Local Electric Field Enhancement Research Articles

Local Field Enhancement Due to the Edge States of Nanoplasmonic Crystal

In this paper, we describe the effect of local electric field enhancement due to the existence of photonic edge states in a nanoplasmonic crystal. These states can be excited by a normal incident wave and are localized along the continuous line defect, where translational symmetry is broken. The nanoplasmonic crystal is formed by a triangular lattice of SiO2 cylinders on top of SiO2 and Ag thin films. Numerical simulations demonstrated that edge modes that are concentrated around a defect in a nanophotonic crystal may result in 12 field enhancements of the electric field for the incident plane wave of wavelength 545 nm. This effect can be employed for improving the sensitivity of surface-enhanced Raman scattering (SERS) spectroscopy, increasing the Purcell factor of quantum systems and improving the efficiency of higher harmonic generation.

Effect of Geometrical Parameters on Local Electric Field Enhancement of Bimetallic Three-Layered Nanotubes by Using Quasi-static Theory

Effect of Geometrical Parameters on Local Electric Field Enhancement of Bimetallic Three-Layered Nanotubes by Using Quasi-static Theory

Synergistic coupling of interface ohmic contact and LSPR effects over Au/Bi24O31Br10 nanosheets for visible-light-driven photocatalytic CO2 reduction to CO.

The challenge of synergistically optimizing different mechanisms limits the further improvement of plasmon-mediated photocatalytic activities. In this work, an Au/Bi24O31Br10 composite, combining an interface ohmic contact and localized surface plasmon resonance (LSPR), is prepared by a thermal reduction method. The LSPR effect induces the local resonance energy transfer effect and the local electric field enhancement effect, while the interface ohmic contact forms a stronger interface electric field. The novel synergistic interaction between the interface ohmic contact and LSPR drives effective charge separation and provides more active sites for the adsorption and activation of CO2 with improved photocatalytic efficiency. The optimized 0.6 wt% Au (5.7 nm) over Bi24O31Br10 nanosheets showed an apparently improved photocatalytic activity without any sacrificial reagents, specifically CO and O2 yields of 44.92 and 17.83 μmol g-1 h-1, and demonstrated superior stability (only lost 6%) after continuous reaction for 48 h, nearly 5-fold enhanced compared to Bi24O31Br10 and a great advantage compared with other bismuth-based photocatalysts.

Surface ionization waves propagating over non-planar substrates: wavy surfaces, cut-pores and droplets

Atmospheric pressure plasmas intersecting with dielectric surfaces will often transition into surface ionization waves (SIWs). Several applications of these discharges are purposely configured to be SIWs. During propagation of an SIW over a dielectric surface, the plasma charges the surface while responding to changes in geometrical and electrical material properties. This is particularly important for non-planar surfaces where polarization of the dielectric results in local electric field enhancement. In this paper, we discuss results from computational investigations of negative and positive SIWs propagating over nonplanar dielectrics in three configurations—wavy surfaces, cuts through porous materials and water droplets on flat surfaces. We found that negative SIWs are particularly sensitive to the electric field enhancement that occurs at the crests of non-planar surfaces. The local increase in ionization rates by the electric field enhancement can result in the SIW detaching from the surface, which produces non-uniform plasma exposure of the surface. Positive SIWs tend to adhere to the surface to a greater degree. These trends indicate that treatment of pathogen containing droplets on surfaces may be best performed by positive SIWs. The same principles apply to the surfaces cut through pores. Buried pores with small openings to the SIW may be filled by plasma by either flow of plasma into the pore (large opening) or initiated by photoionization (small opening), depending on the size of the opening compared to the Debye length.

Design of locally enhanced electric field in dielectric loaded rectangular resonator for quantum microwave measurements

Rydberg-atom electrometers have the remarkable advantages of self-calibration and high sensitivity. Based on the classical electromagnetic theory, a localized electric field enhancement structure of a hybrid rectangular resonator (RR) is proposed to improve the sensitivity of quantum microwave measurement. It should be noted that the prototype of the hybrid RR is fabricated and measured at 9.925 GHz. The results of full-wave simulations show that the uniform and high electric field enhancement in the TE101 fundamental mode is realized. The transient process of resonance is simultaneously simulated, and the time to settle steady state is given as about 104 ns. As indicated through experimental results that the structure can reach 24 dB (enhancement factor of 15.8). As a result, the method proposed in this study, based on atomic measurement capabilities, enables us to improve the measurement sensitivity further and promotes the practical development of quantum microwave measurement technology.

