Nanoplasmonic Devices Research Articles

Active plasmonic nanodevices: From basic principles to emerging applications

AbstractTunable plasmonics has shown a wide range of applications in (bio)chemical sensing, displays, actuators, photonic chips, biomedicine, etc. in the last 2 decades. This review focuses on their recent development from the device perspective, which involves the understanding of fundamental principles and specific applications with desired functionality and compatibility. We classify these active plasmonic devices based on the nature of their structures and working environment as colloidal‐based, chip‐based, and colloidal chip‐based to further elaborate their performance and functions. We also highlight recent progress on tunable surface‐enhanced Raman spectroscopy, metasurfaces, and chiroptics to show the emerging applications of tunable plasmonic systems. We conclude this review with a general perception of the research trend in this field and challenges for their practical applications.

Charge Transfer Plasmons Enabled by Supramolecular Plug: From Optoelectronic Switching to Enhanced Chiral Sensing.

Miniaturization and integration of plasmonic nanodevices are fundamentally limited by quantum tunneling, which leads to quantum plasmonics with reduced local E-field intensity. Despite significant efforts devoted to modeling and deterring the detrimental effect of quantum plasmonics, the modulation and application of electron transport through the subnanometer gaps seems rarely exploited due to the limited tunability of conventional quantum materials. Here, we establish a supramolecular plasmonic system made of pillar[5]arene complexes and plasmonic resonators (nanoparticle-on-mirror, NPoM). The supramolecular assemblies significantly enhance the gap conductance of NPoM, which results in a blue-shift of the coupled plasmons. Plasmonic hot-electron transport with laser excitation further modulates the gap plasmons, which are fully reversible and beneficial for enhanced chiroptic sensing. Such a conductive supramolecular plasmonic system not only suggests an optoelectronic switching strategy for charge transfer plasmons but also provides a superior sensing platform for single molecules.

In Situ TEM Imaging Reveals the Dynamic Interplay Between Attraction, Repulsion and Sequential Attraction-Repulsion in Gold Nanoparticles.

Recent efforts on manipulating metal nanoparticles (NPs)using an electron beam have offered new insights into nanoparticle behavior, structural transition, and the emergence of new properties. Despite an increasing understanding of the dynamics of electron beam-induced coalescence of NPs, several phenomena are yet to be investigated. Here, we show that repulsion between two NPs is as favorable as coalescence under electron beam irradiation at room temperature. Using small-sized (D ≈ 5.9nm) and large-sized (D ≈ 11.0nm) gold (Au) NPs, and different electron dose rates, a unique sequential attraction-repulsion between NPs is disclosed. The real-time in situ transmission electron microscopy imaging suggest that at a low dose rate, two small-sized AuNPs with 1.0nm particle-particle distance undergo repulsion to 18nm with a diffusion rate of 0.4nmmin-1. For large-sized AuNPs, the repulsion rate is 0.08nmmin-1 at a low dose rate and is comparable to that of small-sized AuNPs at a high dose rate. Surprisingly, large-sized AuNPs at a high electron dose rate displayed attraction in the first 15min, followed by rapid repulsion. This unique sequential attraction-repulsion behavior of NPs offers possibilities to manipulate interparticle distance and properties without inducing dimensional changes for advanced photonic and plasmonic nanodevices.

Charge transfer plasmons in nanoparticle arrays on graphene: Theoretical development

The properties of charge transfer plasmons (CTPs) in periodic metallic nanoparticle arrays (PMNPAs) on the single-layer graphene surface are studied within a computationally efficient original hybrid quantum-classical model. The model is based on the proven assumption that the carrier charge density in doped graphene remains unchanged under plasmon oscillations. Calculated CTP frequencies for two PMNPA geometries are shown to lie within the THz range and to be factorized, i.e., presented as a product of two independent factors determined by the graphene charge density and the PMNPA geometry. Equations are derived for describing the CTP frequencies and eigenvectors, i.e., oscillating nanoparticle charge values. It is shown that the CTP plasmons having a band structure containing a wave vector and a band number, like to phonons in periodic media, can be divided into an acoustic mode and optical CTP modes. For the acoustic modes, the CTP group velocity tends to zero at k→0, but reaches a value of ∼VFermi in graphene inside the Brillouin zone, while for the optical modes, the group velocity dispersion is extremely weak, although their energy is higher than the acoustic plasmon energies. It is shown that the calculated dependence of CTP frequencies on the carrier concentration in graphene is in good agreement with experimental data. We believe that the proposed model can help in designing various graphene-based terahertz nanoplasmonic devices of complex geometry due to very high computational efficiency.

