Tunable Plasmon Research Articles

THz Scattering and Tunable Plasmonic Resonances from Graphene‐Coated Gold Nanowires

THz Scattering and Tunable Plasmonic Resonances from Graphene‐Coated Gold Nanowires

Theoretical Design of Near-Infrared Tunable Surface Plasmon Resonance Biosensors Based on Gate-Controlled Graphene Plasmons

A tunable near-infrared surface plasmon resonance (SPR) biosensor based on gate-controlled graphene plasmons is numerically investigated by using the finite element method (FEM) and the transfer matrix method (TMM). The novel properties of chemical potential sensing make the proposed sensor promising in the application of ultra-sensitive and highly specific biosensing technology. The sensitivity of chemical potential sensing in wavelength interrogation mode can be calculated to be 1.5, 1.89, 2.29, 3.21, 3.73 and 4.68 nm/meV, respectively, at the resonance wavelengths of 1100, 1200, 1310, 1550, 1700 and 1900 nm. The figure of merit (FOM) achieves 129.3, 101.1, 84.5, 67.7, 69.5 and 59.7 eV−1, respectively, at these resonance wavelengths. The sensitivity of chemical potential sensing in gate voltage interrogation mode also can be calculated to be 156.9822, 143.6147, 131.0779, 111.0351, 101.3415 and 90.6038 mV/meV, respectively, at the incident wavelengths of 1100, 1200, 1310, 1550, 1700 and 1900 nm. The FOM achieves 135.6, 103.0, 88.9, 62.2, 66.6 and 61.5 eV−1, respectively, at these incident wavelengths. Theoretical estimates suggest that the limit of detection (LOD) of the sensor’s DNA sensing can reach the level of femtomolar or even attomolar, comparable to and even lower than that of 2D nanomaterial-enhanced metal SPR sensors with AuNPs as a sensitivity enhancement strategy. The feasibility of preparation and operation of this new concept SPR biosensor is also analyzed and discussed.

Artificial Photosynthesis of Ammonia by Semiconducting Plasmonic NIR Energy

Artificial photosynthesis of ammonia is one of the most promising paths toward carbon neutrality and sustainability. However, nitrogen photo-fixation to produce ammonia in ultrapure water is still challenging due to the thermodynamic and kinetic requirements of the nitrogen reduction reaction. An ideal photocatalyst is expected to have energetic electrons to drive the nitrogen reduction reaction, as well as enough affinity for chemisorption and activation of nitrogen molecules at the surface. Compared with plasmonic metal catalysts, plasmonic semiconducting nanomaterials are excellent candidates due to the tunable plasmon absorption over a wide range of spectra allowing efficient utilization of solar energy, abundant hot carriers that may overcome the interfacial energy barriers, and low-cost. The localized surface plasmonic resonance (LSPR) effects can also promote charge separation and interfacial transfer. Here, we report metal oxides with tunable oxygen concentration and copper chalcogenides with tunable copper deficiency for photocatalytic nitrogen reduction in ultrapure water. Efficient ammonia production has been achieved under near-infrared (NIR) light illumination. We have demonstrated that for plasmonic semiconducting photocatalysts, the performance is not only dictated by the defects, their negative effects in trapping carriers are also important. Figure 1

Dual dynamically tunable terahertz graphene-based plasmonic induced transparency and slow light effects

A novel single-layer graphene-based structure is designed in this article. This structure consists of two graphene strips and two graphene blocks. The components of this structure generate two bright modes and one dark mode in the terahertz region, and these three modes undergo destructive interference, leading to the phenomenon of double plasmonic induced transparency. The graphene of this structure has continuity, and the Fermi level can be adjusted by adjusting the bias voltage applied to the structure. Compared with those discontinuous structures, it is easier to achieve tuning function. The structure uses the finite-difference time-domain for data simulation, uses the coupled mode theory for theoretic calculation, and compares the transmission spectra obtained by the two methods. Through observation, it can be found that the frequency positions of the peaks and dips of the simulated transmission spectrum increase with the increase of the Fermi level, showing a perfect linear relationship, which indicates that this structure has great prospects in the modulator. In addition, the structure has achieved good results in the slow light effect, and after measurement, the peak values of group index and group delay can reach up to 380 and 0.241 ps, respectively. By utilizing these advantages, this structure can provide more possibilities for the development and research of slow light fields.

