Localized Surface Plasmon Resonance Modes Research Articles

Breaking plasmonic symmetry through the asymmetric growth of gold nanorods

The optoelectronic properties of asymmetric metal nanostructures are of current interest for applications in photonics, sensing, and catalysis. Here, we break the symmetry of the localized surface plasmon resonance of gold nanorods by selective overgrowth of a single tip via a high-yield ( > 80 % ) wet-chemical method. While optical spectroscopy exhibits a bathochromic shift of the nanoparticle plasmon resonance, cathodoluminescence and electron energy loss spectroscopy measurements reveal a breaking of the symmetry of the associated localized surface plasmon resonance mode, which results in the subwavelength concentration of electromagnetic energy. The simple, one-step postsynthetic modification allows control of nanoparticle structural parameters, and we demonstrate how the asymmetric energy redistribution leads to increases in the surface-enhanced Raman scattering of a model analyte attached to the surface of the nanostructures. The spatial localization of energy in these nanostructures may find applications in nanofocusing, nanoimaging, and light harvesting.

Electrochemically-Assisted Site-Selective Redox Reactions through Plasmonic Hole/Electron Ejection

Anisotropic growth and modification of plasmonic nanoparticles have been of significant interest because their optical properties are depending strongly on anisotropy of the particle shape and environment.1,2 Some researchers previously reported anisotropic reduction reactions including Ag and Au nanoparticle growth3,4 and Pt deposition onto Au nanoparticles5 under excitation of localized surface plasmon resonance (LSPR). Recently, our group demonstrated “site-selective” oxidative dissolution of Ag nanoparticles6-8 and deposition of PbO2 onto Au nanoparticles9 on the basis of plasmonic hot hole ejection10 assisted by a semiconductor such as TiO2. Irradiation of light with different wavelengths resulted in oxidation reactions at different sites corresponding to excited LSPR modes. However, only oxidation reactions are possible for nanoparticles on n-type semiconductors (electron transport layers). In this study, we found that both oxidation and reduction reactions, including oxidative PbO2 deposition, coordinative dissolution of Au in the presence of Cl-, and reductive deposition of Pt, take place site-selectively on Au nanoparticles through electrochemically-assisted plasmonic hole/electron ejection without using a semiconductor. A Au nanocube-depoisted indium tin oxide (ITO) electrode was immersed in an electrolyte solution containing Pb(NO3)2, KCl, or H2[PtCl6] and potential of +0.95, +0.85, or +0.55 V vs. Ag|AgCl (sat. KCl) was applied to the electrode in a three-electrode system, respectively. Distal or proximal mode2 was excited by visible light after the current became almost constant in the dark. The figure shows SEM images of the electrode surface after light irradiation. Oxidative PbO2 deposition, Au dissolution, and reductive Pt deposition are observed preferentially at the top face of the nanocubes after distal mode excitation (panels a, b, and c, respectively) while the reactions proceeded at the interfacial region between the nanocube and ITO in the case of proximal mode (panels d, e, and f, respectively).11 Similar site-selective reactions were also observed on Au nanorods under excitation of transverse and longitudinal modes.11 These nanofabrication techniques are potentially applicable not only to control of LSPR properties but also to fabrication of high-performance plasmonic photocatalysts and chiral plasmonic materials. S. Link, M. A. El-Sayed, J. Phys. Chem. B 1999, 103, 8410.2. L. J. Sherry, S.-H. Chang, G. C. Schatz, R. P. Van Duyne, Nano Lett. 2005, 5, 2034.3. R. Jin, Y. C. Cao, E. Hao, G. S. Métraux, G. C. Schatz, Nature 2 003, 425, 487.4. Y. Zhai, J. S. DuChene, Y.-C. Wang, J. Qiu, A. C. Johnston-Peck, B. You, W. Guo, B. DiCiaccio, K. Qian, E. W. Zhao, F. Ooi, D. Hu, D. Su, E. A. Stach, Z. Zhu, W. D. Wei, Nat. Mater. 2016, 15, 889.N. H. Kim, C. D. Meinhart, M. Moskovits, J. Phys. Chem. C 2016, 120, 6750.E. Kazuma, N. Sakai, T. Tatsuma, Chem. Commun. 2011, 47, 5777.I. Tanabe, T. Tatsuma, Nano Lett. 2012, 12, 5418.K. Saito, I. Tanabe, T. Tatsuma, J. Phys. Chem. Lett. 2016, 7, 4363.H. Nishi, M. Sakamoto, T. Tatsuma, Chem. Commun. 2018, 54, 11741.T. Tatsuma, H. Nishi, Nanoscale Horiz. 2020, 5, 597.H. Nishi, T. Tatsuma, Nanoscale 2019, 11, 19455. Figure 1