Hybrid Plasmonic Modes for Enhanced Refractive Index Sensing

AbstractCompared to single nanoparticles, strongly coupled plasmonic nanoparticles provide attractive advantages owing to their ability to exhibit multiple resonances with unique spectral features and higher local field intensity. These enhanced plasmonic properties of coupled metal nanoparticles have been used for various applications including realization of strong light‐matter interaction, photocatalysis, and sensing. In this article, the basic physics of hybrid plasmonic modes in coupled metallic nanodimers is reviewed and their potentials for refractive index sensing are assessed. In particular, the spectral line shapes of various modes of hybrid plasmons including bonding and antibonding modes in symmetric nanodimers, Fano resonances in asymmetric nanodimers, charge transfer plasmons in linked nanoparticle dimers, hybrid plasmon modes in nanoshells, gap modes in particle‐on‐mirror configurations, and hybrid magnetoplasmonic modes in heterodimers are overviewed. Beyond the dimeric nanosystems, the potentials of surface lattice resonances in periodic nanoparticle arrays for sensing applications are also showcased. Finally, based on the critical assessment of the recent research on coupled plasmonic modes, the outlook on the future prospects of hybrid plasmon‐based refractometric sensing are discussed. Given their tunable resonances and ultranarrow spectral features, coupled metal nanoparticles are expected to play key roles in developing precise plasmonic nanodevices with extreme sensitivity.

Dual-Modal Nanoplasmonic Light Upconversion through Anti-Stokes Photoluminescence and Second-Harmonic Generation from Broadband Multiresonant Metal Nanocavities.

Metal nanocavities can generate plasmon-enhanced light upconversion signals under ultrashort pulse excitations through anti-Stokes photoluminescence (ASPL) or nonlinear harmonic generation processes, offering various applications in bioimaging, sensing, interfacial science, nanothermometry, and integrated photonics. However, achieving broadband multiresonant enhancement of both ASPL and harmonic generation processes within the same metal nanocavities remains challenging, impeding applications based on dual-modal or wavelength-multiplexed operations. Here, we report a combined experimental and theoretical study on dual-modal plasmon-enhanced light upconversion through both ASPL and second-harmonic generation (SHG) from broadband multiresonant metal nanocavities in two-tier Ag/SiO2/Ag nanolaminate plasmonic crystals (NLPCs) that can support multiple hybridized plasmons with high spatial mode overlaps. Our measurements reveal the distinctions and correlations between the plasmon-enhanced ASPL and SHG processes under different modal and ultrashort pulsed laser excitation conditions, including incident fluence, wavelength, and polarization. To analyze the observed effects of the excitation and modal conditions on the ASPL and SHG emissions, we developed a time-domain modeling framework that simultaneously captures the mode coupling-enhancement characteristics, quantum excitation-emission transitions, and hot carrier population statistical mechanics. Notably, ASPL and SHG from the same metal nanocavities exhibit distinct plasmon-enhanced emission behaviors due to the intrinsic differences between the incoherent hot carrier-mediated ASPL sources with temporally evolving energy and spatial distributions and instantaneous SHG emitters. Mechanistic understanding of ASPL and SHG emissions from broadband multiresonant plasmonic nanocavities marks a milestone toward creating multimodal or wavelength-multiplexed upconversion nanoplasmonic devices for bioimaging, sensing, interfacial monitoring, and integrated photonics applications.

