Plasmonic States Research Articles

Complex Permittivity Spectra of Granular Polymer Composites with Dispersed Ag-Coated Cu Flakes

AbstractConductive particle-containing granular composites with tuneable negative permittivity are being studied to improve the performance of electromagnetic devices, such as shielding materials. In this study, we investigated the relative complex permittivity and electrical conductivity of granular composites of polyphenylene sulfide (PPS) resin and Ag-coated Cu flakes in the radio- to microwave-frequency range and compared them with those of PPS/bare Cu flake composites. Electrical conductivity measurements revealed that the PPS/Ag-coated Cu flake composites have a lower percolation threshold (φc) than the PPS/bare Cu flake composites, whereas the electrical conductivity of the PPS/Ag-coated Cu flake composites in the percolated particle state was higher at the same particle volume fraction. At particle contents above φc, a low-frequency plasmonic state of conduction electrons was achieved in the percolated particle chains in both composites, and negative permittivity spectra were obtained. The percolated PPS/Ag-coated Cu flake composites had a negative permittivity up to a higher frequency than the percolated PPS/bare Cu flake composites. Furthermore, the Drude model was used to analyze the negative permittivity spectra of the composites in the percolated particle state. The plasma frequency of the composites with percolated Ag-coated Cu flakes was higher than that of the composites with percolated bare Cu flakes. Thus, coating Ag on Cu particles improved the conductivity of the composite, leading to negative permittivity up to higher frequencies. This study contributes to the enhancement of the negative permittivity achieved by granular composites, which is useful for microwave technology applications. Graphical Abstract

Highly Tunable Light Absorber Based on Topological Interface Mode Excitation of Optical Tamm State.

Optical absorbers based on Tamm plasmon states are known for their simple structure and high operational efficiency. However, these absorbers often have limited absorption channels, and it is challenging to continuously adjust their light absorption rates. Here, we propose a Tamm plasmon state optical absorber composed of a layered stack structure consisting of one-dimensional topological photonic crystals and graphene nano-composite materials. Using the four-by-four transfer matrix method, we investigate the structural relationship of the absorber. Our results reveal that topological interface states (TISs) effectively excite the optical Tamm state (OTS), leading to multiple absorption peaks. This expands the number of absorption channels, with the coupling number of the TIS determining the transmission quality of these channels-a value further adjustable by the period number of the photonic crystals. Tuning the filling factor, refractive index, and thickness of the graphene nano-composite material allows for a wide range of control over the device's absorption rate, from 0 to 1. Additionally, adjusting the defect layer thickness, incident angle, and Fermi energy enables us to control the absorber's operational bandwidth and the switching of its absorption effect. This work presents a new approach to expanding the tunability of optoelectronic devices.

Theoretical study of an electrochemically controlled polymer nanoantenna for optical switch

Conventional metallic nanoantennas allow the control of light at the nanoscale, but their untunable structural settings and material properties limit their optical modulation. Methods for dynamical control and modulation of light have become a hot topic in the development and application of nanooptics. Here, we propose a bowtie polymer poly (3,4-ethylenedioxythiophene:sulfate) (PEDOT:Sulf) nanoantenna that enables dynamical control of the optical responses by electrochemical modulation of the plasmonic (oxidated) and dielectric (reduced) states of polymers. The switch effect of the nanoantenna is related to its electric polar mode. In addition, we explore the dependence of the optical response of the nanoantenna on structural parameters in detail. The tunable response of the nanoantenna has promising applications in optical switch and encoding in information transmission.

Reversible Modulation of Plasmonic Coupling of Gold Nanoparticles Confined within Swellable Polymer Colloidal Spheres.

Dynamic optical modulation in response to stimuli provides exciting opportunities for designing novel sensing, actuating, and authentication devices. Here, we demonstrate that the reversible swelling and deswelling of crosslinked polymer colloidal spheres in response to pH and temperature changes can be utilized to drive the assembly and disassembly of the embedded gold nanoparticles (AuNPs), inducing their plasmonic coupling and decoupling and, correspondingly, color changes. The multi-responsive colloids are created by depositing a monolayer of AuNPs on the surface of resorcinol-formaldehyde (RF) nanospheres, then overcoating them with an additional RF layer, followed by a seeded growth process to enlarge the AuNPs and reduce their interparticle separation to induce significant plasmonic coupling. This configuration facilitates dynamic modulation of plasmonic coupling through the reversible swelling/deswelling of the polymer spheres in response to pH and temperature changes. The rapid and repeatable transitions between coupled and decoupled plasmonic states of AuNPs enable reversible color switching when the polymer spheres are in colloidal form or embedded in hydrogel substrates. Furthermore, leveraging the photothermal effect and stimuli-responsive plasmonic coupling of the embedded AuNPs enables the construction of hybrid hydrogel films featuring switchable anticounterfeiting patterns, showcasing the versatility and potential of this multi-stimuli-responsive plasmonic system.

