD with the aid of controlling the reaction geometry with growth under a free molecular regime leads to the highest quality graphene with I 2D /I G ratio of ∼3.58 and I D /I G ratio of ∼0.154. The flow regime-controlled CVD-grown SLG integrated with AgNS and its SERS enhancement mechanism is explored for trace detection of R6G. The graphene with its ability to modulate the electronic structure and tune it relative to the highest occupied molecular orbital-lowest occupied molecular orbital (HOMO-LUMO) levels of R6G molecules resulted in improved SERS signal by about an order for graphene-AgNS hybrid structure as compared to bare AgNS. The obtained findings paved the way for the futuristic and reliable hybrid SERS substrate for trace-level detection of a wide range of chemical entities. [Display omitted] [ABSTRACT FROM AUTHOR]

A giant electric field on a subwavelength scale is highly beneficial for boosting the light–matter interaction. In this paper, we investigated a hybrid structure consisting of a hemispheric dimer array and a gold film and realized resonant mode coupling of the surface lattice resonance (SLR) and surface plasmon polariton (SPP). Mode coupling is demonstrated by observing anti-crossing in reflection spectra, which corresponds to Rabi splitting. Although the resonance coupling does not enter the strong coupling regime, an improved quality factor (Q~350) and stronger electric field enhancement in the gap region of the dimer (i.e., hot spot) in our hybrid structure are obtained compared to those of the single dimer or dimer array only. Remarkably, the magnitude of electric field enhancement over 500 can be accessible. Such high field enhancement makes our hybridized structure a versatile platform for the realization of ultra-sensitive biosensing, low-threshold nanolasing, low-power nonlinear optical devices, etc.

Moving the polarization of the incident wave along a meridian of the Poincaré sphere, experimentally we show that the coupling with the fundamental Bloch's surface waves of the mode, provide a spatially coherent, macroscopic spinmomentum locked propagation along the symmetry axes of the PhCM. This novel mechanism of light-spin manipulation enables a versatile implementation of spin-optical structures that may pave the way to novel strategies for light spin technology and photonic multiplatform implementations.

Metallic nanogaps are being widely used for sensing applications, owing to their ability to confine and enhance electromagnetic field within the hot spots. Since the enhanced field does not confine itself perfectly within the gap, however, fringe fields well away from the gap are of potential use as well in real systems. Here, we extend the concept of near field absorption enhancement by quantitatively analyzing terahertz absorption behavior of water molecules outside the hot spots of sub-20 nm-wide, ∼100 μm-long nanotrenches. Contrary to point-gaps which show negligible field enhancement at distances larger than the gap width, our extended nanogap act as a line source, incorporating significant amount of absorption enhancement at much longer distances. We observe absorption enhancement factors of up to 3600 on top of a 5 nm-wide gap, and still well over 300 at 15 nm away. The finding is well supported by theoretical analyses including modal expansion calculations, Kirchhoff integral formalism and antenna theory. Our results provide means to quantitatively analyze light-matter interactions beyond the hot spot picture and enable application of nanogaps for sensitive surface analyses of various material systems.

Plasmonic effects that enhance electric fields and amplify optical signals are crucial for improving the resolution of optical imaging systems. In this paper, a metal-based plasmonic nanostructure (MPN) is designed to increase the resolution of an optical imaging system by amplifying a specific signal while producing a plasmonic effect via a dipole nanoantenna (DN) and grating nanostructure (GN), which couple the electric field to be focused at the center of the unit cell. We confirmed that the MPN enhances electric fields 15 times more than the DN and GN, enabling the acquisition of finely resolved optical signals. The experiments confirmed that compared with the initial laser intensity, the MPN, which was fabricated by nanoimprint lithography, enhanced the optical signal of the laser by 2.24 times. Moreover, when the MPN was applied in two optical imaging systems, an indistinguishable signal that was similar to noise in original was distinguished by amplifying the optical signal as 106 times in functional near-infrared spectroscopy(fNIRS), and a specific wavelength was enhanced in fluorescence image. Thus, the incorporation of this nanostructure increased the utility of the collected data and could enhance optical signals in optics, bioimaging, and biology applications. [ABSTRACT FROM AUTHOR]

