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Localized surface plasmon interaction of colloidal gold nanoparticles and the resultant changes in the linewidth of plasmon bands are reported. The evolution of the plasmon band in colloids is investigated by increasing the number of particles per unit volume. The volume of the solvent is reduced from 15 to 3 ml by the simple evaporation method. It is observed that the linewidth of the plasmon band varies in a non-uniform manner, which is attributed to the interaction of plasmons from the surface of gold nanoparticles rather than aggregation effects. Indication of aggregation effects such as a progressive redshift in plasmon peak and continuous broadening of linewidth were absent. Gold nanoparticles are prepared using laser ablation of the gold target with nanosecond laser pulses using pure water as a solvent. Change in the linewidth of plasmon bands on colloidal gold nanoparticles with minimized size distribution prepared using laser fluences viz. 5.09, 10.19, 15.28, 20.38 and 25.48 J/cm2 are explored.

The performance improvement of solid-state triplet-triplet annihilation-based photon upconversion (TTA-UC) systems is required for the application to various solar devices. The performance can be improved by making use of the local strong electric field generated through the excitation of localized surface plasmon (LSP) resonance of metal nanostructures. However, since the improvement is effective only within the limited nanospace around nanoparticles (i.e., the near-field effect), a methodology for improving the performance over a wider spatial region is desirable. In this study, a significant improvement in the threshold light excitation intensity (Ith) (77% decrease) as the figure of merit and the upconverted emission intensity (6.3 times enhancement) in a solid-state TTA-UC film with a thickness of 3 μm was achieved by stacking the film with periodic Ag half-shell arrays. The highest-enhanced upconverted emission was obtained by tuning the diffuse reflectance peak, which results from the excitation of LSP resonance of the Ag half-shell arrays, to overlap well with the photoexcitation peak of the sensitizer in the TTA-UC film. The intensity of the enhanced upconverted emission was independent of the distance between the lower edge of the TTA-UC film and the surface of half-shell arrays in the nanometer order. These results suggest that the performance improvement was attributed to the photoexcitation enhancement of the sensitizer by elongating the excitation light path length inside the TTA-UC film, which was achieved through a strong backward scattering of the incident light based on the LSP resonance excitation (i.e., the far-field effect). In addition, the upconverted emission was improved using half-shell arrays comprising low-cost Al, although the enhancement factor was 3.5, which was lower than that of Ag half-shell arrays. The lower enhancement may be attributed to a decrease in the backward scattering of the excitation light owing to the intrinsic strong interband transition of Al at long visible wavelengths.

The optical and dielectric properties of plasmonic of Fe2O3/Au and Fe3O4/Au core/shell nanoparticles were studied using Finite Element computational approach. The optical response of these nanostructures was investigated through the computation of the real and the imaginary parts of the effective dielectric permittivity and the absorption cross-section in the visible-near infrared spectral range. Our findings are as follows. Firstly, we have compared our obtained numerical results with those predicted by Maxwell–Garnett effective medium theory. Secondly, the obtained results reveal that the localized surface plasmons resonance (LSPR) peak shifts to near infrared for a Fe2O3/Au-nanoparticle are similar to that of a Fe3O4/Au-nanoparticle having the same geometric parameters. Thirdly, the optical characteristics of the plasmonic nanoparticles were also studied. Finally, we hope that the developed numerical method can be extended to investigate the electromagnetic coupling within or between particles and its effect on the plasmonic behaviors. This makes the core/shell composite nanoparticles extremely interesting for magnetic, optical and biomedical applications.

Recently, localized surface plasmon resonances (SPRs) of metallic nanoparticles (NPs) have been widely used to construct plasmonic nanohybrids for heterogeneous photocatalysis. For example, the combination of plasmonic Au NPs and TiO2 provides pure TiO2 visible-light activity. The SPR effect induces an electric field and consequently enhances light scattering and absorption, favoring the transfer of photon energy to hot carriers for catalytic reactions. Numerous approaches have been dedicated to the improvement of SPR absorption in photocatalysts. Here, we have designed a core@shell-satellite nanohybrid catalyst whereby an Ag NP core, as a plasmonic resonator featuring unique dual functions of strong scattering and near-field enhancement, is encapsulated by SiO2 and TiO2 layers in sequence, with Au NPs on the outer surface, Ag@SiO2@TiO2-Au, for efficient plasmonic photocatalysis. By varying the size and number of Ag NP cores, the Au SPR can be tailored over the visible and near-infrared spectral region to reabsorb the scattered photons. In the presence of the Ag core, the incident light is efficiently confined in the reaction suspension by undergoing multiple scattering, thus leading to an increase of the optical path to the photocatalysis. Moreover, using numerical analysis and experimental verifications, we demonstrate that the Ag core also induces a strong near-field enhancement at the Au-TiO2 interface via SPR coupling with Au. Consequently, the activity of the TiO2-Au plasmonic photocatalyst is significantly enhanced, resulting in a high H2 production rate under visible light. Thus, the design of a single structural unit with strong scattering and field enhancement, induced by a plasmonic resonator, is a highly effective strategy to boost photocatalytic activity.