Surface-Enhanced Raman Scattering Studies of Au-Ag Bimetallic Nanoparticles with a Tunable Surface Plasmon Resonance Wavelength Synthesized by Picosecond Laser Irradiation

Here, we present a simple and green method of preparing Au-Ag bimetallic nanoparticles (NPs) with a tunable surface plasmon resonance (SPR) wavelength by using picosecond laser irradiation. Au-Ag alloy NPs have been produced by irradiating the solutions containing respective metallic salts in a polyvinyl alcohol (PVA) matrix using a picosecond laser in a single-step process. The SPR wavelength of the Au-Ag bimetallic NPs is observed to be shifted/changed with the Au-Ag concentration and the laser irradiation parameters. The Au-Ag NPs embedded in the PVA matrix are advantageous for Surface-Enhanced Raman scattering (SERS) applications. The estimated enhancement factors (EFs) were observed to vary as a function of conditions of the Au-Ag bimetallic alloy NPs synthesis and also on the concentration of Au at a fixed input fluence of irradiation. The SERS active platforms of Au-Ag bimetallic NPs showed EFs as high as of the order of 108 for Crystal Violet (CV) dye samples at nano molar concentrations. The present study demonstrates a simple, single-step, and green method that fabricates Au-Ag alloy-based nanocomposites suitable for SERS investigations with significantly higher orders of EFs.

Ultrasmall and tunable TeraHertz surface plasmon cavities at the ultimate plasmonic limit

The ability to confine THz photons inside deep-subwavelength cavities promises a transformative impact for THz light engineering with metamaterials and for realizing ultrastrong light-matter coupling at the single emitter level. To that end, the most successful approach taken so far has relied on cavity architectures based on metals, for their ability to constrain the spread of electromagnetic fields and tailor geometrically their resonant behavior. Here, we experimentally demonstrate a comparatively high level of confinement by exploiting a plasmonic mechanism based on localized THz surface plasmon modes in bulk semiconductors. We achieve plasmonic confinement at around 1 THz into record breaking small footprint THz cavities exhibiting mode volumes as low as {V}_{cav}/{lambda }_{0}^{3} sim 1{0}^{-7}-1{0}^{-8}, excellent coupling efficiencies and a large frequency tunability with temperature. Notably, we find that plasmonic-based THz cavities can operate until the emergence of electromagnetic nonlocality and Landau damping, which together constitute a fundamental limit to plasmonic confinement. This work discloses nonlocal plasmonic phenomena at unprecedentedly low frequencies and large spatial scales and opens the door to novel types of ultrastrong light-matter interaction experiments thanks to the plasmonic tunability.

Tunable Tamm plasmon cavity as a scalable biosensing platform for surface enhanced resonance Raman spectroscopy

Surface enhanced Resonance Raman spectroscopy (SERRS) is a powerful technique for enhancing Raman spectra by matching the laser excitation wavelength with the plasmonic resonance and the absorption peak of biomolecules. Here, we propose a tunable Tamm plasmon polariton (TPP) cavity based on a metal on distributed Bragg reflector (DBR) as a scalable sensing platform for SERRS. We develop a gold film-coated ultralow-loss phase change material (Sb2S3) based DBR, which exhibits continuously tunable TPP resonances in the optical wavelengths. We demonstrate SERRS by matching the TPP resonance with the absorption peak of the chromophore molecule at 785 nm wavelength. We use this platform to detect cardiac Troponin I protein (cTnI), a biomarker for early diagnosis of cardiovascular disease, achieving a detection limit of 380 fM. This scalable substrate shows great promise as a next-generation tunable biosensing platform for detecting disease biomarkers in body fluids for routine real-time clinical diagnosis.

Tunable plasmon refractive index sensor and a slow-light device optimized by an improved genetic algorithm based on a MIM waveguide

A structure is proposed in this article consisting of a stub metal–insulator–metal (MIM) waveguide coupled with an embedded T-shaped square ring resonator (ETSRR). The transmission characteristics and magnetic field distribution of the design are analyzed in detail using the finite element method (FEM). Furthermore, the geometric parameters are optimized using an improved genetic algorithm to enhance device performance. The proposed structure is therefore an ideal candidate for realizing a refractive index sensor and slow-light device, with potential applications in various fields such as sensing and communication. Moreover, our study provides valuable insights to the design of surface plasmon polarition (SPP) waveguides with computer assistance.

