Local Field Enhancement Effect Research Articles

Pressure-less spark plasma sintering effect on non-conventional necking process during the initial stage of sintering of copper and alumina

In the present study, we focus on the characterization of the necking mechanisms during the early stages of pressure-less spark plasma sintering (PL-SPS) compared to conventional sintering (CS) of two different types of powdered materials (Cu and α-Al2O3). SEM observations of the evolution of particle morphology and necks from the as-received powders to sintered ones show the nature of the neck between particles which were either in contact or not. For alumina, no particular necking process (melt or viscous bridge) was observed regardless of the sintering conditions (PL-SPS and CS), even for a very high heating rate 455 °C/min. For copper, this neck morphology is unequivocally not typical of conventional ones, thus, suggesting mass transport by an ejection mechanism. This particular morphology was seen occasionally. In comparison, the conventionally sintered Cu particles presented a smoother surface, with conventional curved necks suggesting the contribution of surface diffusion mechanisms. Based on partial pressure calculations, a direct thermal effect might not explain the observed non-conventional neck for copper. On the other hand, local field enhancement effect and local favourable thermal breakdown voltage conditions are described and discussed in order to support the experimental results.

Local-field enhancement effect on the nonlinear optical response of gold-silver nanoplanets

We report on the nonlinear optical properties of Au-Ag nanoplanets produced by ion implantation and irradiation in silica, experimentally investigated by means of the single beam z-scan technique. The measurements provided experimental evidence of the intense local-field enhancement effect theoretically demonstrated for these plasmonic nanosystems. In particular, this has a dramatic impact on their nonlinear absorption behavior and results in a tunable changeover from reverse saturable absorption to saturable absorption by slightly varying the pump intensity and in the possibility to activate and observe nonlinear phenomena of the electron dynamics otherwise unaccessible in the intensity range that can be employed to study these materials. Finally, for the nanoplanet configuration we found a dramatic decrease of the intensity-dependent absorption coefficient, which could be very promising for obtaining optical gain materials.

Gold nanoshell coated NaYF4nanoparticles for simultaneously enhanced upconversion fluorescence and darkfield imaging

Lanthanide-doped upconversion nanocrystals (UCN) converting low energy photons to high energy photons have emerged as an efficient and versatile bioimaging and therapeutic tool. However, the upconversion efficiency of the UCNs is low, which limits their applications. Plasmonic modulation makes it possible to enhance the luminescence of these nanocrystals. We hypothesize that the enhancement of the upconversion luminescence for all the emission peaks simultaneously could be achieved if the UCNs are coated with a gold nanoshell and the surface plasmon resonance (SPR) peak is tuned to the near-infrared (NIR) region and made resonant with the absorption of the UCNs, thereby substantially increasing the excitation flux via local field enhancement (LFE) effect. Furthermore, the nanoparticles could be used for darkfield imaging due to the light scattering caused by the gold nanoshell. Herein, we report a poly-(amino acid)-templated gold-shell encapsulation of the silica coated NaYF4:Yb,Er UCNs and show how a deft tuning of the SPR peak from visible to NIR region dramatically transforms the luminescence quenching into an enhancement effect and how the nanoparticles are used for combined upconversion fluorescence and darkfield light scattering imaging.

Effects of surface modification on nonlinear optical performance of gold nanoparticles

Two kinds of gold nanoparticles with different surface-capping groups (Au-DT and Au-DT-CTAB), 1-dodecanthiol and cetyltrimethylammonium bromide (CTAB) are prepared by a two-phase method. Structures and linear optical properties of the materials are characterized using transmission electron microscopy and ultraviolet--visible absorption spectroscopy. The effects of surface modification on nonlinear optical (NLO) performance and optical limiting behavior of gold nanoparticles are investigated using the openZ-scan technique at a laser wavelength of 532 nm. The results show that Au-DT-CTAB shows an enhanced NLO effect in comparison with Au-DT. The secondary modification with CTAB can not only improve local field enhancement effect but also make the contribution of thermoelectrons to NLO performance of gold nanoparticles on laser irradiation.

