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While plasmonic designs have dominated recent trends in structural color, schemes using localized surface plasmon resonances and surface plasmon polaritons that simultaneously achieve high color vibrancy at ultrahigh resolution have been elusive because of tradeoffs between size and performance. Herein we demonstrate vibrant and size-invariant transmissive type multicolor pixels composed of hybrid TiOx-Ag core-shell nanowires based on reduced scattering at their electric dipolar Mie resonances. This principle permits the hybrid nanoresonator to achieve the widest color gamut (~74% sRGB area coverage), linear color mixing, and the highest reported single color dots-per-inch (58,000~141,000) in transmission mode. Exploiting such features, we further show that an assembly of distinct nanoresonators can constitute a multicolor pixel for use in multispectral imaging, with a size that is ~10-folds below the Nyquist limit using a typical high NA objective lens., Tradeoffs between size and performance have limited plasmonic structural color vibrancy at high resolution. Here the authors present a nanophotonic resonant metal-coated nanowire capable of being used as a size invariant, vibrant multicolor pixel.

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.

Light emission excited by stable tunnel junctions has attracted interest for potential use in optoelectronic device integration. However, these electrically driven sources cannot provide a high ele...

Electrochemical surface-enhanced Raman scattering measurements of single layer graphene provide unique information on resonant excitation induced by localized surface plasmons under controlled electron or hole doping. The highly confined electromagnetic field from the LSPs of the Au nanodimer structures prepared on defect-free graphene can generate holes and electrons of the electrochemical potentials beyond the limit of far-field light illumination. The electrochemical in situ SERS spectra prove nonzero wavevector excitation through the observation of normally forbidden Raman bands in graphene. The present findings point to a novel approach to breaking the limit of optoelectronic interactions and photochemical reactions of graphene and other semiconductors.

We introduce zinc oxide (ZnO) functionalized porous gold nanoparticles that exhibit strong second harmonic (SH) emission due to an efficient coupling of localized surface plasmons to ZnO excitons. ...

Semiconductor nanowires (NWs) have widely been studied as an ideal platform for developing electronic, photovoltaic, photonic devices and biological probes in the nanoscale. The ability to synthesize high-quality NWs of various materials with a precise control in shape, doping and crystal structure is the key to the growth of NW-based technologies. In the past decade, there has been growing interest in controllably creating NW heterojunctions and periodically-modulated superlattices (SLs) because it is expected to bring new functionalities that are not present in uniform NWs. In particular, the interaction of NW SLs with light has been one of the central interests because the diameter and modulation length scale are on the same order as the wavelength of light in the optical regime. Also, degenerately-doped semiconductor NWs exhibit localized surface plasmon resonances (LSPRs), which comprises unexpected long-range interactions when the plasmon resonators are regularly placed in NW SLs. In this review, I will summarize the recent progress in photonics research of NW SLs. The topics discussed include preparation and types of NW SLs, light-trapping and light-emission properties, and plasmonic optical- and thermal-transport properties.

The distance dependence of localized surface plasmon (LSP)-coupled Forster resonance energy transfer (FRET) between Si quantum dots (QDs) is experimentally and theoretically investigated utilizing ...

Localized surface plasmon-enhanced diamond UV photodetectors with different Ir nanoisland arrays had been successfully fabricated. Three different Ir nanoisland arrays with the diameters of 20(D20), 30(D30) and 40(D40) nm were deposited on the diamond surface, respectively, and their height was 10 nm. Ti/Au metal electrodes were patterned on Ir nanoisland arrays area and bare diamond surface to form UV photodetectors. According to photoelectric performance test results, the responsivities of diamond photodetectors with Ir nanoislands were far greater than that of diamond photodetector, and the D40 showed the highest photocurrent and responsivity at 210 nm, and the D20 indicated the highest UV/vis rejection ratio. The results of simulated extinction spectra exhibited three resonance peaks at UV and visible region for each sample, indicating that D20 had the highest ratio of UV/vis, which was coincide with experiment results.

In this paper, single silver nanocube dimer with nanometer-sized gap is designed and numerically simulated. We demonstrate that the electric fields can be highly confined in the gap of nanocube dimer, leading to ultrasmall mode volume of ≈2 × 10-7 μm3. Furthermore, the strong plasmon-exciton coupling in single nanocube dimer coupled with J-aggregate molecules is investigated using coupled oscillator model and we show that the strong plasmon-exciton coupling can be tuned by changing the background refractive index and the concentration of J-aggregate molecules. The tuning of dual strong plasmon-exciton couplings between single rounded silver nanocube dimer and J-aggregate molecules is also investigated, and dual strong couplings can be achieved closely approaching the quantum optics limit benefiting from the ultrasmall mode volume of the proposed system. The proposed systems can be easily prepared and have high experimental feasibility, which has potential applications in integrated nanophotonics such as sensing and all-optical switches.