Nanofabrication of plasmon-tunable nanoantennas for tip-enhanced Raman spectroscopy.

Plasmon-tunable tip pyramids (PTTPs) are reproducible and efficient nanoantennas for tip-enhanced Raman spectroscopy (TERS). Their fabrication method is based on template stripping of a segmented gold pyramid with a size-adjustable nanopyramid end, which is capable of supporting monopole localized surface plasmon resonance (LSPR) modes leading to high spectral enhancement when its resonance energy is matched with the excitation laser energy. Here, we describe in detail the PTTP fabrication method and report a statistical analysis based on 530 PTTPs' and 185 ordinary gold micropyramids' templates. Our results indicate that the PTTP method generates probes with an apex diameter smaller than 30 nm on 92.4% of the batch, which is a parameter directly related to the achievable TERS spatial resolution. Moreover, the PTTPs' nanopyramid edge size L, a critical parameter for LSPR spectral tuning, shows variability typically smaller than 12.5%. The PTTP's performance was tested in TERS experiments performed on graphene, and the results show a spectral enhancement of up to 72-fold, which is at least one order of magnitude higher than that typically achieved with gold micropyramids. Imaging resolution is in the order of 20 nm.

Nearfield excited state imaging of bonding and antibonding plasmon modes in nanorod dimers via stimulated electron energy gain spectroscopy

Stimulated electron energy loss and gain spectroscopy (sEELS and sEEGS) are used to image the nearfield of the bonding and antibonding localized surface plasmon resonance modes in nanorod dimers. A scanning transmission electron microscope equipped with an optical delivery system is used to simultaneously irradiate plasmonic nanorod dimers while electron energy loss and gain spectra of the active plasmons are collected. The length of the nanorod dimer is varied such that the bonding and antibonding modes are resonant with the laser energy. The optically bright bonding mode is clearly observed in the resonant sEEG spectrum images and, consistent with spontaneous EELS, no direct evidence of the hot spot is observed in sEEG. s-polarized irradiation does not stimulate the energy gain of the optically dark antibonding mode. However, when phase retardation is introduced by tilting the longitudinal axis, the otherwise dark antibonding mode becomes sEEG active.

Near field excited state imaging via stimulated electron energy gain spectroscopy of localized surface plasmon resonances in plasmonic nanorod antennas

Continuous wave (cw) photon stimulated electron energy loss and gain spectroscopy (sEELS and sEEGS) is used to image the near field of optically stimulated localized surface plasmon resonance (LSPR) modes in nanorod antennas. An optical delivery system equipped with a nanomanipulator and a fiber-coupled laser diode is used to simultaneously irradiate plasmonic nanostructures in a (scanning) transmission electron microscope. The nanorod length is varied such that the m = 1, 2, and 3 LSPR modes are resonant with the laser energy and the optically stimulated near field spectra and images of these modes are measured. Various nanorod orientations are also investigated to explore retardation effects. Optical and electron beam simulations are used to rationalize the observed patterns. As expected, the odd modes are optically bright and result in observed sEEG responses. The m = 2 dark mode does not produce a sEEG response, however, when tilted such that retardation effects are operative, the sEEG signal emerges. Thus, we demonstrate that cw sEEGS is an effective tool in imaging the near field of the full set of nanorod plasmon modes of either parity.

