Local Electric Field Distribution Research Articles

Switching the plasmon coupling of fractional hollow AuAg nanobox by asymmetrical etching of the inner Ag core

Herein, a sub-40 nm fractional hollow AuAg nanobox is asymmetrically filled with Ag atoms inside the nanobox until it is gradually transformed into a solid AuAg nanobox, and the discrete dipole approximation (DDA) method is applied to calculate the corresponding extinction spectra in this process. It is observed that the height of the inner Ag core could cause a non-monotonous shift of the surface plasmon resonance (SPR) band, which first has a linear blue shift and then a near-exponential red shift, indicating that the height of the inner Ag core could be presented as a key factor to tune the core-dependent non-monotonous SPR shift. A local electric field analysis reveals that the non-monotonous SPR shift may be attributed to the switching of plasmon coupling, then inducing the SPR properties of nanoshell and dimer, respectively. Furthermore, we find that the refractive index of both the dielectric cavity and ambient medium could tune the switching threshold of the Ag core height corresponding to the plasmon coupling. It is also revealed that the switching of plasmon coupling could significantly affect the local electric field intensity and its distribution. Consequently, we believe that the asymmetrical Ag core could increase the tunability of an SPR shift and change the local electric field distribution, which provides the potential for SPR-based biosensing and surface-enhanced Raman scattering (SERS) applications.

Core-shell structure-induced high displacement response in piezoelectric ceramics: A theoretical design

In this work, a series of piezoelectric composites with core-shell structure are proposed to pursue high displacement response under a low applied electric field. The shell and core consist of piezoelectric and non-piezoelectric material, respectively. A finite element method (FEM) is introduced to simulate the distribution of local electric field and the displacement response. The results show that the largest piezoelectric displacement response of these core-shell structural composites reaches twenty-five times larger than that of pure piezoelectric ceramic under the applied electric field of 2 kV/mm, which can be explained by the fact that the local electric field inside the shell is enhanced up to dozens of times as large as the applied electric field. It is also suggested that the displacement response of piezoelectric composites can be heightened by adopting smaller shell volume fraction, or increasing the permittivity or decreasing the Young's modulus of the core.

Creating Orientation-Independent Built-In Hot Spots in Gold Nanoframe with Multi-Breakages

In this study, the plasmonic extinction spectra and local field distributions of three different gold nanoframe models with multi-breakages are simulated based on the discrete dipole approximation (DDA) method. By tuning the length of one breakage, there are two clearly separated surface plasmon resonance (SPR) peaks which show a clear blue shift as the broken length increases, and the local field enhancement factor reaches a maximum of 140.8 when the broken length is 2 nm. The changing of plasmonic field interaction and the increased restoring force may be used to explain the resonance blue shift. In these three models, the three-dimensional (3D) local electric field distributions confirm that the hot spot regions mainly concentrate on the interior broken surfaces when the incident electric field is polarized along the broken edge. Moreover, the gold nanoframe with three breakages can create the polarization orientation-independent built-in hot spots inside the broken surfaces. Therefore, the local field enhancement and hot spot regions may be controlled by adjusting the number of breakages and the orientation of polarized field. Consequently, these simulated results about the plasmonic optical properties in gold nanoframe provide a theoretical guidance for the design of polarization orientation-independent SERS substrate, which could create the built-in hot spots and improve the SERS activity.

A Method to Enhance the Electric Field Intensity in a Gold Sub-microhole by Adding Copper Microspheres

We report a method to enhance the electric field intensity in a gold sub-microhole structure. The local electric field distribution was simulated using a finite-difference time-domain (FDTD) solution for the three-dimensional reversed trapezoidal hole structure with and without microspheres and analyzed the transmittance, reflectance and absorptance spectra. Among various sizes for one microsphere, the strongest local electric field occurred for a microsphere with a size of 1 μm. Furthermore, the local electric field intensity was increased when two and three microspheres of 1 μm in size were added.