Localized surface plasmon resonances (LSPR) are widely employed for improving the upconversion luminescence (UCL) and photocatalysis. Here, we prepare a nano-semiconductor heterostructure (NSH) consisting of Er-Yb:TiO2 nanosheets (NTs) integrated with plasmonic MoO3-x NTs in a two-step solvothermal processes. The LSPR of MoO3-x amplifies and transfers the near-infrared (NIR) energy to the neighboring Er-Yb:TiO2 UC system, leading to a 182-fold increase in green emissions. Moreover, the LSPR effect extends the absorption range of the Er-Yb:TiO2/MoO3-x NSH from the visible to the NIR region. The interface of the Er-Yb:TiO2/MoO3-x NSH acts as a charge carrier channel to separate the plasmon-induced electrons and holes effectively. We perform H2 production experiments of Er-Yb:TiO2/MoO3-x NSH from ammonia borane (BH3NH3). Upon the excitation of a 980 nm laser, the H2 production of the Er-Yb:TiO2/MoO3-x NSH is 1.5 times and 61 times higher than that of the MoO3-x NTs and BH3NH3. In addition, the H2 yield is 2.5 times and 52 times higher than that of the MoO3-x NTs and BH3NH3 under the irradiation of simulated sunlight (AM 1.5), demonstrating the superior photocatalytic properties of the Er-Yb:TiO2/MoO3-x NSH.

The enhancement of the electric field in plasmonic nanostructures on a Si substrate in the near-infrared range is studied theoretically. Two-dimensional square arrays of circular holes of various diameters in a gold film serve as metasurfaces allowing the conversion of the external electromagnetic radiation into surface plas-mon modes at the Au-Si interface. It is established that illumination of nanostructures from the side of the Si substrate provides a higher field enhancement compared to the case of frontal illumination, since the incident light wave in the former case reaches the gold interface without passage through subwavelength holes for which the transmittance is extremely low. The plasmonic field enhancement, as a function of the diameter of holes of the array, shows the maximum at which the Bloch plasmon polaritons propagating along the Au-Si interface are transformed to localized surface plasmon modes. Two types of localized plasmons are detected. The short-wavelength plasmon is excited along the array diagonals and exists at any angles of incidence of light on the structure. The long-wavelength plasmon occurs only at nonzero angles of incidence and is located along orthogonal directions parallel to the sides of the square array. These results are directly related to the problem of fabricating effective silicon photodetectors with quantum dots.

We have observed solid-state growth of pre-existing silver nanoparticles (AgNPs) upon exposure to trace (ppb) concentrations of reactive gases at room temperature. The consequent change in localized surface plasmon resonances alters the visible absorbance of dried, printed sensor spots made from inks of 10 nm-AgNPs and provides a novel mechanism for trace detection and dosimetry of reactive gases. Colorimetric sensor arrays based on these AgNP inks offer dosimetric identification of acidic and oxidizing gases and other reactive vapors with limits of detection below ppb levels for 1 h exposures. For an array of AgNP inks with various capping agents, a unique color response pattern is observed for each specific analyte. Excellent discrimination among 11 reactive gases was demonstrated using standard chemometric methods. The chemically induced sintering of NPs paves the way for novel solid-state sensors for the ultrasensitive detection of reactive gases and their application to the monitoring of trace airborne pollutants.

Growth of anisotropic nanostructures enables the manipulation of optical properties across the electromagnetic spectrum by fine morphological tuning of the nanoparticles. Among them, stellated metallic nanostructures present enhanced properties owing to their complex shape, and hence, the control over the final morphology becomes of great importance. Herein, a seed-mediated method for the high-yield production of goldrich-copper concave branched nanostructures and their structural and optical characterization is reported. The synthesis protocol enabled excellent control and tunability of the final morphology, from concave pentagonal nanoparticles to five-fold branched nanoparticles, named "nanostars". The anisotropic shape was achieved via kinetic control over the synthesis conditions by selective passivation of facets using a capping agent and assisted by the presence of copper chloride ions, both having a crucial impact over the final structure. Optical extinction measurements of nanostars in solution indicated a broad spectral response, hiding the properties of the individual nanostars. Hence, single-particle scattering measurements of individual concave pentagonal nanoparticles and concave nanostars were performed to determine the origin of the multiple plasmon bands by correlation with their morphological features, following their growth evolution. Finite-difference time-domain calculations delivered insights into the geometry-dependent plasmonic properties of concave nanostars and their packed aggregates. Our results uncover the intrinsic scattering properties of individual nanostars and the origin of the broad spectral response, which is mostly due to z-direction packed aggregates.

In this paper, a dynamic plasmonic subtractive color filter is investigated. The proposed filter consists of aluminum disks immersed in nematic liquid crystal. The performance of the structure is based on the interaction between liquid crystal and localized surface plasmons, which the transmittance colors are electrically controlled by the applied voltage. The optical efficiency and the full-width at half-maximum (FWHM) of the filter are attained to be about 80 percent and 40–45 nm, respectively. Moreover, the suggested color filter is polarization-insensitive due to its symmetric geometry.

Fiber-based photonic nanostructures with potential employment in nano/microscale optical devices are attracting a growing interest. In this work, we report on the emission features of polymer fibers made of 4(dicyanomethy-lene)-2-tert-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)4H-pyran (DCJTB) doped polyvinyl pyrrolidone (PVP) with diameters in the range of 1.5–2 μm, realized by electrospinning method. In the fibers, silver nanoparticles (Ag NPs) are introduced as scatters, where multimode random lasing action is achieved. Experiments indicate that strengthened lasing shot has been triumphantly realized in the existence of metal Ag NPs. By optimizing the ratio of Ag NPs to DCJTB during the process of the preparation, random lasing emission has been realized with much cut down thresholds to 0.55 mW cm−2. The microscopic resonators may be shaped both by randomly oriented polymeric fibers and multiple scattering of Ag NPs which offer special opportunities to design multiple light scattering and random laser. Besides, the localized surface-plasmon resonance (LSPR) of Ag NPs is excited, which couples with output emission of DCJTB to improve the lasing efficiency. This system is a promising candidate for the coming growth of all-plastic, micro- to macroscale optical tables for signal transmission and processing.