Zinc Oxide Nanorod Surface-Enhanced Raman Scattering Substrates without and with Gold Nanoparticles Fabricated through Pulsed-Laser-Induced Photolysis

We fabricated surface-enhanced Raman scattering (SERS) substrates using gold nanoparticle (AuNP)-decorated zinc oxide (ZnO) nanorods (NRs). Prior to decoration with AuNPs, ZnO NRs on the glass substrate fabricated using the sol–gel method could enhance the SERS signal for detecting 10−5 M rhodamine 6G (R6G). Microscopic analysis revealed that the thermal-annealing process for fabricating the seed layers of ZnO facilitated the growth of ZnO NRs with the highly preferred c-axis (002) orientation. A decrease in the diameter of ZnO NRs occurred because of the use of annealed seek layers further increased the surface-to-volume ratio of ZnO NRs, resulting in an increase in the SERS signal for R6G of 10−5 M. To combine the localized surface plasmon resonance (LSPR) mode with the charge transfer (CT) mode, ZnO NRs were decorated with AuNPs through pulsed-laser-induced photolysis (PLIP). However, the preferred vertical (002) orientation of ZnO NRs was prone to the aggregation of AuNPs, which hindered the SERS signal. The experimental results revealed that ZnO NRs with the crystalline structure of horizontal (100) and (101) orientations facilitated the growth of homogeneous, independent and isolated AuNPs which serves as “hot spots” for SERS signal of detecting R6G at a low concentration of 10−9 M. Comparing to previous fabrication of SERS substrate, our method has advantage to fabricate AuNP-decorated ZnO NR in a short time. Moreover, the optimization of the SERS behaviors for different fabrication conditions of AuNPs using the PLIP method was investigated in detail.

Near- and mid-infrared plasmonic Fano resonances induced by different geometric configurations in subwavelength nanostructures

Abstract Plasmonic Fano resonances, which result from the interaction between two plasmon modes in subwavelength nanostructures, provide a unique way to realize promising applications in light manipulation technology. Here, we investigate the infrared plasmonic Fano resonances of subwavelength periodic hole arrays with different geometric configurations in a metallic film containing Z-shaped hole arrays, cross-shaped aperture arrays, and gammadion-shaped hole arrays (GSHAs). Specifically, the infrared plasmonic Fano resonance in the GSHA structure, without considering rotational symmetry breaking, can be interpreted as stemming from the coupling between the bonding and antibonding localized surface plasmon resonance modes. By considering the rotational symmetry breaking in the GSHA structure, it is possible to actualize plasmonic double- and triple-Fano resonances in the near-infrared or mid-infrared region. Moreover, the plasmonic double- and triple-Fano resonances between the first- and second-NIR optical windows, as well as in the mid-infrared region can be controlled by appropriately regulating the related length of the arms in the GSHA structure. Our results show that infrared plasmonic Fano resonances might pave the way for the exploration of applications in optical communications and information processing.

Optical Nanoantennas for Tip-Enhanced Raman Spectroscopy

The role of plasmon resonance on the optical efficiency of nanoantennas for tip-enhanced Raman spectroscopy (TERS) is reviewed. Technical details on surface plasmon polaritons (SPP), localized surface plasmon resonance (LSPR), and the plasmon gap mode are provided. Nanotechnology engineering is necessary to adequate the nanoantenna's size, shape and composition to match resonance conditions with the exciting radiation source. Computational simulation guides the development of new types of plasmonic nanoantennas with different materials and morphologies, specially designed to reach target applications. An overview on a recently developed nanoantenna composed by a truncated micropyramidal body with a nanopyramid end is presented. The characteristic length L of the nanopyramid tip is dimensioned to fine-tune LSPR modes, giving rise to the so-called plasmon-tunable tip pyramid (PTTP). The plasmonic properties of this type of probe were investigated by electron energy loss spectroscopy and computational simulations, reveling that PTTPs act as monopole nanoantennas. TERS results obtained with the PTTPs demonstrate the achievement of unprecedent levels of field enhancement mediated by LSPR with excellent reproducibility rate.

