Electric Field Enhancement Factor Research Articles

Silicon nitride (Si3N4) leads to enhanced performance of silica-silver based plasmonic sensor for colorectal cancer detection under optimum radiation damping

Silicon Nitride (Si3N4) possesses large refractive index and transparent behaviour in a broad spectral range from ultraviolet to infrared. These properties of Si3N4 facilitate an efficient light-matter interaction leading to enhanced light confinement. In this work, we have investigated Si3N4-based plasmonic sensor for pathogenic colorectal tissues detection at a wavelength of 1000 nm. The sensor structure consists of fused silica prism and Ag–Si3N4 heterojunction. The figure-of-merit (FOM) of the sensor is optimized by judiciously coordinating the thickness of Ag layer (dM) and Si3N4 layer (dA) under optimum radiation damping (ORD). An optimized FOM as high as 6011 RIU−1 (at dM = 47.3 nm) has been achieved corresponding to dA = 8.6 nm under ORD. At ORD, the corresponding power loss ratio (PLR) is as high as 2.773, and the normalized electric field enhancement factor (FEF) is about 1.06. The magnitude of combined performance factor (CPF), which is the product of FOM, PLR and FEF, of the proposed sensor is as large as 17668.61 RIU−1. The proposed application of Si3N4 in plasmonic sensor in combination with ORD condition leads to substantially enhanced sensing performance and has been explored for the first time to the best of our knowledge.

Optical gain-tunable wideband metasurface device with high electric field enhancement

The metasurface devices with high electric field enhancement factor values have been widely discussed in recent years. However, these types of metasurface devices usually have very strict minimum spacing limitations, which seriously affect the difficulty of device fabrication and the reproducibility of experiments. In this work, we proposed a metasurface based on a metal-insulator-metal configuration that significantly enhances the electric field enhancement factor of the surface plasmon resonance structure on the upper surface by utilizing a bottom metal-SiO2 spiral lens. The results indicated that the gain bandwidth of this proposed device is more than 100 nm with a maximum electric field gain of 377 within the orange-red wavelength range. Furthermore, the electric field enhancement factor can be adjusted based on the number of rings in the spiral lens. Moreover, the minimum fabrication scale of this device is 130 nm, which facilitates easier fabrication and experimental replication. The focal pattern of the electric field generated inside the spiral lens with different polarization states of light was also examined.

Taking advantage of an axisymmetric plasmonic structure and grooves to nanofocus and ultraenhance a radially polarized electric field

This study investigates the enhancement and nanofocusing of a radially polarized electric field by a conical plasmonic structure (CPS). The CPS is a dielectric cone with nanometer metal cladding on a dielectric substrate. Concentric circular slanted grooves are etched on the surface of the dielectric substrate. These grooves converge the incident field on the structure. Angled periodic gratings are engraved on the CPS metal surface near the tip, creating a plasmonic momentum and contributing to the field enhancement above the apex. The symmetry of the incident radially polarized light and the structure significantly boosts nanofocusing and field enhancement. The optimal width of the nanofocusing and the electric field enhancement factor obtained are approximately 9 nm and 30000, respectively. Because of its impressive effects, this scheme is a valuable tool for plasmonic, optics, and laser applications.

Optical anapole modes in hybrid metal–dielectric nanoantenna for near-field enhancement and optical sensing

Metal–dielectric nanostructures in the optical anapole modes are essential for light–matter interactions due to the low material loss and high near-field enhancement. Herein, a hybrid metal–dielectric nanoantenna composed of six wedge-shaped gold (Au) nanoblocks as well as silica (SiO2) and silicon (Si) nanodiscs is designed and analyzed by the finite element method (FEM). The nanoantenna exhibits flexibility in excitation and manipulation of the anapole mode through the strong coupling between the metal and dielectrics, consequently improving the near-field enhancement at the gap. By systematically optimizing the structural parameters, the electric field enhancement factors at wavelengths corresponding to the anapole modes (AM1 and AM2) can be increased to 518 and 1482, respectively. Moreover, the nanoantenna delivers great performance in optical sensing such as a sensitivity of 550 nm/RIU. The results provide guidance and insights into enhancing the coupling between metals and dielectrics for applications such as surface-enhanced Raman scattering and optical sensing.

Dimensional analysis on microscale gas breakdown with electric field nonuniformity and positive space charge effects

A dimensional method was employed to evaluate the microscale gas breakdown characteristics at atmospheric pressure, resulting in a universal breakdown curve applicable to different types of gases (e.g., Ar, Xe, Ne, and N2). As the gap distance decreases, the breakdown mode transitions from ion-induced secondary electron emission to the field emission regime. In the field emission regime, the positive space charge effect becomes more significant. We discovered that incorporating the positive space charge effect in the field emission regime can be achieved by modifying the local electric field enhancement factor β. Consequently, we propose an effective electric field enhancement factor, βeff, which scales linearly with β, to accurately reproduce the breakdown curve while considering the positive space charge effect. This proposed approach significantly simplifies the numerical model. Additionally, we examined the effects of gas pressure, gap distance, cathode properties (e.g., work function and secondary electron emission coefficient), and electric field nonuniformity.