A highly selective, sensitive, and rapid colorimetric sensor for the determination of dopamine (DA) was developed using the color change of S-doped carbon dots functionalized gold nanoparticles (S-CDs@Au NPs). The base of the method is the formation of a complex between the amine groups of dopamine with carboxylic groups of S-CDs@Au NPs followed by their aggregation with Fe3+ ions which acts as the linkers causing a red shift from 520 to 670 nm in the localized surface plasmon peak of S-CDs@Au NPs. The ratio of absorbance intensity at 670 nm to 520 nm was monitored as the analytical signal for determination of dopamine. The parameters affecting the analytical signal including reaction time, solution pH, the concentration of Au NPs and concentration of Fe3+ were optimized. At optimized conditions, the calibration curve was linear in the concentration range of 0.81–16.80 μM of dopamine. The detection and quantification limits were 0.23 μM and 0.77 μM, respectively. The intra-day and inter-day relative standard deviation (RSDs) at 5.0 μM of DA were 3.9% and 5.6%, respectively (n = 5). The applicability of the method for determination of DA in dopamine ampoule, urine and serum human samples was investigated.

The controllable catalytic reaction plays a pivotal role in heterogeneous catalysis. Surface-enhanced Raman scattering (SERS) and tip enhanced Raman spectroscopy (TERS) are considered promising techniques for the study of catalytic reactions due to the highly localized sensitivity of SERS and the nanoscale spatial resolution of TERS. Herein, Ag/Au composite films were employed as catalyst for in situ monitoring of the catalytic reaction of 4‑nitrobenzenethiol (4NBT) to p, p'‑dimercaptoazobenzene (DMAB). The catalytic reaction of 4NBT adsorbed on Au film can be manipulated at the nanoscale using TERS by controlling the height between the tip-apex and the sample surface in Ag tip-Au substrate geometry. According to finite difference time domain (FDTD) simulations, the 'hot electron' induced by the localized surface plasmon is sufficient for promoting the catalytic reaction. These findings provide a novel way for controllable graph drawing of molecules at the nanoscale level.

Electrochemical tip-enhanced Raman spectroscopy (EC-TERS) appears as a promising in situ nanospectroscopic tool for characterization and understanding of the electrochemical interfacial processes at the nanometer scale and molecular level. However, the wide application of EC-TERS is hampered by its low sensitivity as a result of the optical path distortion due to the refractive index mismatch of the multilayer media (air, glass, and electrolyte). Here, we propose a new side-illumination EC-TERS setup by coupling a water immersion objective with a high numerical aperture to a scanning tunneling microscope scanning head customized with a large open space and a compact spectroelectrochemical cell. It not only effectively eliminates the optical distortion but also increases the sensitivity remarkably, which allows sensitive monitoring of the electrochemical redox processes of anthraquinone molecules. More importantly, EC-TERS is able to independently control the tip position and laser illumination position. By utilizing this feature, we reveal that the irreversible reduction reaction of anthraquinone observed in EC-TERS is induced by the synergistic effect of the negative potential and laser illumination rather than the localized surface plasmon. The highly improved sensitivity and the flexibility to control the tip and laser illumination position on the nanometer scale endows EC-TERS as an important tool for the fundamental understanding of the photo- or plasmon electrochemistry and the interfacial structure-activity relationship of important electrochemical systems.

Titanium nitride (TiN) continues to prove itself as an inexpensive, robust, and efficient alternative to gold in plasmonic applications. Notably, TiN has improved hot electron-harvesting and photocatalytic abilities compared to gold systems, which we recently attributed to the role of oxygen in TiN and its native semiconducting TiO2–x surface layer. Here, we explore the role of localized surface plasmon resonances (LSPRs) on electron harvesting across the TiN/TiO2–x interface and probe the resilience of TiN nanostructures under high-power laser illumination. To investigate this, we fabricate TiN strips, in which the lateral confinement allows for the polarization-selective excitation of the LSPR. Using ultrafast pump–probe spectroscopy, optical characterization, and Raman vibrational spectroscopy, we relate the differences and changes observed in the electron behavior to specific material properties. We observe plasmon-enhanced electron harvesting beyond what is expected resulting from the enhanced absorption of the plasmonic mode. We accredit this to the surface oxide damping the plasmon resonance, providing additional nonradiative loss channels. Subsequently, we show that low-power annealing of the surface oxide layer reduces the trap density at the interface and increases the initial harvested electron concentration. The unique properties of TiN make it important in the future development of plasmonic electron-harvesting applications.

Localized surface plasmon resonances can increase the quantum efficiency of photon emitters through both absorption and spontaneous emission enhancement effects. Despite extensive studies, experime...

