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Tunable extraordinary optical transmission (EOT) with graphene is realized using a novel metallic ring–rod nested structure in the terahertz frequency regime. The generated double-enhanced transmission peaks primarily originate from the excitation of localized surface plasmon resonances (LSPRs). On using graphene, the resonating surface plasmon distribution changes in the reaction plane, which disturbs the generation of LSPRs. By regulating the Fermi energy (Ef) of the graphene to reach a certain level, an adjustment from bimodal EOT to unimodal EOT is obtained. As the Ef of the graphene integrated beneath the rod increases to 0.5 eV, the transmittance of the peak at 2.42 THz decreases to 6%. Moreover, the transmission peak at 1.77 THz virtually disappears due to the Ef increasing to 0.7 eV when the graphene is placed beneath the ring. The significant tuning capabilities of the bimodal EOT indicate its promising application prospects in frequency-selective surfaces, communication, filtering, and radar.

Infrared phototransistors with very high performance show great potential in optoelectronic application, attributable to the intrinsic high transconductive gain of the transistor structure and therefore very large photo-responsivity. To distinguish multispectral information with phototransistors, however, the coincident spectral light has to been laterally dispersed and thereby coupled to the individual photo-gates sensing different target bands. Here, the dual-frequency plasmonic photo-coupler based on a single perforated metallic layer is numerically designed in the infrared region to improve photon absorption efficiency at two target wavelengths. The geometric parameters of the plasmonic grating composed of large and small cross-shaped holes are independently tuned to control the resonance frequencies under different incident (x- and y-) polarization conditions. While the dual-frequency resonant modes are induced by the hybridization between localized surface plasmons (LSPs) and propagating surface plasmons (PSPs), it is found that LSPs play the dominant role and can be effectively adjusted to achieve the target dual-frequency response. More importantly, the spectral response with low- (high-) frequency resonance corresponding to large (small) cross-hole region matches the spatially distributed photogates of the phototransistor structure and therefore realizes near-field enhancement and hence large photoresponsivity at target dual frequencies. In addition, the spectral response for x- and y-polarizations can be unified despite of the apparently broken symmetry between these two polarizations. Our work provides a general strategy to realize sensitive multiband-infrared phototransistors which require only state-of-the-art planar technology and are applicable for highly sensitive infrared photodetection.

Developing a simple structure using low-cost material that enables both large-scale fabrication and broadband absorption response is highly desirable but very challenging for achieving high-performance metamaterial absorber. Herein, we propose and numerically investigate an ultra-broadband and wide-angle insensitive perfect metamaterial absorber in the ultraviolet to near-infrared (UV–NIR) region based on a simple metal–dielectric–metal structure. The proposed absorber structure consists of a periodic array of a tungsten hexagonal prism and a tungsten ground plane separated by a silicon dioxide dielectric substrate. The proposed absorber achieves an ultra-broadband absorption response in the range of 275–1000 nm with an absorptivity above 90 $$\%$$ and a relative bandwidth of 106.8 $$\%$$ at normal incidence, which covers from the UV to NIR region. The absorption efficiency is maintained with the figure of merit $$\eta _{OBW}$$ higher than 90 $$\%$$ for a wide incident angle up to 40 $$^{o}$$ for transverse electric (TE) polarization and 65 $$^{o}$$ for transverse magnetic (TM) polarization. The effects of structural parameters and different metallic materials on the absorption performance are presented. In addition, the physical mechanism is analyzed using the surface density and distributions of electric and magnetic fields that are attributed to both localized surface plasmon (LSP) and propagating surface plasmon (PSP) resonances. Owing to outstanding merits of simple structure, low cost, and high absorption performance, the designed absorber can be suitable for many applications in the UV–NIR spectrum such as thermal emitters and solar cells.

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.

Lanthanide-doped nanoparticles have great potential for energy conversion applications, as their optical properties can be precisely controlled by varying the doping composition, concentration, and surface structures, as well as through plasmonic coupling. In this Perspective we highlight recent advances in upconversion emission modulation enabled by coupling upconversion nanoparticles with well-defined plasmonic nanostructures. We emphasize fundamental understanding of luminescence enhancement, monochromatic emission amplification, lifetime tuning, and polarization control at nanoscale. The interplay between localized surface plasmons and absorbed photons at the plasmonic metal-lanthanide interface substantially enriches the interpretation of plasmon-coupled nonlinear photophysical processes. These studies will enable novel functional nanomaterials or nanostructures to be designed for a multitude of technological applications, including biomedicine, lasing, optogenetics, super-resolution imaging, photovoltaics, and photocatalysis.

Exploitation of strong light-matter interactions in plasmonic systems is vital for both fundamental studies and the development of new applications, which enables exceptional physical phenomena and promotes potential applications in nanophotonics, information communication, and quantum information processing. Here, we present an analytic model of the interaction between localized surface plasmon resonances and excitons, where a semiclassical method is utilized. Two kinds of metal nanoparticles (nanosphere and nanoellipsoid) are considered in our study. We derive the relations between the plasmon-exciton coupling strength and the geometry and material parameters of the coupled systems when the nanoparticles are put in an excitonic medium, which give an important guide to achieve strong plasmon-exciton coupling. Rabi splittings and anticrossing behavior are also demonstrated in the calculated extinction spectra. Furthermore, we propose an analytic model to describe the strong coupling between excitons and plasmon in a core-shell nanorod structure which is widely used in experiments. Our study provides a simple yet rigorous prescription to both analyze and design plexcitonic systems aiming at strong light-matter interactions.

