Showing papers on "Surface plasmon resonance published in 2018"

Localized Surface Plasmon Resonance in Semiconductor Nanocrystals

Abstract: Localized surface plasmon resonance (LSPR) in semiconductor nanocrystals (NCs) that results in resonant absorption, scattering, and near field enhancement around the NC can be tuned across a wide optical spectral range from visible to far-infrared by synthetically varying doping level, and post synthetically via chemical oxidation and reduction, photochemical control, and electrochemical control In this review, we will discuss the fundamental electromagnetic dynamics governing light matter interaction in plasmonic semiconductor NCs and the realization of various distinctive physical properties made possible by the advancement of colloidal synthesis routes to such NCs Here, we will illustrate how free carrier dielectric properties are induced in various semiconductor materials including metal oxides, metal chalcogenides, metal nitrides, silicon, and other materials We will highlight the applicability and limitations of the Drude model as applied to semiconductors considering the complex band structures

Active Plasmonics: Principles, Structures, and Applications

Abstract: Active plasmonics is a burgeoning and challenging subfield of plasmonics. It exploits the active control of surface plasmon resonance. In this review, a first-ever in-depth description of the theoretical relationship between surface plasmon resonance and its affecting factors, which forms the basis for active plasmon control, will be presented. Three categories of active plasmonic structures, consisting of plasmonic structures in tunable dielectric surroundings, plasmonic structures with tunable gap distances, and self-tunable plasmonic structures, will be proposed in terms of the modulation mechanism. The recent advances and current challenges for these three categories of active plasmonic structures will be discussed in detail. The flourishing development of active plasmonic structures opens access to new application fields. A significant part of this review will be devoted to the applications of active plasmonic structures in plasmonic sensing, tunable surface-enhanced Raman scattering, active plasmoni...

Hot Hole Collection and Photoelectrochemical CO2 Reduction with Plasmonic Au/p-GaN Photocathodes

Abstract: Harvesting nonequilibrium hot carriers from plasmonic-metal nanostructures offers unique opportunities for driving photochemical reactions at the nanoscale. Despite numerous examples of hot electron-driven processes, the realization of plasmonic systems capable of harvesting hot holes from metal nanostructures has eluded the nascent field of plasmonic photocatalysis. Here, we fabricate gold/p-type gallium nitride (Au/p-GaN) Schottky junctions tailored for photoelectrochemical studies of plasmon-induced hot-hole capture and conversion. Despite the presence of an interfacial Schottky barrier to hot-hole injection of more than 1 eV across the Au/p-GaN heterojunction, plasmonic Au/p-GaN photocathodes exhibit photoelectrochemical properties consistent with the injection of hot holes from Au nanoparticles into p-GaN upon plasmon excitation. The photocurrent action spectrum of the plasmonic photocathodes faithfully follows the surface plasmon resonance absorption spectrum of the Au nanoparticles and open-circuit...

Recent Advances in Resonant Waveguide Gratings

Abstract: Resonant waveguide gratings (RWGs), also known as guided mode resonant (GMR) gratings or waveguide-mode resonant gratings, are dielectric structures where these resonant diffractive elements benefit from lateral leaky guided modes from UV to microwave frequencies in many different configurations. A broad range of optical effects are obtained using RWGs such as waveguide coupling, filtering, focusing, field enhancement and nonlinear effects, magneto-optical Kerr effect, or electromagnetically induced transparency. Thanks to their high degree of optical tunability (wavelength, phase, polarization, intensity) and the variety of fabrication processes and materials available, RWGs have been implemented in a broad scope of applications in research and industry: refractive index and fluorescence biosensors, solar cells and photodetectors, signal processing, polarizers and wave plates, spectrometers, active tunable filters, mirrors for lasers and optical security features. The aim of this review is to discuss the latest developments in the field including numerical modeling, manufacturing, the physics, and applications of RWGs. Scientists and engineers interested in using RWGs for their application will also find links to the standard tools and references in modeling and fabrication according to their needs.

