Dipole Plasmon Resonance Research Articles

Dual-wavelength superscattering in plasmonic core-shell nanostructures for transparent structural color

Structural coloration generates some of the most vibrant colors in nature and has numerous applications. Inspired by the recently reported transparent displays relying on wavelength-selective scattering, we address the novel problem of transparent structural color, which requires nanoparticles to have a narrow-band and broad-angle scattering response. Although superscattering beyond the single-channel limit has important prospects for enhancing transparent displays, it has not yet been reported. Here, we propose a simple dielectric-gold core–shell nanoparticle capable of superscattering at blue (λ = 450 nm) and green (λ = 532 nm) wavelengths, along with a dipolar surface plasmon resonance (SPR) at the red wavelength (λ = 640 nm), making it suitable for full-color transparent displays. We demonstrate that the superscattering at λ = 450 nm arises from the overlap of the epsilon-near-zero (ENZ) dipolar and quadrupolar modes. Furthermore, the coupling of conventional quadrupolar and dipolar modes can also enhance the scattering efficiency at λ = 532 nm, breaking the single-channel limit. Lastly, we show that the optimized nanoparticles can confine the scattering light within the forward hemisphere at λ = 450 nm and 532 nm, due to the interaction of quadrupolar and dipolar modes. Additionally, they exhibit dipole far-field radiation characteristics at λ = 640 nm with a wide angular beamwidth > 60°. The simple structural nature and unique scattering properties of proposed dielectric-gold core–shell nanoparticles hold promise applications in full-color transparent displays, spectroscopy, and biomedical imaging.

Seedless synthesis of Au nanoplates with tunable plasmonic peaks

Au nanoplates with tunable in-plane dipolar localized surface plasmon resonance peaks in a broad range from the visible to near-infrared region were obtained in high yield using a seedless wet chemical growth method after purification. Cetyltrimethylammonium chloride was used as a surfactant, while hydrogen peroxide and sodium borohydride were used as the weak and strong reducing agents, respectively. The edge length and in-plane dipolar localized surface plasmon resonance peak of the Au nanoplates could be adjusted by varying the amounts of hydrogen peroxide and sodium borohydride. The Au nanoplates were further used as the saturable absorber to generate pulsed laser output in a passively Q-switched solid-state laser at approximately 2 µm. Our study offers a new method for obtaining Au nanoplates with tunable plasmonic peaks over a broad range.

Enhanced inverse Faraday effect and time-dependent thermo-transmission in gold nanodisks

Abstract Nonmagnetic media can be magnetized by light via processes referred to as an inverse Faraday effect (IFE). With nonmagnetic metal nanostructures, the IFE is dominated by the presence of light-induced solenoidal surface currents or plasmons with orbital angular momenta, whose properties depend on both the light and nanostructure geometry. Here, through a systematic study of gold nanodisks with different sizes, we demonstrate order-of-magnitude enhancement of the IFE compared to a bare gold film. Large IFE signals occur when light excites the dipolar plasmonic resonance of the gold nanodisk. We observe that the spectral response of the IFE signal mirrors the spectral response of time-dependent thermo-transmission signals. Our careful quantitative experimental measurements and analysis offer insight into the magnitude of IFE in plasmonic structures for compact, low-power, magneto-optic applications.

Bandwidth of quantized surface plasmons: competition between radiative and nonradiative damping effects.

We investigate the damping effects of coherent electron oscillations on the bandwidth of a quantized nanoparticle plasmon resonance. The nanoparticle (NP) is treated as a two-level quantum system, and the total relaxation time involves both the population relaxation time associated with radiative processes and the collisional relaxation time associated with nonradiative processes that result in dephasing/decoherence of electron oscillations. We describe the optical response of NPs to an external electromagnetic field by the optical Bloch equations employing the density matrix formalism to capture the quantum description nature of dipolar plasmon resonance and suggest a generalized criterion for the validity of dipole approximation. Then we explore the competition between the radiative and nonradiative damping in determining the plasmon bandwidth of two typical NP models; metallic nanospheres and dielectric core-metal shell NPs (nanoshells). We show that the frequency of plasmon resonance, in addition to the NP size, plays an important role in the competition between the damping mechanisms. Consequently, the damping processes are significantly influenced by the factors that determine the resonance frequency, such as the core size, the dielectric constant of the medium, and the shell thickness (for nanoshells). For both models of NPs, we identify the optimum parameters that achieve a narrower plasmon bandwidth (minimal damping), which is a prerequisite for advanced sensing and medical applications. We demonstrate excellent agreement of the simulated spectral features of the plasmon resonance with previously reported experimental results for a single NP where the inhomogeneous broadening of the plasmon line is excluded. For NP ensembles where inhomogeneous broadenings and interface chemical effects are significant, our theoretical approach successfully predicts the overall trend of size-dependent damping rates.

