Plasmonic Structures Research Articles

(Invited) Quantitative Photonic Characterization and Modelling of Light Emission, Confinement, and Enhancement in Nanostructured Materials

Optical spectroscopy and imaging provide non-destructive, contactless, and fast strategies to study the nature and technological aspects of thin films and nanostructured materials for photonic and optoelectronic applications. Furthermore, the design, engineering, and optimization of such devices requires quantitative information with high-precision standards in measuring and modelling as is the case, for example, in the determination of the optical critical dimension (OCD) in the semiconductor industry. Our application of these strategies to the study of tunable self-assembled nanolasers, hybrid photonic-plasmonic sensors, and photovoltaic devices, among many other materials and devices has led us to the development of i) new modelling strategies based on the Finite-Difference Time-Domain (FDTD) method, and ii) home-made customizable characterization strategies based on spectroscopic ellipsometry (SE). The advantages of the FDTD method include its ability to i) obtain a wide spectral response from one time-domain simulation, ii) model single non-periodic structures, and iii) flexibility and generality to include, for example, non-linear and thermal effects. On its part, SE stands out from other optical techniques because, as a self-referenced and phase sensitive strategy, it can deliver extreme precision and sensitivity and has demonstrated flexibility that has been implemented in multiple spectral ranges and operation conditions. With this in mind, our group has systematically demonstrated the synergic use of FDTD-SE strategy, with complementary strengths and close-matched precision, in a range of materials and devices. We will report the fundamentals, status of our on-going efforts, and a critical review of the perceived limitations and expected outcomes of the FDTD-SE strategy as a quantitative tool for photonic and plasmonic subwavelength structures of interest in optoelectronic, sensing, and energy applications.We gratefully acknowledge the financial support from the RGC (Projects CityU - 11210218, 11219919, 11215121 and 11310122) and ITC (Project ITS/461/18) of HKSAR, China.

Ultrafast spatiotemporal control of orthogonally directional surface plasmon polariton via a compact nanoantenna

Ultrafast spatiotemporal control over the launch direction of surface plasmon polariton (SPP), which is highly desirable for the realization of integrated nanophotonic devices and ultrafast data processing systems within plasmonic nano-circuitry, remains a significant challenge. In particular, ultrafast spatial-temporal switching of SPP directional emissions in orthogonal directions has not yet been reported. Here, we propose a novel compact plasmonic nanoantenna structure design for spatiotemporal control of SPP launch at the nano−femto scale. This device possesses the capacity to launch the SPP directionally into different orthogonal output channels by changing the polarization direction of incident light. More importantly, ultrafast switching of the SPP directional launch at a femtosecond time scale has been proposed via adjusting the instantaneous polarization state of the excitation light. This study can lay the foundation for the development of miniaturized signal processing systems for high-speed data processing, and highly integrated nanophotonic devices, as well as for enhancing the functionality of next-generation optical nanocircuits.

3985Utilizing EllipticalRingIMI-Plasmonic Waveguides, Nanomaterials in Nanophotonic Structure for All-Optical 2 × 1 Demultiplexer

In many industries, particularly electronics, photonic devices are indispensable. However, the diffraction limit and miniaturization are the two problems that have hampered the development of photonics devices. These problems are resolved by plasmonic devices, which enable nanophononics and nanodevices. One of the primary all-optical demultiplexer components utilized in an all-optical Athematic Logic Unit (ALU), which is regarded as the basic building block for all-optical computers, is a plasmonic demultiplexerThis paper provides a new design for an elliptical ring insulator-metal-insulator (IMI) plasmonic waveguide-based all-optical demultiplexer (Demux). The suggested device has a small footprint (300 nm × 250 nm) and works at a 1550 nm wavelength. Demux has a 0.5 transmission threshold between logic zero and logic one states. Transmission (T), extinction ratio (contrast ratio (CR)), modulation depth (MD), and insertion loss (IL) are the four metrics that best explain the performance of the plasmonic Demux. The suggested structural dimensions are outstanding and optimal based on the values of MD for Demux which is (95.87%). The device's maximum transmission efficiency is 56.84%. The suggested plasmonic Demux structure makes a substantial contribution to all-optical signal processing Nano-circuits and nano-photonics integrated circuits. Using COMSOL Multiphysics, wesimulate the proposed plasmonic Demux using the Finite Element Method (FEM).