Plasmonic spin-multiplexing metasurface for controlling the generation and in-plane propagation of surface plasmon polaritons

Surface plasmon polaritons (SPPs) are electromagnetic waves that travel along a metal–dielectric interface and are finding an ever-increasing number of applications in newly emerging nano-photonic and optoelectronic technologies. Different from the traditional approach to excite SPPs using prism or grating, metallic metasurfaces incorporating nano-slots with different orientations enable the photonic spin-dependent directional coupling of SPPs, which shows the unique spin tunability. However, the propagations of these generated SPPs are still correlative due to the conjugated phase profiles of metasurfaces for two incident orthogonal spin states. Here, we propose a plasmonic spin-multiplexing metasurface composed of nano-slots with different geometric dimensions and orientations to efficiently control the near-field generation and in-plane propagation of SPPs. By taking into account both the geometric phase and resonant phase of the nano-slots, the metasurface can generate two independent and fully decoupled SPP fields for a pair of orthogonal spin states. As proof-of-concept, we design a series of spin-multiplexing metasurfaces to numerically demonstrate different near-field optical functionalities, including spin-controlled plasmonic bi-focusing, self-accelerating beams, and vortices. We envision this approach may have potential applications in designing polarization-dependent tunable plasmonic nano-devices.

Advances in electrochromic device technology through the exploitation of nanophotonic and nanoplasmonic effects.

Research regarding electrochromic (EC) materials, such materials that change their color upon application of an electrochemical stimulus, has been conducted for centuries. However, most recently, increasing efforts have been put into developing novel solutions to utilize these on-off switching materials in advanced nanoplasmonic and nanophotonic devices. Due to the significant change in dielectric properties of oxides such as WO3, NiO, Mn2O3 and conducting polymers like PEDOT:PSS and PANI, EC materials have transcended beyond simple smart window applications and are now found in plasmonic devices for full-color displays and enhanced modulation transmission and photonic devices with ultra-high on-off ratios and sensing abilities. Advancements in nanophotonic ECDs have further decreased EC switching speed by several orders of magnitude, allowing integration in real-time measurement and lab-on-chip applications. The EC nature of such nanoscale devices promises low energy consumption with low operating voltages paired with bistability and long lifetimes. We summarize these novel approaches to EC device design, lay out the current short comings and draw a path forward for future utilization.

Floquet engineering of dressed surface plasmon polariton modes in plasmonic waveguides

We present a comprehensive study surface plasmon polariton (SPP) propagation on planar metallic waveguides under a dressing field. We perform a set of analytical calculations of the periodic time-dependent Schr\"odinger equation to study the interaction of an intense electromagnetic field with a metallic system. We model the strong light coupling to the metallic system using a nonperturbative procedure. In this paper, we show that, by introducing Floquet theory into the dressed metal, the behavior of the Floquet states are similar to the phase-modulated signals in the communication system. This will reveal a new perspective on the underlying science in an intricate, dressed quantum system. Furthermore, we examine the impurity scattering effects on charge transport in disordered plasmonic metals using the generalized Floquet-Fermi golden rule and provide a novel approach to diminish the losses in plasmonic materials using the dressing field. To gauge the effectiveness of our results, we introduce a figure of merit to compare the performance of plasmonic metals, subjective to a dressing field. The calculated dressed SPP characteristics suggest that high-efficiency SPP propagation can be achieved in practice. Our findings open up new directions for state-of-the-art nanoplasmonic devices.