Selective detection of Cysteine via plasmonic silver nanotriangles in the presence of KI with an emphasis on mechanism

Silver nanotriangles (Ag NTs), as the plasmonic sensor, were synthesized for the selective and sensitive detection of Cysteine in the aqueous media in the presence of KI. The identification of Cysteine, among other biogenic amino acids, was achieved within the range of 5–80 μM using UV–Vis spectroscopy; i.e., a red-shift was observed in the wavelength of the dipole plasmon resonance (λDPR) in the presence of Cysteine. The detection limit of the sensor was estimated 120 nM. The mechanism behind this selective detection was attributed to the inhibition effect of the Cysteine in the oxidation of the sharp corners of Ag NTs that would happen in the presence of KI. The concentration of Cysteine was correlated with the λDPR red-shift that stems from the Cysteine stabilization of Ag NTs against KI.

Ultra-narrowband, electrically switchable, and high-efficiency absorption in monolayer graphene resulting from lattice plasmon resonance

We propose a novel approach to obtain the ultra-narrowband, electrically switchable, and high-efficiency absorption in the monolayer graphene. The monolayer graphene is sandwiched between the silica substrate and a square array of silver nanospheres, which is covered by a very thick silica layer. The fundamental role of the thick silica cover layer is to homogenize the surrounding medium of the silver nanospheres, and thus efficiently exciting the lattice plasmon resonance. The lattice plasmon resonance arising from the coupling between the dipolar plasmon resonance of silver nanospheres and the zero-order diffraction wave at Wood anomaly can enhance the electromagnetic fields at the graphene surface, and thus greatly improve the near-infrared light absorption of the monolayer graphene with the maximum absorption efficiency up to 45%. Owing to the low radiation loss of the lattice plasmon resonance, the absorption linewidth of the monolayer graphene can be largely compressed to only several nanometers (3.2 nm ∼ 7.4 nm). Moreover, the absorption of the monolayer graphene in our proposed nanostructures has a nearly 100% modulation depth to exhibit an excellent switching property. Our work will be helpful for some graphene-based photoelectric devices.

Dipol'naya plazmonnaya moda v nanorazmernykh poluprovodnikovykh kvantovykh tochkakh tipa "yadro-obolochka" s geteroperekhodom vtorogo roda

Excited states of nanosize two-component semiconductor core–shell crystals with a type II heterojunction are analyzed. It is demonstrated that the dipole plasmon resonance dominates in their photoabsorption spectra. It is found that the variation of the potential barrier height between the core and the shell in a comparatively narrow range leads to a fundamental change in the form of the collective mode from the surface plasmon resonance typical of the photoabsorption spectra of conducting nanosize particles to the rotational plasmon mode, for which only angular degrees of freedom are excited.

Bandwidth-tunable absorption enhancement of visible and near-infrared light in monolayer graphene by localized plasmon resonances and their diffraction coupling

Bandwidth-tunable light absorption enhancement in monolayer graphene is practically important for graphene-based photoelectric devices. Especially, it is still a huge challenge to achieve high-efficiency graphene absorption with extremely narrow sub-nanometer bandwidth much smaller than one nanometer. In this work, both broadband and narrowband absorption peaks of monolayer graphene are numerically achieved in visible and near-infrared wavelength ranges. The broadband absorption peak is ascribed to localized dipolar plasmon resonances in individual silver nanodisks, and the narrowband absorption peak arises from collective first-order diffraction coupling effect in periodic array of silver nanodisks. By changing the array period, the full width at half maximum (FWHM) of the broadband absorption peak can vary from 100 nm to 50 nm. Correspondingly, the FWHM of the narrowband absorption peak is tuned from about 6.4 nm to only 0.25 nm, thus realizing an ultra-narrow sub-nanometer bandwidth.