Degenerately hydrogen doped molybdenum oxide nanodisks for ultrasensitive plasmonic biosensing

Abstract: Plasmonic biosensors based on noble metals generally suffer from low sensitivities if the perturbation of refractive-index in the ambient is not significant. By contrast, the features of degenerately doped semiconductors offer new dimensions for plasmonic biosensing, by allowing charge-based detection. Here, this concept is demonstrated in plasmonic hydrogen doped molybdenum oxides (H x MoO 3 ), with the morphology of 2D nanodisks, using a representative enzymatic glucose sensing model. Based on the ultrahigh capacity of the molybdenum oxide nanodisks for accommodating H + , the plasmon resonance wavelengths of H x MoO 3 are shifted into visible-near-infrared wavelengths. These plasmonic features alter significantly as a function of the intercalated H + concentration. The facile H + deintercalation out of H x MoO 3 provides an exceptional sensitivity and fast kinetics to charge perturbations during enzymatic oxidation. The optimum sensing response is found at H 1.55 MoO 3 , achieving a detection limit of 2 × 10 -9 m at 410 nm, even when the biosensing platform is adapted into a light-emitting diode-photodetector setup. The performance is superior in comparison to all previously reported plasmonic enzymatic glucose sensors, providing a great opportunity in developing high performance biosensors.

Symmetrical dual D-shape photonic crystal fibers for surface plasmon resonance sensing.

Abstract: Symmetrical dual D-shape photonic crystal fibers (PCFs) for surface plasmon resonance (SPR) sensing are designed and analyzed by the finite element method (FEM). The performance of the sensor is remarkably enhanced by the directional power coupling between the two fibers. We study the influence of the structural parameters on the performance of the sensor as well as the relationship between the resonance wavelengths and analyze refractive indexes between 1.36 and 1.41. An average spectral sensitivity of 14660 nm/RIU can be achieved in this sensing range and the corresponding refractive index resolution is 6.82 × 10-6 RIU. The characteristics of a single D-shape PCF-SPR sensor with the same structural parameters are compared with those of the dual PCFs sensor and the latter has distinct advantages concerning the spectral sensitivity, resolution, amplitude sensitivity, and figure of merits (FOM).

Spiral Photonic Crystal Fiber-Based Dual-Polarized Surface Plasmon Resonance Biosensor

Abstract: We numerically demonstrate a surface plasmon resonance biosensor-based on dual-polarized spiral photonic crystal fiber (PCF). Chemically stable gold material is used as the active plasmonic material, which is placed on the outer layer of the PCF to facilitate practical fabrication. Finite-element method-based numerical investigations show that the proposed biosensor shows maximum wavelength sensitivity of 4600 and 4300 nm/RIU in ${x}$ - and ${y}$ -polarized modes at an analyte refractive index of 1.37. Moreover, for analyte refractive index ranging from 1.33 to 1.38, maximum amplitude sensitivities of 371.5 RIU−1 and 420.4 RIU−1 are obtained in ${x}$ - and ${y}$ -polarized modes, respectively. In addition, the effects of changing pitch, different air hole diameter of the PCF and thickness of the gold layer on the sensing performance are also investigated. Owing to high sensitivity, improved sensing resolution and appropriate linearity characteristics, the proposed dual-polarized spiral PCF can be implemented for the detection of biological analytes, organic chemicals, biomolecules, and other unknown analytes.

Dynamics of Charge-Transfer Behavior in a Plasmon-Induced Quasi-Type-II p–n/n–n Dual Heterojunction in Ag@Ag3PO4/g-C3N4/NiFe LDH Nanocomposites for Photocatalytic Cr(VI) Reduction and Phenol Oxidation

Abstract: In this work, a series of heterostructure Ag@Ag3PO4/g-C3N4/NiFe layered double hydroxide (LDH) nanocomposites were prepared by a combination of an electrostatic self-assembly and in situ photoreduction method. In this method, positively charged p-type Ag3PO4 was electrostatically bonded to the self-assembled negatively charged surface of the n-n-type g-C3N4/NiFe (CNLDH) LDH hybrid material with partial reduction of Ag+ to metallic Ag nanoparticles (NPs) by the photogenerated electrons and available surface -OH groups of LDH under visible light irradiation. The presence of Ag3PO4 as a p-type semiconductor, the surface plasmon resonance (SPR) effect of metallic Ag NPs, and oxygen vacancies as Ov-type defects in NiFe LDH could greatly achieve the quasi-type-II p-n/n-n dual heterojunctions, which was revealed by the shifted conduction band and valence band potentials in Mott-Schottky (M-S) analysis. Among all the optimized heterostructures, CNLDHAgP4 could achieve the highest photocatalytic Cr(VI) reduction rate of 97% and phenol oxidation rate of 90% in 2 h. The heterostructure CNLDHAgP4 photocatalyst possesses a unique morphology consisting of cubic phases of both Ag NPs and Ag3PO4, which adhered to the thin and curvy layers of the CNLDH hybrid for smooth electronic and ionic charge transport. Furthermore, the intimate Schottky barriers formed at the interface of quasi-type-II p-n/n-n dual heterojunctions were verified by the photoluminescence, linear sweep voltammetry, M-S, electrochemical impedance study, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy studies. The SPR effect of Ag NPs and oxygen vacancies as Ov-type defect in NiFe LDH can effectively accelerate the threshold of charge separation and be the main reason for the enhanced activity achieved by the as-fabricated heterostructure photocatalyst.