In this paper, the deposition and optical properties of charge-stabilized gold nanoparticles on silicon oxide substrates is studied, which have been derivatised with (aminopropyl) triemethoxysilane. Monodispersed charged-stabilized colloidal gold nanoparticles with diameters between 20-150 nm were prepared and their self-assembly and optical properties on silica substrates is studied. Atomic force microscopy (AFM) is employed to investigate the nanoparticle monolayers ex situ. Analysis of AFM images provide evidence that the formation of the colloidal nanoparticle monolayers is governed by random sequential adsorption. The results indicate that the ionic strength of the suspension influences the spatial distribution of the nanoparticles. For all sizes of the Au nanoparticles tested, optical simulations of extinction coefficients made by finite-difference time domain (FDTD) indicate a resonance peak in the range of 510-600 nm wavelength of the visible range of the electromagnetic spectrum. The results indicate a simple and inexpensive approach of assembly of plasmonic nanostructures that can find applications in metamaterials and light waveguides.

Tungsten disulfide (WS2) has been demonstrated for optoelectronic devices due to its favorable semiconducting band gaps, high stability and higher carrier mobility than other transition metal dichalcogenides (TMDs). However, the photoresponsivity of WS2-based photodetector is low due to the poor optical absorbance, which limits its application in high-performance photodetection. Here, we show an easy realized method to improve the responsivity of WS2 detectors by Au nanospheres (NPs). The Au NPs concentrate free space electromagnetic wave efficiently by localized surface plasmon resonances (LSPR), strongly enhance the electric field on WS2 films. As a result, more carriers are excited with the assistant of LSPR. With optimized design, the detector exhibited several times to ten folds enhancement from near infrared to visible spectrum region, and reach an excellent high responsivity of 1050 A/W at the wavelength of 590 nm. Furthermore, the photodetector showed an excellent temperature stability after annealing at 300 °C on air environment. The work provides a new way for high-performance and stable photodetector for extreme and harsh environment.

Electron beam or photonic excitation of localized surface plasmon resonances (LSPRs) in gold nanoparticles and their subsequent nonradiative relaxation create a nonuniform charge distribution near the metal–semiconductor interface via hot-electron injection from gold nanoparticles to the monolayer MoS2 conduction band states. These charge domains induce lattice compression in the MoS2 lattice because of the inverse piezoelectric response arising due to the noncentrosymmetric nature of the crystal lattice. Our high-resolution transmission electron microscopy studies reveal that as much as 9–10% biaxial compressive strain is generated in free-standing monolayer MoS2 in the vicinity of gold nanoparticles, which relaxes rapidly within 50 nm from the edge of the gold nanoparticle. The metal interface-induced hot-electron injection via photonic excitation of LSPRs and the resultant lattice distortion also manifest in shifts as well as broadening of A1g(Γ) and E2g1(Γ) Raman modes of the monolayer MoS2 in presenc...

The electromagnetic metamaterials are the recent entrants, into the classification of smart materials for structural health monitoring (SHM). Their applications in SHM have raised the curiosity due to their rapid executable speeds in wide-frequency domains. The speed of obtaining health output signals for engineering structures is about 1/100th of the time taken by existing smart material-based frequency domain techniques such as piezoelectric material-based techniques. Recently, we developed an ultra-sensitive near-field sensing technique using metamaterial localized surface plasmon (LSP) ‘sensor’ which produced diagnosable ‘confined surface electromagnetic waves’ for SHM. This paper presents the same near-field sensing technique in the frequency domain but using metamaterial ‘waveguides’ based on propagating surface plasmon polaritons (SPPs)/surface waves. For the experiments, a novel robust metamaterial waveguide coupling zone was designed and applied for monitoring longitudinal and lateral displacements in civil engineering prototype structures such as channels and pipelines. In the context of SHM, coupling zone and metamaterial waveguide resemble fiber Bragg grating (FBG) sensor and optical fiber waveguide, respectively. Thus, if properly realized, these metamaterials can co-exist with the existing FBG/optical fiber techniques for applications in civil engineering.

Shape, size, and homogeneity affect the biological activity of gold nanoparticles (AuNPs) in nanomedicine and catalytic applications. Here we biosynthesized monodispersed isotropic and polydispersed anisotropic spherical AuNPs from leaf and seed extract broths of the medicinal plant Peganum harmala L. (Ph. L). Synthesized AuNPs were characterized by ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy (FT-IRS), field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). The antimicrobial activity of AuNPs against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) human pathogens was also assessed. Leaf- and seed-derived AuNPs had characteristic localized surface plasmon resonances of 530 and 578 nm, respectively. TEM, FE-SEM, EDX, and XRD revealed the formation of elemental face-centered cubic spherical monodispersed isotropic AuNPs of average size 43.44 nm and polydispersed anisotropic AuNPs of average size 52.04 nm from leaf and seed extract broths, respectively. FT-IR revealed polyphenols and alcohols as responsible for AuNP capping, reduction, and protection. Anisotropic AuNPs showed no antibacterial activity, whereas isotropic AuNPs showed good inhibition of both E. coli and S. aureus. This represents a simple and ecofriendly protocol for the green synthesis of monodispersed isotropic spherical AuNPs, which may have value in a variety of applications.

The surface enhanced-Raman spectroscopy (SERS) of the graphene was measured using Au nanodimers prepared by angle-resolved nanosphere lithography and 785 nm laser with increasing power. It is found that the ratio between D band and 2D band changes with laser power. The change is attributed to the effect of localized surface plasmon (LSP), which causes the restructuring of Au nanodimers and oxidation of graphene. We established the method to characterize the formation of the defects in graphene using SERS.