Self-Functional Off-Stoichiometry Polymeric Materials: Potential for Tunable Plasmonic Applications

Self-Functional Off-Stoichiometry Polymeric Materials: Potential for Tunable Plasmonic Applications

Near-infrared tunable Tamm plasmons high-performance hot electron photodetector based on Ag/Ge2Sb2Te5 low Schottky barrier

Hot electron photodetector is a typical hot electron optoelectronic device, which can realize the narrow band photoelectric detection with high tunability and sensitivity. The Tamm plasmons (TPs) based on the planar metal film/distributed Bragg reflector (DBR) has the advantages of simple structure, low manufacturing cost, and high absorption efficiency. A multilayer thin film device structure for high-performance near-infrared hot electron metal-semiconductor-metal photodetectors is proposed. The structure is based on Ag/Ge2Sb2Te5 (GST) Schottky barrier and TPs formed by SiO2/MoS2 DBR. The simulation results of hot electron emission theory show that DBR can effectively extend the absorption spectrum of Ag film and the response spectrum of the device, and enhance the absorption rate of Ag film and the response of the device. The responsivity which is up to 53 mA/W can be obtained by adjusting the structure parameters of the DBR, the thickness of the Ag film, and the GST layer. At the same time, we also propose a digital display system based on the arrangement of crystalline GST and amorphous GST. It provides a new way for the realization of high-performance near-infrared hot electronic devices and is conducive to expanding the application field of hot electronic photodetectors.

Dynamic tunable multiple plasmon induced transparency sensor and optical switch in dual-polarization excitation in a terahertz graphene metamaterial

This paper proposes the development of a simplified graphene-based terahertz device that exhibits multiple plasmon induced transparency (PIT) effects in x-polarized and y-polarized waves. The PIT device is composed of “Z-shaped” and “parallel strips” structures, which demonstrate multiple transparency windows under x-polarized and y-polarized incident light within the frequency range of 2-15 THz. Additionally, under x-polarized incident, the device demonstrates wideband transparency at 3.4 THz. By comparing the transmission spectra of individual and combined structures, we observe that the initial transmission valley of the single two horizontal stripes structure transforms into a PIT curve in the combined structure, while the transmission valley of the other individual structures remains transmission. The PIT device demonstrates a peak sensitivity of 3THz/RIU for x-polarized waves and 2.9THz/RIU for y-polarized waves when employed as a light sensor. PIT as a light switch can attain a maximum modulation depth of 81.4% for x-polarized waves and 71.2% for y-polarized waves at Fermi energy levels ranging from 0.5eV to 1.2eV. The presented PIT device shows promise for applications in high-sensitivity optical sensing and optical switching.

Sunlight Driven Reversible and Tunable Plasmon Resonance in 2D Amorphous Molybdenum Oxide

AbstractTwo‐dimensional molybdenum oxide (2D MoO3), as a non‐noble metal semiconductor material, is of particular significance for exploring the localized surface plasmon resonance (LSPR). However, the high excitation energy and the irreversible LSPR performance significantly restrict its practical application. To resolve these challenges, the hydrogen intercalated 2D amorphous MoO3 is investigated, and it can be observed that tunable plasmon resonances in the visible and near‐infrared regions occur. More importantly, the LSPR effect can be triggered by visible light and monochromatic light. For the first time, it is found out that the hydrogen intercalated 2D amorphous MoO3 presents a light‐modulated reversible LSPR effect, and its color can transfer from dark blue under illumination to transparent in light‐off. Additionally, solar energy can be effectively stored in bulk‐amorphous MoO3 materials. Therefore, these findings may provide a new platform to utilize sun power.

Nonlinear Plasmonics in Nanostructured Phosphorene.

Phosphorene has emerged as an atomically thin platform for optoelectronics and nanophotonics due to its excellent optical properties and the possibility of actively tuning light-matter interactions through electrical doping. While phosphorene is a two-dimensional semiconductor, plasmon resonances characterized by pronounced anisotropy and strong optical confinement are anticipated to emerge in highly doped samples. Here we show that the localized plasmons supported by phosphorene nanoribbons (PNRs) exhibit high tunability in relation to both edge termination and doping charge polarity and can trigger an intense nonlinear optical response at moderate doping levels. Our explorations are based on a second-principles theoretical framework, employing maximally localized Wannier functions constructed from ab initio electronic structure calculations, which we introduce here to describe the linear and nonlinear optical response of PNRs on mesoscopic length scales. Atomistic simulations reveal the high tunability of plasmons in doped PNRs at near-infrared frequencies, which can facilitate the synergy between the electronic band structure and plasmonic field confinement to drive efficient high-harmonic generation. Our findings establish nanostructured phosphorene as a versatile atomically thin material candidate for nonlinear plasmonics.