Three-Dimensional random network of metacomposites by synergizing Multi-Walled carbon Nanotube-Carbon black for tunable Epsilon-Negative and Epsilon-Near-Zero responses

Epsilon-near-zero (ENZ) and epsilon-negative (EN) responses are remarkable properties of electromagnetic (EM) metamaterials that have sparked considerable interest. This paper introduces an innovative strategy using ternary metacomposites that achieve excellently tunable ENZ (|ε’| < 1) and EN (ε’ < 0) parameters within the radio-frequency band. The approach leverages a synergistic effect of multi-walled carbon nanotube-carbon black (MWCNT-CB) composites integrated into a polyaniline (PANI) matrix to construct three-dimensional (3D) carbon networks. As the loading content of MWCNT-CB increases, these networks evolve from clusters, enabling a finely tunable range of EN parameters from 100 to 103. The ENZ response occurs at approximately 265 MHz and 830 MHz, triggered by dielectric resonance due to electric dipoles at MWCNT-CB/PANI interfaces and a low-frequency plasmonic state in the 3D MWCNT-CB networks, respectively. This research establishes a foundation for tunable ENZ and EN responses by introducing a new class of ternary metacomposites.

Percolation-Triggered Negative Permittivity in Nano Carbon Powder/Polyvinylidene Fluoride Composites.

Percolating composites exhibiting negative permittivity have garnered considerable attention due to their promising applications in the realm of electromagnetic shielding, innovative capacitance devices, coil-less inductors, etc. Nano carbon powder/polyvinylidene fluoride (CP/PVDF) percolating composites were fabricated that exhibit Drude-type negative-permittivity behavior upon reaching the CP percolation threshold. This phenomenon is attributed to the formation of a plasmonic state within the interconnected CP network, enabling the delocalization of electrons under the alternating electric field. Furthermore, a significant (nearly two orders of magnitude) increase in the conductivity of sample is observed at a CP content of 12.5 wt%. This abrupt change coincides with the percolation phenomenon, suggesting a transition in the conduction mechanism. To elucidate this behavior, comprehensive analyses of the phase composition, microstructure, AC conductivity, and relative permittivity were performed. Additionally, the sample containing 5 wt% CP exhibits a remarkably high permittivity of 31.5, accompanied by a relatively low dielectric loss (tanδ < 0.2). The findings expand the potential applications of PVDF, while the fabricated percolating composites hold promise for electromagnetic shielding, antennas, and other electromagnetic devices.

Long-range molecular energy transfer mediated by strong coupling to plasmonic topological edge states

Abstract Strong coupling between light and molecular matter is currently attracting interest both in chemistry and physics, in the fast-growing field of molecular polaritonics. The large near-field enhancement of the electric field of plasmonic surfaces and their high tunability make arrays of metallic nanoparticles an interesting platform to achieve and control strong coupling. Two dimensional plasmonic arrays with several nanoparticles per unit cell and crystalline symmetries can host topological edge and corner states. Here we explore the coupling of molecular materials to these edge states using a coupled-dipole framework including long-range interactions. We study both the weak and strong coupling regimes and demonstrate that coupling to topological edge states can be employed to enhance highly-directional long-range energy transfer between molecules.

Plasmonic Bound States in the Continuum Metasurface-Semiconductor-Metal Architecture Enables Efficient Hot-Electron-Based Photodetector.

Plasmonic hot-electron-based photodetectors (HEB-PDs) have received widespread attention for their ability to realize effective carrier collection under sub-bandgap illumination. However, due to the low hot electron emission probability, most of the existing HEB-PDs exhibit poor responsivity, which significantly restricts their practical applications. Here, by employing the binary-pore anodic alumina oxide template technique, we proposed a compact plasmonic bound state in continuum metasurface-semiconductor-metal-based (BIC M-S-M) HEB-PD. The symmetry-protected BIC can manipulate a strong gap surface plasmon in the stacked M-S-M structure, which effectively enhances light-matter interactions and improves the photoresponse of the integrated device. Notably, the optimal M-S-M HEB-PD with near-unit absorption (∼90%) around 800 nm delivers a responsivity of 5.18 A/W and an IPCE of 824.23% under 780 nm normal incidence (1 V external bias). Moreover, the ultrathin feature of BIC M-S-M (∼150 nm) on the flexible substrate demonstrates excellent stability under a wide range of illumination angles from -40° to 40° and at the curvature surface from 0.05 to 0.13 mm-1. The proposed plasmonic BIC strategy is very promising for many other hot-electron-related fields, such as photocatalysis, biosensing, imaging, and so on.