A novel 3D plasmonic p-n heterojunction photocatalyst: Ag nanoparticles on flower-like p-Ag2S/n-BiVO4 and its excellent photocatalytic reduction and oxidation activities

Abstract: A novel 3D structure Ag/p-Ag2S/n-BiVO4 plasmonic p-n heterojunction photocatalyst was successfully fabricated via a depositing p-type Ag2S on n-type BiVO4, followed by light reduction. In this innovative plasmonic p-n heterojunction photocatalyst strcture, p-n heterojunction can play the role of suppression of charge recombination, and surface plasmon resonance of Ag can enhance the absorption of visible light confirmed by finite difference time domain (FDTD) simulations method. For the photocatalytic oxidation of oxytetracycline hydrochloride (OTH) and reduction of Cr6+, the Ag/p-Ag2S/n-BiVO4exhibits excellent photocatalytic performance, compared with BiVO4 and p-Ag2S/n-BiVO4. The results of active species detection reveal that h+ radical is the main reactive species in the photocatalytic oxidation of OTH. Moreover, 13 photocatalytic degradation intermediates and products of OTH were also identified by the gas chromatography-mass spectrometer (GC-MS). Finally, the photocatalytic oxidation and reduction mechanism over Ag/p-Ag2S/n-BiVO4 was discussed in detail. The present study will benefit the development of the new plasmonic p-n heterojunction photocatalysts and would be of great importance to meet ever-increasing environmental demands in the future.

Facet-dependent interfacial charge separation and transfer in plasmonic photocatalysts

Abstract: Surface plasmon resonance (SPR) induced plasmonic photocatalysis provides a brand new way for more efficient light absorption and utilization to achieve better solar light conversion. Although the SPR effect in metal-semiconductor photocatalysis has been widely investigated, the SPR-driven interfacial charge separation and transfer patterns between the two counterparts have not yet been fully revealed. The plasmonic metal-semiconductor photocatalytic systems require to be rationally designed, especially for the facet-aspect of the semiconductor, which can dominantly endow the contacting interface with diverse charge transfer patterns. Taken Bi metal deposited at the typical (001) and (010) facets of BiOBr nanosheets as a case study, we demonstrate that the surface charge alternation on the (010) facet highly favors the interfacial charge separation and transfer, by providing a new route of [Bi2O2]2+ → plasmonic metal → Br− for interfacial carriers transfer. The charge alternation on discrepant semiconductor facets in essence makes the plasmonic photocatalytic system be different in charge transportation pattern. These new findings are further validated in extensive composite systems composed of alternative plasmonic metal (Ag and Au) and semiconductors (BiOCl and BiOI). The perspective here can open numerous possibilities for the rational design of more efficient plasmonic photocatalysts.

Light-Enhanced Carbon Dioxide Activation and Conversion by Effective Plasmonic Coupling Effect of Pt and Au Nanoparticles

Abstract: Photocatalytic reduction of carbon dioxide (CO2) is attractive for the production of valuable fuels and mitigating the influence of greenhouse gas emission. However, the extreme inertness of CO2 and the sluggish kinetics of photoexcited charge carrier transfer process greatly limit the conversion efficiency of CO2 photoreduction. Herein, we report that the plasmonic coupling effect of Pt and Au nanoparticles (NPs) profoundly enhances the efficiency of CO2 reduction through dry reforming of methane reaction assisted by light illumination, reducing activation energies for CO2 reduction ∼30% below thermal activation energies and achieving a reaction rate 2.4 times higher than that of the thermocatalytic reaction. UV–visible (vis) absorption spectra and wavelength-dependent performances show that not only UV but also visible light play important roles in promoting CO2 reduction due to effective localized surface plasmon resonance (LSPR) coupling between Pt and Au NPs. Finite-difference time-domain simulations...