Fast and hydrosensitive switching of plasmonic nanocavities via photothermal effect

Metallic nanoplasmonics, due to its extremely small size and ultrafast speed, has been one of the key components for next-generation information technology. It is vital that the highly tunable nanoplasmonic system in the solid state can be achieved for optoelectronic devices, which, still remains elusive for the visible region. Here we sandwich vanadyl oxalate ( VOC 2 O 4 ) thin films in-between gold nanoparticles and gold film to establish thermo-responsive nanoantennas. The thickness of the VOC 2 O 4 composite films remains almost unchanged within the temperature cycles between 15°C and 80°C, while the refractive index of the films decreases with the increase of temperature due to the dehydration, which results in blueshift of the plasmon peak up to 60 nm. The plasmon resonances can be fully recovered when the temperature cools down again. This process is reversible within the temperature range of 15°C–80°C, which can be optically modulated with photothermal effect. Such thermo-responsive plasmonic nanoantenna works in the solid state with hundreds of kilohertz switching speed, which is highly compatible with traditional optoelectronic devices. It can be envisioned that this thermo-responsive optical thin film can be a promising candidate for integrated nanoplasmonic and optoelectronic devices.

Radially Polarized Second-Harmonic Generation from a Single-Element Nanoantenna via Dark Plasmon Coupling of Nonlinear Polarization

Controlling the process of second-harmonic (SH) generation at the nanoscale is important in photonic applications but remains challenging in nanophotonics. Herein, based on theoretical and experimental studies, we found that a cross-shaped single-element plasmonic nanoantenna resonating with bright and dark modes at the fundamental (excitation) and SH wavelengths, respectively, generates radially polarized ring-shaped SH radiations with axial symmetry by exciting the bright dipole mode with linearly polarized light. Mode expansion analysis of the generated SH radiation revealed that the radial polarization arises from a dark breathing mode in which coherent dipoles are radially distributed along the arms of the cross-shaped antenna. This study reveals that surface SH polarization generated by the electric near-field of the bright mode at the fundamental wavelength efficiently is coupled to the dark modes rather than the bright mode because its spatial distribution has the same symmetry as the dark modes. By engineering bright and dark modes at the fundamental and SH wavelengths, respectively, novel plasmonic nanodevices that simultaneously perform polarization control and efficient wavelength conversion are expected.

Two-color laser PEEM imaging of horizontal and vertical components of femtosecond surface plasmon polaritons

Explicit visualization of different components of surface plasmon polaritons (SPPs) propagating at dielectric/metal interfaces is crucial in offering chances for the detailed design and control of the functionalities of plasmonic nanodevices in the future. Here, we reported independent imaging of the vertical and horizontal components of SPPs launched from a rectangular trench in the gold film by a 400-nm laser-assisted near-infrared (NIR) femtosecond laser time-resolved photoemission electron microscopy (TR-PEEM). The experiments demonstrate that distinct imaging of different components of SPPs field can be easily achieved by introducing the 400-nm laser. It can circumvent the risk of sample damage and information loss of excited SPPs field that is generally confronted in the usual NIR laser TR-PEEM scheme. The underlying mechanism for realizing distinct imaging of different components of the SPPs field with two-color PEEM is revealed via measuring the double logarithmic dependence of photoemission yield with the 800-nm and 400-nm pulse powers of different polarizations. Moreover, it is found that the PEEM image quality of the vertical and horizontal components of the SPPs field is nearly independent of the 400-nm pulse polarization. These results pave a way for SPPs-based applications and offer a possible solution for drawing a space–time field of SPPs in three dimensions.

Tunable multiband metamaterial coherent perfect absorber based on graphene and vanadium dioxide

In this paper, we propose a tunable multiband metamaterial coherent perfect absorber, where vanadium dioxide (VO2) square particles are periodically arranged on the two sides of polysilicon–silica–graphene–silica–polysilicon​ structure. The absorption spectrum of our absorber exhibits three peaks with high absorptivity which are originated from the plasmon resonance modes of graphene and VO2 particle. Benefitting from the tunable conductivity of graphene, the adjustment range of the absorption peak based on the first-order plasmon resonance mode of graphene is as much as 7.88μm when the Fermi level of graphene is increased from 0.3 to 1 eV. As VO2 is changed from metal phase to insulating phase, the absorption peak stemming from the plasmon resonance mode of VO2 particle disappears. The modulation depth of absorption peak can achieve up to 98.85% by tuning the relative phase of two coherent light beams. The resonance wavelengths and intensities of absorption peaks are also dependent on the array period, side length of VO2 particle and the thickness of silica layer. In addition, the change of surrounding refractive index causes a shift of the absorption peak corresponding to VO2 particle. Our findings are helpful for the engineering of actively tunable nano plasmonic devices and metamaterials.