Poly(vinylidene fluoride)-based nanocomposite employing oriented Bi2S3 nanorods with double-shell structure for high dielectric performance and loss suppression

For polymer-based nanocomposites, designing the nanostructures of fillers, their distribution inside matrix as well as interfaces with the polymer is of crucial importance to achieve high dielectric performances. One-dimensional semiconductor Bi2S3 nanorods coated with homogeneous SiO2 and polydopamine (PDA) double shell layers were imported into the poly(vinylidene fluoride) (PVDF) with parallel arrangement via uniaxial stretching to form Bi2S3@SiO2@PDA/PVDF nanocomposite. The dielectric performances of oriented Bi2S3@SiO2@PDA/PVDF were studied in comparison with its counterparts employing Bi2S3 fillers without shell layers or alignment. A microcapacitor model was used to accurately estimate the dielectric constant along perpendicular direction. Coating conductive Bi2S3 nanorods with insulating SiO2@PDA double layer remarkably reduces the dielectric loss of the nanocomposite, while alignment of one-dimensional Bi2S3@SiO2@PDA nanorods endows electrical properties anisotropy, which was understood from J-V curves measured along two directions and moreover, via three-dimensional finite element analysis, unambiguously revealing the effects of aligned core-shell structured fillers on local electric field and current density distribution. This study provides a promising and facile approach for designing high performance dielectrics.

Probing Adsorption Configurations of Small Molecules on Surfaces by Single-Molecule Tip-Enhanced Raman Spectroscopy.

Determining the adsorption configurations of organic molecules on surfaces, especially for relatively small molecules, is a key issue for understanding the microscopic physical and chemical processes in surface science. In this work, we have applied low-temperature ultrahigh-vacuum tip-enhanced Raman scattering (TERS) technique to distinguish the configurations of small 4,4'-bipyridine (44BPY) molecules adsorbed on the Ag(111) surface. The observed Raman spectra exhibit notable differences in the spectral features which can be assigned to three different molecular orientations, each featuring a specific fingerprint pattern based on the TERS selection rule that determines the distribution of the relative intensities of different vibrational peaks. Furthermore, such a small molecule can in turn act as a local probe to provide information on the local electric field distribution at the tip apex. Our work showcases the capability of TERS technique for obtaining information on adsorption configurations of small molecules on surfaces down to the single-molecule level, which is of fundamental importance for many applications in the fields of molecular science and surface chemistry.

Spatial–Temporal Evolution of a Radial Plasma Jet Array and Its Interaction with Material

This paper investigates the behavior of a radial plasma jet array and its interaction with various cylindrical targets. The jet array comprises six individual plasma jets arranged around a circle at even spaces, directed towards a common central axis, where the cylindrical objects are to be treated. The interaction of the six jets without the target is studied. The effect of pulse rise time on the electrical and optical properties of the plasma jets is investigated. The spatial–temporal evolution of the plasma jet array and its interaction with (1) dielectric target, (2) floating metallic target and (3) grounded metallic target, are studied respectively. It is calculated that the velocity of the ionization front in these three cases, although differs amongst themselves, is in general greater than that in the no-target case. The luminosity and the profile of the ionization wave front are noticeably different in these three cases: comparing to the no-target case, the intensity of the ionization front reduces with the presence of a dielectric target, while the luminosity of the ionization wave front is enhanced with the presence of a metallic target (either floating or grounded). Optical emissions at the quartz nozzle exit and at the central axis are different with different targets. The different behavior of the jet array with the presence of different targets is attributed to the local electric field distribution, which will be discussed in this paper.

High-accuracy wavefront sensing for x-ray free electron lasers

Systematic understanding and real-time feedback capability for x-ray free electron laser (FEL) accelerator and optical components are critical for scientific experiments and instrument performance. Single-shot wavefront sensing enables characterization of the intensity and local electric field distribution at the sample plane, something that is important for understanding scientific experiments such as nonlinear studies. It can also provide feedback for alignment and tuning of the FEL beam and instrumentation optics, leading to optimal instrument performance and greater operational efficiency. A robust, sensitive, and accurate single-shot wavefront sensor for x-ray FEL beams using single grating Talbot interferometry has been developed. Experiments performed at the Linac Coherent Light Source (LCLS) demonstrate 3σ sensitivity and accuracy, both better than λ/100, and retrieval of hard x-ray (λ=0.13 nm, E=9.5 keV) wavefronts in 3D. Exhibiting high performance from both unfocused and focused beams, the same setup can be used to systematically study the wavefront from the FEL output, beam transport optics, and endstation focusing optics. This technique can be extended for use with softer and harder x rays with modified grating configurations.