Resonance Energy Transfer-Promoted Photothermal and Photodynamic Performance of Gold-Copper Sulfide Yolk-Shell Nanoparticles for Chemophototherapy of Cancer.

Abstract: Gold (Au) core@void@copper sulfide (CuS) shell (Au–CuS) yolk–shell nanoparticles (YSNPs) were prepared in the present study for potential chemo-, photothermal, and photodynamic combination therapy, so-called “chemophototherapy”. The resonance energy transfer (RET) process was utilized in Au–CuS YSNPs to achieve both enhanced photothermal and photodynamic performance compared with those of CuS hollow nanoparticles (HNPs). A series of Au nanomaterials as cores that had different localized surface plasmon resonance (LSPR) absorption peaks at 520, 700, 808, 860, and 980 nm were embedded in CuS HNPs to screen the most effective Au–CuS YSNPs according to the RET process. Thermoresponsive polymer was fabricated on these YSNPs’ surface to allow for controlled drug release. Au808–CuS and Au980–CuS YSNPs were found capable of inducing the largest temperature elevation and producing the most significant hydroxyl radicals under 808 and 980 nm laser irradiation, respectively, which could accordingly cause the most sev...

[INVITED] Recent advances in surface plasmon resonance based fiber optic chemical and biosensors utilizing bulk and nanostructures

Abstract: Surface plasmon resonance has established itself as an immensely acclaimed and influential optical sensing tool with quintessential applications in life sciences, environmental monitoring, clinical diagnostics, pharmaceutical developments and ensuring food safety. The implementation of sensing principle of surface plasmon resonance employing an optical fiber as a substrate has concomitantly resulted in the evolution of fiber optic surface plasmon resonance as an exceptionally lucrative scaffold for chemical and biosensing applications. This perspective article outlines the contemporary studies on fiber optic sensors founded on the sensing architecture of propagating as well as localized surface plasmon resonance. An in-depth review of the prevalent analytical and surface chemical tactics involved in configuring the sensing layer over an optical fiber for the detection of various chemical and biological entities is presented. The involvement of nanomaterials as a strategic approach to enhance the sensor sensitivity is furnished concurrently providing an insight into the diverse geometrical blueprints for designing fiber optic sensing probes. Representative examples from the literature are discussed to appreciate the latest advancements in this potentially valuable research avenue. The article concludes by identifying some of the key challenges and exploring the opportunities for expanding the scope and impact of surface plasmon resonance based fiber optic sensors.

Visible light-assisted room temperature gas sensing with ZnO-Ag heterostructure nanoparticles

Abstract: Noble metal-metal oxide nanohybrids play an ever-increasing role in photocatalytic applications. Here, a ZnO-Ag nanoparticle prepared by a modified polymer-network gel method was utilized for room temperature light-assisted NO2 gas detection. Since a heterojunction forms between the two materials and surface oxygen vacancies increase, the sensitivities of the sensors to NO2 gas (0.5–5 ppm) under various light (λ = 365–520 nm) illumination conditions are enhanced in comparison with those of pure ZnO sensor. Surface plasmon resonance (SPR) was found to result in the excellent visible-light performance of this ZnO-Ag nanostructure. More importantly, by tuning the working wavelength using different LED light sources, we can obtain an optimized sensitivity. When blue-green LED (470 nm, 75 mW/cm2) is used, the 3 mol% Ag-loaded ZnO sensor shows the highest sensitivity as well as superior stability and selectivity. The effect of humidity on the sensor performance is also discussed in detail.