Design of silver nanoparticles with graphene coatings layers used for LSPR biosensor applications

A new hybrid graphene nanoplasmonic structure, using silver nanoparticles (AgNPs) coated with a graphene film and deposited on a substrate is proposed in this paper. The aim is to obtain a plasmonic response with high sensitivity for plasmonic biosensors. We show, through the calculation of absorption spectra, that the localized surface plasmon resonance (LSPR) obtained in the SiOx/AgNPs/Graphene nanostructure is very sensitive to variations in the thickness of the graphene and those of the refractive index of the detection medium. The study reveals a shift in plasmon resonance peaks resulting from the coupling between the AgNPs networks and the covering graphene layer. We obtained the red-shift of LSPR modes from 412 nm to 548 nm when the thickness of the graphene layer increases from 0.34 nm to 9 nm. We have shown that the increase in graphene thickness significantly affects the sensitivity of the device under study. An optimal sensitivity value is obtained for a graphene thickness of 9 nm, with a 304.60% gain in sensitivity value compared to the structure without graphene. These properties should enhance these nano-device and make them a preferred choice for biosensors applications, over other current biosensors.

Longitudinal Dipole Modes of AuNRs for Photocatalytic Enhancement of Ultrathin Rutile TiO2 Nanosheets

Rutile-phase titanium dioxide (TiO2) nanosheets with a thickness of 4 nm were successfully prepared. Excellent visible light catalytic degradation effects have been observed from these nanosheets. To enhance the catalytic performance, aurum nanorods (AuNRs) were incorporated with the TiO2 nanosheets. Compared with sole TiO2 nanosheets, the Janus structures of the combined TiO2 and AuNRs (TiO2@AuNRs) showed three times the reaction rate for the degradation of Rhodamine B under visible and near-infrared light (> 410 nm, 300 W). This is attributed to the wide response range of AuNRs, which is demonstrated by the absorption spectra of the AuNRs colloids. The introduction of AuNRs with different aspect ratios in TiO2@AuNRs revealed better catalytic activities for AuNRs with larger aspect ratios. To study the physical mechanism of photocatalytic enhancement, the finite difference time domain method has been performed to simulate the optical properties of TiO2@AuNRs. The simulation results showed that the photocatalytic improvement of TiO2@AuNRs was caused by the longitudinal localized surface plasmon resonance mode of AuNR. Through the excitation of the longitudinal mode, 40 times enhancement of the near-field intensity can be observed. The results indicate that AuNRs can be used to improve the photocatalytic activity of TiO2 nanosheets through the injection of hot electrons from AuNR into TiO2.

Nanosecond switchable localized surface plasmons through resettable contact angle behavior in silver nanoparticles

In this article, we show nanosecond switchable localized surface plasmon resonance (LSPR) dipole and quadrupole modes from silver (Ag) nanoparticles on fused quartz substrates. Near-spherical Ag nanoparticles (contact angle of 166°± 9 ) were synthesized by Ultra Violet (UV) laser dewetting of Ag thin films under a glycerol fluid environment. Under a single 9 nanosecond laser pulse irradiation of the particles in air, the particles were changed into a near-hemispherical shape (with contact angle of 103°± 7 ). The resulting changes in particle contact area and volume fraction in the dielectric media resulted in substantial shift in the wavelength and intensity of the dipolar and quadrupolar LSPR modes to the violet side of visible spectrum. This switching of the plasmon resonance wavelength position could be repeated over multiple cycles by resetting the contact angle by laser re-irradiation under glycerol. This reusable nanoparticle system with reversible plasmonic properties within nanosecond time scales could prove a cost-effective way of designing high speed plasmonic devices in desired wavelength regions.