The absorption and reflection of electromagnetic waves by various particles in the earth’s atmosphere allow the passage of only certain electromagnetic wavelengths to reach the ground, called Earth’s atmosphere transparent window. In this study, perfect absorption was theoretically obtained in the range of near- and mid-infrared earth’s atmospheric transparency window using a simple absorber with metal-dielectric-metal structure. The numerical simulations showed the average absorption to reach 96.2% at wavelengths from 2000 to 6000 nm. Also, the broadband absorption was noticed and attributed to combined physical mechanisms, such as anti-reflection effect, localized surface plasmon polariton, propagating surface plasmon polarization, Fabry–Perot cavity and slow light mode. Meanwhile, the proposed absorber displayed simple-structure, low-cost, wide-angle, and polarization-independent. In sum, the proposed absorber might be useful for future applications related to atmospheric transparency window, such as remote sensing, energy harvesting, infrared detection, and stray light elimination.

We present a strong coupling system realized by coupling the localized surface plasmon mode in individual silver nanogrooves and propagating surface plasmon modes launched by periodic nanogroove arrays with varied periodicities on a continuous silver medium. When the propagating modes are in resonance with the localized mode, we observe a √N scaling of Rabi splitting energy, where N is the number of propagating modes coupled to the localized mode. Here, we confirm a giant Rabi splitting on the order of 450-660 meV (N = 2) in the visible spectral range, and the corresponding coupling strength is 160-235 meV. In some of the strong coupling cases studied by us, the coupling strength is about 10% of the mode energy, reaching the ultrastrong coupling regime.

Localized surface plasmons (LSPs) are a potentially valuable property for the practical use of small size metallic particles. Exploiting the LSPs in metallic nanoparticle (NP)-based solar cells was shown to increase the efficiency of solar panels. A large extinction cross section of NPs allows for high scattering of light at the surface of the panel, which reduces the panel thickness, allowing for small size and low-cost solar cells. In this paper, the extinction cross-section of spherical nanoparticles is studied and simulated numerically. Surface plasmons were first modeled using the Drude’s model then the scattering and absorption cross-sections were derived. Commercial3D simulation software was used to model the near field distribution of the three NP structures. A spherical nanoparticle made of silver was modeled first and the field distribution inside the sphere was presented. The extinction cross-section was also calculated. Two other structures were also presented; a silica NP was first coated with silver shell then a silver NP was coated with silica shell. These structures were studied to estimate the effects of the surroundings on the extinction cross-section. The results show that the silica NP coated with a silver shell provides a high extinction cross-section and can be considered as a good choice for the LSPs-based solar cells.

Within a mid-IR few-cycle laser, the generation of MHz isolated attosecond pulses via nanoplasmonic field enhancement in a structure that consisted of a metal coupled nanoparticle-disk, an insulator spacer, and a thin metal film is theoretically investigated. The interaction between the localized surface plasmons caused by the coupled nanodisks and the metal layer results in increased electric field. The resonance wavelengths of these two types of surface plasmons supported by the nanostructure are tailored by changing the coupled nanoparticle-disk size and the material type. Numerical calculations are used to optimize nanostructure and attain plasmonic field enhancement factors up to 86. The HHG process is studied by the time–frequency analysis. Our studies show that only short trajectories contribute to HHG and also, the chirp of these harmonics is very low. As a result, an isolated 40 as pulse without phase compensation is obtained directly by superposing the chirp-free high-order harmonics.

This article presents the architecture of optical microring resonator based on surface plasmon polaritons using different profile materials like silicon (Si), silver (Ag) and gold (Au). It is observed that 3.53e-005 w/m, 6.92e-005 w/m, 7.05e-005 w/m received optical powers are achieved in silicon (Si), silver (Ag) and gold (Au) profile materials, respectively, of optical microring resonator at 0.1 w/m minimum input transmission power for 1.55 μm input transmission wavelength. The result shows that the silicon profile is best for designing the optical microring resonator in terms of received optical power.

Visualization of surface plasmon polariton (SPP) propagation at dielectric/metal interfaces is indispensable in providing opportunities for the precise designing and controlling of the functionalities of future plasmonic nanodevices. Here, we report the visualization of SPPs propagating along the buried organic/metal interface of fullerene (C60)/Au(111), through dual-colored two-photon photoemission electron microscopy (2P-PEEM) which precisely visualizes the SPP propagation of plasmonic metal nanostructures. Although SPPs excited by near-infrared photons at the few monolayer C60/Au(111) interface are clearly visualized as interference beat patterns between the SPPs and incident light, faithfully reflecting SPP properties modulated by the overlayer, photoemission signals are suppressed for thicker C60 films, due to less valence electrons participating in 2P-photoemission processes. With the use of silver (Agn (n = 21 and 55)) nanoclusters, which exhibit enhancement of overall photoemission intensities due to localized surface plasmons functioning as SPP sensitizers, it is revealed that the 2P-PEEM is applicable to the imaging of SPPs for thick C60/Au(111) interfaces, where SPP properties are hardly modulated by the added small amount (∼0.1 monolayer) of Agn sensitizers.