Physics-Guided Neural-Network-Based Inverse Design of a Photonic–Plasmonic Nanodevice for Superfocusing

Controlling the nanoscale light-matter interaction using superfocusing hybrid photonic-plasmonic devices has attracted significant research interest in tackling existing challenges, including converting efficiencies, working bandwidths, and manufacturing complexities. With the growth in demand for efficient photonic-plasmonic input-output interfaces to improve plasmonic device performances, sophisticated designs with multiple optimization parameters are required, which comes with an unaffordable computation cost. Machine learning methods can significantly reduce the cost of computations compared to numerical simulations, but the input-output dimension mismatch remains a challenging problem. Here, we introduce a physics-guided two-stage machine learning network that uses the improved coupled-mode theory for optical waveguides to guide the learning module and improve the accuracy of predictive engines to 98.5%. A near-unity coupling efficiency with symmetry-breaking selectivity is predicted by the inverse design. By fabricating photonic-plasmonic couplers using the predicted profiles, we demonstrate that the excitation efficiency of 83% on the radially polarized surface plasmon mode can be achieved, which paves the way for super-resolution optical imaging.

Nanoscale Manipulating Silver Adatoms for Aqueous Plasmonic Electrochromic Devices

AbstractPlasmonic colors are attractive building blocks for flat panel displays due to their broad color gamut and unprecedented subwavelength resolution. The exploration of reversible silver (Ag) electrodeposition for switchable plasmonic colors is considered as a promising strategy toward dynamically reconfigurable color displays. To date, the current reversible Ag electrodeposition‐based electrochromic devices are energy‐inefficient as the platforms are realized in nonaqueous electrolytes that require high working voltage. However, the high working voltage in an aqueous electrolyte leads to uncontrolled nucleation growth of Ag particles, thus rendering its application for color displays impractical. Herein, the first demonstration of the manipulation of Ag adatoms for aqueous plasmonic electrochromic devices through underpotential deposition is presented. It is shown that the Ag nanoparticles underpotential deposition not only enables a reversible voltage‐activated wide range of dynamic plasmonic color change of 100 nm, but also facilitates size control of the grown Ag nanoparticles. These findings provide a favorable and novel platform for low energy‐consumption tunable photonic and nanoplasmonic devices, as well as a simple and reliable process for rapid, scalable, and green preparation of tunable plasmonic Ag nanoparticles.

Plasmonic Nanosensors: Design, Fabrication, and Applications in Biomedicine

Current advances in the fabrication of smart nanomaterials and nanostructured surfaces find wide usage in the biomedical field. In this context, nanosensors based on localized surface plasmon resonance exhibit unprecedented optical features that can be exploited to reduce the costs, analytic times, and need for expensive lab equipment. Moreover, they are promising for the design of nanoplatforms with multiple functionalities (e.g., multiplexed detection) with large integration within microelectronics and microfluidics. In this review, we summarize the most recent design strategies, fabrication approaches, and bio-applications of plasmonic nanoparticles (NPs) arranged in colloids, nanoarrays, and nanocomposites. After a brief introduction on the physical principles behind plasmonic nanostructures both as inherent optical detection and as nanoantennas for external signal amplification, we classify the proposed examples in colloid-based devices when plasmonic NPs operate in solution, nanoarrays when they are assembled or fabricated on rigid substrates, and nanocomposites when they are assembled within flexible/polymeric substrates. We highlight the main biomedical applications of the proposed devices and offer a general overview of the main strengths and limitations of the currently available plasmonic nanodevices.