The extension of plasmonics to materials beyond the conventional noble metals opens up a novel and exciting regime after the inspiring discovery of characteristic localized surface plasmon resonances (LSPRs) in doped semiconductor nanocrystals originating from the collective oscillations of free holes in the valence band. We herein prepare colloidal monodisperse eccentric dual plasmonic noble metal-nonstoichiometric copper chalcogenide (Au@Cu2−xSe) hybrid hetero-nanostructures with precisely controlled semiconductor shell size and two tunable LSPRs in both visible (VIS) and near-infrared (NIR) regions associated with Au and Cu2−xSe, respectively. Through systematic evaluations of the photocatalytic performance of Au@Cu2−xSe upon sole NIR and dual VIS + NIR simultaneous excitations, we are capable of unambiguously elucidating the role of plasmonic coupling between two dissimilar building blocks on the accelerated photocatalytic reactions with greater rate constants from both experimental and computational perspectives. The significantly enhanced strength of the electromagnetic field arising from efficient plasmonic coupling under the excitation of two LSPRs results in the superior activities of dual plasmonic Au@Cu2−xSe in photocatalysis. The new physical and chemical insights gained from this work provide the keystone for the rational design and construction of high-quality dual- or even multi-plasmonic nano-systems with optimized properties for widespread applications ranging from photocatalysis to molecular spectroscopies.

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.

Plasmonic composites consisting of silver nanostructures and zinc oxide semiconductor have better photocatalytic performance than pure zinc oxide. To prepare the composites, nanostructures of zinc oxide particles, gold spheres, and three different silver morphology including cubes, spheres, and wires were synthesized. A detailed study of the main mechanisms governing the activity of plasmonic photocatalysts showed that the improvement of photocatalytic performance is attributed to localized surface plasmon resonance-mediated energy transfer from silver to zinc oxide. This mechanism, which is performed using non-radiative (near-field) and radiation (far-field) processes, led to an increase in the concentration of e−/h+ pairs near the semiconductor. We also showed that the increase of the photocatalytic activity depends on the shape of the silver nanostructures in the composites. Our theoretical and experimental studies have shown that composites containing silver cubes have the highest increase of photocatalytic activity compared to other morphologies. The percentage of photocatalytic degradation of methylene blue solution in presence of silver cubes was about 15% higher than that of other morphologies. Therefore, by controlling the shape of noble metal nanostructures, the photocatalytic activity of a semiconductor can be maximized and adjusted.

Rare-earth-doped up-converters with Yb3+ as a sensitizer show a high internal conversion efficiency under the excitation at wavelength λ = 980 nm. For the solar cell applications of up-converters, ...

In plasmonic catalysis, localized surface plasmons can be leveraged to drive chemical reactions. This approach is promising for catalyzing many challenging reactions at relatively low temperatures ...

Doped metal oxide nanocrystals (NCs) exhibit tunable localized surface plasmon resonances (LSPRs) in the infrared spectral region. Compared to the binary oxides commonly studied, plasmonic NCs deri...

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.

This paper proposes a novel design of plasmonic perovskite solar cell (PSC). It consists of an anti-reflective glass of fluorine-doped tin oxide (FTO), a compact buffer layer of n-type titanium dioxide (TiO2), an absorbing thin-film layer of perovskite (MAPbI3) integrated with gold (Au) nanospheres, a layer of p-type doped spiro-OMeTAD, and a layer of the cathode on aluminum (Al). This multilayer design’s primary purpose is to allow the light to enter the PSC with the minimum reflection and trap it in the active layer due to the presence of Au nanospheres. In this layer, the higher efficiency of PSC is achieved by localized surface plasmon resonances (LSPRs) in the wavelength range from 300 to 1100 nm. A reflective Al layer is used at the bottom of the device to reflect the light into the upper layers to considerably enhance the PSC absorption. The three-dimensional finite-difference time-domain method was conducted to find the best solution to Maxwell’s equations so that the best thickness and radius can be selected for each layer and Au nanospheres, respectively. Proper physical dimensions and Au nanospheres played a significant role in numerically indicating that the proposed structures are 60% more absorbent than the other conventional PSCs. In-house simulation software is used to approximate the solar cell by applying the finite element method to develop solutions for the drift–diffusion and Poisson’s equations. The examinations of the previous studies revealed that the current study is the first study that has simulated the real model of Auger recombination in perovskite. The results indicated that the proposed PSC embedded with Au nanospheres has the following properties: the built-in potential of 3.16 V, short-circuit current of 27.97 mA/cm2, the open-circuit voltage of 1 V, maximum power of 24.84 mW/cm2, fill-factor of 0.88, the conduction band of 3 eV, electron quasi-Fermi level of 2.5 eV, the hole quasi-Fermi level of 0.6 eV, and efficiency of 24.84%. Finally, the suggested PSC has performed 62% more efficient than conventional PSCs.