Five-fold plasmonic Fano resonances with giant bisignate circular dichroism.

Chiral metamaterials with versatile designs can exhibit orders of magnitude enhancement in chiroptical responses compared with that of the natural chiral media. Here, we propose an ease-of-fabrication three-dimensional (3D) chiral metamaterial consisting of vertical asymmetric plate-shape resonators along a planar air hole array with extraordinary optical transmission. It is theoretically shown that such chiral metamaterials simultaneously support five-fold plasmonic Fano resonance states and exhibit significant bisignate circular dichroism (CD) with amplitude as large as 0.8 due to the distinctive local electric field distributions. More interestingly, a "bridge" in the proposed double-plate-based architectures can act as a flipped ruler that is able to continuously manipulate optical chirality including the handedness-selective enhancement and the switching of CD signals. Importantly, the proposed designs have been readily fabricated by using a focused-ion-beam irradiation-induced folding technique and they consistently exhibited five-fold Fano resonances with strong CD effects in experiments. The studies are helpful for the understanding, designing and improvement of chiral optical systems towards potential applications such as ultrasensitive biosensing, polarimetric imaging, quantum information processing, etc.

Significantly Enhanced Dielectric Performances and High Thermal Conductivity in Poly(vinylidene fluoride)-Based Composites Enabled by SiC@SiO2 Core-Shell Whiskers Alignment.

Design of composites with ordered fillers arrangement results in anisotropic performances with greatly enhanced properties along a specific direction, which is a powerful tool to optimize physical properties of composites. Well-aligned core-shell SiC@SiO2 whiskers in poly(vinylidene fluoride) (PVDF) matrix has been achieved via a modified spinning approach. Because of the high aspect ratio of SiC whiskers, strong anisotropy and significant enhancement in dielectric constant were observed with permittivity 854 along the parallel direction versus 71 along the perpendicular direction at 20 vol % SiC@SiO2 loading, while little increase in dielectric loss was found due to the highly insulating SiO2 shell. The anisotropic dielectric behavior of the composite is perfectly understood macroscopically to have originated from anisotropic intensity of interfacial polarization based on an equivalent circuit model of two parallel RC circuits connected in series. Furthermore, finite element simulations on the three-dimensional distribution of local electric field, polarization, and leakage current density in oriented SiC@SiO2/PVDF composites under different applied electrical field directions unambiguously revealed that aligned core-shell SiC@SiO2 whiskers with a high aspect ratio significantly improved dielectric performances. Importantly, the thermal conductivity of the composite was synchronously enhanced over 7 times as compared to that of PVDF matrix along the parallel direction at 20 vol % SiC@SiO2 whiskers loading. This study highlights an effective strategy to achieve excellent comprehensive properties for high-k dielectrics.

A facile approach for reducing the working voltage of Au/TiO2/Au nanostructured memristors by enhancing the local electric field

Memristor devices have attracted tremendous interest due to different applications ranging from nonvolatile data storage to neuromorphic computing units. Exploring the role of surface roughness of the bottom electrode (BE)/active layer interface provides useful guidelines for the optimization of the memristor switching performance. This study focuses on the effect of surface roughness of the BE electrode on the switching characteristics of Au/TiO2/Au three-layer memristor devices. An optimized wet-etching treatment condition was found to modify the surface roughness of the Au BE where the measurement results indicate that the roughness of the Au BE is affected by both duration time and solution concentrations of the wet-etching process. Then we fabricated arrays of TiO2-based nanostructured memristors sandwiched between two sets of cross-bar Au electrode lines (junction area 900 μm2). The results revealed a reduction in the working voltages in current–voltage characteristic of the device performance when increasing the surface roughness at the Au(BE)/TiO2 active layer interface. The set voltage of the device (Vset) significantly decreased from 2.26–1.93 V when we increased the interface roughness from 4.2–13.1 nm. The present work provides information for better understanding the switching mechanism of titanium-dioxide-based devices, and it can be inferred that enhancing the roughness of the Au BE/TiO2 active layer interface leads to a localized non-uniform electric field distribution that plays a vital role in reducing the energy consumption of the device.