Enhancement of fluorescent radiation is of great importance for applications including biological imaging, high-sensitivity detectors, and integrated light sources. Strong electromagnetic fields can be created around metallic nanoparticles or in gap of nanostructures, where the local state density of radiating mode is then dramatically enhanced. While enhanced fluorescent emission has been demonstrated in many metallic nanoparticles and nanoparticle pairs, simultaneous mediation of absorption and emission processes of fluorescent emitters remains challenging in metallic nanostructures. Here, we investigate fluorescent emission mediated by metal-dielectric-metal fishnet metasurface, in which localized surface plasmon (LSP) and magnetic plasmon polaritons (MPPs) modes are coupled with absorption and emission processes, respectively. For absorption process, coupling of the LSP mode enables spatially-selective excitation of the fluorescent emitters by rotating the polarization of the pump laser beam. In addition, the polarization-dependent MPP mode enables manipulation of both polarization and wavelength of the fluorescent emission by introducing a rectangular fishnet structure. All the experimental observations are further corroborated by finite-difference time-domain simulations. The structure reported here has great potential for application to color light-emitting devices and nanoscale integrated light sources.

We present an optical fiber biosensor that employs both long-range and localized surface plasmon resonances (SPRs) to sensitively detect very small changes in the resonances due to the surrounding refractive index. A tilted optical fiber Bragg grating inscribed in standard single-mode fiber couples light into the fiber's cladding, where it induces micrometer-scale SPRs in a 50-nm-thick gold coating. The limit of detection of the targeted protein, thrombin, is enhanced by resonance between the long-range SPRs and localized SPRs induced in 13-nm-diameter gold nanoparticles bonded via aptamers to the protein molecules. The sensor demonstrates stable and reproducible response to thrombin concentration down to a limit of detection of 1 n·M, which is three orders of magnitude more sensitive than previous optical fiber protein sensors. Meanwhile, it does not require accurate temperature control because of the elimination of the temperature cross-sensitivity inherent in TFBG devices (core mode). The high sensitivity, simplicity, compact size, and remote monitoring capability of the sensor open many new opportunities for environmental, biological, and medical sensing.

We report on the enhancement effect of metal nanotriangles (NTs) on the photoluminescence and its time-resolved dynamics of tris(8-quinolinolato) aluminum (Alq3). Regularly arranged Al NTs arrays were fabricated on the quartz substrate by means of nanosphere lithography. The absorption peaks corresponded to the localized surface plasmon (LSP) resonance of Al NTs were observed within a visible light region, and it was significantly shifted towards longer wavelength as increasing refractive index of the covering medium. The typical resonance wavelength of LSP of Alq3/Al NTs fabricated with 350 nm-PSt beads was 600 nm. From the PL measurement 2.6-fold PL enhancement was observed in Alq3 with Al NTs at room temperature, whereas the 4.4-fold PL enhancement was observed for Ag NTs with same size. According to the time-resolved PL data, the coupling of LSP with the excitation light field mainly contribute to the observed emission enhancement for the Al NTs, whereas the emission enhancement by Ag NTs can be originated from the direct coupling of LSP and emission which was suggested from the large contribution of short lifetime component.

Photothermal therapy (PTT) based on two-dimensional (2D) nanomaterials has shown significant potential in cancer treatment. However, developing 2D nanomaterial-based theranostic agents with good biocompatibility and high therapeutic efficiency remains a key challenge. Bulk titanium (Ti) has been widely used as biomedical materials for their reputable biocompatibility, whereas nanosized Ti with a biological function remains unexplored. In this work, the 2D Ti nanosheets (NSs) are successfully exfoliated from nonlayer bulk Ti and utilized as an efficient theranostic nanoplatform for dual-modal computed tomography/photoacoustic (CT/PA) imaging-navigated PTT. Besides the excellent biocompatibility obtained by TiNSs as expected, they are found to show strong absorption ability with an extinction coefficient of 20.8 L g-1 cm-1 and high photothermal conversion ability with an efficiency of 61.5% owing to localized surface plasmon resonances, which exceeds most of other well-known photothermal agents, making it quite promising for PTT against cancer. Furthermore, the metallic property and light-heat-acoustic transformation endow 2D Ti with the strong CT/PA imaging signal and efficient cancer therapy, simultaneously. This work highlights the enormous potential of nanosized Ti in both the diagnosis and treatment of cancer. As a paradigm, this study also paves a new avenue for the elemental transition-metal-based cancer theranostics.

Copper sulfide nanocrystals have recently been studied due to their metal-like behavior and strong plasmonic response, which make them an attractive material for nanophotonic applications in the near-infrared spectral range; however, the nature of the plasmonic response remains unclear. We have performed a combined experimental and theoretical study of the optical properties of copper sulfide colloidal nanocrystals and show that bulk CuS resembles a heavily doped p-type semiconductor with a very anisotropic energy band structure. As a consequence, CuS nanoparticles possess key properties of relevance to nanophotonics applications: they exhibit anisotropic plasmonic behavior in the infrared and support optical modes with hyperbolic dispersion in the 670-1050 nm spectral range. We also predict that the ohmic loss is low compared to conventional plasmonic materials such as noble metals in the NIR. The plasmonic resonances can be tuned by controlling the size and shape of the nanocrystals, providing a playground for future nanophotonic applications in the near-infrared.