Оптическая анизотропия пленок из поливилового спирта с металлическими наностержнями при одноосном растяжении

The possibility of obtaining macroscale anisotropic thin films from polyvinyl alcohol with included metal nanorods under uniaxial tension under conditions that do not lead to a change in the morphology of metal nanoparticles is shown. Silver and gold nanorods were obtained by directed growth from nuclei and then embedded in a polymer matrix based on polyvinyl alcohol. Initially isotropic films with absorption independent of the polarization of the probing light became anisotropic after stretching, which manifested itself in the dependence of the extinction spectra on the polarization of the probing radiation. The weakening of the longitudinal dipole plasmon resonance mode with the simultaneous enhancement of the transverse dipole plasmon resonance when the light polarization is rotated from 0 to 90 degree indicates the orientation of the nanorods in the film along the direction of its stretching. In addition to the change in absorption in the bands of dipole modes, a strong orientational dependence of absorption in the band of the quadrupole mode of the plasmon resonance of metal nanorods was found.

Broadband reflective dual-functional polarization convertor based on all-metal metasurface in visible region

In this paper, a broadband reflective dual-functional polarization convertor based on all-metal anisotropic metasurface was proposed and investigated numerically in visible region. The unit-cell of the all-metal anisotropic metasurface based polarization convertor is composed of the Au ellipse nanostructure adhered on an Au substrate. The proposed anisotropic metasurface can convert the incident linear polarization light into its orthogonal counterpart or circular polarization light by adjusting the geometric parameter of the ellipse nanostructure. When the all-metal anisotropic metasurface functioned as a linear-to-linear polarization convertor (LLPC), the conversion efficiency is over 90% operating from 356.5 THz to 536.5 THz. While the metasurface served as a linear-to-circular polarization convertor (LCPC), the absolute value of polarization extinction ratio (PER) is greater than 10 dB from 336.5 THz to 544.5 THz. The simulated electric field distributions on the unit-cell indicate that the higher polarization converion efficiency is mianly originated from the geometry anistropy and excitations of fundamental and higher-order dipolar plasmon resonance. Thus, our design can be found potential applications in many areas, such as remote nano-sensors, nano-antennas, and radiometers in visible region.

Electron energy-loss spectroscopy investigation of multipolar behavior in Al nanostructure as a function of surface coating with PVP and oxidation

The inherent, self-limiting oxidation characteristics of Aluminum (Al) nanospheres and nanocubes of similar dimensions (100 nm edge length) are illustrated utilizing the MATLAB based boundary element method (MNPBEM17) optical and electron energy loss spectroscopy (EELS) simulations. Such model systems conveniently establish not only the distinct dipolar and multi-polar plasmonic resonance behaviors with reference to their respective passivated ligand PVP as well as their self-limiting surface conformal/non-conformal oxide layers, demonstrating the vital fact that Al nanostructures could be a suitable substitution of conventional noble metals, especially for UV-plasmonic applications. In the case of Al nanocubes, both oxidation processes were found to be strongly site-selective (edges, corners and faces), whereas a differential variation is observed in Al nanospheres from the center to the surface, effectively corroborated through the simultaneous correlation of optical spectra with the spatially and energetically resolved EELS maps. Moreover, the robust contribution from dark plasmon resonances was also confirmed in the EELS data along with the induced surface charge distribution calculations, further substantiating their strong dependence on the surrounding dielectric environment concerning their oxide passivation as well. Thus, our present results demonstrate a better understanding of the spatial coherence of the plasmonic behavior with reference to the passivated ligand and (non)-conformal oxidation processes of Al nanostructures, in general, thereby providing a fundamental understanding of the plasmon physics necessary to improve the design and optimization of new nanostructures for nanophotonic, nanoantenna and sensing applications.

Synthesis of silver nanoparticles using bio valorization coffee waste extract: photocatalytic flow-rate performance, antibacterial activity, and electrochemical investigation.