Multiple Fano Resonance Modes based Plasmonic Refractive Index Sensor for Edible Oil Adulteration Detection

Surface plasmon polariton (SPP)-based plasmonic sensors are increasingly replacing traditional bulky sensors in refractive index sensing, biosensing, food adulteration detection, and other applications due to their unique optical features and different Metal-Insulator-Metal (MIM) topologies. The present research introduces a new design for a highly sensitive MIM waveguide-based refractive index sensor. This design incorporates an innovative combination of an inverted U-shaped rectangular split-ring resonator (RSRR), a semi-circle-split-ring resonator (SCSRR), and a stub. The sensor’s wave-guiding capabilities, such as electromagnetic wave transmission, field profile distribution, and sensitivity, are meticulously analyzed using a two-dimensional finite-element method. The key objective of this device is to identify slight differences in the refractive index by observing shifts in resonant wavelength through the light’s interaction with the plasmonic structure. Moreover, optimizing the geometric parameters significantly enhances the sensor’s performance. The optimized sensor achieves a maximum refractive index sensitivity of 2400 nm/RIU, a figure of merit (FOM) of 45.28, and a Q-factor of 39.86, as demonstrated by simulation results. Further investigations reveal the MIM structure’s capacity to detect adulteration in edible oils, underscoring the sensor’s adaptability and its potential for widespread biosensing applications.

High-sensitive and compact plasmonic temperature sensor based on square-shaped ring resonators

In this study, a plasmonic structure based on metal-insulator-metal waveguides and square ring resonators is designed and simulated for temperature sensing. The sensing operation is carried out using an enhancement in the interference of sub-wavelength waves. The effect of various factors, such as the number and geometric dimensions of the resonators, on the sensor's reflection spectrum is thoroughly investigated. The results obtained from the finite-difference time-domain simulations indicate that the sensitivity, figure of merit, and temperature sensitivity values for a square ring resonator are 1281 nm/RIU, 73 RIU−1, and 0.505 nm/°C, respectively. Additionally, by using three square ring resonators, the figure of merit increases to 154 RIU−1. The size of the sensors is smaller than 1 µm2. Due to their highly compact size and desirable sensing characteristics, the proposed sensors have great potential for application in various industrial and medical applications.

Unraveling the multilayer solid-electrolyte interphase in lithium batteries through depth-sensitive plasmon-enhanced Raman spectroscopy: A theoretical and experimental study

The solid-electrolyte interphase (SEI) plays a crucial role in determining the lithium deposition/dissolution behaviors, thus influencing the reversible operation of Li metal batteries renowned for their ultrahigh specific capacity. Recently, we developed a depth-sensitive plasmon-enhanced Raman spectroscopy (DS-PERS) method enabling the in situ and nondestructive characterization of the nanostructure and chemistry of SEI through synergistic plasmonic structures. However, a lack of comprehensive elucidation of the enhancement mechanisms has impeded a detailed understanding of the depth-resolved signal contributions. In this study, we integrate theoretical computations with experimental methodologies to systematically unravel the working principles of the synergistic plasmonic structures, demonstrating that hot spots can effectively detect Raman signals at key locations across various stages of SEI layer evolution. Following Li deposition, the hot spots transfer from the Cu interfaces to the Li interfaces. With the thickening of the deposited Li, the localized surface plasmon resonance of Cu is gradually shielded, leading to the disappearance of hot spots originated from Li-Li coupling. Subsequently, we propose the utilization of Cu@Li-multilayer shell-isolated nanoparticles to compensate and introduce new hot spots, thereby enhancing the depth sensitivity. Our work provides theoretical insights essential for achieving precise depth-resolved PERS characterization.

Operando Colorations from Real-Time Growth of 3D-Printed Nanoarchitectures.