The Study of Nano Optical Antenna Based on Surface Plasmon Resonance

The strong local property of surface plasmon polaritons can break through the diffraction limit, and reduce the propagation of corner scattering on nanoscale. The nanoantenna structure based on the plasmon resonant effect can collect the light energy effectively, and the local field enhancement effects of the structure have extensive application prospect. The field distribution and field enhancement effects of optical antenna under nanoscale are calculated with finite-difference time-domain (FDTD) method. Several different structures of nanooptical antenna are studied, and their enhancement properties are compared in this paper.

Synthesis and optical properties of dyes encapsulated in gold hollow nanoshells

Gold nanomaterials are promising objects for applications in optics and medicine because of their unique properties related to the Surface Plasmon Resonances (SPR) phenomena. It is possible to tune these properties with the control of the size and shape of the nanomaterials. Gold hollow spheres nanomaterials are an interesting concept for encapsulation of either dyes or drugs. The study of their properties and their behavior in a bio-environment still remains scarce and some phenomena are still to be explained in particular regarding local field enhancement effect or quenching of their photophysical properties. In this work we describe a process allowing inclusion of optical dyes in gold nanoshells and evaluate the optical properties.

Nano silver:antimony glass hybrid nanocomposites and their enhanced fluorescence application

A series of KBS antimony glass (K 2O–B2O3–Sb 2O 3) nanocomposites embedding non-spherical silver (Ag 0) nanoparticles have been synthesized by a single-step melt-quench in-situ thermochemical reduction technique without employing any external reducing agent. X-ray and selected area electron diffractions manifest growth of Ag 0 nanoparticles along the (111) and (200) crystallographic planes. The transmission electron microscopic image reveals rod-shaped (longitudinal lengths between 8 and 24 nm) as well as quasi-spherical particles. The quasi-spherical particles show bimodal size distribution. Small quasi-particles have sizes varying from 6 to 24 nm and large quasi-particles ranges from 45 to 105 nm. These complex distributions of particles are also revealed in the UV–Vis absorption spectra and the surface plasmon resonance bands show multiple peaks. These have been explained by electrodynamics theories. When co-doped with Er 2O 3 and excited at 798 nm, the two upconverted emission bands of Er 3+ centered at 536 (green) and 645 (red) nm undergo intensification by 3 and 8 fold respectively. It is due to local electric field enhancement effect of nanoparticles induced by Ag 0 SPR and energy transfer from Ag 0 to Er 3+ ion. These nanocomposites are the promising materials for solar cells, LEDs, display and laser applications.

Laser-launched evanescent surface plasmon polariton field utilized as a direct coherent pumping source to generate emitted nonlinear four-wave mixing radiation

We develop a concept of surface plasmon polaritons (SPPs) based four-wave mixing (4WM), in which a laser-launched evanescent SPP field is utilized as a coherent pumping source to involve directly in a nonlinear 4WM process at the dielectric/metal interface. Conversion efficiency of the resulting 4WM radiation is expected to be dramatically increased due to the local-field enhancement effect. Feasibility of implementing this concept at the air/gold film and graphene flake/gold film interfaces is further examined by numerical simulations. The concept shows intriguing promise for applications in newly emerging nanophotonics, optoelectronics, and active plasmonics.

Synthesis and Photoluminescence Enhancement of Silver Nanoparticles Decorated Porous Anodic Alumina

Silver nanoparticles (Ag NPs) were successfully assembled in porous anodic alumina (AAO) templates via a green silver mirror reaction. The Ag NPs/AAO composite templates then were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray microanalysis (EDX), and X-ray diffraction (XRD). Furthermore, the photoluminescence (PL) properties were also investigated. Compared with the blank AAO, the PL intensity of Ag NPs/AAO templates are enhanced and the maximum enhancement is 2.58 times. Based on the local electric field enhancement effect, the theoretical values were also deduced, which are basically coincident with the experimental.

Scattering focusing and localized surface plasmons in a single Ag nanoring

We investigate the far-field scattering property of a single Ag nanoring. Under oblique excitation, two-focus scatterings with distinct intensities were observed. We show that the two-focus scatterings result from the interference of far-field scattering light from the ring circumference, and the local field enhancement effect of surface plasmons plays the key role in the focus intensity. By finite difference time domain and numerical integer methods, we calculated far-field scattering and surface plasmons’ distributions, and the results are in good agreement with the experiment.

