Local Field Enhancement Effect Research Articles

All-optical tunable dual Fano resonance in nonlinear metamaterials in optical communication range

Low-power, ultra-fast all-optical tunable dual Fano resonance was realized in a metamaterial coated with a non-linear nanocomposite layer composed of gold nanoparticle-doped polycrystalline barium strontium titanate and multilayer tungsten disulphide microsheets. A high non-linear refractive index of −2.148 × 10−11 m2/W was achieved in the nanocomposite material that originated in the non-linearity enhancement associated with the quantum confinement effect, the local-field enhancement effect, and reinforced interactions between photons and the multilayer tungsten disulphide microsheets. An ultra-low threshold pump intensity of 600 kW/cm2 was obtained. An ultra-fast response time of 25.4 ps was maintained because of the fast relaxation dynamics of the bound electrons in the nanoscale polycrystalline barium strontium titanate grains. The large third-order non-linear responses of the metamaterial were confirmed with a high third harmonic generation conversion efficiency of 5.4 × 10−5. This work may help to pave the way towards realization of ultra-high-speed information processing chips and multifunctional integrated photonic devices based on metamaterials.

Fluorescence Enhancement of Metal-Capped Perovskite CH3NH3PbI3 Thin Films**Supported by the Ministry of Science and Technology of China under Grant No 2016YFA0202201, the National Natural Science Foundation of China under Grant Nos 61290304, 11574335 and 61376016, the Youth Innovation Promotion Association of the Chinese Academy of Sciences, and the 333 Project of Jiangsu province under Grant No BRA2017352.

We fabricate nano-structural metal films to improve photoluminescence of perovskite films. When the perovskite film is placed on an ammonia-treated alumina film, stronger photoluminescence is found due to local field enhancement effects. In addition, the oxide spacer layer between the metal (e.g., Al, Ag and Au) substrate and the perovskite film plays an important role. The simulations and experiments imply that the enhancement is related to surface plasmons of nano-structural metals.

Surface Enhanced Visible Light Photocurrent and Switching Behavior of Metal Oxide Semiconductor Electrodes Modified with Plasmonic Nanoparticles

Hematite (α-Fe2O3) is a promising photocatalyst for solar water splitting because of its favorable band gap of 2.2 eV, low cost, and abundance in nature. Surface plasmon-enhanced light absorption for photoelectrochemical water splitting at α-Fe2O3thin film electrode modified with Au nanoparticles (NPs) or nanorods (NRs) is described. About 3 times higher light absorption and photocurrent enhancement are obtained from thin hematite films containing Au NPs than with pristine hematite films. The plasmonic enhancement increases with the amount of Au NPs for the same thickness of hematite. Thickness-dependent study of photoactivity indicates a higher enhancement in hematite thin films compared to thicker films due to reduced charge transport distance and optimal local field enhancement effect. Such enhancement can be obtained by self-assembling Au NRs onto a hematite thin film electrode using electrostatic force between their positively charged cetyltrimethylammonium bromide (CTAB) layer and negatively charged hematite surface functionalized with poly(4-styrenesulfonate). The photoelectrochemical reaction of the plasmon active substrate for water oxidation reaction is performed and compared at various hematite layer thicknesses. When the α-Fe2O3 electrode is biased at a small potential +0.2 V (vs Ag/AgCl), the photocurrent of water oxidation is reduced because of increased recombination of holes and electrons at the surface of the Au NRs. When the bias potential is increased to +0.5 V (vs Ag/AgCl), a plasmon enhancement of the photoelectrochemical reaction of water oxidation at wavelengths near the plasmon resonance condition is observed at the α-Fe2O3 thin film electrodes accompanying a dramatic increase in the background current. The significant increase in photocurrent in the region of surface plasmon absorption is attributed to the enhanced visible light absorption of α-Fe2O3 in the presence of the plasmon active Au NPs and NRs.