Charge transport in conjugated polymer–semiconductor nanoparticle composite near the percolation threshold

This paper describes a new statistical model to predict the frequency dependence of the conductivity of conjugated polymer–semiconductor nanoparticle composites. The model considers AC conduction in an inhomogeneous medium represented by a two-dimensional model of resistor network. The conductivity between two neighboring sites in the polymer matrix and the semiconductor particles is assumed to obey the random free energy barrier model and the Drude model, respectively. The real and imaginary parts of the AC conductivity were determined using the transfer-matrix technique, and the statistical model was applied to experimental data of thin films composed of polyaniline (PANI) and indium–tin–oxide (ITO) nanoparticles. The conductivity critical exponent (s) obtained in two dimensions for PANI/ITO films below the percolation threshold was found to be 2.7, which is greater than the universal value of s described by the classical percolation theory (s = 1.3). This non-universality is explained by the existence of a local electric field distribution in the bulk of the nanocomposite. Finally, these results are discussed in terms of the distribution of potential barriers that vary according to the concentration of ITO amount in the composite.

Open Loop Split Ring Resonator Based Thin Layer Dielectric Sensor

Background: Split ring resonators are fundamental structures used to design metamaterial structures. These split ring resonators are designed for various scientific applications with complex and simple geometrical shapes. Metamaterials provide the extended spectral resolution, which is beyond the scope of conventional devices reported in open literature. Such metamaterials when operated on the non-ionizing terahertz frequencies (0.1-10 THz) are highly suitable for non destructive sensing of living organisms. Methods: The objective of this research work is to evaluate the performance of classic square split ring resonator as a metamaterial biosensor operating at terahertz frequency by depositing thin layers of dielectric materials resembled as hybridized layers of DNA sample. Results: Highly localized surface electric field distribution indicates strong LC resonance at resonant frequency. Electric field is focused on the capacitive coupled split gap area. The effective parameters of biosensor clearly showed left handedness that is negative permittivity and permeability and refractive index. Biosensor was analyzed by observing shift in transmission (S21) coefficients. Resonant frequency shifts itself towards the lower end of terahertz band due to the loading of thin layers of samples that are composed of different dielectric materials. Conclusion: Metamaterial biosensor sense the presence of tiny layers of different dielectric materials. This was due to the fact that disturbances in the surface electric field caused change in transmission of sensor's resonant frequency. The simple design of the sensor would overcome the issue of reusability of circuit. Such sensor would highly be suitable for sensing the presence of tiny bio molecules. Keywords: Metamaterial, dielectric layers, equivalent circuit, sensor, terahertz, split ring resonator.

Refractive index sensing using disk-hole coupling plasmonic structures fabricated on fiber facet

We report a cost-effective and high-throughput method, featuring a double-transfer process and through-fiber curing, to pattern metallic nanostructures on optical fiber facet as portable plasmonic probes for refractive index (RI) sensing. A thin layer of ultraviolet-curable adhesive is coated onto fiber facet to imprint-transfer pre-fabricated metallic nanostructures from a polymeric template to the fiber facet. The reflection spectra of the plasmonic fiber probe in liquid solution samples with various RI are experimentally investigated to demonstrate its capability for real-time and in situ RI sensing. The optical reflection and local electric field distribution of the plasmonic sensing structures are also investigated through numerical modeling. The fiber-facet plasmonic sensor exhibits robust and flexible potential for RI-based sensing applications, and the reported fabrication method is applicable for the production of other functional nanodevices on fiber facets.

Low-cost fabrication and polar-dependent switching uniformity of memory devices using alumina interfacial layer and Ag nanoparticle monolayer

A facile and low-cost process was developed for fabricating write-once-read-many-times (WORM) Cu/Ag NPs/Alumina/Al memory devices, where the alumina passivation layer formed naturally in air at room temperature, whereas the Ag nanoparticle monolayer was in situ prepared through thermal annealing of a 4.5 nm Ag film in air at 150°C. The devices exhibit irreversible transition from initial high resistance (OFF) state to low resistance (ON) state, with ON/OFF ratio of 107, indicating the introduction of Ag nanoparticle monolayer greatly improves ON/OFF ratio by four orders of magnitude. The uniformity of threshold voltages exhibits a polar-dependent behavior, and a narrow range of threshold voltages of 0.40 V among individual devices was achieved upon the forward voltage. The memory device can be regarded as two switching units connected in series. The uniform alumina interfacial layer and the non-uniform distribution of local electric fields originated from Ag nanoparticles might be responsible for excellent switching uniformity. Since silver ions in active layer can act as fast ion conductor, a plausible mechanism relating to the formation of filaments sequentially among the two switching units connected in series is suggested for the polar-dependent switching behavior. Furthermore, we demonstrate both alumina layer and Ag NPs monolayer play essential roles in improving switching parameters based on comparative experiments.