While artificial 3D nanostructures can generate precise and flexible coloration, their real-time color changes during 3D nanoprinting remain unexplored owingto the inherent challenges of in situ transient measurements and observations. In this study, a 3D-printing system which supports the operando observation/measurement of the color dynamics of subwavelength metallic nanoarchitectures fabricated in real time is developed and evaluated. During 3D printing, the dimensions and geometries of the 3D nanostructures grow over time, producing a large library of optical spectra associated with real-time color changes. Only a timer is needed to define the expected colors from a single 3D print run. Fin-like nanostructures are used to toggle colors based on the polarization effect and produce color gradients. Based on structural coloration, nanoarchitectures are designed and printed to animate desired color patterns. Moreover, the resulting color dynamics can also serve as an operando identifier for real-time structural information during 3D nanoprinting. A single print run enables the efficient creation of a comprehensive library of desired colorations owing to the flexibility in time-dependent controllability and 3D geometries at the subwavelength scale. 3D nanoprinted plasmonic structures exhibiting time-varying colorations (4D printing of colors) uniquely redefines the coloring stategy,offering considerable potential for numerousapplications.

Tunable plasmonic tweezers based on nanocavity array structure for multi-site nanoscale particles trapping

The ability of plasmonic optical tweezers based on metal nanostructure to stably trap and dynamically manipulate nanoscale objects at low laser power has been widely used in the fields of nanotechnology and life sciences. In particular, their plasmonic nanocavity structure can improve the local field intensity and trap depth by confining electromagnetic fields to subwavelength volumes. In this paper, the R6G dye molecules with 10−6 M were successfully trapped by using the Ag@Polydimethylsiloxane nanocavity array structure, and a R6G micro-ring was formed under the combined action of plasmonic optical force and thermophoresis. Subsequently, the theoretical investigation revealed that the trapping performance can be flexibly adjusted by changing the structural parameters of the conical nanocavity unit, and it can provide a stable potential well for polystyrene particles of RNP = 14 nm when the cavity depth is 140 nm. In addition, it is found that multiple trapping sites can be activated simultaneously in the laser irradiation area by investigating the trapping properties of the hexagonal conical nanocavity array structure. This multi-site stable trapping platform makes it possible to analyze multiple target particles contemporaneously.

Formation of Highly Tunable Periodic Plasmonic Structures on Gold Films Using Direct Laser Writing (Advanced Optical Materials 20/2024)

Formation of Highly Tunable Periodic Plasmonic Structures on Gold Films Using Direct Laser Writing (Advanced Optical Materials 20/2024)

Polydopamine-mediated facile Silver grown on ZnO Thin Films as High Performance SERS Substrates for R6G Detection

Surface-enhanced Raman spectroscopy (SERS) is a widely known technique that uses plasmonic structures (silver, gold, etc.) to detect low-concentration molecules. However, the limited number of metallic elements with plasmonic properties leads to limitations in their application. The qualitative detection method of SERS holds considerable promise in providing novel platforms for diverse applications, owing to its utilization of hybrid structures. Mussel-inspired polydopamine offers a promising avenue for the fabrication and integration of hybrid structures suitable for the SERS platform. Here, sputtered ZnO thin films were modified with Ag Nanostructures using polydopamine to fabricate a homogeneous Ag@ZnO hybrid high-performance SERS substrate. Ag/ZnO hybrid nanostructures were analyzed by FESEM and XRD to investigate their morphological and structural characterizations. SERS measurements were performed for all silver growth times to understand the effect of the silver growth process and hybrid structure synergy on SERS performance. The Ag@ZnO hybrid structure, cultivated with 24-hour silver growth, exhibited remarkable detectability even at an ultra-low R6G concentration of 10 pM

High Performance Balanced Linear Polarization Photodetector Based on 2D ReS2

AbstractConventional research on linear polarization photodetector for 2D materials has focused on the search for different anisotropic materials, combinations between materials, introducing plasmonic structures, and patterning 2D materials to improve performance. However, these methods provide limited improvement in polarization sensitivity. Here, a balanced photodetector structure is proposed that does not require an additional process and relies only on the presence of anisotropy in the material itself to substantially improve the polarization sensitivity. The balanced photodetector consists of two ReS2 photodetectors, where the single ReS2 photodetector exhibits excellent performance at 650 nm illumination, including a responsivity and detectivity of 0.28 A W−1 and 4.22 × 109 Jones. Benefiting from the anisotropy of ReS2, the single photodetector achieves excellent polarization sensitivity of 2.79 at 650 nm. The balanced photodetector system achieves an excellent performance of ≈20 dB linear polarization extinction ratio and 0.003° Hz−1/2 noise equivalent light polarization difference at 100 kHz. These performances can also be further optimized by adjusting the gate voltage. The results provide a basis for further development of high‐performance polarization photodetector for 2D materials.