Long-range surface plasmon-induced tunable ultralow threshold optical bistability using graphene sheets at terahertz frequency.

A proposal on optical bistability at ultralow switching threshold and lower Fermi-level of graphene around 2 THz is implemented analytically through the proposed long-range surface plasmon resonance configuration by employing local field enhancement effects owing to the excitation of a graphene symmetric mode within graphene sheets. Reported threshold intensity for the optical bistability to date is 1.6 kW/cm2 within the terahertz region and 1.83 MW/cm2 at near-IR range. Whereas the proposed scheme explores the possibility of reducing this threshold down to 143.68 W/cm2, this technique proffers potential applications in nanoillumination, optical memory, and all-optical switching at an ultra-low threshold.

Metal-enhanced upconversion luminescence of NaYF4:Yb/Er with Ag nanoparticles

Single rare earth doped NaYF4 nanoplate with different size of Ag nanoparticles is designed for the investigation of metal enhanced upconversion luminescence effect. Up to twice enhancement is obtained with big Ag nanoparticles. Luminescence quenching effect is also observed with small Ag nanoparticles. Exploration on the enhancement factors are carried out systematically based on the effect of local field enhancement, the coupling of LSPR with emission band, and even the enhanced far field distribution. It is suggested that the excitation enhancement is the reason for the enhancement at both wavelength. Emission enhancement also took a significant part in the result which is that in the system, the enhancement effect at 540nm is greater than that at 650nm.

Local-field enhancement of optical nonlinearities in the AGZO nano-triangle array

Enhancement of the third order optical nonlinearities in Ga and Al co-doped ZnO (AGZO) nano-triangle array was investigated by performing a Z-scan method with a femtosecond laser (800 nm, 40 fs). The AGZO nano-triangle array was fabricated on silica substrates by nanosphere lithography (NSL) method, showing a surface plasmon resonance (SPR) peak around 3 μm. The two photon absorption (TPA) coefficient and nonlinear refractive index of the AGZO nano-triangle array were determined to be 340 cm/GW and 3.22 × 10−2 cm2/GW under an excitation intensity of 26 GW/cm2. It shows a 3.4-fold enhancement of the nonlinear refraction in the AGZO array with respect to that in the AGZO film, which attributes to the local field enhancement effect. The finite-difference time-domain (FDTD) simulation was in agreement with the experimental results. It indicates that the AGZO nano-triangle arrays have potential applications for nonlinear optical devices like all-optical switching, optical limiting and other types of signal processing.

Full Solution-Processed Synthesis and Mechanisms of a Recyclable and Bifunctional Au/ZnO Plasmonic Platform for Enhanced UV/Vis Photocatalysis and Optical Properties.

The synthesis of noble metal/semiconductor hybrid nanostructures for enhanced catalytic or superior optical properties has attracted a lot of attention in recent years. In this study, a facile and all-solution-processed synthetic route was employed to demonstrate an Au/ZnO platform with plasmonic-enhanced UV/Vis catalytic properties while retaining strengthened luminescent properties. The visible-light response of photocatalysis is supported by localized surface plasmon resonance (LSPR) excitations while the enhanced performance under UV is aided by charge separation and strong absorption. The enhancement in optical properties is mainly due to local field enhancement effect and coupling between exciton and LSPR. Luminescent characteristics are investigated and discussed in detail. Recyclability tests showed that the Au/ZnO substrate is reusable by cleaning and has a long shelf life. Our result suggests that plasmonic enhancement of photocatalytic performance is not necessarily a trade-off for enhanced near-band-edge emission in Au/ZnO. This approach may give rise to a new class of versatile platforms for use in novel multifunctional and integrated devices.

Extremely Stable Current Emission of P-Doped SiC Flexible Field Emitters.

Novel P-doped SiC flexible field emitters are developed on carbon fabric substrates, having both low Eto of 1.03-0.73 Vμm-1 up to high temperatures of 673 K, and extremely high current emission stability when subjected to different bending states, bending circle times as well as high temperatures (current emission fluctuations are typically in the range ±2.1%-3.4%).

