Plasmon Resonance Modes Research Articles

Dynamic Spectral Modulation Enabled by Conductive Polymer-Integrated Plasmonic Nanodisk-Hole Arrays.

The electrically driven optical performance modulation of the plasmonic nanostructure by conductive polymers provides a prospective technology for miniaturized and integrated active optoelectronic devices. These features of wafer-scale and flexible preparation, a wide spectrum adjustment range, and excellent electric cycling stability are critical to the practical applications of dynamic plasmonic components. Herein, we have demonstrated a large-scale and flexible active plasmonic nanostructure constructed by electrochemically synthesizing nanometric-thickness conductive polymer onto spatially mismatched Au nanodisk-hole (AuND-H) array on the poly(ethylene terephthalate) (PET) substrate, offering low-power electrically driven switching of reflective light in a wide wavelength range of 550-850 nm. The composite structure of the polymer/AuND-H array supports multiple plasmonic resonance modes with strong near-field enhancement and confinement, which provides an excellent dynamic spectral modulation platform. As a result, the PPy/AuND-H array achieves 18.4% reversible switching of spectral intensity at 780 nm and speedy response time, as well as maintains a stable dynamic modulation range at two-potential cycling between -0.6 and 0.1 V after 200 modulation cycles. Compared to the case of the PPy/AuND-H array, the PANI/AuND-H array obtains a more extensive intensity modulation of 25.1% at 750 nm, which is attributed to the significant differences in the extinction coefficient between the oxidized and reduced states of PANI, but its modulation range degrades apparently after 20 cycles driven at applied voltages between -0.1 and 0.8 V. Additionally, the cycling stability could be further improved by reducing the modulation voltage range. Our proposed electromodulated composite structure provides a promising technological proposal for dynamically plasmonic reconfigurable devices.

Chiral Gold Nanorods with Five‐Fold Rotational Symmetry and Orientation‐Dependent Chiroptical Properties of Their Monomers and Dimers

AbstractChiral plasmonic nanoparticles have attracted much attention because of their strong chiroptical responses and broad scientific applications. However, the types of chiral plasmonic nanoparticles have remained limited. Herein we report on a new type of chiral nanoparticle, chiral Au nanorod (NR) with five‐fold rotational symmetry, which is synthesized using chiral molecules. Three different types of Au seeds (Au elongated nanodecahedrons, nanodecahedrons, and nanobipyramids) are used to study the growth behaviors. Different synthesis parameters, including the chiral molecules, surfactant, reductant, seeds, and Au precursor, are systematically varied to optimize the chiroptical responses of the chiral Au NRs. The chiral scattering measurements on the individual chiral Au NRs and their dimers are performed. Intriguingly, the chiroptical signals of the individual chiral Au NRs and their end‐to‐end dimers are similar, while those of the side‐by‐side dimers are largely reduced. Theoretical calculations and numerical simulations reveal that the different chiroptical responses of the chiral NR dimers are originated from the coupling effect between the plasmon resonance modes. Our study enriches chiral plasmonic nanoparticles and provides valuable insight for the design of plasmonic nanostructures with desired chiroptical properties.

Chiral Gold Nanorods with Five-Fold Rotational Symmetry and Orientation-Dependent Chiroptical Properties of Their Monomers and Dimers.

Chiral plasmonic nanoparticles have attracted much attention because of their strong chiroptical responses and broad scientific applications. However, the types of chiral plasmonic nanoparticles have remained limited. Herein we report on a new type of chiral nanoparticle, chiral Au nanorod (NR) with five-fold rotational symmetry, which is synthesized using chiral molecules. Three different types of Au seeds (Au elongated nanodecahedrons, nanodecahedrons, and nanobipyramids) are used to study the growth behaviors. Different synthesis parameters, including the chiral molecules, surfactant, reductant, seeds, and Au precursor, are systematically varied to optimize the chiroptical responses of the chiral Au NRs. The chiral scattering measurements on the individual chiral Au NRs and their dimers are performed. Intriguingly, the chiroptical signals of the individual chiral Au NRs and their end-to-end dimers are similar, while those of the side-by-side dimers are largely reduced. Theoretical calculations and numerical simulations reveal that the different chiroptical responses of the chiral NR dimers are originated from the coupling effect between the plasmon resonance modes. Our study enriches chiral plasmonic nanoparticles and provides valuable insight for the design of plasmonic nanostructures with desired chiroptical properties.