Gold and silver nanoparticles have unique optical properties. For instance, the intense colour of nanoparticle suspensions results from the excitation of a collective oscillation of surface conduction electrons, named surface plasmons. This excitation is done using an electromagnetic radiation that interacts with nanoparticles having a negative real and small positive imaginary dielectric constant, such as nanoparticles of gold or silver. The plasmonic optical properties of metal nanostructures are dependent on their shape and size, the dielectric properties of the metal and the surroundings and on the possible electromagnetic coupling with the localized surface plasmons in nearby other plasmonic objects. The other important consequence of the excitation of surface plasmons is a local significant enhancement of the electromagnetic field at some places of the illuminated nanoparticles. Specific plasmonic properties of gold and silver nanoparticles have allowed the development of many sensors for chemical analysis, including sensors dedicated for environmental analysis. Some of these sensors are so sensitive that recording of the reliable analytical signal of a single molecule is possible. Here, we review analytical techniques based on plasmonic properties of metallic nanoparticles for environmental analysis. We present the theory and mechanism of interaction of the electromagnetic radiation with the plasmonic nanoparticles. We detail analytical techniques including methods utilizing local enhancement of the intensity of the electromagnetic field induced by plasmons, and hence increase in the efficiency of some optical processes in the proximity of the plasmonic nanoparticles. Those techniques are surface-enhanced Raman scattering, surface-enhanced infrared absorption and metal-enhanced fluorescence and methods based on the change in the optical properties of plasmonic nanoparticles caused by the analyte-induced aggregation or by analyte-influenced growth or etching of plasmonic nanostructures. Environmental compounds include heavy metal cations, metallo-organic compounds, polycyclic aromatic hydrocarbons, pesticides, nitrite ions, bacterial cells and bacterial pathogens.

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.

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.

A long-range surface plasmonic resonance (LR-SPR) biosensor modified with double-antibody sandwich immunoassay and plasmonic coupling is demonstrated for human-immunoglobulin G detection with a low limit of detection (LOD). The double-antibody sandwich immunoassay dramatically changes the average refractive index of the medium layer on the sensor surface. The near-field electron coupling between the localized surface plasmon and the long-range surface plasmon leads to a significant perturbation of the evanescent field. The large penetration depth and the long propagation distance of the long-range surface plasmonic waves facilitate the LR-SPR sensor in the detection of biological macromolecules. The unique light absorption characteristic of the nanocomposite material in the sensor provides the in situ self-compensation for the disturbance. Therefore, besides the inherent advantages of optical fiber sensors, the developed biosensor can realize the detection of biomolecules with high sensitivity, low LOD and high accuracy and reliability. Experimental results demonstrate that the LOD of the biosensor is as low as 0.11 μg/mL in the detection of the phosphate-buffered saline sample, and the spike-and-repetition rate is 105.56% in the detection of the real serum sample, which partly shows the practicability of the biosensor. This indicates that the LR-SPR biosensor provides better response compared with existing similar sensors and can be regarded as a valuable method for biochemical analysis and disease detection.

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.

Plasmonic excitation of metallic nanoparticles can trigger chemical reactions at the nanoscale. Such optical effects can also be employed to selectively and locally graft photopolymer layers at the nanostructure surface, and, when combined with a surface functionalization agent, new pathways can be explored to modify the surface of a plasmonic nanoparticle. Among these approaches, diazonium salt chemistry is seen as an attractive strategy due to the high photoinduced reactivity of these salts. In this work, we demonstrate that it is possible to trigger the site-selective grafting of aryl films derived from diazonium salts on distinct nano-localized area of single gold nanotriangles, by taking advantage of their multipolar localized surface plasmon modes. It is shown the aryl film will preferentially graft in areas where the electric field enhancement is maximum, independently of the considered excited surface plasmon mode. These experimental findings are in very good qualitative agreement with the calculations of the local electric field, using the finite-difference time-domain (FDTD) method. We believe that this plasmonic-based approach will not only pave a new way for the spatially controlled surface functionalization of plasmonic nanoparticles, but also provide a general strategy to attach distinct molecules to hot spot regions on a single nanoparticle, opening promising prospects in sensing and multiplexing, and optically nano-scale patterning of functional groups.

Research on the classical analogy of asymmetric Fano resonances has gained momentum in recent years, owing to the steep dispersion of the Fano-like profile in classical systems, such as plasmonic nanostructures and metamaterials, which has numerous applications. We studied the double Fano-like resonances arising in a waveguide structure made of a periodic array of gold nanospheres placed on the top surface of an indium tin oxide (ITO) film, which is deposited on a silica substrate. These resonances emanate from the interference coupling between the dipolar surface plasmon mode of the individual gold nanospheres and the zero-order transverse electric (TE) and transverse magnetic (TM) waveguide modes within the ITO film. Increasing the array period of the gold nanospheres or thickness of the ITO film shifted the resonance peaks towards the low-frequency side corresponding to the excitation frequencies of the zero-order TE and TM waveguide modes, which were red-shifted. Additionally, the double Fano-like resonance profiles were approximated using an analytical Fano interference model.