Colloidal systems of silver nanoparticles and high-regioregular cationic polythiophene with ionic-liquid-like pendant groups: Optical properties and SERS

We report tuning of structure dependent optical properties of colloidal systems of borate-stabilized silver nanoparticles (Ag NPs) and polythiophene-based cationic polyelectrolyte with ionic-liquid like side groups: poly{3-[6-(1-methylimidazolium-3-yl)hexyl]thiophene-2,5-diyl bromide} (PMHT-Br) towards obtaining local electromagnetic field enhancement effects. Surface-enhanced Raman scattering (SERS) studies showed that the strong electromagnetic field enhancement is related to the formation of aggregates of Ag NPs achieved at the components ratio providing the charge balance between Ag NPs and cationic polythiophene, at which Ag NPs are nearly single-polymer-layer coated, their zeta potential is close to zero and they easily form aggregates in which the mean inter-particle distance enables the occurrence of desired plasmonic effects. Fluorescence quenching is efficient only in the systems with low concentrations of PMHT-Br, in which almost all polymer chains directly interact with the Ag NPs surface.

Surface Plasmon Resonance and Enhanced Fluorescence Application of Single-step Synthesized Elliptical Nano Gold-embedded Antimony Glass Dichroic Nanocomposites

A novel series of elliptical gold (Au0) nanoparticles (18–40 nm) embedded antimony glass (K2O-B2O3-Sb2O3) dichroic nanocomposites have been synthesized by a single-step melt-quench in-situ thermochemical reduction technique. X-ray and selected area electron diffractions manifest growth of Au0 nanoparticles along the (111) and (200) crystallographic planes. The transmission electron microscopic image reveals elliptical Au0 nanoparticles having an aspect ratio varying in the range 1.2–2.1. The dichroic behavior of the nanocomposites arises due to elliptical shape of the Au0 nanoparticles. These nanocomposites show strong surface plasmon resonance (SPR) band of Au nanoparticles in the range 610–681 nm and it exhibit red-shifts with increasing Au concentration. They, when co-doped with Sm2O3 and excited at 949 nm, exhibit about sevenfold enhancement of the upconverted red emission transition of 4G5/2→6H9/2 at 636 nm due to local electric field enhancement effect of Au0 nanoparticles induced by its SPR. These nanocomposites are the promising materials for laser, display, and various nanophotonic applications.

Nanoscale photoluminescence of light-emitting poly (3-methylthiophene) nanotubes hybridized with Au nanoparticles

We reported on the fabrication and nanoscale luminescence characteristics of the hybrid nanotubes (NTs) of light-emitting poly (3-methylthiophene) (P3MT) NT with gold (Au) nanoparticles (NPs) (P3MT/Au-NPs). After hybridizing the Au-NPs onto the surface of P3MT NTs, the light-emitting color of P3MT NTs was dramatically changed from a green to a bright red. From laser confocal microscope photoluminescence (PL) experiments for an isolated single strand of the NTs, we observed a ∼220 times enhancement of the PL peak intensity for the hybrid NT of P3MT/Au-NPs compared to that of the P3MT single NT. The enhancement PL efficiency of the hybrid NT of P3MT/Au-NPs can be explained in terms of a surface plasmon resonance (SPR) and nanoscale local electric field enhancement effects.

Ultrafast nonlinear optical response of Ag nanoparticles embedded in mesoporous thin films

Highly dispersed silver nanoparticles embedded in mesoporous thin films (MTFs) have been synthesized by modification of the interior surface of mesoporous silica with ethylenediamine moieties, which provided the coordination sites for the Ag ions, and subsequent reduction under hydrogen atmosphere. TEM observations show the mesoporous parent films have effectively controlled the growth of the synthesized silver nanoparticles. The composite films had an ultrafast nonlinear response time, as fast as 200 fs, and a third-order nonlinear optical susceptibility of 0.94 × 10−10 esu, which was enhanced by the local field enhancement effect that was present when the silver nanoparticles were embedded in the surrounding dielectric matrix. The origin of the ultrafast nonlinear response and the enhanced nonlinearity of the composite films are attributed to the intraband transition of the free electrons near the Fermi surface of the incorporated silver nanoparticles.