Multilayer-MoS2-microsheet/(Nano-Au:LiNbO3) for all-optical tunable metamaterial-induced transparency

All-optical tunable metamaterial-induced transparency is realized using polycrystalline lithium niobate doped with gold nanoparticles and multilayer molybdenum disulfide microsheets as a third-order nonlinear optical material. A low threshold pump intensity of 90 kW cm−2 is obtained based on nonlinearity enhancement associated with the quantum confinement effect, the local-field enhancement effect, and reinforced interaction between photons and the multilayer molybdenum disulfide microsheets. An ultrafast response time of 27.4 ps is maintained owing to the fast relaxation dynamics of bound electrons in the polycrystalline lithium niobate. This work may pave a way for the realization of ultrahigh speed information processing chips based on metamaterials.

Investigation of temperature on the field electron emission from flexible N-doped SiC nanoneedles

With respect to the effect of local field enhancement, fabrication of nanostructures with clear and sharp tips is critically important for the exploration of field emitters with high performances. In the present work, we report the growth of flexible SiC nanoneedles (SiC-NNs) with sharp tips on carbon cloth substrate via catalyst-assisted pyrolysis of a polymeric precursor. The entire structure of the substrate retains its high flexibility after the growth of SiC and can even be rolled-up. The as-synthesized SiC-NNs are single-crystalline and grow along the [111] direction with a uniform spatial distribution of N dopants. The field emission behaviors of N-doped SiC-NNs flexible cathode exhibit a strong dependence on the temperatures. The turn-on fields (Eto) of cathode are found to decrease from 1.58 to 0.65Vμm−1 with the temperature raised from room temperature (RT) to 500°C. The reduction of Eto could be attributed to the needle-shaped structures of SiC emitters and the decrease of work function (Φ) induced by the raise of temperatures and the incorporated N dopants. Furthermore, the cathode shows notable electron emission stabilities and the fluctuation of current density was only 7.7% after a 5h long lifetime test under 200°C.

Effect of surface plasmon resonance in TiO2/Au thin films on the fluorescence of self-assembled CdTe QDs structure

The exceptional properties of localised surface plasmons (LSPs), such as local field enhancement and confinement effects, resonant behavior, make them ideal candidates to control the emission of luminescent nanoparticles. In the present work, we investigated the LSP effect on the steady-state and time-resolved emission properties of quantum dots (QDs) by organizing the dots into self-assembled dendrite structures deposited on plasmonic nanostructures. Self-assembled structures consisting of water-soluble CdTe mono-size QDs, were developed on the surface of co-sputtered TiO2 thin films doped with Au nanoparticles (NPs) annealed at different temperatures. Their steady-state fluorescence properties were probed by scanning the spatially resolved emission spectra and the energy transfer processes were investigated by the fluorescence lifetime imaging (FLIM) microscopy. Our results indicate that a resonant coupling between excitons confined in QDs and LSPs in Au NPs located beneath the self-assembled structure indeed takes place and results in (i) a shift of the ground state luminescence towards higher energies and onset of emission from excited states in QDs, and (ii) a decrease of the ground state exciton lifetime (fluorescence quenching).

Localized Electric Field of Plasmonic Nanoplatform Enhanced Photodynamic Tumor Therapy