Sustainability drives modern technology. Practices ensuring efficient resource utilization, guided resource handling and promotion of negative ecological footprint befittingly implicate “growth”. With manufacturing being one of the major contributing sectors to a nation's economy, adopting greener fabrication processes, the production of cleaner energy and the development of efficient products are important to achieve technological translation. Herein, a bi-functional hybrid (semiconductor–metal) system comprising zinc oxide nano leaves uniformly decorated with gold nano islands was synthesized using a one-step, room temperature biosynthetic reduction strategy. Being a one-step process, the number of reaction reagents and auxiliary byproducts was limited while material engineering ensured efficient product performance derived from coexistence of localized surface plasmon, semiconduction and their synergistic interaction. Detailed characterization of the as synthesized hybrid system concludes presence of defect states, crystalline nature, engineered band gap, pertinent chemical elemental state and interfacial charge distribution features. The hybrid nanostructures show strong surface-enhanced Raman scattering (SERS) characteristics for model R6G molecules (LOD: 10−10 M). Marked with the presence of symmetric and non-totally symmetric Raman vibrations, the role of electromagnetic and chemical enhancement was equally attributed to improved signal strengths. Contribution from charge transfer was verified using off resonance measurements and by studying the photolytic behavior of the nano-hybrid system. The self-cleaning feature of the nanohybrid was tested against a model bacterial contaminant S. aureus, which was killed with 100% efficiency using ∼60 μg ml−1 under natural sunlight.

This review describes recent studies on coupled plasmonic systems for controlling plasmon dynamics and molecular detection using spectral modulations. The plasmon dephasing time can be controlled by weak and strong coupling regimes between the plasmonic nanostructures or localized surface plasmon resonances (LSPRs) and the other optical modes such as microcavities. The modal coupling induces near-field enhancement by extending the plasmon dephasing time to increase the near-field enhancement at certain wavelengths resulting in the enhancement of molecular detection. On the other hand, the interaction between LSPR and molecular excited or vibrational states also modulates the resonance spectrum, which can also be used for detecting a small number of molecules with a subtle change in the spectrum. The spectral modulation is induced by weak and strong couplings between LSPRs and the electronic or vibrational states of molecules, and this method is sensitive enough to measure a single molecule.

Two-dimensional metal carbides and nitrides, known as MXenes, are an emerging class of materials that are promising for a variety of applications. In this work, using time-dependent density functional theory calculations, we investigate the localized surface plasmon resonances and electric field confinement of pristine and surface-terminated [fluorinated (F) and/or oxidized (O)] mono-layered titanium carbide (Ti3C2) MXene nanoclusters. We found that the nanoclusters (Ti48C32, Ti48C32F32, and Ti48C32O32) exhibit broadband photoabsorption spectra and localized surface plasmon resonances even at low energy in the infrared region (a spectral range of interest for molecular sensing). In addition, the nanoclusters produce a sizable electric field confinement on the surface with a strength that varies with the F/O surface termination. Our findings provide significant theoretical insight into the optical and plasmonic properties of MXene nanoclusters.

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.

In this article, we propose an ultra-compact microwave sensor based on an effective localized surface plasmon (ELSP) resonance for complex permittivity measurement of aqueous ethanol solution. The sensitivity of the sensor is dramatically enhanced thanks to the strong electromagnetic (EM) field coupling and enhancement of the ELSP in a deep-subwavelength scale. An equivalent circuit model of the sensor is established for analyzing the sensing mechanism, and the complex permittivity of the aqueous ethanol solution under test is extracted from the S-parameter through an empirical model. For demonstration, we successfully predict the complex permittivity of aqueous ethanol solution with an ethanol concentration of 0%–90% through simulations and experiments. This ELSP-based sensor features an ultra-compact size of $0.008\lambda _{0}^{2}$ and high sensitivity of 0.57% and can find many applications (liquid permittivity measurement, liquid testing, and so on) in highly integrated systems.