Surface Plasmon Resonance Sensor Based on a Novel D-Shaped Photonic Crystal Fiber for Low Refractive Index Detection

Abstract: A novel D-shaped photonic crystal fiber refractive index sensor based on surface plasmon resonance (SPR) is proposed and numerically studied Different from the normal D-shaped structures, we here used an open-ring channel coated with gold film to excite the plamonic modes The coupling properties and sensing performance of this structure are analyzed using finite element method Simulation results indicate that the sensor has a sensing range from 120 to 129 When the analyte refractive index (RI) is above 125, the anti-crossing effect starts to appear, and the peak loss of the loss spectra remains nearly constant with increasing RI The maximum spectral sensitivity of 11055 nm/RIU and high resolution of $905\times 10^{-6}$ RIU can be obtained at 129 For the purpose of optimizing sensing performance, the effects of the structure parameters on the resonant spectra are also studied The excellent sensing performance makes the proposed SPR sensor a competitive candidate in low refractive index detection applications

Few-layer Ti3C2Tx MXene: A promising surface plasmon resonance biosensing material to enhance the sensitivity

Abstract: In this contribution, a novel surface plasmon resonance (SPR) biosensor with few-layer Ti3C2Tx MXene to enhance the sensitivity is proposed. Few-layer Ti3C2Tx MXene is coated on the surface of metals thin film to act as a protective layer and further to improve the sensitivity. The results show that the sensitivity enhancements at λ = 633 nm are 16.8%, 28.4%, 46.3% and 33.6% for the proposed SPR biosensors based on Au with 4 layers Ti3C2Tx, Ag with 7 layers Ti3C2Tx, Al with 12 layers Ti3C2Tx and Cu with 9 layers Ti3C2Tx, respectively. Moreover, we have discussed the sensitivity of the proposed Au-based SPR biosensor with monolayer Ti3C2Tx MXene works at λ = 532 nm, the result shows that the sensitivity can reach 224.5°/RIU. Our contributions reveal potential applications of few-layer Ti3C2Tx MXene as a new type of biosensing material, and it is therefore anticipated that Ti3C2Tx MXene and other 2D MXene nanomaterials could find promising applications in SPR biosensors.

Sharp Transition from Nonmetallic Au246 to Metallic Au279 with Nascent Surface Plasmon Resonance

Abstract: The optical properties of metal nanoparticles have attracted wide interest. Recent progress in controlling nanoparticles with atomic precision (often called nanoclusters) provide new opportunities for investigating many fundamental questions, such as the transition from excitonic to plasmonic state, which is a central question in metal nanoparticle research because it provides insights into the origin of surface plasmon resonance (SPR) as well as the formation of metallic bond. However, this question still remains elusive because of the extreme difficulty in preparing atomically precise nanoparticles larger than 2 nm. Here we report the synthesis and optical properties of an atomically precise Au279(SR)84 nanocluster. Femtosecond transient absorption spectroscopic analysis reveals that the Au279 nanocluster shows a laser power dependence in its excited state lifetime, indicating metallic state of the particle, in contrast with the nonmetallic electronic structure of the Au246(SR)80 nanocluster. Steady-sta...

Plasmon-mediated charge dynamics and photoactivity enhancement for Au-decorated ZnO nanocrystals

Abstract: With the capability of localizing optical energy via surface plasmon resonance (SPR), plasmonic Au nanostructures hold great promise for enhancing the solar water splitting of semiconductor photocatalysts. While the content of Au plays a critical role in mediating interfacial charge transfer, its quantitative influence on the efficiency of plasmon-assisted water splitting is still not fully understood. This work aimed to explore the correlations among plasmonic metal content, SPR-mediated charge transfer and electromagnetic response, and the resultant photoactivity enhancement toward photoelectrochemical (PEC) water splitting. The PEC system was constructed by employing Au particle-decorated ZnO nanocrystals (ZnO–Au) as the plasmonic photoanode. Time-resolved photoluminescence spectroscopy and finite-difference time-domain simulations were utilized to evaluate the optimal Au content which attained effective charge separation and imposed a significant SPR effect for achieving the largest photoactivity enhancement. The charge transfer at the photoanode/electrolyte interface and its dependence on the Au content were examined with electrochemical impedance analysis, which manifested the effectiveness of the optimal Au content in facilitating the hole transfer kinetics. The present study reports a technical advance in the realization of the quantitative effect of Au for designing sophisticated plasmonic PEC systems that enabled efficient solar-to-fuel energy conversion.

IR-Driven Ultrafast Transfer of Plasmonic Hot Electrons in Nonmetallic Branched Heterostructures for Enhanced H2 Generation.