We investigated electron emission induced by an intense mid-infrared (MIR) field from a nanoscale aluminum-coated grating. The total photoelectron yields clearly show a resonant-like behavior when ...

We introduce zinc oxide (ZnO) functionalized porous gold nanoparticles that exhibit strong second harmonic (SH) emission due to an efficient coupling of localized surface plasmons to ZnO excitons. ...

When localized surface plasmons (LSPs) are coupled to extended surface plasmons (ESPs), higher density of particles causes stronger interaction, larger Rabi splitting (RS), and plasmonic energy ban...

The enhancement of surface plasmon-coupled emission (SPCE) by the synergistic effect of silver nanocubes (AgNCs) and graphene oxide (GO) on gold film has been observed with the enhancement factor over 30. The enhancement mechanisms were investigated through simulating the electromagnetic (EM) field patterns of near field and testing different concentration of AgNCs and thickness of dye layer. The enhancement was mainly triggered by the high electromagnetic field of AgNCs, the interaction between localized surface plasmons (LSP) and propagating surface plasmons (PSP) and the assistance of GO. This synergistic enhancement strategy provides a simple way to increase SPCE signal and enable develop a new fluorescence-based detection system.

The localized surface plasmon enhanced luminescence behaviors of a radiating dipole in an all-inorganic perovskite light-emitting diode (PeLED) by incorporating a gold (Au)-silver (Ag) alloy nanoparticle (NP) in the electronic transport layer are demonstrated. The analyses of finite difference time domain (FDTD) show that the localized surface plasmon resonance (LSPR) wavelength mainly depends on the size and the material composition of NP. An increase of 25% of the luminescence efficiency can be achieved by selecting the proper size and the Au molar fraction of the alloy NP. This result can be attributed to the match between the LSPR wavelength of NP and emission peak of PeLED. And the luminous performance of PeLED can be improved by optimizing the thickness of functional layers. This finding indicates great potential of Au-Ag alloy nanoparticle in developing the efficiency of PeLEDs and provides a new method for the future improvement of PeLEDs.

Localized surface plasmons at nanostructured surfaces are played a key role in a wide range of industrial applications. Here, hexagonal arrays of uniformly distributed Pt nanocylinders were fabricated on the top surface of nanoporous anodic alumina (PAA) membrane using low-cost sputter coating technique under low vacuum. Set of PAA membranes were synthesized at the same conditions and coated with Pt for different periods of time. The implemented growth mechanism allowed the vertical accumulation of Pt nanoparticles to form Pt nanocylinders on the active dots of PAA. SEM images showed nanocylinders of heights ranged from 10.0 ± 0.7 nm to 32.0 ± 2.1 nm based on sputtering time. The nanocylinders rate of growth is 1.22 ± 0.09 nm/min. According to SEM images, the uniformity of the nanocylinders decreased as the porosity of the PAA membrane increased. The optical properties of Pt nanocylinders/PAA membranes were investigated and showed strong transverse, longitudinal, and higher longitudinal surface plasmon modes. Relative to the previously reported SPRs for other Pt nanostructures, our Pt/PAA nanostructures showed stronger SPRs at longer wavelengths due to the using of PAA as a host material, the strong electromagnetic coupling between the very close Pt nanocylinders, and the strong coupling between SPRs and interfernce fringes. Moreover, the effects of sputtering time and membrane porosity on the SPR position, oscillation strength, and bandwidth were studied.

A composite structure based on a Kretschmann structure loaded with silver nano-cube is proposed. A 442-nm laser was used to excite surface plasmons in the composite structure, and the electric field enhancement was numerically simulated using the finite element method. The excitation angles of surface plasmons under conditions of different thicknesses of a PMMA film were obtained by studying the reflection spectrum of the Kretschmann structure. By examining the extinction spectra of silver nano-cubes of different sizes, its optimal size was selected, which is 70 nm. The electric field enhancement factors of the composite structure and the composite PMMA-spaced silver nano-cube and silver film structure were compared in detail. The results show that the coupling of localized surface plasmons and propagating surface plasmons produced by the proposed composite structure mean that its electric field enhancement factor is significantly greater. Moreover, the electric field enhancement factor can be further improved by adding another laser to irradiate the composite structure symmetrically. The high electric field enhancement generated by the composite structure indicates that it has considerable application prospects in surface-enhanced Raman scattering. Keywords: Surface plasmons, Silver nano-cube, Electric field enhancement factor

International audience; Thanks to their small sensing volume, nanosensors based on localized surface plasmon resonances (LSPR) allow the detection of minute amounts of analytes, down to the single-molecule limit. However, the detected analytes are often large molecules, such as proteins. The detection of small molecules remains largely unexplored. Here, we use a hybrid photonic–plasmonic nanosensor to detect a small target molecule (pyridine). The sensor’s design is based on a dielectric photonic microstructure acting as an antenna, which efficiently funnels light toward a plasmonic transducer and enhances the detection efficiency. This sensor exhibits a limit of detection as small as 10–14 mol L–1. Using a calibration procedure based on electrodynamical numerical simulations, we compute the number of detected molecules. This yields a limit of detection in mass of 4 zeptograms (1 zg = 10–21 g), a record value for plasmonic molecular sensors. Our system can hence be seen as an optical molecular weighing scale, enabling room temperature detection of mass at the zeptogram scale.