Plasmon resonance modulation with an external magnetic field (magnetoplasmonics) represents a promising route for the improvement of the sensitivity of plasmon-based refractometric sensing. To this purpose, an accurate material choice is needed to realize hybrid nanostructures with an improved magnetoplasmonic response. In this work, we prepared core@shell nanostructures made of an 8 nm Au core surrounded by an ultrathin iron oxide shell (

Introducing nanostructured metals with ultraviolet plasmonic characters has attracted much attention for fabricating high performance optoelectronic devices in the shorter wavelength spectrum. In this work, platinum nanoparticles (PtNPs) with controlled plasmonic responses in ultraviolet wavelengths were successfully synthesized. To demonstrate the promising availability, PtNPs with desired sizes were deposited on a hexagonal ZnO microwire via Ga-doping (PtNPs@ZnO:Ga MW). Under ultraviolet illumination, typical near-band-edge emission of ZnO:Ga MW was considerably enhanced; meanwhile, the photocurrent is much larger than that of the bare MW. Thereby, the enhanced phenomena of a ZnO:Ga MW is related to localized surface plasmon resonances of the decorated PtNPs. A single MW with a hexagonal cross-section can be a potential platform to construct a whispering gallery mode (WGM) cavity due to its total inner wall reflection. Given this, the influence of PtNPs via ultraviolet plasmons on lasing features of the ZnO:Ga MW was tested. The lasing characteristics are significantly enhanced, including lasing output enhancement, a clear reduction of the threshold and the improvement of the quality factor. To exploit the working principle, PtNPs serving as powerful ultraviolet plasmons can couple with ZnO:Ga excitons, accelerating radiative recombination. Since fabricating stable, typical nanostructured metals with ultraviolet plasmons remains a challenging issue, the results illustrated in the work may offer a low-cost and efficient scheme for achieving plasmon-enhanced wide-bandgap semiconductor based ultraviolet optoelectronic devices with excellent performances.

Shell-isolated nanoparticles (SHINs) have attracted increasing interest for non-interfering plasmonic enhanced sensing in fields such as materials science, biosensing, and in various electrochemical systems. The metallic core of these nanoparticles is isolated from the surrounding environment preventing direct contact or chemical interaction with the metal surface, while still being close enough to enable localized surface plasmon enhancement of the Raman scattering signal from the analyte. This concept forms the basis of the shell isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) technique. To date, the vast majority of SHIN designs have focused on SiO2 shells around spherical nanoparticle cores and there has been very limited published research considering alternatives. In this article, we introduce a new polymer-based approach which provides excellent control over the layer thickness and can be applied to plasmonic metal nanoparticles of various shapes and sizes without compromising the overall nanoparticle morphology. The SHIN layers are shown to exhibit excellent passivation properties and robustness in the case of gold nanosphere (AuNP) and anisotropic gold nanostar (AuNS) core shapes. In addition, in situ SHINERS spectro-electrochemistry measurements performed on both SHIN and bare Au nanoparticles demonstrate the utility of the SHIN coatings. Correlated confocal Raman and SEM mapping was achieved to clearly establish single nanoparticle SERS sensitivity. Finally, confocal in situ SERS mapping enabled visualisation of the redox related molecular structure changes occurring on an electrode surface in the vicinity of individual SHIN-coated nanoparticles.

The dependence of field splitting characteristics of multilaminar plasmonic structure on its metallic components topology is analyzed. It is found that the coupling interaction between metallic-particle-centered localized surface plasmons generates a collective effect, collective metallic-particles-centered plasmons, to dominantly determine the plasmonic resonances of the structure. When the metallic particles filling ratio within the matrix is high, this collective effect may cause resonance splitting phenomenon and greatly enlarge the frequency range of field splitting enhancement, which is the physical mechanism and also the designing guideline for multilaminar plasmonic broadband perfect absorber. The surface plasmon polaritons are concurrently superimposed on the metallic-particles-centered collective effect to establish an inter-group coupling competition effect, which may strengthen or weaken the preexisting resonance processes through constructive or destructive field interference in between. This serves as the theoretical base for narrowband field splitting enhancement applications. Moreover, we have revealed the existence of the corresponding relationship between the specific field splitting resonance and those participating or dominating metallic particles involved, which provides the advantages to finely tailor field splitting characteristics through precise implantation of nanoparticles.