New opportunities for plasmonic applications at high temperatures have stimulated interest in refractory plasmonic materials that show greater stability at elevated temperatures than the more commonly used silver and gold (Au). Titanium nitride (TiN) has been identified as a promising refractory material, with deposition of TiN thin films through techniques ranging from plasma-enhanced atomic laser deposition to sputter deposition to pulsed laser deposition, on a variety of substrates, including MgO, polymer, SiO2, and sapphire. A variety of plasmonic devices have been evaluated, including gratings, nanorods, and nanodisks. An implicit metric for TiN behavior has been the comparison of its plasmonic performance to that of Au, in particular at various elevated temperatures. This paper carries out a one-to-one comparison of bowtie nanoantennas formed of TiN and Au (on both Si and MgO substrates), examining the far-field characteristics, related to the measured near-field resonances. In both cases, the optic...

We theoretically present the nanofocusing of the metal-coated fiber tip under internal excitation of the radial vector beam within visible band based on the finite difference time domain (FDTD) analysis. The electric field intensity enhancement factor of the localized surface plasmons (LSP) mode at the tip apex is quantitatively shown in relation with incident wavelength, coating material, conical angle of tip, and coating film thickness/length. Specially, the evolution of fiber radial vector mode to surface mode with respect to the radius of metal-coated fiber tip is calculated under typical excitation wavelengths of 633 nm and 785 nm. Furthermore, the reason of the tip eliminating far-field background signal is explained, and the transverse electric field distributions of LSP mode and the tip-substrate coupling are also given at the optimal excitation wavelength. These calculation results will be a good reference for the fabrication of metal-coated fiber tips and for the experimental design of the tip-enhanced spectroscopy (TES) system.

A fascinating strategy of molybdenum ions supporting was utilized to enhance green upconversion (UC) emissions of Er-Yb:TiO2 prepared by sol-gel method. Er-Yb:TiO2 nanoparticles exhibited irregular sizes approximately 100–350 nm, which showed stronger red emission and weaker green emissions under the irradiation of near-infrared (NIR). After molybdenum ions supporting, Er-Yb:TiO2 nanoparticles were turned into uniformly dispersed eight prism structure and average particle size reached about 800 nm. Also, the green UC luminescence integrated intensity of Mo/Er-Yb:TiO2 was about 46 times improved than that of Er-Yb:TiO2. Furthermore, a novel photocatalyst of Mo/Er-Yb:TiO2@W18O49 quasi-core/shell heterostructure was designed based on the localized surface plasmon resonances (LSPR) effect of W18O49 through solvothermal process. With the excitation of NIR, the photocatalytic property of Mo/Er-Yb:TiO2@W18O49 for H2 producing from ammonia borane (BH3NH3) was researched. H2 production was about 2-fold enhancement compared with that of W18O49. Besides, the application of natural sunlight for H2 producing was provided. About 3 times H2 yield was obtained in contrast to that of W18O49. This work provided an effective way to enhance UC luminescence intensity and H2 production efficiency for solving energy deficiency problems.

Using Transfer Matrix method combined with Effective Medium Approximation as well as Finite-Difference Time-Domain calculations we have determined the light absorption in organic solar cells with silver nanoparticles embedded in the active layer. In calculations, we introduced additional terms in permittivity of the nanoparticles due to their finite size. Our results show, that the optimal nanoparticle concentration in such a system is about 30% greater than when assuming that the permittivity of the Ag nanoparticles equates that of a continuous silver layer. We have found, that although the absorption curves for both models (with and without the finite size contribution) are similar, the dominant mechanism of absorption enhancement is different. When assuming that the permittivity of silver nanoparticles is that of a continuous Ag layer, the light scattering on the surface of the nanoparticles seems to dominate over localized surface plasmon (LSP) excitation, while when considering the finite sizes of the nanoparticles the opposite is true.

Current presumptive tests for illicit drugs can suffer from false positive results and poor selectivity, and consequentially there is a need to develop new colour spot tests specifically designed to circumvent these existing challenges. In this work, we report on a new fluorescent hybrid nanozyme peroxidase-like catalytic colorimetric sensor and demonstrate proof of concept of this novel colorimetric-specific presumptive test for cocaine. A novel peroxidase-mimic hybrid nanozyme was developed based on the localized surface plasmon resonance-enhanced fluorescence interaction between multi-shaped cationic cetyltrimethylammonium bromide (CTAB)-functionalized gold nanoparticles (AuNPs) and anionic non-cadmium fluorescent-emitting L-cysteine-capped ZnSeS alloyed quantum dots (QDs). The affinity-based interaction of cocaine with the QDs-CTAB-AuNP surface was induced by its distinct structural conformation and this forms the basis for the selective recognition. Thus, the hybrid nanozyme could function both as a catalytic affinity-based receptor and as an optical signal transducer based on the catalysed oxidation of 3,5,5-tetramethylbenzidine by H2O2. A positive bluish-green colour, specific to cocaine recognition, was colorimetrically obtained under optimum catalytic conditions. The optimized assay system detected cocaine within two minutes with unique specificity and distinct colour reaction. Under the optimum cocaine reaction conditions, the analysis of other substances and drugs on the colorimetric response of the QDs-CTAB-AuNP hybrid nanozyme revealed no colour interference, thus demonstrating that the developed probe could be utilized as a presumptive colour spot test for cocaine.