DNA-Condensed Plasmonic Supraballs Transparent to Molecules.

DNA nanotechnology offers an unrivaled programmability of plasmonic nanoassemblies based on encodable Watson-Crick basepairing. However, it is very challenging to build rigidified three-dimensional supracolloidal assemblies with strong electromagnetic coupling and a self-confined exterior shape. We herein report an alternative strategy based on a DNA condensation reaction to make such structures. Using DNA-grafted gold nanoparticles as building blocks and metal ions with suitable phosphate affinities as abiological DNA-bonding agents, a seedless growth of spheroidal supraparticles is realized via metal-ion-induced DNA condensation. Some governing rules are disclosed in this process, including kinetic and thermodynamic effects stemming from electrostatic and coordinative forces with different interaction ranges. The supraballs are tailorable by adjusting the volumetric ratio between DNA grafts and gold cores and by overgrowing extra gold layers toward tunable plasmon coupling. Various appealing and highly desirable properties are achieved for the resulting metaballs, including (i) chemical reversibility and fixation ability, (ii) stability against denaturant, salt, and molecular adsorbates, (iii) enriched and continuously tunable plasmonic hotspots, (iv) permeability to small guest molecules and antifoulingness against protein contaminates, and (v) Raman-enhancing and photocatalytic activities. Innovative applications are thus foreseeable for this emerging class of meta-assemblies in contrast to what is achieved by DNA-basepaired ones.

Edge-induced excitations in Bi[formula omitted]Te[formula omitted] from spatially-resolved electron energy-gain spectroscopy

Among the many potential applications of topological insulator materials, their broad potential for the development of novel tunable plasmonics at THz and mid-infrared frequencies for quantum computing, terahertz detectors, and spintronic devices is particularly attractive. The required understanding of the intricate relationship between nanoscale crystal structure and the properties of the resulting plasmonic resonances remains, however, elusive for these materials. Specifically, edge- and surface-induced plasmonic resonances, and other collective excitations, are often buried beneath the continuum of electronic transitions, making it difficult to isolate and interpret these signals using techniques such as electron energy-loss spectroscopy (EELS). Here we focus on the experimentally clean energy-gain EELS region to characterise collective excitations in the topologically insulating material Bi2Te3 and correlate them with the underlying crystalline structure with nanoscale resolution. We identify with high significance the presence of a distinct energy-gain peak around −0.8eV, with spatially-resolved maps revealing that its intensity is markedly enhanced at the edge regions of the specimen. Our findings illustrate the reach of energy-gain EELS analyses to accurately map collective excitations in quantum materials, a key asset in the quest towards new tunable plasmonic devices.

Chromogenic Mechanisms of Colorimetric Sensors Based on Gold Nanoparticles.

The colorimetric signal readout method is widely used in visualized analyses for its advantages, including visualization of test results, simple and fast operations, low detection cost and fast response time. Gold nanoparticles (Au NPs), which not only exhibit enzyme-like activity but also have the advantages of tunable localized surface plasmon resonance (LSPR), high stability, good biocompatibility and easily modified properties, provide excellent platforms for the construction of colorimetric sensors. They are widely used in environmental monitoring, biomedicine, the food industry and other fields. This review focuses on the chromogenic mechanisms of colorimetric sensors based on Au NPs adopting two different sensing strategies and summarizes significant advances in Au NP-based colorimetric sensing with enzyme-like activity and tunable LSPR characteristics. In addition, the sensing strategies based on the LSPR properties of Au NPs are classified into four modulation methods: aggregation, surface modification, deposition and etching, and the current status of visual detection of various analytes is discussed. Finally, the review further discusses the limitations of current Au NP-based detection strategies and the promising prospects of Au NPs as colorimetric sensors, guiding the design of novel colorimetric sensors.