Aggregates of plasmonic nanoparticles (NPs) are known to show greater electric field amplification, multiple resonant peaks, and precisely controlled spectral tuning compared to their isolated counterpart. The ability of localized surface plasmon mediated electric field amplification is an important criterion for a plasmonic system to act as an efficient Surface Enhanced Raman Scattering (SERS) substrate. Conventional coinage metals like gold (Au), silver (Ag) and copper (Cu) are most widely used SERS substrates, mainly due to their well established synthesis process and large Raman signal amplification. However, there is a pressing need to expand the list of plasmonic materials feasible for SERS substrates to match the exponential growth in SERS research. Identification of new plasmonic substrates will reduce the dependence on conventional plasmonic materials and SERS applications will extend into unexplored spectral regions. Moreover, one can circumvent the limitations arising due to the intrinsic nature of conventional plasmonic materials. Refractory Transition Metal Nitrides (RTMN) such as zirconium nitride (ZrN) and titanium nitride (TiN) has emerged as viable alternatives to coinage metals due mainly to, high electron conductivity, suitability for high temperature applications, optical response in Vis–NIR region, flexible spectral fine-tuning, and bio/CMOS compatibility. To the best of our knowledge, this article presents first-ever theoretical assessment of ZrN and TiN nanoparticle dimers for their suitability in enhancing electric field. Moreover, the role of nanoparticle size, embedding medium and inter-particle separation is quantified through fitting relations whose usefulness is demonstrated by designing nitrides based SERS substrates for selected wavelengths. The present work will provide handy tools to the designers and manufacturers.

The aim of this paper is to present a new efficient and accurate semi-implicit finite-difference time-domain (FDTD) method for modeling thin plasmonic metamaterials supporting spoof surface plasmons. The presented method is formulated by combining Yu–Mittra's conformal FDTD technique for dielectrics, the simplified conformal finite integration technique for perfectly electric conductors (PECs) and the Newmark-Beta method. The resultant scheme is magnetically implicit, has a more relaxed stability condition than that of Yee's FDTD scheme, and allows for accurate modeling of both PEC and dielectric curved surfaces. Energy conservation and stability of the presented scheme is theoretically proved with the energy inequality method. Its formulation can be generalized to a class of magnetically implicit FDTD schemes with weakly conditional and unconditional stability in a unified manner. The presented scheme is used to simulate thin structures supporting spoof surface plasmon polaritons and spoof localized surface plasmons, and also applied to recent plasmonic devices such as planar frequency splitter, ultrathin rainbow trapping device and compact planar metadisk with split-ring resonators. The accuracy and efficiency of the presented scheme are assessed in comparison with the conventional explicit and implicit FDTD methods, and their conformal variants.

In this talk, I will give a scheme to measure the liquid complex permittivity with high sensitivity based an ultra compact effective localized surface plasmons (ELSPs) sensor. Sharp resonance induced by the ELSPs resonator greatly enhance the sensitivity of the measurement. To estimate the complex permittivity of arbitrary unknown liquid, we establish an equivalent circuit model of this ELSPs sensor and build a fitting model based on the frequency shift and return loss. For demonstration, we successfully p redict the complex permittivity of ethanol from 0 to 90% with high precision. This ELSPs based sensor with an ultra compact size of 0.008 $\lambda_{0}^{2}$ and high sensitivity of 0.57% can find many applications (liquid permi ttivity measurement, liquid concentration, liquid testing, etc.) in highly integrated systems.

Raza et al. recently observed the extraordinarily large energy blueshifts of localized surface plasmon resonances and additional surface plasmon resonances in silver nanoparticles encapsulated in silicon nitride [S. Raza, S. Kadkhodazadeh, T. Christensen, M. D. Vece, M. Wubs, N. A. Mortensen, and N. Stenger, Nat. Commun. 6, 8788 (2015)], which are not fully understood yet. By using the quantum model consisting of two subsystems, respectively, for describing the center of mass and intrinsic motions of conduction electrons of a metallic nanosphere and a coupling occurring between the center of mass and conduction electrons outside the metallic nanosphere, we first deduced the general energy and line broadening size dependence of localized surface plasmon resonances, which removes the divergent defect of usual $1/R$ size dependence. Second, we proposed that the additional surface plasmon resonance in a metallic nanosphere originates from the transition of the first excited state to the ground state of the center-of-mass subsystem with energy levels corrected by degenerate-state pairs of the system composed of the center of mass and intrinsic motions of conduction electrons. Then, we implemented this generation mechanism of additional surface plasmon resonances for silver nanoparticles encapsulated in silicon nitride, and the calculated results are consistent with experimental results. Furthermore, we obtained an energy expression of localized surface plasmon resonances, with which we successfully explained the extraordinarily large energy blueshifts of localized surface plasmon resonances in few-nanometer silver nanoparticles encapsulated in silicon nitride. Finally, we calculated the localized and additional surface plasmon resonance energies of silver nanoparticles resting on carbon films, and the calculated results perfectly explain the experimental measurements of Scholl et al. [J. A. Scholl, A. L. Koh, and J. A. Dionne, Nature (London) 483, 421 (2012)]. Within this quantum model, the optical properties of metallic nanoparticles are completely determined by degenerate-state or nearly degenerate-state pairs of the system composed of the center-of-mass and intrinsic motions of conduction electrons. Our calculations also show that additional surface plasmon resonances play almost an equal role as localized surface plasmon resonances for metallic nanoparticles excited by fast-moving electrons.