Suppressing the radiation loss by hybrid Tamm-surface plasmon BIC modes

Tamm plasmon polaritons (TPPs), localized near the boundary of a dielectric Bragg reflector (DBR) and a thin metal film, have attracted much attention for the lower ohm loss and flexible excitation. However, the radiation loss resulting from the direct coupling to the surroundings hinders their applications. Here, we propose and experimentally demonstrate a new type of hybrid plasmonic quasi-bound state in the continuum (BIC) in a Tamm-surface plasmon polariton system to suppress the radiation loss. Leveraging the scattering of the periodic metal array, the TPP interacts with the surface plasmon polariton (SPP) mode and form a Friedrich-Wintgen type quasi-BIC state that originated from the interference of two surface waves with different natures. Through angle resolved reflectance spectrum measurement, the hybrid plasmonic quasi-BIC was observed in the experiment. Our work proposes a new method to design a high Q mode in plasmonic systems, and thus holds promise for applications in the field of light matter interactions.

Lignin-Derived Lightweight Carbon Aerogels for Tunable Epsilon-Negative Response.

Electromagnetic (EM) metamaterials have garnered considerable attention due to their capacity to achieve negative parameters, significantly influencing the integration of natural materials with artificially structural media. The emergence of carbon aerogels (CAs) offers an opportunity to create lightweight EM metamaterials, notable for their promising EM shielding or absorption effects. This paper introduces an efficient, low-cost method for fabricating CAs without requiring stringent drying conditions. By finely tuning the ZnCl2/lignin ratio, the porosity is controlled in CAs. This control leads to an epsilon-negative response in the radio-frequency region, driven by the intrinsic plasmonic state of the 3D carbon network, as opposed to traditional periodic building blocks. This approach yields a tunable and weakly epsilon-negative response, reaching an order of magnitude of -103 under MHz frequencies. Equivalent circuit analysis highlights the inductive characteristics of CAs, correlating their significant dielectric loss at low frequencies. Additionally, EM simulations are performed to evaluate the distribution of the electric field vector in epsilon-negative CAs, showcasing their potential for effective EM shielding. The lignin-derived, lightweight CAs with their tunable epsilon-negative response hold promise for pioneering new directions in EM metamaterials and broadening their application in diverse extreme conditions.

Ultraweakly low-dispersion epsilon-negative response of GR-CNT/PVDF ternary metacomposites

The epsilon-negative (ε’ < 0) response displayed by metacomposites offers notable potential for diverse applications in the design of dielectric and electromagnetic (EM) devices, underpinned by novel principles. However, achieving a weakly low-dispersion ε′-negative performance within the radio frequency (RF) band remains challenging. In this study, we bypassed this issue by constructing three-dimensional (3D) conductive networks through the integration of graphene (GR) and carbon nanotubes (CNT) with polyvinylidene fluoride (PVDF) serving as the matrix material. Leveraging the modifiable GR-CNT network, a ε′-negative response at approximately −20 was attained spanning the 100 MHz-1 GHz range. This ultraweak ε′-negative response was attributed to the formation of a moderate plasmonic state of free carriers within the metacomposites. Further, simulations were conducted, assessing the electric field vector distribution of the ε′-negative materials, revealing promising EM shielding performance. Concurrently, this investigation elucidates the RF ε′-negative response mechanism, paving the way for the practical application of metacomposites.