Given the sub-wavelength trapping challenges in the optical tweezers, the plasmonic tweezers serve as a bridge by breaking the diffraction limit. Hence, the development of plasmonic tweezers can open up many potential applications in biology, medicine, and chemistry. In this paper, using localized surface plasmons (LSPs) of graphene nanodisk with a resonance frequency of 20 THz, we design a lab-on-a-chip optophoresis system, which can be utilized to effectively trap the nanoparticles. The LSPs of graphene nanodisk generate a large field gradient in the deep sub-wavelength area around the resonance frequency. We show that by an appropriate choice of chemical potentials of the graphene nanodisks, the strong optical near-field forces desired for trapping can be generated under the illumination of the THz source when the polystyrene (PS) nanoparticles are located in the vicinity of graphene nanodisks. Numerical simulations show that the designed system with graphene nanodisks of 250 nm in diameter and chemical potentials of $\mu _{c} = 0.6$ eV can trap the PS nanoparticles of 12 nm in diameter and larger with a THz source intensity of 19 $mW/{\mu } {m^{2}}$ , demonstrating acceptable sensitivities for variations in the nanoparticle diameter and refractive index. Moreover, at the same source intensity, the graphene nanodisks with $\mu _{c} = 0.7$ eV can trap the PS nanoparticle as small as 9.5 nm in diameter.

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.

Molecular bond dissociation and formation reactions induced by localized surface plasmons of metal nanostructures are promising reactions in terms of the effective utilization of sunlight. The plas...

Plasmonic materials interact strongly with light to focus and enhance electromagnetic radiation down to nanoscale volumes. Due to this localized confinement, materials that support localized surface plasmon resonances are capable of driving energetically unfavorable chemical reactions. In certain cases, the plasmonic nanostructures are able to preferentially catalyze the formation of specific photoproducts, which offers an opportunity for the development of solar-driven chemical synthesis. Here, using plasmonic environments, we report inducing an intramolecular methyl migration reaction, forming 4-methylpyridine from N-methylpyridinium. Using both experimental and computational methods, we were able to confirm the identity of the N-methylpyridinium by making spectral comparisons against possible photoproducts. This reaction involves breaking a C-N bond and forming a new C-C bond, highlighting the ability of plasmonic materials to drive complex and selective reactions. Additionally, we observe that the product yield depends strongly on optical illumination conditions. This is likely due to steric hindrance in specific regions on the nanostructured plasmonic substrate, providing an optical handle for driving plasmonic catalysis with spatial specificity. This work adds yet another class of reactions accessible by surface plasmon excitation to the ever-growing library of plasmon-mediated chemical reactions.

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.

We theoretically demonstrates large field enhancement at the close-packed, truncated octahedral gold nanoparticle array by using a finite difference time domain method. A multiple peak at the visible and near infrared frequency implies the multiple resonance in the nanostructures, corresponding to the dipolar and quadrupolar mode excitation of electric field at the single octahedral particles. The splitting of two adjacent resonant peak as a function of the distance of the particles implies the existence of the significant coupling between the resonant modes of the individual nanoparticles. The electric field profile at the gap between the particles shows the field enhancement due to such mode couplings, where dipolar and quadrupolar mode are simultaneously involved. Such evolution of mode coupling with increasing gap distance confirms the resonant modes excitation and their coupling is the origin of the strong field enhancement. Simulation with different polarization of the incident light denotes the dominant coupling mode is governed by the size of the interaction area. Importantly, electric field at the gap is hugely enhanced up to 17 at the optimal gap distance of 4 nm.

Metallic nanoparticles have been used to harvest energy from a light source and transfer it to adsorbed gas molecules, which results in a reduced chemical reaction temperature. However, most reported reactions, such as ethylene epoxidation, ammonia decomposition and H–D bond formation are exothermic, and only H–D bond formation has been achieved at room temperature. These reactions require low activation energies ( 3.1 eV) can be initiated at room temperature by using localized surface plasmons in the deep-UV range. As an example, by leveraging simultaneous excitation of multiple localized surface plasmon modes of Al nanoparticles by using high-energy electrons, we initiate the reduction of CO2 to CO by carbon at room temperature. We employ an environmental transmission electron microscope to excite and characterize Al localized surface plasmon resonances, and simultaneously measure the spatial distribution of carbon gasification near the nanoparticles in a CO2 environment. This approach opens a path towards exploring other industrially relevant chemical processes that are initiated by plasmonic fields at room temperature. Metallic nanoparticles used to harvest energy from a light source typically result in reduced chemical reaction temperature. Endothermic reactions requiring higher activation energy can now be initiated at room temperature using localized surface plasmons in the deep-UV range.

The plasmonics of two–dimensional materials, such as graphene, has become an important field over the past decade. The active tunability of graphene via electrical gating or chemical doping has generated a great deal of excitement among engineers seeking sensing devices. Consequently there is significant demand for robust and highly accurate computational capabilities which can simulate such materials. The class of High–Order Perturbation of Surfaces methods have proven to be particularly appropriate for this purpose. In this contribution we describe our recent efforts to utilize both Dirichlet–Neumann Operators and Impedance–Impedance Operators in these schemes. In addition, we present detailed numerical results which not only validate our simulations using the Method of Manufactured Solutions, but we also describe Localized Surface Plasmon Resonances in graphene nanotubes enclosing rod–shaped dielectric materials.