On-chip plasmonic circuitry offers a promising route to meet the ever-increasing requirement for device density and data bandwidth in information processing. As the key building block, electrically-driven nanoscale plasmonic sources such as nanoLEDs, nanolasers, and nanojunctions have attracted intense interest in recent years. Among them, surface plasmon (SP) sources based on inelastic electron tunneling (IET) have been demonstrated as an appealing candidate owing to the ultrafast quantum-mechanical tunneling response and great tunability. However, the major barrier to the demonstrated IET-based SP sources is their low SP excitation efficiency due to the fact that elastic tunneling of electrons is much more efficient than inelastic tunneling. Here, we remove this barrier by introducing resonant inelastic electron tunneling (RIET)—follow a recent theoretical proposal—at the visible/near-infrared (NIR) frequencies and demonstrate highly-efficient electrically-driven SP sources. In our system, RIET is supported by a TiN/Al2O3 metallic quantum well (MQW) heterostructure, while monocrystalline silver nanorods (AgNRs) were used for the SP generation (localized surface plasmons (LSPs)). In principle, this RIET approach can push the external quantum efficiency (EQE) close to unity, opening up a new era of SP sources for not only high-performance plasmonic circuitry, but also advanced optical sensing applications., On-chip circuits based on plasmonic systems are a promising potential technology. Here the authors present efficient, on-chip, localized plasmonic excitation based on resonant inelastic electron tunneling with metallic quantum well junction.

Because spoof surface plasmons cannot flexibly transmit on the ultrathin metallic spiral structures, this paper proposes ultrathin metallic spiral structures composed of double spiral arms, and analyses the transmission characteristics. Through simulation calculations, it is found that the resonant frequency of a single ultrathin metallic spiral structure is consistent with the resonant frequency of the dimer structures. In addition, when the rotation angle between the dimer structures is changed, the resonance frequency is basically unchanged. In order to study the influence factors of the magnetic resonance characteristics, the single structure and the dimer structures are scanned separately. The results show that spoof localized surface plasmons can be transmitted on the bend path, and the change of the relative permittivity of the dielectric substrate will not affect its resonant frequency. The increase of the width and the number of spiral turns will cause the resonant frequency of the single structure and the dimer structure to redshift respectively.

The quantum behavior of surface plasmons has received extensive attention, benefiting from the development of exquisite nanotechnology and the diverse applications. Blueshift, redshift, and nonshift of localized surface plasmon resonances (LSPRs) have all been reported as the particle size decreases and enters the quantum size regime, but the underlying physical mechanism to induce these controversial size dependences is not clear. Herein, we propose an improved semiclassical model for modifying the dielectric function of metal nanospheres by combining the intrinsic quantized electron transitions and surface electron injection or extraction to investigate the plasmon shift and LSPR size dependence of the charged Au nanoparticles. We experimentally observe that the nonmonotonic blueshift of LSPRs with size for Au nanoparticles is turned into an approximately monotonic blueshift by increasing the electron donor concentration in the reduction solution, and it can also be transformed to an approximately monotonic redshift after surface passivation by ligand molecules. Moreover, we demonstrate controlled blueshift and redshift for the electron and hole plasmons in ${\mathrm{Cu}}_{2\ensuremath{-}x}\mathrm{S}@\mathrm{Au}$ core-shell nanoparticles by injecting electrons. The experimental observations and the theoretical calculations clarify the controversial size dependences of LSPR reported in the literature, reveal the critical role of surface electron injection or extraction in the transformation between the different size dependences of LSPRs, and are helpful for understanding the nature of surface plasmons in the quantum size regime.

Induced circular dichroism (ICD) has been used to detect biomolecular conformations through the coupling between chiral molecules and achiral metal nanostructures with the localized surface plasmon (LSP). However, this ICD is always weak and cannot be dynamically adjusted. Here, we put dielectric and graphene nanostructures on a metal-substrate for restricting more light energies and obtaining dynamic adjustable performance. A composite nanostructure array composed of achiral silicon-nanorods on a metal-substrate and graphene-ribbons (ASMG) is theoretically investigated. Two strong ICD signals appear in the THz region. Near-field magnetic distributions of ASMG reveal that the two strong ICD signals are mainly due to the surface plasmon resonances (SPPs) on the metal-substrate and LSP in the graphene nanostructures, respectively. The ICD signals strongly depend on the geometric parameters of ASMG and are dynamically adjusted by just changing the Fermi levels of graphene-ribbons. In addition, left-handed ASMG and right-handed ASMG can be used to identify the chiral molecular solutions with different chiralities. The maximum enhancement factor of the chiral molecular solutions could reach up to 3500 times in the THz region. These results can help to design dynamically adjustable THz chiral sensors and promote their application in biological monitoring and asymmetric catalysis.