Electrically tunable and switchable perfect infrared absorber based on ENZ material

In this paper, a dynamically tunable and switchable perfect infrared absorber is put forward, which is composed of a gold ring array, an indium tin oxide (ITO) layer, an alumina (Al2O3) spacer and a continuous Au film from top to bottom. Epsilon-near-zero (ENZ) mode in ITO layer is excited by localized surface plasmon resonance (LSPR) mode of the gold ring. With the increase of the biasing voltage V, the carrier concentration of ITO material decreases, and the absorption peak caused by ENZ resonance blue shifts obviously. Notice that our infrared absorber can realize bidirectional switching of “ON” and “OFF” states at 1210 nm, with modulation depth of 70 % and switching contrast (SC) of 241 %, manifesting its excellent electrical regulation performance. After verification, the switching performance of our absorption structure has a high precision tolerate of the manufacturing process. A clear Fano type absorption curve appears in the wavelength range 1000 nm–1300 nm, under the biasing voltage V of 3.4 V. Moreover, a series of small absorption peaks are produced by Fabry-Pérot (F–P) resonance in the horizontal plane caused by the standing wave in the ENZ layer, and this phenomenon is unexpected. We propose a theoretical interpretation for the absorption mechanism in both cases based on multiple interference model. It is also proved that the proposed infrared absorber is polarization insensitive and exhibits high absorptance (>90 %) over an incident range of 0 deg–60 deg. The electrically tunable absorption switch function makes our absorber have potential in selective thermal emitters, infrared sensors, infrared stealth, beam focusing and other fields.

Enhanced optical sensing with metal-insulator-metal nanohole arrays integrated with silver nanoparticles

The field of plasmonic sensing has witnessed rapid advancements in recent years. This work proposes an innovative methodology that employs metal–insulator-metal (MIM) nanohole arrays integrated with ring-shaped silver nanoparticles (AgNPs) to serve as an effective plasmonic refractive index sensor. The hybrid substrates are prepared using a combination of nanosphere lithography (NSL), reactive ion etching, and an enhanced plasmonic site-selective photocatalytic reaction, ensuring large-area fabrication, high throughput, and cost-effectiveness. The resonance peaks observed in the visible-NIR spectra are attributed to the coupling of surface plasmon resonance modes between MIM structures and AgNPs. The resonance wavelength exhibits sensitively to changes in the surrounding medium within the refractive index range of 1 to 1.5, with a remarkable sensitivity of 835 nm/RIU. Our findings reveal the significant potential of this technology for advancing optical sensing applications.

Epsilon-near-zero material-based bi-layer metamaterials for selective mid-infrared radiation

Selective mid-infrared (MIR) radiation is highly desirable in many applications. However, there are still great challenges to simultaneously achieve MIR camouflage and radiative cooling utilizing simple structure. This work theoretically and experimentally proposes a bi-layer metamaterial composed of aluminum doped zinc oxide (AZO) nanoparticles embedded in Al2O3 matrix on the aluminum film. The bi-layer metamaterial exhibits high performance in MIR camouflage with radiative cooling, a low emissivity ( = 0.11, = 0.20) in atmospheric windows and a high emissivity ( = 0.81) in non-atmospheric windows. The interaction of the epsilon-near-zero (ENZ) mode and localized surface plasmon resonance (LSPR) mode is responsible for the perfect emission over the wavelength range of 5–8 m. Additionally, the proposed selective MIR emitter supports large-angle incidence and has great polarization insensitivity. This demonstrates that epsilon-near-zero material-based bi-layer metamaterial is highly promising for the development of selective mid-infrared radiation.

Investigation of the SERS application of gold films deposited on uncured polydimethylsiloxane with tunable LSPR

We present an approach to investigate the localized surface plasmon resonance and surface-enhanced Raman scattering of gold films deposited on uncured polydimethylsiloxane via thermal evaporation. Differing from solid substrates, the liquid surface of uncured polydimethylsiloxane can serve as an isotropic substrate on which gold atoms nucleate and disperse to form characteristic microstructures in a controlled manner. By adjusting experimental parameters during film deposition, the absorption of resonant plasmon modes can be tuned in the visible spectral range due to the control of particle size and distribution in Au films. Furthermore, Raman measurements are conducted to investigate the enhancement of Raman signals in these films, and the experimental results are verified by simulation analysis. This work exhibits tunability of surface plasmon resonance frequency and enhanced Raman detection capability by depositing metal films on liquid surfaces, thus providing potential applications of these films in flexible biosensors and chemical detection.