Abstract: The ultrafast transfer of plasmon-induced hot electrons is considered an effective kinetics process to enhance the photoconversion efficiencies of semiconductors through strong localized surface plasmon resonance (LSPR) of plasmonic nanostructures. Although this classical sensitization approach is widely used in noble-metal-semiconductor systems, it remains unclear in nonmetallic plasmonic heterostructures. Here, by combining ultrafast transient absorption spectroscopy with theoretical simulations, IR-driven transfer of plasmon-induced hot electron in a nonmetallic branched heterostructure is demonstrated, which is fabricated through solvothermal growth of plasmonic W18 O49 nanowires (as branches) onto TiO2 electrospun nanofibers (as backbones). The ultrafast transfer of hot electron from the W18 O49 branches to the TiO2 backbones occurs within a timeframe on the order of 200 fs with very large rate constants ranging from 3.8 × 1012 to 5.5 × 1012 s-1 . Upon LSPR excitation by low-energy IR photons, the W18 O49 /TiO2 branched heterostructure exhibits obviously enhanced catalytic H2 generation from ammonia borane compared with that of W18 O49 nanowires. Further investigations by finely controlling experimental conditions unambiguously confirm that this plasmon-enhanced catalytic activity arises from the transfer of hot electron rather than from the photothermal effect.

Adsorption of gaseous ethylene via induced polarization on plasmonic photocatalyst Ag/AgCl/TiO2 and subsequent photodegradation

Abstract: The removal of nonpolar gaseous ethylene molecules on the plasmonic photocatalyst Ag/AgCl/TiO2 was examined under simulated sunlight irradiation, to find that it has a markedly high activity for the oxidation of ethylene molecules. Systematic experiments, carried out to probe the cause for this observation, indicate that the strong electric field mainly on the Ag nanoparticles (NPs) generated by their surface plasmon resonance (SPR) induces polarization in gaseous ethylene molecules hence enhancing their adsorption on the catalysts and their subsequent photodegradation, and that TiO2 acts as a substrate for dispersing Ag/AgCl nanoparticles to have a larger active surface area. This study provides new ideas towards designing advanced photocatalysts for the degradation of nonpolar gaseous molecules.

Dual-polarized highly sensitive plasmonic sensor in the visible to near-IR spectrum.

Abstract: We propose and numerically characterize the optical characteristics of a novel photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor in the visible to near infrared (500-2000 nm) region for refractive index (RI) sensing. The finite element method (FEM) is used to design and study the influence of different geometric parameters on the sensing performance of the sensor. The chemically stable plasmonic material gold (Au) is used to produce excitation between the core and plasmonic mode. On a pure silica (SiO2) substrate, a rectangular structured core is used to facilitate the coupling strength between the core and the surface plasmon polariton (SPP) mode and thus improves the sensing performance. By tuning the geometric parameters, simulation results show a maximum wavelength sensitivity of 58000 nm/RIU (Refractive Index Unit) for the x polarization and 62000 nm/RIU for the y polarization for analyte refractive indices ranging from 1.33 to 1.43. Moreover, we characterize the amplitude sensitivity of the sensor that shows a maximum sensitivity of 1415 RIU-1 and 1293 RIU-1 for the x and y polarizations, respectively. To our knowledge, this is the highest sensitivity for an SPR in published literature, and facilitates future development of sensors for accurate and precise analyte measurement. The sensor also attains a maximum figure of merit (FOM) of 1140 and fine RI resolution of 1.6 × 10-6. Owing to strong coupling strength, high sensitivity, high FOM and improved sensing resolution, the proposed sensor is suited for real-time, inexpensive and accurate detection of biomedical and biological analytes, biomolecules, and organic chemicals.

Analysis of a Surface Plasmon Resonance Probe Based on Photonic Crystal Fibers for Low Refractive Index Detection

Abstract: A photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) probe with gold nanowires as the plasmonic material is proposed in this work. The coupling characteristics and sensing properties of the probe are numerically investigated by the finite element method. The probe is designed to detect low refractive indices between 1.27 and 1.36. The maximum spectral sensitivity and amplitude sensitivity are 6 × 103 nm/RIU and 600 RIU−1, respectively, corresponding to a resolution of 2.8 × 10−5 RIU for the overall refractive index range. Our analysis shows that the PCF-SPR probe can be used for lower refractive index detection.

Recent Advances of Plasmonic Nanoparticles and their Applications.