The spoof localized surface plasmon (LSP) has been widely investigated but mostly with fixed multipole resonances. This Letter proposes a method to generate multipole resonances by adding a slit on the metallic ring of a complementary LSP. This slit theoretically introduces two new boundary conditions and new modes. To validate this approach, complementary LSPs with and without slits at three different angular positions are theoretically analyzed and numerically simulated. To validate and demonstrate the potential application of the proposed LSP structure, a bandpass filter (BPF) in a single-layer substrate is designed and measured by exciting the LSP with a slit on the metallic ring. The measured results show that by simply adding a slit, the BPF achieves a fractional bandwidth of 42.7% (2.5 GHz), for both | S 11 | < − 10 d B and | S 21 | within 1 dB variation. In the passband, a flat group delay between 0.57 ns and 0.75 ns is obtained. Moreover, the proposed structure features a low profile and a compact radius of 0.136 wavelength. By dynamically controlling slit/slits with varactors or diodes, the proposed structure is theoretically promising to be reconfigurable at microwave and even terahertz frequencies.

Localized surface plasmon and Klein tunneling resonances are two phenomena that were previously thought to be unrelated, where the former plays an important role in subwavelength optics while the latter is fundamental to relativistic quantum mechanics and physics of Dirac materials. We develop a rigorous theory for spin-1 Dirac-Weyl particles, which establishes a striking analogy between the two phenomena and unveils a deep connection between the distinct physical contexts, paving the way for gate-controlled surface plasmon mimetic electronics as well as for realizing localized spoof plasmons in a scope wider than previously thought. A possible experimental scheme is articulated.

Surface plasmon enhanced processes and hot-carrier dynamics in plasmonic nanostructures are of great fundamental interest to reveal light-matter interactions at the nanoscale. Using plasmonic tunnel junctions as a platform supporting both electrically- and optically excited localized surface plasmons, we report a much greater (over 1000x) plasmonic light emission at upconverted photon energies under combined electro-optical excitation, compared with electrical or optical excitation separately. Two mechanisms compatible with the form of the observed spectra are interactions of plasmon-induced hot carriers and electronic anti-Stokes Raman scattering. Our measurement results are in excellent agreement with a theoretical model combining electro-optical generation of hot carriers through non-radiative plasmon excitation and hot-carrier relaxation. We also discuss the challenge of distinguishing relative contributions of hot carrier emission and the anti-Stokes electronic Raman process. This observed increase in above-threshold emission in plasmonic systems may open avenues in on-chip nanophotonic switching and hot carrier photocatalysis., 21 pages, 4 figures, plus 27 pages Supporting Info with 7 figures

Owing to their tunable electromagnetic properties, subwavelength structures such as metamaterials have enabled novel applications across fields of engineering. In particular, metal-insulator-metal (MIM) plasmonic metamaterials have demonstrated efficient light energy absorption based on localized surface plasmon resonances. Due to these properties, MIM plasmonic resonance structures present its potential applications for photon absorption or emission at elevated temperatures, such as thermophotovoltaics. However, majority of reported MIM plasmonic structures are built with materials with a lower melting point such as gold or silver. Therefore, there are needs to explore how refractory materials affect the resonance properties of MIM plasmonic structures for high-temperature applications. In this work, we numerically report MIM plasmonic metamaterials built with highly refractory materials. Based on finite-difference timedomain (FDTD) simulation results, light absorption of these metamaterials peaks as high as 99.9% at the wavelength of 8.3 μm. This strong, selective absorption is attributed to the localized surface plasmon resonance. The results of this study suggest that the applications of MIM plasmonic devices may be extended for higher-temperature environments.

We propose the mechanism of edge state-led mode coupling under topological protection; i.e., localized surface plasmons almost do not have any influence on the edge state, while the edge state greatly changes the local field distribution of surface plasmons. Based on this mechanism, in the well-designed topological photonic structure containing a resonant plasmon nanoantenna, an obvious absorption reduction in the spontaneous emission spectra appears due to the near-field deformation around the antenna induced by the edge state. Because a plasmon antenna with ultrasmall mode volume provides large Purcell enhancement and simultaneously the photonic crystal guides almost all scattering light into its edge state, the rate of nonscattering single photons reaches more than 10^{4}γ_{0}. This topological state-led mode coupling mechanism and induced absorption reduction, which are based on topological protection, will have a profound effect on the study of composite topological photonic structures and related micro- and nanoscale cavity quantum electrodynamics. Also, nonscattering large Purcell enhancement will provide practical use for on-chip quantum light sources, such as single-photon sources and nanolasers.

Solar energy is a clean and renewable energy source that has the potential to replace fossil fuel with effective con- version of solar energy to electrical power. Research into thin film solar cells has been of priority because of the lower usage of semiconducting material and thereby lower cost. But the thin film solar cells may also result in low device efficiency caused by inefficient absorption. Researchers are still looking for a better design of solar cell for enhanced performance in terms of light trapping and photocurrent. Various methods have been proposed for enhanced light trapping and efficiency. The nanostructured metal particles in solar cells is shown to produce absorption enhancement due to localized surface plasmon. In this context, we per- form a numerical investigation on the broadband light absorption enhancement in thin-film plasmonic solar cell with nanoparticle array over the silicon layer using Finite Difference Time Domain (FDTD) method. The choice of proper metal nanoparticles, size of nanoparticles and interparticle spacing are crucial in the study. Silver and gold are most studied materials due to their surface plasmon resonances located in the visible range. Aluminium is an abundant material whose surface plasmon resonance is located in the UV region. We performed a detailed investigation into the effect of nanoarray of silver, gold and aluminium nanoparticles over the silicon layer of the plasmonic thin film solar cell on the broadband absorption enhancement of the solar cell. The obtained result were compared for ascertaining the choice of material, size and interparticle spacing for optical absorption enhancement.