It is well known that biogenic synthesis, as compared to other processes, has proven to be highly effective in the fabrication of silver nanoparticles (AgNPs). Thus, our current study focused on synthesizing AgNPs using coffee waste extract (CWE). CWE contains many compounds identified by HPLC, which reduce, cap, and stabilize AgNPs in its solution. The as-synthesized AgNPs were produced with a monodispersed small size around 20 nm and exhibited in-plane dipole plasmon resonances of hexagonal nanoplates. AgNPs were characterized by both physical and spectroscopic methods, which confirmed their nanoscale dimensions with a hexagonal shape. The as-prepared AgNPs (12 mg) enabled the photodegradation of phenol compounds (20 mL) with a removal efficiency of ~ 94.6% in a short time in the presence of citric acid. Additionally, the second promising application of AgNPs was the tendency to remove the hazard 2,4 dinitroaniline (2,4 DNA) with a percent more than 97% while using only 7 mg of AgNPs. Moreover, the green synthesized AgNPs are superior in inhibiting bacterial growth and killing most infected microbes such as B. subtilis, P. aeruginosa, S. aureus, and E. coli. The electrochemical characteristics of the AgNPs were evaluated using a three-electrode system. The calculated specific capacitance was 280 F g−1 at 0.56 A g−1. Furthermore, after 1000 cycles at 2.2 A g−1, the AgNPs electrode demonstrates an excellent cycling stability behavior with 94.8% capacitance retention. Based on the previous promising results, it can be concluded that CWE is an environmentally benign extract to prepare AgNPs with low cost, saving and easily used for many great domains in photocatalytic, phenol compound removals, and production of functional nanodevices.

Nonlinear light amplification via 3D plasmonic nanocavities.

Plasmonic nanocavities offer prospects for the amplification of inherently weak nonlinear responses at subwavelength scales. However, constructing these nanocavities with tunable modal volumes and reduced optical losses remains an open challenge in the development of nonlinear nanophotonics. Herein, we design and fabricate three-dimensional (3D) metal-dielectric-metal (MDM) plasmonic nanocavities that are capable of amplifying second-harmonic lights by up to three orders of magnitude with respect to dielectric-metal counterparts. In combination with experimental estimations of quantitative contributions of constituent parts in proposed 3D MDM designs, we further theoretically disclose the mechanism governing this signal amplification. We discover that this phenomenon can be attributed to the plasmon hybridization of both dipolar plasmon resonances and gap cavity resonances, such that an energy exchange channel can be attained and helps expand modal volumes while maintaining strong field localizations. Our results may advance the understanding of efficient nonlinear harmonic generations in 3D plasmonic nanostructures.

Giant dipole plasmon resonance in fluorene (C13H10) molecules

We report the observation of the giant dipole plasmon resonance in the fluorene molecule $({\mathrm{C}}_{13}{\mathrm{H}}_{10})$, a polycyclic aromatic hydrocarbon, upon collisions with H-like silicon ions. An idea of using highly charged ions to create a large perturbation strength is exploited to observe the plasmon state effectively in the electron double-differential distribution. The signature of plasmon excitation is observed directly as a characteristic broad peak in the electron double-differential spectrum. Such an excited state could not be observed for the same molecule when the low charged ions having lower perturbation were used. This is explained by a model based on dipole approximation and linear response theory for the giant plasmon resonance. The angular distribution of these electrons is modeled using the photoelectron angular distribution for an oscillating dipole superimposed with the postcollision interaction due to the long-range Coulomb interaction between the plasmon electrons and the receding projectile ions.

Composite silver nanosurfaces of dipole and quadrupole surface plasmon resonances for fluorescence enhancements

AbstractComposite silver colloidal films (SCFs) prepared with the binary mixtures of homogeneous silver nanoparticles of distinct particle size show strong fluorescence enhancements with 4‐dimethylamino‐4′‐nitrobiphenyl (DNBP). The small and large silver nanoparticles with an average diameter of 82 and 186 nm were chosen for the best spectral overlap between the dipole and quadrupole surface plasmon resonance bands of nanoparticles, respectively, and the emission band of DNBP. From the optimal fluorescence enhancements and strong changes of emission kinetics of DNBP, the composite SCFs of homogeneous silver nanoparticles can be applicable to the development of sensitive fluorescence probes for imaging and sensing purposes.

Ultranarrow and Tunable Fano Resonance in Ag Nanoshells and a Simple Ag Nanomatryushka.