Coupled-plasmon induced optical nonlinearities in anisotropic arrays of gold nanorod clusters supported in a polymeric film

Exploiting a giant plasmonic field enhancement in an anisotropic array of gold nanorod clusters in a polyvinyl alcohol (PVA) film, we have experimentally studied its nonlinear absorptive and refractive response. Gold nanorod cluster-PVA nanocomposites were prepared, and the uniaxial alignment was obtained by mechanically stretching the films. Using the Z-scan method and excitation with 100 fs pulses at 800 nm, intensities up to 70 GW/cm2 at 20 Hz, saturation of both nonlinear absorption and nonlinear refraction were observed. The results are discussed in light of a plasmonic effect arising from the gold nanorod clusters aligned in the stretched polymeric matrix. A polarization dependent sign reversal of the nonlinear refraction was observed, which can find applications in nanoscale photonic devices. The results are supported by finite element analysis of local electric field distribution in the arrays of gold nanorod clusters.

Contamination effects on charge distribution measurement of high voltage glass insulator string

Abstract It is certain that accumulated charge greatly enhances the local electric field distribution of insulator and may lead to breakdown even under nominal voltage. Although research on charge distribution has gained worldwide attention for the past few decades, yet the study of charge distribution on its surface is still insufficient. Therefore, this paper presents the charge distributions measurement on the surfaces of glass insulators string without grading ring subject to clean and contaminated conditions. The experimental results revealed that the distribution of charge for glass insulator recently removed from service has negative distribution pattern and this is further supported by the simulation work results. Charge injection and extraction occurring at the metal-dielectric interface greatly affects the charge amplitude of the adjacent insulators. This study also revealed that the presence of contamination affect the charge distribution of the insulator located near to ground electrode.

Investigations of CuFeS2 semiconductor mineral from ocean rift hydrothermal vent fields by Cu NMR in a local field

The results of investigating natural samples of chalcopyrite mineral CuFeS2 from massive oceanic sulfide ores of the Mid-Atlantic ridge by the 63Cu nuclear magnetic resonance (NMR 63Cu) in a local field at room temperature are presented. The significant width of the resonance lines found in the 63Cu NMR spectrum directly testifies to a wide distribution of local magnetic and electric fields in the investigated chalcopyrite samples. This distribution can be the consequence of an appreciable deviation of the structure of the investigated chalcopyrite samples from the stoichiometric one. The obtained results show that the pulsed 63Cu NMR can be an efficient method for studying the physical properties of deep-water polymetallic sulfides of the World Ocean.

Dichroic nonlinear absorption response of silver nanoprism arrays

The dichroic nonlinear absorption of Ag nanoprism arrays is interpreted using FEM simulations of the polarization-dependent local electric field distribution.

The role of bulk charge transport processes in electrical tree formation and breakdown mechanisms in epoxy resins

Electrical treeing experiments have been conducted at different temperatures and levels of absorbed moisture in Araldite CY1311 epoxy resin samples above their glass transition temperature, i.e. when the resin was in a flexible state. The fractal dimension of the electrical trees obtained and the rate of tree growth were found to depend on the environmental factors: temperature and humidity. It has also been found that at certain levels of temperature and moisture absorbed in the samples, a transition occurs from electrical treeing degradation to breakdown by thermal runaway. Complementary investigations of the dielectric properties of the same epoxy resin system have revealed that a bulk quasi-dc (QDC) charge transport mechanism takes place above the glass transition temperature, and we show that the characteristic features of the dielectric response are related to the shape of the electrical treeing degradation and the transition to thermal breakdown. This is explained qualitatively through the effect of the bulk QDC charge transport process in modifying the local space charge electric field distribution.