This paper reports a rigorous group theoretical method to selectively excite dark mode plasmons of any axially symmetric structures with cylindrical vector beams, based on symmetry analysis of the single V-point cylindrical vector beams basis.

Properties of plasmonic materials are associated with surface plasmons—the electromagnetic excitations coupled to coherent electron charge density oscillations on a metal/dielectric interface. Although decay of such oscillations cannot be avoided, there are prospects for controlling plasmon damping dynamics. In spherical metal nanoparticles (MNPs), the basic properties of localized surface plasmons (LSPs) can be controlled with their radius. The present paper handles the link between the size-dependent description of LSP properties derived from the dispersion relation based on Maxwell’s equations and the quantum picture in which MNPs are treated as “quasi-particles.” Such picture, based on the reduced density matrix of quantum open systems ruled by the master equation in the Lindblad form, enables to distinguish between damping processes of populations and coherences of multipolar plasmon oscillatory states and to establish the intrinsic relations between the rates of these processes, independently of the size of MNP. The impact of the radiative and the nonradiative energy dissipation channels is discussed.

In this Letter, we report a scheme to design multifunctional and multichannel all-optical logic gates based on the in-plane coherent control of localized surface plasmons in an Au nanorod (NR) array on the Si substrate. By using theoretical analysis and structural optimization, we numerically demonstrate a four-channel all-optical logic gate device that can switch three basic logic operations on each NR only by controlling the phase differences of incident beams. This device is ultra-compact in size and shows high extensibility for parallel logic operations, which may be applied in future high-speed on-chip integrated optical computing.

At the interfaces of metal and dielectric materials, strong light-matter interactions excite surface plasmons; this allows electromagnetic field confinement and enhancement on the sub-wavelength scale. Such phenomena have attracted considerable interest in the field of exotic material-based nanophotonic research, with potential applications including nonlinear spectroscopies, information processing, single-molecule sensing, organic-molecule devices, and plasmon chemistry. These innovative plasmonics-based technologies can meet the ever-increasing demands for speed and capacity in nanoscale devices, offering ultrasensitive detection capabilities and low-power operations. Size scaling from the nanometer to sub-nanometer ranges is consistently researched; as a result, the quantum behavior of localized surface plasmons, as well as those of matter, nonlocality, and quantum electron tunneling is investigated using an innovative nanofabrication and chemical functionalization approach, thereby opening a new era of quantum plasmonics. This new field enables the ultimate miniaturization of photonic components and provides extreme limits on light-matter interactions, permitting energy transport across the extremely small plasmonic gap. In this review, a comprehensive overview of the recent developments of quantum plasmonic resonators with particular focus on novel materials is presented. By exploring the novel gap materials in quantum regime, the potential quantum technology applications are also searched for and mapped out.

The tunability of the longitudinal localized surface plasmon resonances (LSPRs) of metallic nanoarcs is demonstrated with key relationships identified between geometric parameters of the arcs and their resonances in the infrared. The wavelength of the LSPRs is tuned by the mid-arc length of the nanoarc. The ratio between the attenuation of the fundamental and second order LSPRs is governed by the nanoarc central angle. Beneficial for plasmonic enhancement of harmonic generation, these two resonances can be tuned independently to obtain octave intervals through the design of a non-uniform arc-width profile. Because the character of the fundamental LSPR mode in nanoarcs combines an electric and a magnetic dipole, plasmonic nanoarcs with tunable resonances can serve as versatile building blocks for chiroptical and nonlinear optical devices.

Complementary metasurfaces composed of randomly-placed arrays of aligned rods or slits are fabricated out of giant magnetoresistance Ni81Fe19/Au multilayers (MLs), a material whose optical properties change under the application of an external static magnetic field. The two metasurfaces are studied from both the experimental and theoretical viewpoints. The induced magnetic modulation (MM) of both the far-field signal and the resonant near field, at the rod/slit localized surface plasmon frequency, are found to obey the Babinet’s principle. Furthermore, the near-field MM is found to be higher than the far-field counterpart. At resonance, both arrays show spots with high values of the magnetic modulated intensity of the electric near field (MM hot-spots). We show that this high magnetic modulation of the near-field intensity is very promising for the future development of high sensitivity molecular sensing platforms in the Mid- and Far-IR, using Magnetic-Modulation of Surface-Enhanced Infrared Absorption (MM-SEIRA) spectroscopy, Ministerio de Economía y Competitividad (AMES (MAT 2014-58860-P), CSIC13-4E-1794, MIRRAS(MAT2017-84009-R), PID2019-107432GB-I00, Quantum Spin Plasmonics (FIS2015-72035-EXP)); Ekonomiaren Garapen eta Lehiakortasun Saila, Eusko Jaurlaritza (KK-2018/00001); Hezkuntza, Hizkuntza Politika Eta Kultura Saila, Eusko Jaurlaritza (No. IT-1164-19); Comunidad de Madrid (S2013/ICE- 2822 (Space-Tec), SINOXPHOS-CM (S2018/BAA-4403)).