Analytical Modeling Based on Modified Effective Medium Theories for Optical Properties of Photovoltaic Material-Incorporated Plasmonic Nanoparticles

Theoretical guidance on the optical properties of plasmonic nanoparticles (NPs) is of significant importance in tremendous numbers of fields like photovoltaics. The incorporation of plasmonic NPs into photovoltaic material can promote optical absorption either via the excitation of localized surface plasmon resonance (LSPR) modes or due to multiple light scattering. Since most fabrication techniques for the incorporation of NPs into photovoltaic material result in a random array of NPs with various sizes, numerical simulations based on solving the Maxwell equations are computationally expensive and prohibitively slow for this large number of NPs. Therefore, in this paper, based on modified effective medium theories, taking into account finite size of NPs, size dispersion for NPs, extrinsic dynamic effect, and intrinsic confinement effect, fast and cost-effective analytical modeling, considering both LSPR and scattering effects, is presented to obtain the optical properties of photovoltaic material incorporated by spherical NPs with nonuniform size and random distribution. Then, by means of presented analytical modeling, considering reasonably low and high volume fractions of NPs in addition to small and large size of NPs, the effect of different parameters of embedded NPs into organic and inorganic photovoltaic materials is explored.

Magnetic circular dichroism in plasmonic Ag–Au core–shell nanoparticles: how does the magneto-optical activity tune?

Magnetic circular dichroism (MCD) is demonstrated for plasmonic bimetallic nanoparticles. They have an Ag–Au core–shell configuration, which can be synthesized using a seeded growth technique. In the seeded growth process, when the amount of Au (as coating metal) added to the Ag core is small, both ordinary (lower-energy) and extraordinary (higher-energy) modes of localized surface plasmon resonance (LSPR) are detected in optical extinction spectra, suggesting successful formation of well-defined core–shell morphology with a rather thin shell (= AgAu alloy) thickness. Interestingly, the related MCD, showing a typical bisignate magnetoplasmonic response, is more distinct than the extinction signal in the ordinary LSPR mode, but strong damping is found upon thin shell formation. Hence, such bimetallic nanosystems have an advantage of systematic tuning of their magnetoplasmonic behavior, but may not be favorable to obtaining large magneto-optical (MO) activity or MCD amplitudes. The damped MCD response is discussed from a viewpoint of spectral inhomogeneity.

Plasmonic Metasurface for Spatially Resolved Optical Sensing in Three Dimensions.

The highly localized sensitivity of metallic nanoparticles sustaining localized surface plasmon resonance (LSPR) enables detection of minute events occurring close to the particle surface and forms the basis for nanoplasmonic sensing. To date, nanoplasmonic sensors typically consist of two-dimensional (2D) nanoparticle arrays and can therefore only probe processes that occur within the array plane, leaving unaddressed the potential of sensing in three dimensions (3D). Here, we present a plasmonic metasurface comprising arrays of stacked Ag nanodisks separated by a thick SiO2 dielectric layer, which, through rational design, exhibit two distinct and spectrally separated LSPR sensing peaks and corresponding spatially separated sensing locations in the axial direction. This arrangement thus enables real-time plasmonic sensing in 3D. As a proof-of-principle, we successfully determine in a single experiment the layer-specific glass transition temperatures of a bilayer polymer thin film of poly(methyl methacrylate), PMMA, and poly(methyl methacrylate)/poly(methacrylic acid), P(MMA-MAA). Our work thus demonstrates a strategy for nanoplasmonic sensor design and utilization to simultaneously probe local chemical or physical processes at spatially different locations. In a wider perspective, it stimulates further development of sensors that employ multiple detection elements to generate distinct and spectrally individually addressable LSPR modes.

Chemical interface damping for propagating surface plasmon polaritons in gold nanostripes.