Metallic nanoparticles exhibit localized surface plasmon resonances resulting from the coherent oscillation of free electrons in response to electric field from incident electromagnetic radiation. In this work, the dependence of peak surface plasmon resonance of gold nanoparticles on the particle size using UV–Vis spectra is shown. Small-sized gold nanoparticles (10–15 nm) were prepared through citrate reduction method. From theoretical modelling based on their resonance peaks and full wave at half maximum, the gold nanoparticles were found to have a narrow size distribution of ∼12 nm optimized over 1.0–1.10 mL of the citrate. A comparison of the experimental data and data from multiple scattering theory revealed that the plasmon resonances were centered at wavelengths between 520 and 518 nm for all samples under citrate volume range from 0.85 to 1.15 mL. Further analysis indicated that, small sized AuNPs exhibited multiple resonances, which could be attributed to the radiative interband recombination between the sp- and d-bands.

Ferroelectric ceramics possess great application potential in optoelectronic and solar energy devices. However, ferroelectric ceramics normally have large band gaps, strongly inhibiting their photovoltaic performances. In this work, we use a strategy to enhance the visible light absorption of ferroelectric ceramics by incorporating Au nanoparticles into the ferroelectric BaTiO3(BT) matrix. The BT-Au nanohybrids are preliminarily synthesized as the “building blocks”, which are assembled and then sintered as the 0–3 type composite ceramic. We find that the UV–vis absorption of composite ceramic is improved by localized surface plasmon resonances (LSPRs). While the ferroelectric property of the 0–3 type BT-Au ceramic remains robust. As a result, the composite ceramics show excellent ferroelectric photovoltaic effect with a photocurrent being approximately seven times as that in pure BT ceramics and an open-circuit voltage of 6 V. These findings suggest that interfacial control of ceramic composites may act an effective approach to optimize the photovoltaic responses in ferroelectric ceramics.

When localized surface plasmons (LSPs) are coupled to extended surface plasmons (ESPs), higher density of particles causes stronger interaction, larger Rabi splitting (RS), and plasmonic energy ban...

The presence of a surrounding medium strongly affects the spectral properties of localized surface plasmons at metallic nanoparticles. Vice versa, plasmonic resonances have large impact on the electric polarization in a surrounding or supporting material. For applications, e.g., in light-converting devices, the coupling of localized surface plasmons with polarizations in semiconducting substrates is of particular importance. Using photoemission electron microscopy with tunable laser excitation, we perform single-particle spectroscopy of silver nanoclusters directly grown on Si(100). Two distinct localized surface plasmon modes are observed as resonances in the two-photon photoemission signals from individual silver clusters. The strengths of these resonances strongly depend on the polarization of the exciting electric field, which allows us to assign them to plasmon modes with polarizations parallel and perpendicular, respectively, to the supporting silicon substrate. Our mode assignment is supported by simulations which provide insight into the mutual interaction of charge oscillations at the particle surface with electric polarizations at the silver/silicon interface.

Periodic arrays of plasmonic nanostructures are able to strongly confine light at the nanometer scale because of surface lattice resonances. These resonances are the result of electromagnetic coupling between single-particle localized surface plasmon resonances and Bragg resonances of the periodic lattice. Here, we investigate the effect of a finite size refractive index environment on the formation of surface lattice resonances by increasing the thickness of a polymer coating in nanometer-scale increments. Wet-chemically synthesized, spherical silver and gold nanoparticles with soft hydrogel shells are self-assembled into macroscopic, hexagonally ordered arrays on glass substrates using an interface-assisted approach. The resulting periodic plasmonic monolayers are subsequently coated by a polymer matching closely the refractive index of the glass support. The optical response of the plasmonic arrays is studied using far-field extinction spectroscopy and supported by numerical simulations. We show the formation of surface lattice resonances as well as higher order resonances in finite thickness polymer coatings. The resonance positions are determined by the interparticle spacing as well as the plasmonic material. Additionally, we demonstrate that a coating thickness of 450 nm is sufficient to support strong in-plane surface lattice resonances. This enables us to prepare macroscopic, free-standing polymer films with embedded plasmonic nanoparticle arrays, which feature strong surface lattice resonances.

We report a one-pot seedless green method for the synthesis of gold-silver (AuAg) spiky branched nanostars, with gold (90%) being the major component. Here, the zwitterionic surfactant lauryl sulfobetaine (LSB) is employed in the synthesis of bimetallic nanostars. The concentration of LSB plays an important role in determining the shape of nano-objects. A minimum LSB concentration of 50 mM is required for the formation of spiky branched nanostars, the size of which is controlled by increasing the LSB concentration. Two distinct intense localized surface plasmon resonances in the near-infrared (NIR) and short-wavelength infrared ranges are observed. The molecular structure of LSB causes LSB molecules to assemble into spherical micelles that act as a soft template for the growth of the nano-objects. An analysis of the mechanisms behind the formation of the nanostars suggests that there is a rapid growth of spikes followed by the formation of a spherical core at the center. AuAg nanostars with evenly spaced spikes and low branching demonstrate great potential as efficient nanocatalysts, surface-enhanced Raman scattering-active substrates and for photothermal therapy, active in both the visible and NIR regions.

The enhancement of surface plasmon-coupled emission (SPCE) by the synergistic effect of silver nanocubes (AgNCs) and graphene oxide (GO) on gold film has been observed with the enhancement factor over 30. The enhancement mechanisms were investigated through simulating the electromagnetic (EM) field patterns of near field and testing different concentration of AgNCs and thickness of dye layer. The enhancement was mainly triggered by the high electromagnetic field of AgNCs, the interaction between localized surface plasmons (LSP) and propagating surface plasmons (PSP) and the assistance of GO. This synergistic enhancement strategy provides a simple way to increase SPCE signal and enable develop a new fluorescence-based detection system.