Local Electric Field Enhancements of Two Closely Spaced Subwavelength Spheres in Microwaves

The local electric field enhancement (LEFE) among powdered metals or dielectrics in microwaves has been widely applied in many fields, but it is still a challenge to describe the LEFE intuitively. This article presents a simple model to predict the LEFE in two closely spaced subwavelength spheres in microwaves, based on the quasistatic electric field approximation and the dipole–dipole interaction. The results show that this LEFE is related to the radius of spheres, the separation distance, and the permittivity of spheres. The proposed model is able to predict the LEFE accurately if the electric length of the two spheres is within one-tenth of a wavelength when put in free space or a waveguide. The proposed model can benefit in predicting the LEFE in subwavelength metals or dielectrics, which can benefit a wide range of applications.

A Novel Method for Carbendazim High-Sensitivity Detection Based on the Combination of Metamaterial Sensor and Machine Learning.

Benzimidazole fungicide residue in food products poses a risk to consumer health. Due to its localized electric-field enhancement and high-quality factor value, the metamaterial sensor is appropriate for applications regarding food safety detection. However, the previous detection method based on the metamaterial sensor only considered the resonance dip shift. It neglected other information contained in the spectrum. In this study, we proposed a method for highly sensitive detection of benzimidazole fungicide using a combination of a metamaterial sensor and mean shift machine learning method. The unit cell of the metamaterial sensor contained a cut wire and two split-ring resonances. Mean shift, an unsupervised machine learning method, was employed to analyze the THz spectrum. The experiment results show that our proposed method could detect carbendazim concentrations as low as 0.5 mg/L. The detection sensitivity was enhanced 200 times compared to that achieved using the metamaterial sensor only. Our present work demonstrates a potential application of combining a metamaterial sensor and mean shift in benzimidazole fungicide residue detection.

PECVD of Vertical Graphene: Local Plasma or Nonlocal Plasma?

Using the plasma-enhanced chemical vapor deposition method, we grow vertical graphene thin films onto SiO2/Si substrates, which is a special format of graphene composed of numerous macroscopically uniformly distributed graphene flakes approximately vertically arranged. The growth parameters, including the growth temperature, growth time and plasma power, are systematically studied and optimized. Most importantly, the function of plasma has been revealed. In the same deposition machine, we have altered the plasma electrode and heater configurations, and found that the vertical graphene can only grow in local plasma environment. That is, the samples have to be well immersed in the plasma sheath electric field. In this way, the vertical growth of graphene and the local enhancement of electric field can form a positive feedback loop, resulting in the continuous growth of vertical graphene. This experiment clarifies the function of plasma electric field in the vertical graphene growth, and can offer hints for the growth of other vertical two-dimensional materials as well. The vertical graphene films are scalable, transfer-free and lithographically patternable, which is compatible with standard semiconductor processing and promising for optoelectronic applications. We have characterized the optical properties of the as-grown vertical graphene films, where a nearly zero transmittance is observed for 1100–2600[Formula: see text]nm wavelengths, indicating a superstrong absorption in the black colored vertical graphene.

Study of EPR-based nanodielectrics under operational conditions for DC cable insulation

A model DC material based on ethylene propylene rubber (EPR) including the pure EPR and the EPR-based nanodielectrics incorporated with two different nanoclays, Kaoline and Talc, under operational conditions was investigated. The operational conditions include a 20 kV/mm electric field at 25 °C, a 20 kV/mm electric field at 50 °C with a thermal gradient, and a 40 kV/mm electric field at 50 °C with a thermal gradient and polarity reversal. Space charge distribution, surface potential, and electrical conductivity were measured to characterize the model DC material and interpret the discrete charge dynamics in the bulk and at the interface of the three samples. The experimental results revealed that the electrical conductivity of Talc-filled nanodielectric has the least dependency on electric field and temperature, which reduces the conductivity gradient across the dielectric. Moreover, the successful suppression of space charge and the lower dielectric time constant in the Talc-filled nanodielectric result in a tuning electric field in the bulk not only under normal operating conditions but also more importantly under polarity reversal conditions. The maximum of absolute charge density decreases from 10.6 C/m3 for EPR to 2.9 C/m3 for the Talc-filled nanodielectric under 40 kV/mm with polarity reversal and at 50 °C with the thermal gradient. The maximum of local electric field enhancement for the mentioned condition reduces significantly from 97 kV/mm, 142% enhancement, for EPR to 45 kV/mm, only 12.5% enhancement, for the Talc-filled nanodielectric.