Wall thickness dependent double optical bistability in gold nanotube: A physical mechanism based on local field enhancement

The intrinsic optical bistability (OB) in a two-phase composite, a nonlinear gold nanotube embedded in a linear dielectric host, is investigated by theoretical calculation. Based on quasistatic approximation and Kerr nonlinearity, we obtain the local electric field in a certain position of the gold nanotube as a function of the incident field. In addition to the single OB, the appearance of double OB and optical tristability are also reported. It is shown that both wavelength and wall thickness can dramatically affect the optical bistable behavior of gold nanotube. Both the critical wavelength and the region of double OB decrease obviously with increasing the wall thickness. Thus double OB only appears in the thinner gold tube and is absent as the wall thickness exceeds the critical value. Furthermore, all these OB characteristics have been explained by the local field enhancement effect.

Surface Enhanced Raman Scattering from an Ag Nanorod Array Substrate: The Site Dependent Enhancement and Layer Absorbance Effect

We have designed experiments to put Raman probe molecules on different locations of Ag nanorod array substrates and found that the apparent enhancement factor for surface enhanced Raman scattering (SERS) is about 50−200 times from the surface of the nanorods than that from the Ag thin film surface under an Ag nanorods array. When excited from the top of Ag nanorod array substrates, the ratio of SERS intensity excited by s-polarization to that excited by p-polarization is 1.8 to 2.2, while when excited from the bottom of Ag nanorod array substrates, this ratio becomes 0.77. These effects cannot be interpreted directly by the local electric field enhancement effect. By combining the local electric field effect calculated by the three-dimensional finite-difference time-domain method and the anisotropic optical absorbance of the SERS signal from the anisotropic Ag nanorod array, the numerical calculations semiquantitatively agree with the experimental results.

Local electric field enhancement and polarization effects in a surface-enhanced Raman scattering fiber sensor with chessboard nanostructure

A surface-enhanced Raman scattering fiber sensor with chessboard nanostructure on a cleaved fiber facet is studied by finite-difference time-domain method. Surface plasmons at the metal coated nanostructured fiber facet can be effectively excited and strong local electric field enhancement is obtained. Studies on the influence of light polarization demonstrate a large polarization dependence of the field enhancement factor while the polarization effects on the plasmon resonance wavelength are relatively small.

Numerical simulation of probe induced surface plasmon resonance coupling nanolithography

A new nanolithographic technology, the probe induced surface plasmon resonance coupling nanolithography (PSPRN), is presented and analyzed numerically by using finite difference time domain method for the loss and dispersive materials. The PSPRN uses a fundamental mode Gaussian beam with wavelength of 514.5nm to excite the Kretschmann surface plasmon resonance, and utilizes the metal probe local-field enhancement effect to realize nanolithography. The influences of different distances between probe and recording layer and different sizes of tip on local field enhancement and the distribution of electric field intensity amplitude on the surface of recording layer were investigated. Results show that the local field enhancement effect is most significant and the electric field intensity amplitude contrast ratio is maximal when the probe is in contact with the recording layer. When the distance between tip and recording layer is 5nm, the distribution width of the relative electric field intensity amplitude above the critical value for near-field nanolithography on the surface of recording layer is close to the size of the tip.

Enhanced luminescence from europium complex owing to surface plasmon resonance of silver nanoparticles

The effect of Ag nanoparticles on the luminescent properties of the europium complex, where the complex is ethylenediamine tetra acetate (EDTA), was investigated in the aqueous solution system. We observed the formation of nanoparticle aggregates and the appearance of a new absorption and enhancement of the emission intensity for the complex solution containing Ag nanoparticles when the pH of the complex solution is 3–4.6. Furthermore, with increasing Ag nanoparticles concentration enhancement efficiency first increases and then decreases. The enhancement effect was discussed in terms of the effects of nanoparticle aggregates, the local electromagnetic field enhancement effect and optical absorption due to surface plasmon resonance.

Spectral tuning of localised surface plasmon-polariton resonance in metallic nano-crescents

The utilisation of plasmonic effects in metallic nanostructures is gaining importance for applications in molecular sensing. Of special interest is the local field enhancement effect, which enables surface-enhanced Raman scattering and significantly boosts the sensitivity of the Raman technique. For in vivo biological research, the ability to excite the resonance of localised surface plasmon-polaritons within the biological window is often desired. A new nanostructure called the nano-crescent is introduced and exhibits strong plasmonic activities within the biological window using a novel intra-particle plasmonic coupling scheme.