Polarization dependent exciton-plasmon coupling in PEA2PbI4/Al and its application to perovskite solar cell.

This paper reports the strong coupling between Al nanostructure and two-dimensional (2D) layered perovskite PEA2PbI4 (PEPI) films. The high exciton binding energy of 118 meV and long carrier lifetime of 216 ps are characterized from the 2D PEA2PbI4 film, which indicates that the excitons in perovskite are robust and can couple to metal plasmons. The ordinary and extraordinary optical dispersions are revealed from the anisotropic 2D perovskite. The transmission spectra of PEA2PbI4/Al nanoparticle arrays are simulated under different polarization excitations, and the typical anti-crossing behaviors originating from exciton-plasmon strong coupling are demonstrated. We found that compared with transverse magnetic (TM) polarization, transverse electric (TE) polarization excitation is more conducive to the realization of exciton-plasmon coupling with a larger Rabi splitting. Furthermore, the PEA2PbI4/Al nanoparticle arrays are proposed, which present polarization-dependent local electrical field enhancement due to the exciton-local surface plasmon polariton coupling. Additionally, it is noticed that the proposed plasmonic structure increases the photo-generation rate inside the active material with improved current density. Therefore, the 2D proposed plasmonic design increases the power conversion efficiency (PCE) with an enhancement of 3.3% and 1.3% relative to the planar structures for TE and TM polarizations, respectively. This study provides a deeper understanding of polarized exciton-plasmon coupling properties, promoting the development of the field of plasmon and providing guidance for the design and preparation of efficient optoelectronic devices.

High-performance plasmonics nanostructures in gas sensing: a comprehensive review.

Plasmonic nanostructures have emerged as indispensable components in the construction of high-performance gas sensors, playing a pivotal role across diverse applications, including industrial safety, medical diagnostics, and environmental monitoring. This review paper critically examines seminal research that underscores the remarkable efficacy of plasmonic materials in achieving superior attributes such as heightened sensitivity, selectivity, and rapid response times in gas detection. Offering a synthesis of pivotal studies, this review aims to furnish a comprehensive discourse on the contemporary advancements within the burgeoning domain of plasmonic gas sensing. The featured investigations meticulously scrutinize various plasmonic structures and their applications in detecting gases like carbon monoxide, carbon dioxide, hydrogen and nitrogen dioxide. The discussed frameworks encompass cutting-edge approaches, spanning ideal absorbers, surface plasmon resonance sensors, and nanostructured materials, thereby elucidating the diverse strategies employed for advancing plasmonic gas sensing technologies.

Optically printed plasmonic fiber tip-assisted SERS-based chemical sensing and single biological cell studies