Magnesium nanostructures have recently emerged as an outstanding material with new and intriguing plasmonic properties. Here we investigate the optical properties of pristine and pyridine adsorbed magnesium nanodisks having diameter spanning in the range of 0.50 nm–2.0 nm. We base our calculations on computationally efficient time-dependent density-functional theory calculations. Our results demonstrate that pristine magnesium nanodisks possess localized surface plasmon resonances. The adsorption of a dipole-carrying molecule significantly alters their plasmonic response due to the strong plasmon splitting, leading to new features in their optical response. We believe that magnesium nanodisks provide a versatile platform for sensing and in the design of novel ultra-sensitive plasmonic devices.

We employ a broadband Ti:sapphire femtosecond oscillator to simultaneously launch two localized surface plasmon modes in rectangular plasmonic nanoholes. The resonant frequencies of these two modes...

Metal-oxide nanocrystals doped with aliovalent atoms can exhibit tunable infrared localized surface plasmon resonances (LSPRs). Yet, the range of dopant types and concentrations remains limited for many metal-oxide hosts, largely because of the difficulty in establishing reaction kinetics that favors dopant incorporation by using the co-thermolysis method. Here we develop cation-exchange reactions to introduce p-type dopants (Cu+, Ag+, etc.) into n-type metal-oxide nanocrystals, producing programmable LSPR redshifts due to dopant compensation. We further demonstrate that enhanced n-type doping can be realized via sequential cation-exchange reactions mediated by the Cu+ ions. Cation-exchange transformations add a new dimension to the design of plasmonic nanocrystals, allowing preformed nanocrystals to be used as templates to create compositionally diverse nanocrystals with well-defined LSPR characteristics. The ability to tailor the doping profile postsynthetically opens the door to a multitude of opportunities to deepen our understanding of the relationship between local structure and LSPR properties., Doping semiconductor nanocrystals with impurity atoms is a key pathway for tuning their plasmonic properties. Here, the authors use a cation exchange strategy to dope p-type or n-type metal ions into n-type metal-oxide nanocrystals, post-synthetically tailoring their localized surface plasmon resonances in the infrared region.

The localized surface plasmon enhanced luminescence behaviors of a radiating dipole in an all-inorganic perovskite light-emitting diode (PeLED) by incorporating a gold (Au)-silver (Ag) alloy nanoparticle (NP) in the electronic transport layer are demonstrated. The analyses of finite difference time domain (FDTD) show that the localized surface plasmon resonance (LSPR) wavelength mainly depends on the size and the material composition of NP. An increase of 25% of the luminescence efficiency can be achieved by selecting the proper size and the Au molar fraction of the alloy NP. This result can be attributed to the match between the LSPR wavelength of NP and emission peak of PeLED. And the luminous performance of PeLED can be improved by optimizing the thickness of functional layers. This finding indicates great potential of Au-Ag alloy nanoparticle in developing the efficiency of PeLEDs and provides a new method for the future improvement of PeLEDs.

Localized surface plasmons at nanostructured surfaces are played a key role in a wide range of industrial applications. Here, hexagonal arrays of uniformly distributed Pt nanocylinders were fabricated on the top surface of nanoporous anodic alumina (PAA) membrane using low-cost sputter coating technique under low vacuum. Set of PAA membranes were synthesized at the same conditions and coated with Pt for different periods of time. The implemented growth mechanism allowed the vertical accumulation of Pt nanoparticles to form Pt nanocylinders on the active dots of PAA. SEM images showed nanocylinders of heights ranged from 10.0 ± 0.7 nm to 32.0 ± 2.1 nm based on sputtering time. The nanocylinders rate of growth is 1.22 ± 0.09 nm/min. According to SEM images, the uniformity of the nanocylinders decreased as the porosity of the PAA membrane increased. The optical properties of Pt nanocylinders/PAA membranes were investigated and showed strong transverse, longitudinal, and higher longitudinal surface plasmon modes. Relative to the previously reported SPRs for other Pt nanostructures, our Pt/PAA nanostructures showed stronger SPRs at longer wavelengths due to the using of PAA as a host material, the strong electromagnetic coupling between the very close Pt nanocylinders, and the strong coupling between SPRs and interfernce fringes. Moreover, the effects of sputtering time and membrane porosity on the SPR position, oscillation strength, and bandwidth were studied.

A composite structure based on a Kretschmann structure loaded with silver nano-cube is proposed. A 442-nm laser was used to excite surface plasmons in the composite structure, and the electric field enhancement was numerically simulated using the finite element method. The excitation angles of surface plasmons under conditions of different thicknesses of a PMMA film were obtained by studying the reflection spectrum of the Kretschmann structure. By examining the extinction spectra of silver nano-cubes of different sizes, its optimal size was selected, which is 70 nm. The electric field enhancement factors of the composite structure and the composite PMMA-spaced silver nano-cube and silver film structure were compared in detail. The results show that the coupling of localized surface plasmons and propagating surface plasmons produced by the proposed composite structure mean that its electric field enhancement factor is significantly greater. Moreover, the electric field enhancement factor can be further improved by adding another laser to irradiate the composite structure symmetrically. The high electric field enhancement generated by the composite structure indicates that it has considerable application prospects in surface-enhanced Raman scattering. Keywords: Surface plasmons, Silver nano-cube, Electric field enhancement factor