Near-infrared plasmonic nanoparticles demonstrate great potential in disease theranostic applications. Herein a nanoplatform, composed of mesoporous silica-coated gold nanorods (AuNRs), is tailor-designed to optimize the photodynamic therapy (PDT) for tumor based on the plasmonic effect. The surface plasmon resonance of AuNRs was fine-tuned to overlap with the exciton absorption of indocyanine green (ICG), a near-infrared photodynamic dye with poor photostability and low quantum yield. Such overlap greatly increases the singlet oxygen yield of incorporated ICG by maximizing the local field enhancement, and protecting the ICG molecules against photodegradation by virtue of the high absorption cross section of the AuNRs. The silica shell strongly increased ICG payload with the additional benefit of enhancing ICG photostability by facilitating the formation of ICG aggregates. As-fabricated AuNR@SiO2-ICG nanoplatform enables trimodal imaging, near-infrared fluorescence from ICG, and two-photon luminescence/photoacoustic tomography from the AuNRs. The integrated strategy significantly improved photodynamic destruction of breast tumor cells and inhibited the growth of orthotopic breast tumors in mice, with mild laser irradiation, through a synergistic effect of PDT and photothermal therapy. Our study highlights the effect of local field enhancement in PDT and demonstrates the importance of systematic design of nanoplatform to greatly enhancing the antitumor efficacy.

Plasmon Mediated Multiphoton Photoemission Microscopy of Au Nanoholes and Nanohole Dimers

Multiphoton photoemission from “nanoholes” and “nanohole dimers” fabricated by nanosphere shadow lithography in a thin Au film are investigated by ultrafast scanning photoionization microscopy (SPIM), which provides detailed information on laser polarization and local electric field enhancement effects for novel 2D plasmonic architectures. The net photoemission signals (at 800 nm) from isotropic nanohole monomers both (i) below (d ≪ λ) and (ii) comparable to (d ≈ λ) the diffraction limit are insensitive to laser polarization, though SPIM images of the larger species clearly reveal strongly enhanced electron emission from nanohole tangent edges perpendicular to incident laser polarization. Fundamentally contrasting behavior is observed for intrinsically anisotropic plasmonic architectures such as nanohole dimers. Specifically, small nanohole dimers reveal enhanced electron emission for λ = 800 nm light polarized perpendicular to the dimer axis, whereas larger nanohole dimers produce optimum electron yields...

Influences of Au nanoparticle density on the performance of GaAs solar cells

The influence of the Au nanoparticle density on the performance of single-junction GaAs solar cells has been investigated. The single-junction GaAs solar cells are grown on (100) GaAs substrates by using a low-pressure metalorganic chemical vapor deposition (MOCVD) system. Au nanoparticles are dispersed on the surfaces of the cells by micro-pipetted casting and the density of the dispersed nanoparticles varies from 4.7 × 109 to 4.3 × 1010 cm−2. The conversion efficiencies of the GaAs solar cells are observed to depend strongly on the Au nanoparticle densities. For Au nanoparticle densities lower than 2.8 × 1010 cm−2, the conversion efficiency improvement of the GaAs solar cells mainly originates from the antireflection coating effect. In contrast, for the sample with a Au nanoparticle density of 2.8 × 1010 cm−2, the antireflection effect decreases due to the shadow effect and the local field enhancement effect due to the Au nanoparticles starts to be effective. The GaAs solar cell with a Au nanoparticle density of 1.9 × 1010 cm−2 shows a maximum conversion enhancement compared to that of the reference sample.

Effect of local field enhancement on the nonlinear terahertz response of a silicon-based metamaterial

We demonstrate the strong effect of the local field enhancement on the nonlinear terahertz response of a hybrid photoexcited silicon/double concentric ring metamaterial structure. The ring resonators enhance the local terahertz electric field by more than a factor of ten, pushing the terahertz-semiconductor interaction into the high-field regime even for moderate-strength incident terahertz pulses. In this regime, terahertz field-induced intervalley scattering in the photoexcited silicon substrate dynamically alters the substrate conductivity, which in turn strongly modifies the pulse transmission. The spatial distribution of the local field enhancement within the resonator structure results in a modified bandwidth, amplitude, and central frequency of the transmission resonance occurring on a subcycle time scale. These results demonstrate an enhancement of the nonlinear terahertz response of silicon-based metamaterials that must be accounted for in the design of terahertz nonlinear devices.