BackgroundPrecise localized printing of plasmonic nanoparticles at desired locations can find a plethora of applications in diverse areas, including nanophotonics, nanomedicine, and microelectronics. The focused laser beam-assisted optical printing technique has illustrated its potential for the localized printing of differently shaped plasmonic particles. However, the technique is either time-consuming or often requires focused optical radiation, limiting its practical applications. While the optothermal printing technique has recently emerged as a promising technique for the direct and rapid printing of plasmonic nanoparticles onto transparent substrates at lower laser intensities, its potential to print the plasmonic nanoparticles to the core of the optical fiber platforms and utilize it for biological cell trapping as well as an analytical platform remains unexplored. ResultsHerein, we demonstrate the thermal-convection-assisted printing of the Ag plasmonic nanoparticles from the plasmonic colloidal solution onto the core of single-mode optical fiber and its multi-functional applications. The direct printing of plasmonic structure on the fiber core via the thermal-convection mechanism is devoid of the requirement of any additional chemical ligand to the fiber core. Further, we demonstrated the potential of the developed plasmonic fiber probe as a multifunctional surface-enhanced Raman spectroscopic (SERS) platform for sensing, chemical reaction monitoring, and single-cell studies. The developed SERS fiber probe is found to detect crystal violet in an aqueous solution as low as 100 pM, with a plasmonic enhancement of 107. Additionally, the capability of the fiber-tip platform to monitor the surface plasmon-driven chemical reaction of 4-nitrothiophenol (4NTP) dimerizing into p, p’-dimercaptoazobenzene (DMAB) is demonstrated. Further, the versatility of the fiber probe as an effective platform for opto-thermophoretic trapping of single biological cells such as yeast, along with its Raman spectroscopic studies, is also shown here. SignificanceIn this study, we illustrate for the first time the optothermal direct printing of plasmonic nanoparticles onto the core of a single-mode fiber. Further, the study demonstrates that such plasmonic nanoparticle printed fiber tip can act as a multi-functional analytical platform for optothermally trap biological particles as well as monitoring plasmon-driven chemical reactions. In addition, the plasmonic fiber tip can be used as a cost-effective SERS analytical platform and is thus expected to find applications in diverse areas.

Scintillation Level of Scattered Radio Waves in the Equatorial Ionosphere

Scintillation effects of propagating and scattered radio waves (RWs) are considered analytically and numerically in the equatorial terrestrial ionosphere applying the statistical characteristics. Analytical calculations of the second-order statistical moments of the phase fluctuations of the ordinary and extraordinary RWs in the conductive collision ionospheric magnetoplasma (COCOIMA) are carried out for the first time using the Wentzel-Kramers-Brilluen method and the modified smooth perturbation method in consideration of the diffraction effects. Polarization coefficients of these waves in the equatorial ionosphere have been derived for the first time. The scintillation level includes the variance and the correlation functions of scattered RWs. Statistical moments contain complex refractive index, anisotropy coefficient characterizing irregular plasmonic structures, tilt angle of prolate irregularities concerning to the external magnetic field, permittivity components of the equatorial ionosphere, Hall's, Pedersen and longitudinal conductivities. A new feature of the "Fountain Effect" has been discovered in the equatorial ionosphere at weak and moderate scintillations caused due to anisotropy parameters of electron density fluctuations. Anisotropy parameters of electron density inhomogeneities influence the scintillation index of both the ordinary and extraordinary radio waves shifting maximums of the curves in the opposite directions at weak and moderate scintillations. Numerical calculations are carried out using the hybrid anisotropic correlation function of electron density fluctuations containing both exponential and power-law spectral functions having arbitrary spectral index, applying the experimental data.

All-optical multichannel switch and slow light based on dynamically tunable plasmon-induced transparency

The triple plasmon-induced transparency (PIT) effect based on a metal–insulator–metal waveguide structure comprising two groups of big and small disk resonators (BSDRs) is investigated theoretically and numerically. As a tool employed to explain the PIT, N-order coupled mode theory (CMT), is established, and the calculated results of the triple-PIT effect exhibit excellent consistency with finite-difference time-domain simulations. The influence of the separation between the small disk resonators on the triple-PIT response is discussed in detail through the dynamical equation. Further research shows that the central wavelengths of the triple-PIT transmission window can be adjusted with extremely low pump intensity and ultrafast optical response when monolayer graphene covers the surface of the BSDRs. Meaningfully, light traveling at resonant wavelengths can be effectively slowed down, with the highest group index reaching 368. Based on the PIT effect, a low-power and ultrafast switch is realized with a modulation amplitude of more than 93% at the corresponding wavelengths of the eight depressions. Thus, not only do the insights put forward new ideas, to the best of our knowledge, for highly tunable optoelectronic devices, but the results from the N-order CMT also offer new theory progress and references in the plasmonic waveguide structures.