Tunable optical topological transitions of plasmon polaritons in WTe2 van der Waals films

Naturally existing in-plane hyperbolic polaritons and the associated optical topological transitions, which avoid the nano-structuring to achieve hyperbolicity, can outperform their counterparts in artificial metasurfaces. Such plasmon polaritons are rare, but experimentally revealed recently in WTe2 van der Waals thin films. Different from phonon polaritons, hyperbolic plasmon polaritons originate from the interplay of free carrier Drude response and interband transitions, which promise good intrinsic tunability. However, tunable in-plane hyperbolic plasmon polariton and its optical topological transition of the isofrequency contours to the elliptic topology in a natural material have not been realized. Here we demonstrate the tuning of the optical topological transition through Mo doping and temperature. The optical topological transition energy is tuned over a wide range, with frequencies ranging from 429 cm−1 (23.3 microns) for pure WTe2 to 270 cm−1 (37.0 microns) at the 50% Mo-doping level at 10 K. Moreover, the temperature-induced blueshift of the optical topological transition energy is also revealed, enabling active and reversible tuning. Surprisingly, the localized surface plasmon resonance in skew ribbons shows unusual polarization dependence, accurately manifesting its topology, which renders a reliable means to track the topology with far-field techniques. Our results open an avenue for reconfigurable photonic devices capable of plasmon polariton steering, such as canaling, focusing, and routing, and pave the way for low-symmetry plasmonic nanophotonics based on anisotropic natural materials.

Tunable strong plasmon–exciton coupling based modulator employing borophene and deep subwavelength perovskite grating

Two-dimensional materials support deeply confined and tunable plasmonic modes, which have great potential for achieving device miniaturization and flexible manipulation. In this paper, we propose a diffraction-unlimited system (period ≈ λ/20) composed of borophene layer and perovskite grating to investigate the strong coupling between the borophene guiding plasmon (BGP) and perovskite exciton (PE) modes. The resonant energy of the BGP mode could be electrically tuned to match the energy of the PE mode, and a remarkable Rabi splitting is attained under zero-detuning conditions. The splitting energy could reach 230 meV due to the strong field enhancement provided by the BGP mode. Taking advantage of the proposed electrically tunable hybrid system, not only is the reflective amplitude modulation depth up to 99.9%, but the 1.76π phase range modulation is achieved. Furthermore, by increasing the distance between the borophene layer and perovskite grating, a passive parity-time symmetry breaking could be observed with the vanished energy splitting. Our results deepen our understanding of light–matter interactions at the sub-wavelength scale and provide a guideline for designing active plasmonic devices.

Tuning of graphene plasmons by ferroelectric superdomain for mid-infrared photodetector with high responsivity

A new strategy is demonstrated for confining graphene plasmons to resonantly enhance light–matter interactions for tunable mid-IR detection. Our devices consist of integrating monolayer graphene without patterning onto a nanoribbon-connected ring-shaped ferroelectric superdomain with alternately up- and down-polarization. The simulations show that our devices have a tunable spectral response from 11.7 to 19.5 μm by both reconfiguring the ferroelectric superdomain and varying the ferroelectric-gated graphene Fermi level. A highest photoresponsivity of 796–947 A W−1 has been achieved in 10–20 μm. The proof-of-concept photodetector offers the possibility to simplify the fabrication of plasmonic devices and helps the development of applications of tunable mid-IR detection.

A Novel BioNEMS Sensor Based on Tunable Plasmonic Modes of a Grating MIM Structure

In this paper, a novel optical BioNEMS (Bio Nano-Electro-Mechanical-Systems) sensor using a nanomechanical plasmonic structure is proposed to develop a high performance label-free biosensor. The present device is composed of a functionalized BioNEMS cantilever coated by a gold layer as a part of the proposed plasmonic grating waveguide. This plasmonic system is based on the light interaction with a metallic nanostructure as a metal-insulator-metal (MIM) Bragg grating where an air gap acts as the insulator. Passing patient samples through the functionalized surface of the nanocantilever, the biological interactions release a stress on the surface because of binding events. The cantilever can be thus deflected by inducing a differential surface stress. Therefore, the air gap distance (the insulator width) between two parts of the plasmonic grating structure is changed to excite surface plasmon polaritons in a different wavelength. Furthermore, the present biosensor is analyzed by numerical and analytical approaches and its functional characteristics are obtained as follows: optical sensitivity of 7872 nm/RIU, figure of merit (FOM) of 394 RIU^-1, mechanical sensitivity of 1.2 µm/Nm^-1. According to the results, the proposed label-free identification method can be used as a sensitive platform for detection of biomarkers in point of care testing (POCT) applications.