With implication of developments of plasmonic biochips, we investigated laser trapping of cyanobacteria (CB) on a gold nanostructure, where a nanopyramidal dimer array was integrated. Upon near-inf...

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

Localized surface plasmon resonances (LSPRs) in metal nanoparticles can drive chemical reactions at their surface, but it is often challenging to disentangle the exact activation mechanism. The decay of LSPRs can lead to photothermal heating, electromagnetic hot spots, and the ejection of nonthermalized charge carriers, but all of these processes typically occur simultaneously and on ultrafast time scales. Here, we develop a plasmon-assisted Au@Ag core@shell nanorod synthesis in which each plasmon-decay mechanism can be independently assessed. Using different illumination wavelengths combined with extinction spectroscopy, transmission electron microscopy, thermal characterization, and finite-difference time-domain simulations, we unequivocally identify the transfer of interband holes to ascorbic acid as the rate-limiting step in the silver shell growth reaction. Our conclusion is corroborated by single-particle studies of gold nanospheres that display isotropic reactivity, consistent with interband hole-driven nanoparticle syntheses. Our strategy for distinguishing among plasmon-activation mechanisms can be extended to a variety of light-driven processes, including photocatalysis, nanoparticle syntheses, and drug delivery.

Ultrafast laser irradiation can induce morphological and structural changes in plasmonic nanoparticles. Gold nanorods (Au NRs), in particular, can be welded together upon irradiation with femtosecond laser pulses, leading to dimers and trimers through the formation of necks between individual nanorods. We used electron tomography to determine the 3D (atomic) structure at such necks for representative welding geometries and to characterize the induced defects. The spatial distribution of localized surface plasmon modes for different welding configurations was assessed by electron energy loss spectroscopy. Additionally, we were able to directly compare the plasmon line width of single-crystalline and welded Au NRs with single defects at the same resonance energy, thus making a direct link between the structural and plasmonic properties. In this manner, we show that the occurrence of (single) defects results in significant plasmon broadening.

In the past couple of decades, the development of plasmonic nanosensors underwent rapid progress in the fields of fabrication, integration, and realized applications. Localized surface plasmon reso...

Interaction between light and plasmon oscillations in semiconductor nanocrystals has received significant attention in recent years driven, in part, by the possibility of coupling between plasmonic and semiconducting properties. Such coupling could lead to a variety of new applications in plasmonics, photonics, and optoelectronics. In this Concept we discuss the methods for generation of localized surface plasmon resonances in colloidal semiconductor nanocrystals and their unique magneto-optical properties. Different means of introducing free charge carriers, including aliovalent doping, non-stoichiometry, and external charging, are first compared and contrasted. The resulting plasmons can be manipulated using circularly polarized light and external magnetic field, allowing for the formation of the magnetoplasmon modes. The concept of using these magnetoplasmon modes as a new degree of freedom for controlling excitonic states and charge-carrier polarization is introduced and discussed. We also highlight some notable recent examples of controlling plasmon-exciton interactions and comment on their implications for future research in sustainable information technology.

In nanolithographic metallic gratings we investigate the dependence of photonic band gaps on geometrical parameters. Finite element modeling was used to develop a model for an optoelectronic device with periodicity of 470 nm and concomitantly the electronic response of a nanofabricated metal-semiconductor-metal photodetector grating was experimentally studied under a sweeping monochromatic light source. The grating spectral response increased in the region between 470 nm and 520 nm, corroborating the computational results. This increase is understood to occur because photons with wavelength shorter than approximately 520 nm are energetic enough to excite interband transitions in the Au, but the period of the structure acts as a cutoff where incident photons with wavelength shorter than the period are less likely to form surface plasmon polaritons. This cutoff originates from a photonic band gap. Magnetic field intensity profiles at the 3 dB cutoff indicate that a surface plasmon wave exists where each finger interacts with the next through overlapping magnetic fields, suggesting that the cutoff is a surface plasmon wave effect. Localized surface plasmon effects were observed at longer wavelengths in the modeled absorbance. The effects of three geometrical parameters on the spectral dependence of modeled absorbance were investigated.

Exotic electronic excitations beyond normal selection rules would open novel possibilities for photoenergy conversion. The large intensity gradient of electromagnetic fields resulting from the confinement of localized surface plasmons at the molecular scale could exceed the limit of light–matter interactions via modification of electronic excitation selection rules. We discuss the possible application of surface-enhanced Raman scattering as a probe for exotic electronic excitations by reviewing studies on small numbers of molecules at the surface of plasmonic metal nanostructures. Future innovative photo-functionalization is also discussed by considering the excited states produced by the exotic electronic excitations.