The concept of an equivalent circuit is a simple and effective method for studying the role of plasmonic and non-plasmonic nano-objects in nanodevices. This work discusses an equivalent circuit and optical properties for nanoslit and its surrounding medium. Based on the characteristic impedance approach, a new model was designed for an equivalent circuit of nanoslit. To control the amount of electric field and power flow, a novel idea of silver-gold nanoslit is presented. Its results are compared with silver-silver nanoslit and gold–gold nanoslit. The results of this study show that the response of the nanoslit can be tailored by optimizing the parameters, including the refractive index of the surrounding medium, permittivity and permeability of the materials and subwavelength parameters of the nanoslit. Using this approach, it would be possible to design complex equivalent circuits in the future for nanodevices. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) possess many unique properties that make them ideal for field emission. However, screening due to high density and poor substrate adhesion limits their application. We tested the field emission of various patterned vertically aligned carbon nanotube (VACNT) arrays adhered to copper substrates using carbon paste. After many fabrication steps to improve uniformity, we found that the field emission was dominated by individual CNTs that were taller than the bulk VACNT arrays. After testing a sample with silver epoxy as the binder, we found that the failure mechanism was adhesion to the substrate. Using energy dispersive x-ray spectroscopy, we found that the carbon paste migrated into the VACNT bulk volume while the silver epoxy did not. The migration of carbon paste into the volume may explain why the carbon paste had greater adhesion than the silver epoxy., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

Chiral nano-emitters have recently received great research attention due to their technological applications and the need for a fundamental scientific understanding of the structure-property nexus of these nanoscale materials. Lead halide perovskite nanocrystals (LHP NCs) with many interesting optical properties have anticipated great promise for generating chiral emission. However, inducing high anisotropy chiral emission from achiral perovskite NCs remains challenging. Although chiral ligands have been used to induce chirality, their anisotropy factors (g lum ) are low [10 -3 to 10 -2 ]. Herein, the generation of high anisotropy circularly polarized photoluminescence (CPL) from LHP NCs is demonstrated using chiral metasurfaces by depositing nanocrystals on top of prefabricated resonant photonic structures (2D gammadion arrays). This scalable approach results in CPL with g lum to a record high of 0.56 for perovskite NCs. Furthermore, the differences between high-index dielectric chiral metasurfaces and metallic ones are explored for inducing chiral emission. More importantly, the generation of simultaneous multi-wavelength circularly polarized light is demonstrated by combining dielectric and metallic chiral metasurfaces., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

In this study, we have investigated the optical property of single and coupled gold nanoparticle (AuNP) using the finite-difference time-domain (FDTD) method. The initial study facilitated us to simulate the bowtie antenna where we investigated the key performance parameters of optical nano antennas such as extinction efficiency, plasmon coupling, near -and far-field enhancement, transmission and reflection as a function of size, and separation. The findings of this study will be beneficial to design a more complicated optical nano antenna, tuning the frequency in THz range varying the size, shape and geometry and also to meet the future need of 6G communication and beyond. [ABSTRACT FROM AUTHOR]

Abstract A finite-difference time-domain method is developed for studying the plasmon enhancement of light absorption from vertically aligned GaAs nanowire arrays decorated with Au nanoparticles. Vertically aligned GaAs nanowires with a length of 1 µm, a diameter of 100 nm and a periodicity of 165–500 nm are functionalized with Au nanoparticles with a diameter between 30 and 60 nm decorated in the sidewall of the nanowires. The results show that the metal nanoparticles can improve the absorption efficiency through their plasmonic resonances, most significantly within the near-bandgap edge of GaAs. By optimizing the nanoparticle parameters, an absorption enhancement of almost 35% at 800 nm wavelength is achieved. The latter increases the chance of generating more electron–hole pairs, which leads to an increase in the overall efficiency of the solar cell. The proposed structure emerges as a promising material combination for high-efficiency solar cells.

Plasmonic devices have witnessed their success in optical applications due to the boosted light-matter interactions in the subwavelength scale. Among them, optical fiber-based configurations offer excellent portability and accessibility. Here, we report a novel kind of plasmonic fiber devices by introducing Tamm plasmon polaritons (TPPs) into the fiber-optic community. TPPs are cavity modes confined between a distributed Bragg reflector (DBR) and a metallic layer, resulting in high quality factor ∼100, strong field-intensity enhancement of 92, immunity to ambient perturbations, and flexible tunability. As the fabrication process only requires thin-film deposition, fiber-based TPP system is relatively low-cost and high-repeatability. This scenario extends the scope of plasmonic devices and open up new perspectives for active and passive fiber-optic systems. [ABSTRACT FROM AUTHOR]

The effects of interface charges on the performances of gate-all-around (GAA) GaN vertical nanowire MOSFETs with different geometries have been studied. Geometrical effect on the gate current of vertical GAA GaN nanowire MOSFET has also been analysed for the first time. In the ideal condition, the circular geometry nanowire (CGN) MOSFET exhibits the best performance with subthreshold swing (SS) of 62 mV/dec, drain-induced barrier lowering (DIBL) of 14 mV/V, and ON/OFF current ratio ( $I_{ON}/I_{OFF}$ ) of ~108. The triangular or hexagonal geometry nanowire (TGN or HGN) MOSFET suffer from large gate leakage current due to the field enhancement at sidewall corners. It is also known that interface traps at the sidewall surface of vertical nanowires deteriorate the overall device performance. The HGN MOSFET with m-plane sidewall demonstrates the best performance with SS of 69 mV/dec and DIBL of 13 mV/V, while the TGN MOSFET with a-plane sidewall exhibits the worst performance with SS of 112 mV/dec and DIBL of 101 mV/V.