Leakage radiation microscopy has been used to examine chemical interface damping (CID) for the propagating surface plasmon polariton (PSPP) modes of Au nanostripes-nanofabricated structures with heights of 40 or 50 nm, widths between 2 and 4 µm, and 100 µm lengths. Real space imaging was used to determine the propagation lengths LSPP of the leaky PSPP modes, and back focal plane measurements generated ω vs k dispersion curves, which yield the PSPP group velocities vg. The combination of these two experiments was used to calculate the PSPP lifetime via T1 = LSPP/vg. The difference in T1 times between bare and thiol coated nanostripes was used to determine the dephasing rate due to CID ΓCID for the adsorbed thiol molecules. A variety of different thiol molecules were examined, as well as nanostripes with different dimensions. The values of ΓCID are similar for the different systems and are an order-of-magnitude smaller than the typical values observed for the localized surface plasmon resonances (LSPRs) of Au nanoparticles. Scaling the measured ΓCID values by the effective path length for electron-surface scattering shows that the CID effect for the PSPP modes of the nanostripes is similar to that for the LSPR modes of nanoparticles. This is somewhat surprising given that PSPPs and LSPRs have different properties: PSPPs have a well-defined momentum, whereas LSPRs do not. The magnitude of ΓCID for the nanostripes could be increased by reducing their dimensions, principally the height of the nanostructures. However, decreasing dimensions for the leaky PSPP mode increases radiation damping, which would make it challenging to accurately measure ΓCID.

Formation of normal surface plasmon modes in small sodium nanoparticles.

Formation of surface plasmon modes in sodium nanoclusters containing 20-300 atoms was studied using the G0W0 approximation. It is shown that in the small Na nanoparticles up to 2 nm in size, the loss function Im[ε-1] is dominated by a single peak corresponding to localized surface plasmon resonance (LSPR). For particles of 2 nm and more, a resonance corresponding to surface plasmon polariton (SPP) oscillations begins to form, as well as a resonance corresponding to volume plasmon (VP) excitations. Considering the above, the linear size of a particle in the range of 0.7-3.7 nm can be estimated as the lower limit for metal nanodevices operating with SPPs. On the example of spherical nanoparticles consisting of a silicon core coated with sodium atoms, it is shown that the LSPR mode is selectively suppressed while the SPP mode is not. Such composite structures can be considered as an example of nanoplasmonic devices with selectively tuned characteristics.

Scattering and absorption characteristics of graphene coated metamaterial cylinder

Terahertz (THz) wave interaction from graphene coated metamaterial cylinder has been investigated analytically and numerically. The analytical formulation of electromagnetic fields is being modeled in the frame work of Mie theory while the modeling of the graphene is done by random phase approximation method. The causality principle based Kramer-Kroing relations are used to simulate the DNG metamaterial, while the DPS metamaterial is modeled by the Drude relations of SiO2. The analytical formulation is developed for both parallel and perpendicular polarized waves. The impedance boundary conditions (IBC) approach is used to model the infinitely thin graphene coating on metamaterial cylinder. Further the IBC at the interface of graphene layer and metamaterial cylinder are applied to compute the unknown scattering coefficients. The efficiency factors i.e., scattering efficiency (Qsca), extinction efficiency (Qexc) & absorption efficiency (Qabs) and bistatic radar cross section (RCS) have been computed analytically as well as numerically for both micro and nano cores. The influence of graphene parameters i.e., chemical potential (μc) & scattering rate (τ1) and size of metamaterial cylinder (R) on the scattering efficiency (Qsca) and extinction efficiency (Qexc) has been analyzed for DPS and DNG cores. It is observed that the in the nano regime, for perpendicularly polarized wave, graphene coated metamaterial cylinder supports the localized surface plasmon resonance (LSPR) modes and LSPR is found sensitive to the change in the graphene parameters and core size. However, it is reported that the parallel polarized wave has same response towards the DPS and DNG cores in the nano regime. It is concluded that under suitable parameters the graphene coating may provide extraordinary degree of freedom to actively control the THz interactions i.e., scattering efficiency, extinction efficiency and bistatic RCS. The present work may have potential applications in designing and manufacturing of Electromagnetic invisibility, cloaking and target protection devices for THz region.