Metasurface Absorbers with Film-Coupled Au Nanoclusters to Achieve Broadband and Polarization-Independent Absorption of UV-Vis Light.

Metasurface absorbers (MAs) have attracted widespread interest in the recent study of subwavelength artificial optical metasurfaces, although most reported MAs suffer from the actualities of costly and time-consuming fabrications, narrow working bandwidth, polarization-dependent responses, etc., somewhat limiting their practical applications. Herein, we introduce a facile and low-cost method to fabricate MAs with excellent absorption performances via the self-assembly of synthesized Au nanoclusters (NCs) on a Au film spaced by a nanoscale-thick dielectric SiO2. Interestingly, the proposed MAs with well-designed Au film-coupled Au NCs (i.e., an appropriate surface coverage of Au NCs and the compatible thickness of the SiO2 spacer) exhibited a measured average absorbance above 90% within a broad UV-vis wavelength band (200-800 nm). In addition, owing to the MAs' topological symmetry, their UV-vis absorption behaviors presented polarization insensitivity with the incident light angles ranging from 20 to 50°. It has been demonstrated that the excited different surface plasmon resonance modes between Au NCs and the adjacent Au film were vital; in addition, the light-trapping effects from "V"-shaped structures of Au NCs were favorable for the designed MAs with enhanced light absorption. We believe that such MAs and the potential self-assembly fabrication strategy may facilitate scalable optical applications such as photothermalvoltaics, ultraviolet protection, optical storage, and sensing.

Perfect Solar Absorber Based on Four-Step Stacked Metamaterial

Solar absorbers are of great significance in the development of new energy technologies. However, the current approaches are mostly complex and fail to achieve high absorption rates across a wide range of wavelengths. Here, we propose a four-step stacked metamaterial solar absorber that achieves near-perfect absorption. Our four-step stacked absorber (FSSA) boasts an average absorption rate of 96.32% from 499 nm to 2348.3 nm, and a high average absorption rate of 94.96% from 300 nm to 2500 nm. Electromagnetic mode analysis and the impedance matching theory were employed to analyze the designed FSSA, which revealed that the high absorption rates are due to the propagating surface plasmon resonance (PSPR) and localized surface plasmon resonance (LSPR) modes. The FSSA offers broadband, high absorption rates, and high spectrum selectivity. Additionally, the structural parameters are adjusted to optimize the proposed perfect solar absorber. This proposed absorber can have promising applications in the renewable energy industry.

Magnetic Field Sensor Based on Magnetic Optical Surface Plasmon Resonance

Surface plasmon resonance with high sensitivity is widely used in molecular dynamics detection. Herein, a magneto‐optic surface plasmon resonance (MOSPR) sensor based on Au/Co/Au thin film for detecting magnetic fields is developed. The strong coupling between the magneto‐optical waveguide mode and the surface plasmon resonance mode is analyzed and the linear relationship between the reflectivity of the MOSPR sensor and the magnetic field is established. The response, response–recovery time, and dispersion relationship for different magnetic fields are also numerically simulated. Additionally, experimental data on the MOSPR sensor's response to magnetic fields at room temperature (25 °C) are obtained. During the experiment, a differential signal in the light path is applied to reduce the noise generated by the environment. The results demonstrate that the MOSPR sensor exhibits high response, ultrafast response time, and long‐term stability. The study provides a promising approach for detecting magnetic fields with high sensitivity and accuracy.

Design of an agile optical switcher based on a 1D silver plasmonic nanograting filled with a nonlinear Kerr material

In this paper, we investigate the nonlinear optical response characteristics of a metallic nanograting with nonlinear Kerr media within its slits using the finite element method. The proposed nanograting system is illuminated by a nanosecond Gaussian pulse laser under normal incidence and the electric filed pointing across the slits. The results show a perfect linear absorption at resonance wavelength thanks to the coupling of the surface plasmon resonance (SPR) mode and photon cavity mode. We simulate the transient nonlinear absorption variation of the system when the pulse laser is set up at either resonance or off-resonance wavelengths. The results indicate that the unit linear absorption drastically decreases by increasing the laser fluence around the center of the pulse. Interestingly, one can also enhance the weak linear off-resonance absorption to the value of unit by increasing the pulse laser fluence. The higher the laser fluence, the higher the maximum absorption contrast between linear and nonlinear regimes occurs owing to the nonlinear Kerr effect. Indeed, when the laser fluence reaches a critical value, it can excite the Kerr nonlinearity, which changes the coupling strength of SPR mode and the photon cavity mode leading to the absorption adjustment in the nanograting. These properties indicate the possibility of utilizing the proposed nanograting in dual functional absorber and nonabsorber systems, which make it an appropriate candidate for agile optical switching devices.