Regulation of enzymes is highly relevant toward orchestrating cell-free and stepwise biotransformations, thereby maximizing their overall performance. Plasmonic nanomaterials offer a great opportunity to tune the functionality of enzymes through their remarkable optical properties. Localized surface plasmon resonances (LSPR) can be used to modify chemical transformations at the nanomaterial's surface, upon light irradiation. Incident light can promote energetic processes, which may be related to an increase of local temperature (photothermal effects) but also to effects triggered by generated hotspots or hot electrons (photoelectronic effects). As a consequence, light irradiation of the protein-nanomaterial interface affects enzyme functionality. To harness these effects to finely and remotely regulate enzyme activity, the physicochemical features of the nanomaterial, properties of the incident light, and parameters governing molecular interactions must be optimized. In this Perspective, we discuss relevant examples that illustrate the use of plasmonic nanoparticles to control enzyme function through LSPR excitation. Finally, we also highlight the importance of expanding the use of plasmonic nanomaterials to the immobilization of multienzyme systems for light-driven regulation of cell-free biosynthetic pathways. Although this concept is living its infancy, we encourage the scientific community to advance in the development of novel light-controlled biocatalytic plasmonic nanoconjugates and explore their application in biosensing, applied biocatalysis, and biomedicine.

A light delivery system based on localized surface plasmon (LSP) is the key component of heat-assisted magnetic recording (HAMR). We demonstrated a novel resonator–antenna system as the light delivery system for HAMR. We numerically analyzed the interaction mechanism between the resonator waveguide and the antenna. The localized enhanced resonated field of the resonator can improve the electric-field enhancement of the antenna. Based on the interaction mechanism, we proposed the ring resonator to achieve higher electric-field enhancement of light spots as the resonated field can be several times higher than input light under the resonance condition. The input laser energy can be recycled by limiting the energy in the ring waveguide without using higher power laser sources. Numerical results show that the nanofocusing performance in the ring resonator system would be much better than normal light systems. The maximum electric-field enhancement of light spots can be 124, and the absorption efficiency can be about 10% in the ring-lollipop system. The proposed resonator–antenna system can effectively increase the nanofocusing performance of the light delivery system for HAMR.

The photocatalytic reduction of CO2 with H2O to fuels and chemicals using solar energy is one of the most attractive but highly difficult routes. Thus far, only a very limited number of photocatalysts has been reported to be capable of catalyzing the photocatalytic reduction of CO2 under visible light. The utilization of the localized surface plasmon resonance (LSPR) phenomenon is an attractive strategy for developing visible-light photocatalysts. Herein, we have succeeded in synthesizing plasmonic MoO3−x-TiO2 nanocomposites with tunable LSPR by a simple solvothermal method. The well-structured nanocomposite containing two-dimensional (2D) molybdenum oxide (MoO3−x) nanosheets and one-dimensional (1D) titanium oxide nanotubes (TiO2-NT) showed LSPR absorption band in the visible-light region, and the incorporation of TiO2-NT significantly enhanced the LSPR absorption band. The MoO3−x-TiO2-NT nanocomposite is promising for application in the photocatalytic reduction of CO2 with H2O under visible light irradiation.

Three-dimensional (3D) plasmonic structures have attracted great attention because abnormal wetting behavior of plasmonic nanoparticles (NPs) on 3D nanostructure can enhance the localized surface plasmons (LSPs). However, previous 3D plasmonic nanostructures inherently had weak plasmonic light absorption, low electrical conductivity, and optical transmittance. Here, we fabricated a novel 3D plasmonic nanostructure composed of Ag NPs as the metal for strong LSPs and 3D nano-branched indium tin oxide (ITO BRs) as a transparent and conductive framework. The Ag NPs formed on the ITO BRs have a more dewetted behavior than those formed on the ITO films. We experimentally investigated the reasons for the dewetting behavior of Ag NPs concerning the geometry of ITO BRs. The spherical Ag NPs are spatially separated and have high density, thereby resulting in strong LSPs. Finite-domain time-difference simulation evidenced that spatially-separated, high-density and spherical Ag NPs formed on ITO BRs dramatically boost the localized electric field in the active layer of organic solar cells (OSCs). Photocurrent of PTB7:PCBM OSCs with the ITO BRs/Ag NPs increased by 14%.

Plasmonic Au/TiO2 thin film works as a stable water oxidation photoanode. Here we show that site-selective deposition of nanosized CoOx as a water oxidation cocatalyst at the edge of Au nanoparticles on the TiO2 film improves the photoelectrochemical water oxidation activity. The nanosized CoOx was deposited by a photoassisted electrochemical method onto the Au/TiO2 thin film. The CoOx loading amount was controllable by changing the amount of electric charge that flowed during the deposition, which influenced the photoelectrochemical performance. Under visible light, the optimized CoOx/Au/TiO2 thin film generated stable photoanodic current, which was similar to 3 times higher than that obtained using Au/TiO2.