Electric Field-Driven Air Purification Filter for High Efficiency Removal of PM2.5 and SO2: Local Electric Field Induction and External Electric Field Enhancement

Removal rate and durability are the two most important parameters of an ideal air purification filter to remove inhalable particles and toxic gases. Here, based on the interaction of a local electric field and an external electric field, a novel coaxial core–shell CuO@NH2-MIL-53(Al) nanowire array was synthesized on a rigid copper net, which was used to remove PM2.5 and SO2 simultaneously. The removal rates of PM2.5 by the filter with and without an external electric field can reach 98.72% and 44.41%, respectively, and the adsorption capacity of SO2 can reach 4.87 mol/m2. After repeated filtration and cleaning for 10 cycles, the air pollution removal efficiency can be kept almost stable.

Dopamine-mediated self-assembled anisotropic Au nanoworms conjugated with MoS2 nanosheets for SERS-based sensing

Surface-enhanced Raman scattering (SERS) utilizing plasmonic metals coupled with transition metal dichalcogenide (TMD) has received increasing attention in bio-applications due to the synergistically enhanced detection sensitivity. However, there have been several issues to be addressed such as strong SERS background signals and low Raman intensities of analytes. In this study, we report a novel approach for high SERS performance based on anisotropic hybrid plasmonic nanostructures of gold nanoworms (Au NWs) conjugated with 2D Molybdenum disulfide (MoS2) nanosheets. To significantly enhance the SERS enhancement factor (EF), we optimized the gap between Au NWs and MoS2 to ~2 nm by controlling the thickness of polydopamine (PDA). Thus, giant localized electric field enhancement and synergistic coupling effect occurred in the hybrid plasmonic nanostructures, generating abundant hot spots. Consequently, SERS EF of the order of ~107 was achieved, which was 104 times higher than that of colloidal Au nanoparticles. Further, we showcase that our AuNW@MoS2 can detect the 10−10 M level thiram, a typical pesticide, under soil-pollutant muddy condition, evidencing the powerful multimodal sensory platform of our hybrid substrates. This work provides new insight into the rational design of plasmon-coupled 2D nanohybrids for high-performance SERS substrates with a premise for the practical and viable biosensing applications.

Frequency-Dependent Synapse Weight Tuning in 1S1R with a Short-Term Plasticity TiOx-Based Exponential Selector.

Short-term plasticity (STP) is an important synaptic characteristic in the hardware implementation of artificial neural networks (ANN), as it enables the temporal information processing (TIP) capability. However, the STP feature is rather challenging to reproduce from a single nonvolatile resistive random-access memory (RRAM) element, as it requires a certain degree of volatility. In this work, a Pt/TiOx/Pt exponential selector is introduced not only to suppress the sneak current but also to enable the TIP feature in a one selector-one RRAM (1S1R) synaptic device. Our measurements reveal that the exponential selector exhibits the STP characteristic, while a Pt/HfOx/Ti RRAM enables the long-term memory capability of the synapse. Thereafter, we experimentally demonstrated pulse frequency-dependent multilevel switching in the 1S1R device, exhibiting the TIP capability of the developed 1S1R synapse. The observed STP of the selector is strongly influenced by the bottom metal-oxide interface, in which Ar plasma treatment on the bottom Pt electrode resulted in the annihilation of the STP feature in the selector. A mechanism is thus proposed to explain the observed STP, using the local electric field enhancement induced at the metal-oxide interface coupled with the drift-diffusion model of mobile O2- and Ti3+ ions. This work therefore provides a reliable means of producing the STP feature in a 1S1R device, which demonstrates the TIP capability sought after in hardware-based ANN.

Self-assembly of smooth muscle myosin filaments: adaptation of filament length by telokin and Mg·ATP.