Outstanding tunable electrical and optical characteristics in monolayer silicene at high terahertz frequencies

Silicene, a zero-bandgap semimetallic advanced material, has received much attention due to its extraordinary electronic and optical characteristics, enabling its use in plasmonic nano-devices. This material is able to be tuned without degrading its high carrier mobility. In this work, by applying rigorous numerical techniques, the optical and electrical properties of silicene at high terahertz frequencies are calculated. Under the influence of environmental effects including the Fermi level, temperature, and external electric field, the optical conductivity and refractive index of silicene are investigated using the tight-binding model. The effects of the Fermi level from 0 to 1 eV, the external electric field from 0 to 2.5 \({\text{V}}/{\dot{\text{A}}}\), and temperature from 5 to 400 K are investigated with respect to the optical properties of silicene. One of the interesting features of silicene is its adjustable bandgap, which we present here.

Platinum nanoparticle sensitized plasmonic-enhanced broad spectral photodetection in large area vertical-aligned MoS2 flakes

2D MoS2 holds immense potential for electronic and optoelectronic applications due to its unique characteristics. However, the atomic-scale thickness of MoS2 hinders the optical absorbance, thereby limiting its photodetection capability. Vertically-aligned MoS2 (VA-MoS2) has an advantage of strong optical absorption and quick intra-layer transport, offering high speed operation. The coupling of plasmonic metal nanostructure with MoS2 can further enhance the light–matter interaction. Pt/Pd (as opposed to Ag/Au) are more promising to design next-generation nano-plasmonic devices due to their intense interband activity over a broad spectral range. Herein, we report Pt nanoparticle (NPs) enhanced broadband photoresponse in VA-MoS2. The optical absorbance of MoS2 is enhanced after the integration of Pt NPs, with a four-fold enhancement in photocurrent. The formation of Schottky junction at Pt-MoS2 interface inhibits electron transmission, suppressing the dark current and substantially reducing NEP. The plasmonic-enabled photodetector shows enhanced responsivity (432 A W−1, 800 nm) and detectivity (1.85 × 1014 Jones, 5 V) with a low response time (87 ms/84 ms), attributed to faster carrier transport. Additionally, a theoretical approach is adopted to calculate wavelength-dependent responsivity, which matches well with experimental results. These findings offer a facile approach to modulate the performance of next-generation optoelectronic devices for practical applications.

A DNA‐Based Plasmonic Nanodevice for Cascade Signal Amplification

AbstractHere, we describe a DNA circuit‐aided, origami nanodevice‐based plasmonic system, which performs DNA‐regulated, cascade amplification of faint chemical/biological signals. In this system, two gold‐nanorods (GNRs) are co‐assembled onto a DNA lock‐containing, tweezer‐like DNA origami template. Logic circuits serve as recognition and amplification elements for specific messengers, producing DNA keys for driving conformational changes of the plasmonic nanodevices. In the presence of input signals including nucleic acids, adenosines, chiral tyrosinamides or specific receptors expressed by tumor cells, the plasmonic nanodevices can be activated to perform dynamic structural motions, reporting robust responses via plasmonic circular dichroism (CD) spectral changes. This DNA nanodevice‐based system provides a different design to enrich the strategies for constructing synthetic nanomachines, enabling the customized bottom‐up nanostructure construction for sensitive biological signaling.

A DNA-Based Plasmonic Nanodevice for Cascade Signal Amplification.

Here, we describe a DNA circuit-aided, origami nanodevice-based plasmonic system, which performs DNA-regulated, cascade amplification of faint chemical/biological signals. In this system, two gold-nanorods (GNRs) are co-assembled onto a DNA lock-containing, tweezer-like DNA origami template. Logic circuits serve as recognition and amplification elements for specific messengers, producing DNA keys for driving conformational changes of the plasmonic nanodevices. In the presence of input signals including nucleic acids, adenosines, chiral tyrosinamides or specific receptors expressed by tumor cells, the plasmonic nanodevices can be activated to perform dynamic structural motions, reporting robust responses via plasmonic circular dichroism (CD) spectral changes. This DNA nanodevice-based system provides a different design to enrich the strategies for constructing synthetic nanomachines, enabling the customized bottom-up nanostructure construction for sensitive biological signaling.