Optical band structure with enhanced plasmonic effect of SiO2/rGO bilayer deposited by spray pyrolysis

Reduced graphene oxide (rGO) has been extensively studied as an alternative plasmonic material which offers activity at broad wavelength region. A bilayer film combining SiO2 and rGO was successfully deposited on a glass substrate by spray pyrolysis. For a comparative review, the rGO from commercial product (rGO-com) and from our samples (rGO-csc) derived from biomass (coconut shell) are used in this study. X-ray diffractometry (XRD), scanning electron microscopy (SEM), and X-ray photoemission spectroscopy (XPS) were used to characterize these materials. The existence of plasmonic state was clarified by investigating the real component of the dielectric function and by applying the base layer correction of optical conductivity, derived from UV–Vis spectra at wavelength of 300–1000 nm. The real part of the dielectric constant was approximately −20 and −10 for SiO2/rGO-csc and SiO2/rGO-com films respectively. Meanwhile, the optical conductivity for both samples has confirmed a peak of around ∼3.5 eV, indicating the presence of correlated plasmon. Broadly speaking, the rGO can be employed to generate the plasmon effect in term of either conventional or correlated plasmons. This result also offers the groundwork for the development of potentially far-reaching discipline of graphene plasmonics, where the usage of biomass-derived rGO-like compounds leading to increasing optical characteristics is interestingly superior to that of the commercial rGO.

Modulating molecular plasmons in naphthalene via intermolecular interactions and strong light-matter coupling.

We conducted a theoretical investigation on the modulation of plasmon-like resonances in naphthalene - the so-called molecular plasmons - through intermolecular interactions and strong light-matter coupling. The configuration interaction with single excitations (CIS) approach and its quantum electrodynamics extension (QED-CIS-1) are used to describe the molecular plasmon states under these interactions. We detail the effects of changing intermolecular distances of the naphthalene dimer and incorporating the naphthalene molecule into optical cavities, both allowing for precise control of naphthalene's plasmonic responses. Our results show significant shifts of the plasmon peak in the absorption spectra of naphthalene, depending on the spatial configuration of the dimer and cavity parameters such as polarization, frequency, and coupling strength. Further investigation of the naphthalene dimer in a cavity reveals a synergistic effect on the plasmon peak when the two types of interactions are combined. This research provides insights into the plasmonic behavior of simple polyacenes like naphthalene and opens up possibilities for plasmon modulation in more complex systems.

Extremely low-frequency plasmonic state achieved in AC-ZnO polymer composite for tuned negative permittivity applications

Flexible composites with negative permittivity behaviour have generated a lot of attention due to their potential applications in the electromagnetic field and novel capacitance. This work aimed to design and explore surface microstructure-induced negative permittivity flexible composites for their metamaterial properties. The composites were synthesized using poly (methyl methacrylate) or PMMA, activated carbon (AC), and zinc oxide (ZnO) through an in-situ polymerization process. The composite was designed to acquire negative permittivity in the extremely low-frequency regime by increasing the AC and ZnO filling content. The microstructure formation, real permittivity, and ac conductivity of the composites were investigated, and it was observed that the negative permittivity and its magnitude could be controlled by changing the amount of the filler, AC_ ZnO. Flexible composites with suitable permittivity values for ELF applications can create heavy industrial demand.

Tunable negative permittivity performance of carbon/silicon dioxide ceramic metacomposites under external DC bias voltage

Metacomposites with negative permittivity have gained increasing momentum in recent years due to their unique electromagnetic characteristics and considerable potential application. However, how to adjust negative permittivity is still a big technical challenge to overcome. In this paper, silicon dioxide (SiO2) ceramic metacomposites consisting of carbon fibers (CFs) were fabricated by vacuum hot press sintering, and their negative permittivity might be modified by adjusting the filler content and applying external direct current (DC) bias voltages. As the CF content increased, the electrical conductivity of composites increased markedly, and the conduction mechanism transformed to a metal-like conductivity from hopping conductivity. The permittivity values of composites with high CF contents were negative at the test frequency range owing to the appearance of a low plasmonic state of unbound electrons in the percolating carbon networks. The conductivity of the composites increased when DC bias voltage was applied, because some of the accumulated local electrons at the CF-SiO2 interface could absorb energy and become free electrons. Larger bias voltages led to increased concentration of free electrons, so the absolute values of the negative permittivity raised according to the Drude model and the frequency band of negative permittivity became wider. This work presents an effective approach for adjusting the negative permittivity value and frequency band, which is advantageous in clarifying the realization and regulation mechanisms of negative permittivity.

Vibrational Probe at the Electrochemical Interface: Dependence on Plasmon Coupling and Potential of the Lineshape in Two-Dimensional Infrared Spectroscopy.

Two-dimensional infrared spectroscopy of vibrational probes at an electrode surface shows promise for studying the structural dynamics at an active electrochemical interface. This interface is a complex environment where the solution structures in response to the applied potential. A strategy for achieving the necessary monolayer sensitivity is to use a plasmonically active electrode, which enhances the electromagnetic fields that produce the spectroscopic response. Here, we show how the coupling between the plasmon and the vibrations of the molecular monolayer impacts the FTIR and 2D IR spectroscopy, with an emphasis on the electrochemical potential difference spectra. We show how mixing between the vibrational and plasmonic states gives rise to the distortions that are observed in these measurements. This provides an important step toward 2D IR measurements of vibrational probes at the electrochemical interface as a tool for probing the structural dynamics in the double layer.