The contractile apparatus of smooth muscle is malleable to accommodate stress and strain exerted on the muscle cell and to maintain optimal contractility. Structural lability of smooth muscle myosin filaments is believed to play an important role in the cell's malleability. However, the mechanism and regulation of myosin filament formation is still poorly understood. In the present in vitro study, using a static light scattering method, length distributions were obtained from suspensions of short myosin filaments (SFs) formed by rapid dilution or long ones (LFs) formed by slow dialysis. The distributions indicated the presence of dynamic equilibriums between soluble myosin and the SFs; i.e.: trimers, hexamers and mini filaments, covering the range up to 0.75µm. The LFs were more stable, exhibiting favorable sizes at about 1.25, 2.4 and 4.5µm. More distinct distributions were obtained from filaments adsorbed to a glass surface, by evanescent wave scattering and local electric field enhancement. Addition of telokin (TL) to the suspensions of unphosphorylated SFs resulted in widening of the soluble range, while in the case of the LFs this shift was larger, and accompanied by reduced contribution of the soluble myosin species. Such changes were largely absent in the case of phosphorylated myosin. In contrast, the presence of Mg·ATP resulted in elongation of the filaments and clear separation of filaments from soluble myosin species. Thus, TL and Mg·ATP appeared to modify the distribution of myosin filament lengths, i.e., increasing the lengths in preparing for phosphorylation, or reducing it to aid dephosphorylation.

Efficient Excitation and Tuning of Multi-Fano Resonances with High Q-Factor in All-Dielectric Metasurfaces.

Exciting Fano resonance can improve the quality factor (Q-factor) and enhance the light energy utilization rate of optical devices. However, due to the large inherent loss of metals and the limitation of phase matching, traditional optical devices based on surface plasmon resonance cannot obtain a larger Q-factor. In this study, a silicon square-hole nano disk (SHND) array device is proposed and studied numerically. The results show that, by breaking the symmetry of the SHND structure and transforming an ideal bound state in the continuum (BIC) with an infinite Q-factor into a quasi-BIC with a finite Q-factor, three Fano resonances can be realized. The calculation results also show that the three Fano resonances with narrow linewidth can produce significant local electric and magnetic field enhancements: the highest Q-factor value reaches 35,837, and the modulation depth of those Fano resonances can reach almost 100%. Considering these properties, the SHND structure realizes multi-Fano resonances with a high Q-factor, narrow line width, large modulation depth and high near-field enhancement, which could provide a new method for applications such as multi-wavelength communications, lasing, and nonlinear optical devices.

Flexible nanoparticle-on-mirror strategy for ultrasensitive molecule detection by directionally coupling surface plasmon polaritons

Applying local surface plasmon resonance (LSPR) to a nanoparticle-on-mirror (NPOM) configuration for realizing highly sensitive molecule detection using surface-enhanced Raman scattering (SERS) typically enhances the Raman signal by 106–1010 under limiting conditions. We propose a special nanoparticle-fishbone structure (NPFS) system, which incorporates the surfaceplasmon polariton (SPP) coupler of the fishbone structure into the NPOM configuration, to achieve ultra-high local electric field enhancement by plasmon hybridizing the LSPR mode of metallic nanoparticles and the SPP mode of the fishbone array structure. During the numerical simulation, the NPFS system exhibited a SERS enhancement factor of 1011, which is two orders of magnitude higher than that of the NPOM system; the SERS experimental results further demonstrated its outstanding performance. These findings indicate that introducing a well-designed SPP coupler on the metallic film can further improve the advantages of various NPOM configurations. The proposed approach can open new horizons for designing nanoscale photonic devices for ultrasensitive molecule detection.

Active metal–graphene hybrid terahertz surface plasmon polaritons

Abstract Surface plasmon polaritons (SPPs) are propagating electromagnetic surface waves with local electric field enhancement and nondiffraction limit at optical frequencies. At terahertz (THz) frequencies, a metal line with periodic grooves can mimic the optical SPPs with the same high cut-off response, which is referred to as designer SPPs. Here, by replacing metal grooves with graphene sheets, a novel active metal–graphene hybrid SPP device achieves significant phase modulation. Theoretically, the dispersion curves of THz SPPs are determined by the dimensions and periodicity of the grooves. Changing the chemical potential of graphene sweeps the effective groove depth, which correspondingly shifts the SPP cut-off frequency and modulates the slow-wave phase. A prototype device is fabricated and characterized under varying bias applied for graphene. The experiment demonstrates that the cut-off frequency red shifts from 200 to 177 GHz, and the phase variation is as large as 112° at 195 GHz under a low bias from −0.5 to 0.5 V. Simultaneously, the SPP transmittance is modulated by a factor of more than 3 dB from 140 to 177 GHz due to the graphene absorption. The proposed structure reveals a novel approach to study the nonreciprocal and topological SPPs with active modulation in the THz range.