An innovative method of the vertical coupling effect improvement to the tandem Cu(In, Ga)Se2/perovskite solar cells using Ag cluster nanostructures

The efficiency of double-junction CIGS/Perovskite-based solar cells has significantly improved through recent research. This study presents a new plasmonic structure for these optical devices, utilizing cluster nanostructures to increase photon absorption between 650 and 1137 nm wavelength ranges. The proposed nanostructure includes two vertically coupled silver nanoparticles embedded at the center of the bottom active layer (CIGS) that absorb most of the incoming light to CIGS within the active layer. The electric field produced by the coupling of the nanoparticles has a superior performance. To analyze the effect of nanoparticle coupling on CIGS/Perovskite solar cell performance, evaluated the short-circuit current density and power conversion efficiency for single and cluster nanostructures with a single nanoparticle in the middle of CIGS. The structures with a single nanoparticle displayed Jsc = 16.89 mA cm−2 and PCE = 31.76%, while the cluster nanostructure represents Jsc = 19 mA cm−2 and PCE = 35.81%. Not only did the use of the cluster nanostructure significantly improve absorption and performance compared to the bare case, but it also exhibited a suitable improvement compared to the single nanoparticle.

Impact of Tamm plasmon structures on fluorescence and optical nonlinearity of graphene quantum dots

Graphene Quantum Dots (GQDs) are crucial in biomedicine for sensitive biosensing and high-resolution bioimaging and in photonics for their nonlinear optical properties. Integrating GQDs with photonic structures enhances optical properties by optimizing light-matter interactions and enabling precise control over their emission wavelengths. In this work, we explore a facile synthesis method for GQDs by pulsed laser irradiation in chlorobenzene and highlight the transformative potential of Tamm Plasmon Cavity (TPC) structures for tuning and amplifying the photoluminescence and nonlinear optical properties of GQDs. The characterization of GQDs revealed their exceptional properties, including efficient optical limiting and stable photoluminescence. The study demonstrated that the TPC structure significantly amplifies nonlinear optical effects due to the high light-matter interaction, indicating the potential for advanced optical systems, including optical limiters and nonlinear optical devices. Furthermore, introducing GQDs into the TPC structure leads to a significant enhancement and tuning of fluorescence emission. The Purcell effect, in combination with the confined electromagnetic fields within the TPC, increases the spontaneous emission rate of GQDs and subsequently enhances the fluorescence intensity. This enhanced and tunable fluorescence has exciting implications for high-sensitivity applications such as biosensing and single-molecule detection.

A Highly Sensitive Plasmonic Graphene-Based Structure for Deoxyribonucleic Acid Detection

In this study, a Kretschmann structure with a hybrid layer of graphene–WS2 is designed to develop a sensitive biosensor for deoxyribonucleic acid detection. The biosensor incorporates a 45 nm gold layer as the active layer and a thin film of chrome as the adhesive layer. Through the optimization of the graphene and WS2 layers, combined with the implementation of a silicon layer, we can enhance the nano-sensor’s sensitivity. The thin silicon layer acts as a protective barrier for the metal, while also increasing the volume of interaction. Consequently, by adjusting the thickness of the active metal and adding a silicon layer, we achieve higher sensitivity and a lower full width at half maximum, leading to sensitivity of 333.33°/RIU. The designed structure is analyzed using numerical techniques and the finite difference time domain method, allowing us to obtain the optical characteristics of the surface plasmon polariton sensor. Various parameters are calculated and evaluated to determine the optimal conditions for the sensor. Furthermore, the total size of the sensor is 2.228 µm2.

Sensor with combined plasmonic and magnetic activities

Sensors utilizing magneto-optical surface plasmon resonance are gaining increasing scientific and practical attention to detect atmospheric gases and humidity. The magneto-optic surface plasmon resonance wavelength is defined by the plasmonic structure's geometry and structure, making it immune to electromagnetic interference outside its resonance frequency range. The present study investigates their application for the detection of atmospheric gases including humidity. In contrast to conventional sensors, magneto-optic sensors exhibited excellent performance in terms of sensitivity (10 times greater), higher quality factor (up to 76 times higher) and design simplicity in terms of layer thickness optimization, integration, and robustness. These results suggest significant potential for utilization of magneto-optic sensors across multiple industries.