Recently, plasmonic nanofluids (i.e., a suspension of plasmonic nanoparticles in a base fluid) have been widely employed in direct-absorption solar collectors because the localized surface plasmon supported by plasmonic nanoparticles can greatly improve the direct solar thermal conversion performance. Considering that the surface plasmon resonance frequency of metallic nanoparticles, such as gold, silver, and aluminum, is usually located in the ultraviolet to visible range, the absorption coefficient of a plasmonic nanofluid must be spectrally tuned for full utilization of the solar radiation in a broad spectrum. In the present study, a modern design process in the form of a genetic algorithm (GA) is applied to the tailoring of the spectral absorption coefficient of a plasmonic nanofluid. To do this, the major components of a conventional GA, such as the gene description, fitness function for the evaluation, crossover, and mutation function, are modified to be suitable for the inverse problem of tailoring the spectral absorption coefficient of a plasmonic nanofluid. By applying the customized GA, we obtained an optimal combination for a blended nanofluid with the desired spectral distribution of the absorption coefficient, specifically a uniform distribution, solar-spectrum-like distribution, and a step-function-like distribution. The resulting absorption coefficient of the designed plasmonic nanofluid is in good agreement with the prescribed spectral distribution within about 10\% to 20\% of error when six types of nanoparticles are blended. Finally, we also investigate how the inhomogeneous broadening effect caused by the fabrication uncertainty of the nanoparticles changes their optimal combination., 4 figures

In this article, we present a theoretical study on localized surface Plasmon of spherical Ag nanoparticles (NPs) done by numerical simulation. A plane EM wave was used to determine absorption cross-section and results showed that excitation of LSPPs produced an electric field on the surface of the nanoparticle. This field causes a large cross sectional area that influences higher scattering of incident photon at the surface of an absorber layer. It was concluded that LSPPs excitations in small size spherical particles can be utilized in low-cost solar cells to increase PCE of solar panels and can be expanded to many other fields of optoelectronic technologies ranging from solar cells, through photo diodes to optical bio-sensing applications.

Recently, studies have been carried out on attempts to combine surface-enhanced Surface-enhanced Raman spectroscopy (SERS) substrates that can be based on either localized surface plasmon (LSP) or surface plasmon polaritons (SPP) structures. By combining these two systems, the drawbacks of each other can be solved. However, the manufacturing methods involved so far are sophisticated, labor-intensive, expensive, and also technically demanding. We propose a facile method for the fabrication of a flexible plasmonic nanoslit SERS sensor. We utilized the pattern on periodic optical disks (DVD-R) as a cheap substitute for printing the periodic pattern on PDMS with soft imprint lithography. Ag nanoslit (AgNS) was fabricated by serial bideposition using a dynamic oblique angle deposition (DOD) technique. The nanoslit structures were physically and optically characterized, and the experimental results were compared to the numerical simulation studies; Monte Carlo and the finite-difference time-domain (FDTD) simulation. The Ag nanoslit structure showed an excellent SERS enhancement, and its biosensing capability was demonstrated by the sensing of bilirubin.

Plasmonic color generation has attracted much research interest because of the unique optical properties of plasmonic nanocrystals that are promising for chromatic applications, such as flat-panel displays, smart windows, and wearable devices. Low-cost, monodisperse plasmonic nanocrystals supporting strong localized surface plasmon resonances are favorable for the generation of plasmonic colors. However, many implementations so far have either a single static state or complexities in the particle alignment and switching mechanism for generating multiple displaying states. Herein, we report on a facile and robust approach for realizing the electrochemical switching of plasmonic colors out of colloidal plasmonic nanocrystals. The metal nanocrystals are coated with a layer of polyaniline, whose refractive index and optical absorption are reversibly switched through the variation of an applied electrochemical potential. The change in refractive index and optical absorption results in the modulation of the plasmonic scattering intensity with a depth of 11 dB. The electrochemical switching process is fast (∼5 ms) and stable (over 1000 switching cycles). A device configuration is further demonstrated for switching plasmonic color patterns in a transparent electrochemical device, which is made from indium tin oxide electrodes and a polyvinyl alcohol solid electrolyte. Our control of plasmonic colors provides a favorable platform for engineering low-cost and high-performance miniaturized optical devices.

Synthesis of anisotropic Ag nanoprisms (AgPRs) contributes to the development of high performance plasmonic devices. The localized surface plasmon resonance wavelength of AgPRs was successfully tun...