Dimensional Design for Surface-Enhanced Raman Spectroscopy.

Surface-enhanced Raman spectroscopy (SERS) is a vibrational spectroscopy technique that enables specific identification of target analytes with sensitivity down to the single-molecule level by harnessing metal nanoparticles and nanostructures. Excitation of localized surface plasmon resonance of a nanostructured surface and the associated huge local electric field enhancement lie at the heart of SERS, and things will become better if strong chemical enhancement is also available simultaneously. Thus, the precise control of surface characteristics of enhancing substrates plays a key role in broadening the scope of SERS for scientific purposes and developing SERS into a routine analytical tool. In this review, the development of SERS substrates is outlined with some milestones in the nearly half-century history of SERS. In particular, these substrates are classified into zero-dimensional, one-dimensional, two-dimensional, and three-dimensional substrates according to their geometric dimension. We show that, in each category of SERS substrates, design upon the geometric and composite configuration can be made to achieve an optimized enhancement factor for the Raman signal. We also show that the temporal dimension can be incorporated into SERS by applying femtosecond pulse laser technology, so that the SERS technique can be used not only to identify the chemical structure of molecules but also to uncover the ultrafast dynamics of molecular structural changes. By adopting SERS substrates with the power of four-dimensional spatiotemporal control and design, the ultimate goal of probing the single-molecule chemical structural changes in the femtosecond time scale, watching the chemical reactions in four dimensions, and visualizing the elementary reaction steps in chemistry might be realized in the near future.

Electric Field Enhancement Effect of Aluminum Grating With Nanosecond Pulsed Laser Irradiation

Aluminum grating has wide applications in laser systems and photoelectric equipment. Research on the laser damage characteristics of aluminum grating has guiding significance and application value for improving the laser damage resistance. The aim of this study is to investigate the characteristics of damage induced by nanosecond pulsed lasers on the aluminum grating. To better understand the laser damage characteristics of aluminum grating, herein, Maxwell’s equations were numerically solved according to the finite difference time-domain method, and the electric field model of 1,064 nm Gaussian laser damage aluminum grating was established. The simulation results showed that the light field is modulated by the grating; furthermore, the maximum value of the electric field occurred at the ridge of the grating when the laser is irradiated vertically. Analysis suggested that the electric field distribution is in accordance with the laser energy distribution, and the distribution region of the maximum electric field is a vulnerable location. To further verify the local electric field enhancement effect, based on the 1-on-1 laser damage measurement method, an experimental study of the nanosecond laser (@1,064 nm, 6.5 ns) damage to the aluminum grating was carried out. Moreover, the damage morphology was analyzed using a scanning electron microscope (SEM), and the simulation results showed good agreement with the experimental results.

Excitation wavelength-dependent photoluminescence decay of single quantum dots near plasmonic gold nanoparticles.

Changing the excitation wavelength is a simple but effective strategy to modulate the photophysical cha racteristics of colloidal quantum dots (QDs) near plasmonic nanostructures. It has been observed that the photoluminescence (PL) decay of QDs near plasmonic nanostructures differs when the excitation wavelength is varied, but the exact mechanism is still unclear today. Here, we studied the excitation wavelength dependence of the PL decay of CdSe/CdS core/shell QDs near plasmonic gold nanoparticles at the single QD level. With the aid of statistical science, we demonstrated that the PL decay of a single QD near gold nanoparticles is generally faster when the QD is excited spectrally close to the localized surface plasmon resonance of gold nanoparticles. This excitation wavelength dependence is mainly caused by the varied proportion of photons coming from biexciton emission, which is the result of different local electric field enhancement by gold nanoparticles upon excitation.

Standardizing conductor surface roughness for DC gas-insulated equipment-a careful analysis on local morphology

The gas ionization inside the gas-insulated electric power equipment increases the gas conduction current and introduces charges to the spacer surface, which results in local electric field enhancement and potentially triggers spacer flashover. In this letter, we demonstrated that micro protrusions in a finely finished conductor surface plays a significant role in inducing local gas ionization, resulting in an increased local gas conduction current. A gas conduction current using conductors with higher surface kurtosis S ku was found approximately 10 times higher than that using an electrode with a similar S a but a different machining procedure. The piecewise nonlinear relation between the maximum local field strength and the average roughness was calculated over different kurtosis ranges. A conductor surface roughness evaluation method which combines average height of peak S pa with extreme probability of deviation from mean height of peak S pku was put forward.