Effective strategy to improve photocatalytic activity in concave Au NRs-Pt-CdS hetero-nanostructure

Photocatalytic water splitting for hydrogen (H2) production has been comprehensively investigated for application in the field of energy science. However, the energy conversion efficiency is not satisfactory in some practical aspects. In this work, we proposed a well-controlled synthetic strategy to develop concave gold nanorods (Au NRs) with substantially enhanced photocatalytic performance for H2 production. Concave Au NRs with high-index facets are synthesized using the one-step process in aqueous solution. Morphology evolution and plasmon properties of concave Au NRs are carefully studied by adjusting several key growth parameters. Different from the cylindrical Au NRs synthesized using seed-mediated method, the extinction spectra of concave Au NRs show three plasmon resonance modes (transverse edge mode, transverse hybrid mode, and longitudinal corner mode). Pt nanoparticles and CdS nanocrystals are selectively grown onto Au NRs through the composition design. The photocatalytic H2 production rate of concave Au NRs-Pt-CdS hetero-nanostructure reaches a value as high as 21654.56 μmol·g−1·h−1. These characteristics suggest the great potential of novel faceted metal nanostructures for excellent performance of photocatalysis applications.

Sonocatalytic Optimization of Titanium-Based Therapeutic Nanomedicine.

Recent considerable technological advances in ultrasound-based treatment modality provides a magnificent prospect for scientific communities to conquer the related diseases, which is featured with remarkable tissue penetration, non-invasive and non-thermal characteristics. As one of the critical elements that influences treatment outcomes, titanium (Ti)-based sonosensitizers with distinct physicochemical properties and exceptional sonodynamic efficiency have been applied extensively in the field of nanomedical applications. To date, a myriad of methodologies has been designed to manipulate the sonodynamic performance of titanium-involved nanomedicine and further enhance the productivity of reactive oxygen species for disease treatments. In this comprehensive review, the sonocatalytic optimization of diversified Ti-based nanoplatforms, including defect engineering, plasmon resonance modulation, heterojunction, modulating tumor microenvironment, as well as the development of synergistic therapeutic modalities is mainly focused. The state-of-the-art Ti-based nanoplatforms ranging from preparation process to the extensive medical applications are summarized and highlighted, with the goal of elaborating on future research prospects and providing a perspective on the bench-to-beside translation of these sonocatalytic optimization tactics. Furthermore, to spur further technological advancements in nanomedicine, the difficulties currently faced and the direction of sonocatalytic optimization of Ti-based therapeutic nanomedicine are proposed and outlooked.

Sensitivity-Tunable Terahertz Liquid/Gas Biosensor Based on Surface Plasmon Resonance with Dirac Semimetal

In this paper, we study the sensitivity-tunable terahertz (THz) liquid/gas biosensor in a coupling prism–three-dimensional Dirac semimetal (3D DSM) multilayer structure. The high sensitivity of the biosensor originates from the sharp reflected peak caused by surface plasmon resonance (SPR) mode. This structure achieves the tunability of sensitivity due to the fact that the reflectance could be modulated by the Fermi energy of 3D DSM. Besides, it is found that the sensitivity curve depends heavily on the structural parameters of 3D DSM. After parameter optimization, we obtained sensitivity over 100°/RIU for liquid biosensor. We believe this simple structure provides a reference idea for realizing high sensitivity and a tunable biosensor device.

Study on the Transmission and the Field Enhancement of Bi-Rhombic Aperture Arrays Structure

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

Enhanced upconversion luminescence using long-range surface plasmon resonance mode with prism coupler

In the study, we present the significant enhancement of the upconversion luminescence by taking advantage of long-range surface plasmon resonance mode. Compared with the reflection enhanced upconversion luminescence of Ag film, the intensity of upconversion luminescence enhanced by long-range surface plasmon resonance mode is improved 100 times. Additionally, the finite-difference time-domain simulation indicates that the incident light energy can concentrate in the upconversion nanoparticles doped dielectric layer at the long-range surface plasmon resonance mode, which the maximum electric field enhancement factor |E|2/|E0|2 can reach to 58. The experimental result shows that the upconversion luminescence enhancement is related to the thickness of doped Polymethylmethacrylate (PMMA) layer. Furthermore, due to the excited upconversion luminescence having high directionality, it is shown that the strong upconversion luminescence could be received at the specific angle.