Plasmonic metallic nanostructures have attracted much interest for their ability to manipulate light on a subwavelength scale and for their related applications in various fields. In this work, a parabola-like gold nanobowtie (PGNB) on a sapphire substrate was designed as a nano-cavity for confining light waves in a nanoscale gap region. The near-field optical properties of the innovative PGNB structure were studied comprehensively, taking advantage of the time-resolved field calculation based on a finite-difference time-domain algorithm (FDTD). The calculation result showed that the resonance wavelength of the nano-cavity was quite sensitive to the geometry of the PGNB. The values that related to the scattering and absorption properties of the PGNB, such as the scattering cross section, absorption cross section, extinction cross section, scattering ratio, and also the absorption ratio, were strongly dependent on the geometrical parameters which affected the surface area of the nanobowtie. Increased sharpness of the gold tips on the parabola-like nano-wings benefited the concentration of high-density charges with opposite electric properties in the narrow gold tips with limited volume, thus, resulting in a highly enhanced electric field in the nano-cavity under illumination of the light wave. Reduction of the gap size between the two gold nano-tips, namely, the size of the nano-cavity, decreased the distance that the electric potential produced by the highly concentrated charges on the surface of each gold nano-tip had to jump across, therefore, causing a significantly enhanced field in the nano-cavity. Further, alignment of the linearly polarized electric field of the incident light wave with the symmetric axis of the PGNB efficiently enabled the free electrons in the PGNB to concentrate on the surface of the sharp gold tips with a high density, thus, strongly improving the field across the nano-cavity. The research provides a new insight for future design, nanofabrication, and characterization of PGNBs for applications in devices that relate to enhancing photons emission, improving efficiency for energy harvesting, and improving sensitivity for infrared detection. [ABSTRACT FROM AUTHOR]

In common plasmonic configurations, energy loss and field enhancement are mutually restricted. In a vast majority of cases, high confinement goes together with high loss, which is a serious limitation for some applications. In an attempt of breaking this rule, which holds true for surface plasmon polariton (SPP) resonators, a multilayer trench grating microstructure with an asymmetric waveguide is considered. It supports both Fabry-Perot (FP) and cavity modes, whose hybridization exhibits unusual properties. The electric field enhancement was modulated by regulating the corresponding absorption and radiation quality factors. At the same time, energy loss was reduced, which is fundamentally ascribed to the mutual recycling of radiation energy between FP and cavity resonators. The maximum total quality factor and strongest field enhancement were both observed at the vicinity of quasi-static limit, thereby signifying that the structure exhibited simultaneous optimizations of field enhancement and loss inhibition, which is crucial to the design of high-quality SPP-based devices.

This paper presents a torque ripple minimization strategy based on Field Oriented Control for Switched Reluctance Machines. The proposed strategy lay hands on a non-sinusoidal dq transform, known as the dqx transform, and the derivatives of inductance as main variables. The proposed method has been validated through time-step simulations of a 6/4 machine in Matlab/Simulink. The inductance and its derivative waveform have been obtained through Finite Element Analysis of a real machine. The simulations have taken into account the magnetic saturation effects and cross-coupling effects. Results for speed variation through flux weakening/enhancement have also been presented and discussed. The results demonstrate the efficacy of the proposed method, decreasing the torque ripple by 2.9 times of its original value when saturation effects are neglected and by 2.8 times when saturation effects are considered. In addition, the base speed has been increased up to 19.22 % when flux-weakening and flux enhancement simulations have been carried out. [ABSTRACT FROM AUTHOR]

Dielectric dimers composed of spherical Alumina ceramic resonators are studied. The electromagnetic scattering of dimer configurations is analyzed through spherical multipole decomposition. Different configurations of dimer operation are addressed with respect to propagation direction and polarization of the incident wave. In context to forward scattering caused by dipole interaction, measurements are performed in V-band (50–75 GHz) to quantify the corresponding electromagnetic signature of the dielectric dimer. Based on the fundamental dipole modes excited in the subwavelength free-space gap along the dimer axis, electric and magnetic hotspots are proposed, which can be exploited for near-field enhancement-based applications at millimeter-wave frequency. A dedicated frequency-scaled measurement setup is designed to measure the field-enhancement factor between 25 and 30 GHz in the free-space dimer gap, corresponding well to simulated results. [ABSTRACT FROM AUTHOR]