We study theoretically the Fano resonances (FRs) produced by the near-field coupling between the lowest-order (dipolar) sphere plasmon resonance and the dipolar cavity plasmon mode supported by an Ag nanoshell or the hybrid mode in a simple three-layered Ag nanomatryushka constructed by incorporating a solid Ag nanosphere into the center of Ag nanoshell. We find that the linewidth of dipolar cavity plasmon resonance or hybrid mode induced FR is as narrow as 6.8 nm (corresponding to a high Q-factor of ~160 and a long dephasing time of ~200 fs) due to the highly localized feature of the electric-fields. In addition, we attribute the formation mechanisms of typical asymmetrical Fano line profiles in the extinction spectra to the constructive (Fano peak) and the destructive interferences (Fano dip) arising from the symmetric and asymmetric charge distributions between the dipolar sphere and cavity plasmon or hybrid modes. Interestingly, by simply adjusting the structural parameters, the dielectric refractive index required for the strongest FR in the Ag nanomatryushka can be reduced to be as small as 1.4, which largely reduces the restriction on materials, and the positions of FR can also be easily tuned across a broad spectral range. The ultranarrow linewidth, highly tunability together with the huge enhancement of electric fields at the FR may find important applications in sensing, slow light, and plasmon rulers.

High spatial and energy resolution electron energy loss spectroscopy of the magnetic and electric excitations in plasmonic nanorod oligomers.

We leverage the high spatial and energy resolution of monochromated aberration-corrected scanning transmission electron microscopy to study the hybridization of cyclic assemblies of plasmonic gold nanorods. Detailed experiments and simulations elucidate the hybridization of the coupled long-axis dipole modes into collective magnetic and electric dipole plasmon resonances. We resolve the magnetic dipole mode in these closed loop oligomers with electron energy loss spectroscopy and confirm the mode assignment with its characteristic spectrum image. The energy splitting of the magnetic mode and antibonding modes increases with the number of polygon edges (n). For the n=3-6 oligomers studied, optical simulations using normal incidence and s-polarized oblique incidence show the respective electric and magnetic modes' extinction efficiencies are maximized in the n=4 arrangement.

Генерация второй гармоники монослоем сферических двухслойных наночастиц

A model is proposed for calculating the intensity of the second harmonic (SH) when light is reflected from a monolayer consisting of a dielectric core and a plasmon shell of spherical nanoparticles located near the interface of two optically transparent media. The nonlinear polarization of the interface created by nanoparticles, which is the source of SH, is calculated. An increase in the intensity of the reflected SH caused by dipole and quadrupole plasmon resonances in nanoparticles was found. It is shown that the spectral positions of the SH intensity maxima depend significantly on the particle core size and its dielectric permittivity

A novel miniaturized tri-band metamaterial THz absorber with angular and polarization stability

This study presents the design of a novel THz metamaterial absorber with angular stability and polarization insensitivity. The proposed metamaterial absorber is constructed using a square loop enclosing two concentring cross-shaped loops. The proposed unit cell metamaterial has a compact geometry 0.164λeff × 0.164λeff calculated at the lowest operating frequency. The unit cell metamaterial absorber provides dipolar and surface plasmon resonance effect. These resonances provide 98 %, 96 % and 98 % absorption at 0.33 THz, 0.62 THz and 0.82 THz. The parameters of the metamaterial absorber are fully scalable and can be redesigned to suit the needs of any operating frequency by adjusting the lengths of the three loops that compose the unit cell. The symmetric nature of the unit cell absorber provides good polarization stability. The angular stability of the absorber is verified and the results are presented. The proposed metamaterial absorber is a potential choice for use in THz imaging and sensing applications.

Detection of Cobalt Ion Based on Surface Plasmon Resonance of L-Cysteine Functionalized Silver Nanotriangles

A facile and sensitive spectroscopic detection method for the detection of cobalt ion was introduced by the use of the surface plasmon resonance of silver nanotriangles (AgTrngs). After successful capping and functionalizing of AgTrngs, with an average edge length of ~ 54 nm, by trisodium citrate (TSC) and L-Cysteine, they were employed for the detection of cobalt ion based on the change in their in-plane dipole resonance. According to the obtained results, the developed sensor showed a response time as short as 10 s with a detection limit of 3.5 nM in the concentration range of 10–100 nM; in addition, this sensor needs a small volume of samples for cobalt ion determination that makes it ideal for the analysis of the body fluids as well as other aqueous effluents. Finally, based on the transmission electron microscopy, the oxidation of AgTrngs by cobalt ion was proposed as the detection mechanisms that result in the decrease in the in-plane dipole plasmon resonance of AgTrngs.