A spoof surface WGM sensor based on a textured PEC cylinder

Based on the negative permittivity properties of a two-dimensional (2D) textured perfect electric conductor (PEC) cylinder, we design a spoof surface whispering gallery mode (WGM) sensor at microwave band. The sensitivity of the proposed sensor is much higher than that of the traditional dielectric sensor in the same geometry size. Importantly, we show that the physical origin for the improvement of sensitivity is the evanescent-wave amplification and local field enhancement effects. This may open up an avenue for designing metamaterial sensors with superior sensitivity.

Investigation of the interaction between different types of Ag species and europium ions in Ag^+-Na^+ ion-exchange glass

The introduction of silver into the Eu3+-doped sodium–aluminosilicate glasses prepared by Ag+-Na+ ion exchange leads to the formation of different ionic silver species. Under 350nm excitation, effective enhancement of Eu3+ luminescence is ascribed to energy transfer (ET) from silver aggregates to Eu3+ and White light emission was realized by combining red light emission of Eu3+ with blue/green light emission of silver aggregates. The formation of silver aggregates such as Ag2+ was promoted by Eu2+ in the heat treatment process. The local field enhancement effect due to SPR of Ag NPs was not observed. Our research will help to understand the interaction between different types of Ag species and europium ions.

Optical SHG properties of GaAs nanowires irradiated with multi-wavelength femto-second laser pulses

The nonlinear optical properties of semiconductor nanowires are of vital importance in the researches of nano-optics and fabrication of nano-scale optoelectronic components. GaAs is a direct bandgap semiconductor material of wide bandgap, high electron mobility, large χ(2), high laser damage threshold and stable chemical properties, all of which make it a potential nonlinear optical material. In this report, based on the finite element method (FEM), we investigated the optical response and local field enhancement of GaAs nanowires perpendicular to the GaAs substrate surface. Under the radiation of femto-second laser pulses at different wavelengths, efficient second harmonic generation (SHG) signal was acquired from the nanowires. Furthermore, noise-free broadband SHG signal was also detected to be excitated by super-continuous femto-second pulses (1000-1300 nm). The high-efficiency SHG process could be attribated mainly to the local field enhancement effect of the nanowires. Our investigation is the first, as far as we know, demonstrate the SHG properties of GaAs nanowires, and the results suggest that GaAs nanowires are promising in the potential applications in nano-scale optical devices, integrated nanophotonic circuits, from which related nano-optics researches can benefit.

Nanofizyka ta antyvirusna terapiya

A new mechanism of interaction between viruses and nanoparticles is proposed. The mechanism is based on the local-field enhancement effect inherent only in nano-objects and can manifest itself in nanoparticle–virus systems. The basic idea consists in vacuum fluctuations that are always present in any physical system. This mechanism is universal and does not depend on the details of nanoparticle and virus structures, which was confirmed by numerous experiments carried out by us and in other scientific groups. A new method of purification of biofluids from nano-objects such as nanoparticles and viruses is also discussed. The method is based on a selective interaction between nano-objects and either a nanostructured surface, along which a surface plasmon-polariton propagates, or a system of nanothreads, on which a local plasmon-polariton is excited. On the basis of the method proposed for weakening the virus activity due to the action of a suspension of nanoparticles, a new effective way for the production of human leukocytic interferon has been developed and verified experimentally.

Nonlinear optical response of gold–silver nanoplanets

The nonlinear optical properties of AuAg nanoplanets produced by ion implantation and subsequent irradiation in silica have been investigated by means of the single beam z-scan technique. These plasmonic nanosystems evidenced intense local-field enhancement effects, also theoretically demonstrated, that have a dramatic impact on their nonlinear optical response. In particular, the nonlinear absorption behavior was characterized by a tunable changeover from reverse saturable absorption to saturable absorption that can be induced by slightly varying the pump intensity. Owing to this, these systems offer the possibility to activate and observe phenomena otherwise not accessible in the intensity range that can be employed to study these materials without damaging the matrix.