In this paper, a novel spoof surface plasmon polaritons (SSPPs) waveguide based on I-shaped grooves has been presented in order to achieve extraordinary field enhancement of spoof SPPs at deep subwavelength scale. These I-shaped grooves are basically the transformed version of rectangular grooves incorporated by conventional spoof SPP waveguide, made up by virtue of lateral extension on either ends of these grooves. This approach which consists of addressing the grooves shape transformation proves very fruitful to accommodate higher capacitance and therefore leading to ultrahigh field confinement of spoof SPPs by lowering resonance frequency. Compared with plasmonic waveguide with T-shaped grooves which occupies the highest confinement of spoof SPPs than the previously reported different grooves shapes [Journal of Applied Physics 122, 123301 (2017)], the extension of lower ends of the grooves facilitates us with ultra-strong field confinement of spoof SPPs with low-loss feature. The proposed spoof SPP waveguide is more compact and a low cost structure exhibiting a strong response for spoof SPPs than the T-shaped spoof SPP waveguide. As a comparison, SPP-TL with T-shaped grooves results have been presented along with newly proposed SPP-TL with I-shaped grooves. Simulation results show that highly confined spoof SPPs can be generated by embedding I-shaped grooves in spoof SPP transmission line as compared to the spoof SPP TL with T-shaped grooves. Furthermore, a parametric study is presented to show its influence on the confinement. The proposed waveguide can be helpful in developing various integrated plasmonic circuits and systems at microwave frequencies.

In this article, numerical computations applying the finite-difference time-domain (FDTD) method are performed. Lightning electromagnetic fields radiated by a lightning strike to the Gaisberg Tower in Salzburg, Austria, and propagating over irregular terrain are calculated. The field propagation is computed with a three-dimensional (3-D) FDTD and, for comparison, a 2-D cylindrical symmetry FDTD. With topographic height maps, seven different propagation paths for a selected lightning strike to the Gaisberg tower are simulated and the resulting magnetic field (H-field) is compared with the received signal strength at seven sensors of the ALDIS sensor network for that event. The return stroke is represented by a transmission line model and the current waveform recorded at the top of the Gaisberg tower was used. The results of the 3D-FDTD simulation correlate well with H-fields registered at sensor sites in mountainous environments. Hence, 3D-FDTD can represent complex local reflection phenomena correctly, which the 2D-FDTD cannot. The results of recent studies, which show that a lightning strike to a mountain gives rise to a field enhancement at the sensor site for a relatively flat propagation path, could be verified by comparing the FDTD results with a set of existing sensor measurements. For the, otherwise, very hilly terrain conditions in Austria, the field enhancement caused by the mountain is attenuated along the paths to the respective sensors. [ABSTRACT FROM AUTHOR]

A finite-difference time-domain method is developed for studying the plasmon enhancement of light absorption from vertically aligned GaAs nanowire arrays decorated with Au nanoparticles. Vertically aligned GaAs nanowires with a length of 1 µm, a diameter of 100 nm and a periodicity of 165–500 nm are functionalized with Au nanoparticles with a diameter between 30 and 60 nm decorated in the sidewall of the nanowires. The results show that the metal nanoparticles can improve the absorption efficiency through their plasmonic resonances, most significantly within the near-bandgap edge of GaAs. By optimizing the nanoparticle parameters, an absorption enhancement of almost 35% at 800 nm wavelength is achieved. The latter increases the chance of generating more electron–hole pairs, which leads to an increase in the overall efficiency of the solar cell. The proposed structure emerges as a promising material combination for high-efficiency solar cells. [ABSTRACT FROM AUTHOR]

High field enhancement and near-perfect absorption in nanoantennas were realized by using in-plane (between nanoantenna arms), out-of-plane (between nanoantenna and reflector), and array coupling (between nanoantennas in an array); however, it was challenging to satisfy both conditions at the same time. In this paper, we show that a bowtie nanoantenna array integrated with an artificial impedance surface can simultaneously satisfy both high field enhancement and perfect absorption. The artificial impedance surface is implemented as a metallic patch array on a grounded 50 nm-thick SiO2 substrate with reactive impedance surface (RIS) or high impedance surface (HIS) characteristic. Through the proposed design methodology, we designed a bowtie nanoantenna array on an optimum RIS patch array and achieved a high field enhancement factor (E/E0) of 228 and a nearly perfect absorption rate of 98% at 230 THz. This novel design outperforms the previously reported nanoantenna structures and the same bowtie nanoantenna array designed using a conventional grounded SiO2. We also show that the HIS-integrated bowtie antenna array cannot realize both goals at the same time because the highly reflective HIS cannot guarantee perfect absorption. The proposed RIS-combined nanoantenna array with high field enhancement and near-perfect absorption can be used for efficient infrared (IR) and optical detectors, sensors, and energy harvesting devices.