Tailored Engineering of Bimetallic Plasmonic Au@Ag Core@Shell Nanoparticles.

A distinctive synthetic method for the efficient synthesis of multifunctional bimetallic plasmonic Au@Ag core@shell nanoparticles (NPs) with tunable size, morphology, and localized surface plasmon resonance (LSPR) using Triton X-100/hexanol-1/deionized water/cyclohexane-based water-in-oil (W/O) microemulsion (ME) is described. The W/O ME acted as a “true nanoreactor” for the synthesis of Au@Ag core@shell NPs by providing a confined and controlled environment and suppressing the nucleation, growth, agglomeration, and aggregation of the NPs. High-resolution transmission electron microscopic analysis of the synthesized Au@Ag core@shell NPs revealed an “unusual core@shell” contrast, and the selected area electron diffraction and Moiré patterns showed that Au layers are paralleled to Ag layers, thus indicating the formation of Au@Ag core@shell NPs. Interestingly, the UV–visible spectrum of the Au@Ag core@shell NPs exhibited enthralling plasmonic properties by introducing a high-frequency quadrupolar LSPR mode originated from the isolated Au@Ag NPs along with a low-frequency dipolar LSPR mode originated from the coupled Au@Ag NPs. The effective plasmonic enhancement of the Au@Ag core@shell NPs is attributed to the extreme enhancement of the localized electromagnetic field by coupling of the localized surface plasmons of the Au core and Ag shell. The mechanisms for the nucleation and growth of Au@Ag core@shell NPs in W/O ME have been proposed. A unique electron transfer phenomenon between the Au core and Ag shell is elucidated for better understanding and manipulation of the electronic properties, which evinced the development of Au@Ag core@shell NPs through suppression of the galvanic replacement reaction.

Strong Exciton-Plasmon Coupling and Hybridization of Organic-Inorganic Exciton-Polaritons in Plasmonic Nanocavity**Supported by the National Key Research and Development Program of China under Grant No 2016YFA0301300, the National Natural Science Foundation of China under Grant Nos 11574035 and 11374041, and the State Key Laboratory of Information Photonics and Optical Communications.

We investigate strong exciton-plasmon coupling and plasmon-mediated hybridization between the Frenkel (F) and Wannier–Mott (WM) excitons of an organic-inorganic hybrid system consisting of a silver ring separated from a monolayer WS2 by J-aggregates. The extinction spectra of the hybrid system calculated by employing the coupled oscillator model are consistent with the results simulated by the finite-difference time-domain method. The calculation results show that strong couplings among F excitons, WM excitons, and localized surface plasmon resonances (LSPRs) lead to the appearance of three plexciton branches in the extinction spectra. The weighting efficiencies of the F exciton, WM exciton and LSPR modes in three plexciton branches are used to analyze the exciton-polaritons in the system. Furthermore, the strong coupling between two different excitons and LSPRs is manipulated by tuning F or WM exciton resonances.

Dual-frequency CMOS terahertz detector with silicon-based plasmonic antenna.

Multi-frequency Terahertz (THz) detectors have shown great application potentials in THz imaging and sensing systems. For the first time to our knowledge, a novel dual-frequency THz detector with the stacked structure consisting of a silicon-based plasmonic antenna and a metal-based antenna in one compact unit is proposed and fabricated in standard CMOS technology. Compared with the metal antenna, the antenna based on heavy-doped poly-silicon materials enables the detector to excite localized surface plasmon resonance mode, making the effective absorption of the THz waves and thus resulting in the significant responsivity enhancement of the detector. The experimental results show a maximum voltage responsivity up to about 2000 V/W and 450 V/W, while the noise equivalence power is as low as 23 pW/Hz0.5 and 110 pW/Hz0.5 for the silicon antenna and metal antenna at the frequency of 220 GHz and 650 GHz, respectively. The presented dual-frequency detector can be easily implemented in a small size in favor of high-density array integration.