Exploring the potential of broadband Tamm plasmon resonance for enhanced photodetection.

Tamm plasmon polaritons (TPPs) have emerged as a promising platform for photodetector applications due to their strong light-matter interaction and potential for efficient light absorption. In this work, a design for a broadband photodetector (PD) based on the optical Tamm plasmon (OTS) state generated in a periodic metal-semiconductor-distributed Bragg reflector (DBR) geometry is proposed. The transfer matrix method (TMM) was used to study the propagation of electromagnetic waves through the proposed structure. By exciting the structure with incident light and analyzing the electric field profile within the multilayer structure at the resonant wavelength, we observe a distinctive electric field distribution that indicates the presence of Tamm plasmon modes. A comparative study was conducted to investigate the optical properties of a photodetector in the near-infrared (NIR) range by varying parameters such as thickness. By optimizing the thickness, we successfully achieved a broadband photoresponse in the photodetector, with a maximum responsivity of 21.8mA/W at a wavelength of 1354nm, which falls within the photonic bandgap region. FWHM was found to be 590nm for the responsivity spectrum. The geometry also presents maximum absorption with FWHM calculated to be about 871.5nm. The proposed geometry offers a broadband photoresponse, which is advantageous for the advancement of Tamm-based detector technologies. The ability to detect light over a wide operation range makes this mechanism highly beneficial for various applications.

Fine-tunable ε′-negative response derived from low-frequency plasma oscillation in graphene/polyaniline metacomposites

Remarkable ε′-negative responses at radio-frequency endow metacomposites with revolutionary applications in electromagnetic (EM) fields. However, uncovering its regulation mechanism and subsequently achieving fine-tunable ε′-negative response remains challenging. Here, we meticulously designed graphene/polyaniline (GR/PANI) metacomposites above percolation, which directly enable tunable negative permittivity at an order of magnitude of −103. By rationally adjusting the three-dimensional GR network, we were able to form collective low-frequency plasma oscillation of free electrons in composites, which intrinsically contributes to the tunable ε′-negative response. Moreover, an ε′-near-zero (ENZ) response was surprisingly observed at ∼920 MHz due to the ineffectiveness of the plasmonic state at high frequencies. In addition, we carried out equivalent circuit analysis to demonstrate the phase relationship and electrical characteristics of these metacomposites. This work could contribute to a new category of polymer-matrix composites and enable exotic properties beyond their natural and bulk counterparts.

Strong coupling of hybrid states of light and matter in cavity-coupled quantum dot solids

The formation of plasmon-exciton (plexciton) polariton is a direct consequence of strong light-matter interaction, and it happens in a semiconductor–metal hybrid system. Here the formation of plasmon-exciton polaritons was observed from an AgTe/CdTe Quantum Dot (QD) solid system in the strong coupling regime. The strong coupling was achieved by increasing the oscillator strength of the excitons by forming coupled QD solids. The anti-crossing-like behaviour indicates the strong coupling between plasmonic and excitons state in AgTe/CdTe QD solids, resulting in a maximum Rabi splitting value of 225 meV at room temperature. The formation of this hybrid state of matter and its dynamics were studied through absorption, photoluminescence, and femtosecond transient studies.

Tunable flatband plasmonic quasi-bound states in the continuum based on graphene-assisted metasurfaces

Bound states in the continuum (BICs) of plasmonic systems offer a powerful method for enhancing light–matter interaction at the nanoscale. The recent emergence of flatband quasi-BICs has alleviated the limitation of the incident angle of the excitation light on generating high-quality-factor (high-Q-factor) resonances, which makes it feasible to produce substantial near-field enhancement by focused light. However, the current works are limited to passive systems with fixed amplitude and Q-factor, hindering the dynamic tunability of light field enhancement. Here, we design a plasmonic metasurface integrated with monolayer graphene to achieve tunable flatband quasi-BICs. Under the illumination of a tightly focused transverse-magnetic wave, our simulations show that adjusting the chemical potential of graphene can increase Q-factor from 52.5 to 75.9 and improve absorption amplitude from 81% to 95%. These results pave the way for dynamically adjustable near-field enhancement with tightly focused light.