Abstract: In the past half-century, surface plasmon resonance in noble metallic nanoparticles has been an important research subject. Recent advances in the synthesis, assembly, characterization, and theories of traditional and non-traditional metal nanostructures open a new pathway to the kaleidoscopic applications of plasmonics. However, accurate and precise models of plasmon resonance are still challenging, as its characteristics can be affected by multiple factors. We herein summarize the recent advances of plasmonic nanoparticles and their applications, particularly regarding the fundamentals and applications of surface plasmon resonance (SPR) in Au nanoparticles, plasmon-enhanced upconversion luminescence, and plasmonic chiral metasurfaces.

Mapping Nanoscale Hotspots with Single-Molecule Emitters Assembled into Plasmonic Nanocavities Using DNA Origami

Abstract: Fabricating nanocavities in which optically active single quantum emitters are precisely positioned is crucial for building nanophotonic devices. Here we show that self-assembly based on robust DNA-origami constructs can precisely position single molecules laterally within sub-5 nm gaps between plasmonic substrates that support intense optical confinement. By placing single-molecules at the center of a nanocavity, we show modification of the plasmon cavity resonance before and after bleaching the chromophore and obtain enhancements of ≥4 × 103 with high quantum yield (≥50%). By varying the lateral position of the molecule in the gap, we directly map the spatial profile of the local density of optical states with a resolution of ±1.5 nm. Our approach introduces a straightforward noninvasive way to measure and quantify confined optical modes on the nanoscale.

Impacts of surface depletion on the plasmonic properties of doped semiconductor nanocrystals

Abstract: Degenerately doped semiconductor nanocrystals (NCs) exhibit a localized surface plasmon resonance (LSPR) in the infrared range of the electromagnetic spectrum. Unlike metals, semiconductor NCs offer tunable LSPR characteristics enabled by doping, or via electrochemical or photochemical charging. Tuning plasmonic properties through carrier density modulation suggests potential applications in smart optoelectronics, catalysis and sensing. Here, we elucidate fundamental aspects of LSPR modulation through dynamic carrier density tuning in Sn-doped In2O3 (Sn:In2O3) NCs. Monodisperse Sn:In2O3 NCs with various doping levels and sizes were synthesized and assembled in uniform films. NC films were then charged in an in situ electrochemical cell and the LSPR modulation spectra were monitored. Based on spectral shifts and intensity modulation of the LSPR, combined with optical modelling, it was found that often-neglected semiconductor properties, specifically band structure modification due to doping and surface states, strongly affect LSPR modulation. Fermi level pinning by surface defect states creates a surface depletion layer that alters the LSPR properties; it determines the extent of LSPR frequency modulation, diminishes the expected near-field enhancement, and strongly reduces sensitivity of the LSPR to the surroundings.

Precisely Shaped, Uniformly Formed Gold Nanocubes with Ultrahigh Reproducibility in Single-Particle Scattering and Surface-Enhanced Raman Scattering

Abstract: Synthesizing plasmonic nanostructures in an ultraprecise manner is of paramount importance because the nanometer-scale structural details can significantly affect their plasmonic properties. Au nanocubes (AuNCs) have been a highly promising, heavily studied nanostructure with high potential in various fields, but an ultraprecise synthesis from 10 to 100 nm in size over a large number of AuNCs has not been well established. Precisely structured AuNC-based studies for a highly reproducible, quantitative plasmonic signal generation [e.g., quantitative surface-enhanced Raman scattering (SERS)] are needed for reliable use and exploration in the beneficial properties of AuNCs. Here, we developed a strategy for AuNC synthesis with the desired size and shape, ranging from 17 to 78 nm particularly with highly controlled corner sharpness, by precisely controlling the growth rate of different facets and AuNC-specific flocculation which enabled ultrahigh yields (∼98–99%). Importantly, the precisely shaped AuNCs can s...

Probing Nanoparticle Plasmons with Electron Energy Loss Spectroscopy

Abstract: Electron energy loss spectroscopy (EELS) performed in a scanning transmission electron microscope (STEM) has demonstrated unprecedented power in the characterization of surface plasmons. The subangstrom spatial resolution achieved in EELS and its capability of exciting the full set of localized surface plasmon resonance (LSPR) modes supported by a metallic nanostructure makes STEM/EELS an ideal tool in the study of LSPRs. The plasmonic properties characterized using EELS can be associated with geometric or structural features collected simultaneously in a STEM to achieve a deeper understanding of the plasmonic response. In this review, we provide the reader a thorough experimental description of EELS as a LSPR characterization tool and summarize the exciting recent progress in the field of STEM/EELS plasmon characterization.