Broadband Four‐Wave Mixing Enhanced by Plasmonic Surface Lattice Resonance and Localized Surface Plasmon Resonance in an Azimuthally Chirped Grating

AbstractPlasmonic enhancement of nonlinear light–matter interaction can be achieved via dedicated optimization of resonant plasmonic modes that are spectrally matched to the different wavelengths involved in the particular nonlinear optical process. Here, the generation and enhancement of broadband four‐wave mixing (FWM) are investigated in a plasmonic azimuthally chirped grating (ACG). The azimuthally varying grating periodicity in an ACG offers a well‐defined channel to mediate the near field and the far field over a broad range of wavelengths. However, the particular mechanism responsible for field enhancement in such a platform depends on the interplay between the effects manifested by both the groove geometry and the grating's periodicity. This work delineates the collective contribution of groove geometry‐dependent localized surface plasmon resonance and periodicity‐dependent plasmonic surface lattice resonance over a broad range of wavelengths to bring into effect the enhancement of broadband FWM in an ACG.

Characterization of the material and electrical properties depending on the Mg:Ag ratio as a cathode for TEOLED

In this study, Mg:Ag mixed alloy films were comprehensively analyzed as a potential transparent cathode, depending on the deposition ratio of Mg:Ag atoms. It was determined that the work function, refractive index, and film formation characteristics varied depending on the deposition ratio of Mg:Ag, and affected electro-optical characteristics such as transmittance and sheet resistance. In addition, the applicability of the proposed transparent cathode for top emitting organic light-emitting diodes (TEOLEDs) was analyzed by comprehensively considering the TEOLED performance in relation to the Mg:Ag deposition ratio. The TEOLED performance was optimized by adjusting the Mg:Ag transmittance, sheet resistance and appropriate work function, and the emission spectrum could be controlled by localized surface plasmon resonance (LSPR) and cavity mode coupling effect.

Interaction of plasmonic bound states in the continuum

Bound states in continuum (BICs) are believed to have the ability to achieve high quality factor (Q factor) resonances, which is very important for plasmonics. However, the study of plasmonic BICs is not sufficient. Herein, we design and fabricate a metal−insulator−metal (MIM) metasurface and demonstrate a one-dimensional plasmonic BIC experimentally. The even-order localized surface plasmon resonance (LSPR) modes have even parity at normal incidence. The symmetry-protected BIC can be achieved at Γ point. The band structure can be tuned by strong coupling between the localized plasmonic resonance and plasmonic lattice mode. Interestingly, two of the hybrid modes are also BICs. Although BICs cannot interact with the far field, we successfully demonstrate BIC splitting through far-field excitation. By further tuning the pitch of the MIM grating, the Friedrich–Wintgen BIC is also observed. Finally, we propose and preliminarily demonstrate an ultrathin bandpass spatial filter. These findings provide a new platform to study optical multipole BICs and can have applications in fields such as nano lasers, ultrasensitive sensors, filters, nonlinearity enhancement, and quantum optics.

Tunable Layered Gold Nanochips for High Sensitivity and Uniformity in SERS Detection

Reasonable design and controllable fabrication of plasmonic substrates are the keys to achieving surface-enhanced Raman spectroscopy (SERS) detection with high sensitivity and uniformity. The coupling of the two main modes of surface plasmon, the localized surface plasmon resonance (LSPR) mode and the surface plasmon polariton (SPP) mode, has been proven to be an appealing way to obtain excellent SERS responses. Nevertheless, it remains an obstacle to further improve the LSPR-SPP coupling efficiency due to the dramatic nonuniformity of the nanostructure obtained by traditional wet chemical methods. Here, we report a controllable electron-beam lithography (EBL) process for the fabrication of layered Au nanochips. For the optimized Au CFN (cap and film nanostructure) structure, benefiting from the remarkable electric field enhancement induced by the effective LSPR-SPP coupling at the junction of the Au cap and Au film structure, an improved SERS performance with an enhancement factor (EF) of 2.8 × 106 and a low detection limit of 10–13 M are achieved using 4-nitrothiophenol (4-NTP) as the probe molecule. In addition, the Au CFN substrate exhibits a high uniformity over a large area. Such a new strategy for the design of plasmonic substrates with superior LSPR-SPP coupling can be applied in various SERS detection scenarios.