Enhanced upconversion luminescence using long-range surface plasmon resonance mode with prism coupler

In the study, we present the significant enhancement of the upconversion luminescence by taking advantage of long-range surface plasmon resonance mode. Compared with the reflection enhanced upconversion luminescence of Ag film, the intensity of upconversion luminescence enhanced by long-range surface plasmon resonance mode is improved 100 times. Additionally, the finite-difference time-domain simulation indicates that the incident light energy can concentrate in the upconversion nanoparticles doped dielectric layer at the long-range surface plasmon resonance mode, which the maximum electric field enhancement factor |E|2/|E0|2 can reach to 58. The experimental result shows that the upconversion luminescence enhancement is related to the thickness of doped Polymethylmethacrylate (PMMA) layer. Furthermore, due to the excited upconversion luminescence having high directionality, it is shown that the strong upconversion luminescence could be received at the specific angle.

FEM investigation of Cu@SiO2 core-shell nanoparticle for a sensitive and low-cost SERS and SEF substrate

We theoretically investigate the plasmon coupling properties of Cu@SiO2 core-shell system that supports the measurement of surface enhanced Raman spectroscopy (SERS) and surface enhanced fluorescence (SEF) technology. The roles of Cu core and SiO2 shell in tuning LSPR have been quantitatively discussed by calculating the localized electric field enhancement factor (EF), fluorescent quantum yield, SERS and SEF EF in the nanogap based on finite element simulations. In this work, we demonstrate that the SERS and SEF effect strongly depend on the core size, shell thickness and dimer distance. The larger size of Cu core, ultrathin thickness of SiO2 shell and shorter dimer distance could be considered as the ideal substrate. Meanwhile, the strong localized excitation enhancement is a vital contribution to fluorescence spectral. By comparison, it is found that the enhancement effect of the Cu, Au and Ag cores are very close in order of magnitude in the red and near infrared regions, and thus the low-cost Cu core may act as an active substrate in these regions. At the excitation wavelength of 630 nm, the optimized core size of 60 nm and shell thickness of 1 nm provide the maximum Raman and fluorescence EF as high as 9 and 4 orders of magnitude. Our theoretical results not only help understanding the underlying enhancement mechanism for the core-shell SERS and SEF effect, but also contribute to develop the low-cost and sensitive detection technology.

Mechanism analysis of field electron emission of titanium

Field electron emission (FEE) is generally considered to be closely correlated with radio frequency (RF) breakdown in accelerating structures and high-power microwave (HPM) devices. In this study, the field emission characteristics of titanium are investigated by using a field emission test system. With the increase of the number of field emission tests and stability tests, the repeatability of the field emission characteristic curve of titanium tends to be better, and the amplitude of the current oscillation in the stability tests gradually decreases, indicating that the field emission performance of titanium gradually becomes stable. Subsequently, the field emission characteristic curve of titanium is analyzed by adopting the field emission theory of metal microprotrusions. Combined with the analysis of the electric field enhancement effects caused by the surface morphology, the dominant effect of the metal microprotrusions on the FEE of titanium is excluded from the two aspects of the electric field enhancement factor and local maximum emission current density. At last, the field emission theory of dielectric micropoints is introduced to analyze the field emission characteristics of titanium. The electric field enhancement factor of 102 ∼ 103 are explained theoretically. Simultaneously, the reasonable effective emission area and local emission current density are given, which can better explain the field emission phenomena of titanium, such as the sharp decrease in emission current and repeatability of the field emission curve. Hence, it is revealed that the key factor that dominates the FEE of titanium is the dielectric impurities on the surface, rather than the metal microprotrusions.

Simulation and Optimization of CNTs Cold Cathode Emission Grid Structure

Carbon nanotubes (CNTs) show significant advantages in the development of cold cathode X-ray tubes due to their excellent field emission performance; however, there are still some problems, such as short lifetime and the low emission current of large-area CNTs. In this paper, a front-grid carbon nanotube array model was established, and the electric field intensity near the tip of the CNTs' electric field enhancement factor was analytically calculated. A simulation model of a CNT three-dimensional field emission electron gun was established by using computer simulation technology (CST). The effects of grid wire diameter, grid aperture shape, and the distribution of grid projection on the cathode surface on the cathode current, anode current, and electron transmission efficiency were analyzed. The aperture ratio was used to evaluate the grid performance, and the simulation results show that the ideal aperture ratio should be between 65% and 85%. A grid structure combining a coarse grid and a fine grid was designed, which can make the electric field intensity around the grid evenly distributed, and effectively increased the cathode emission current by 24.2% compared with the structure without the fine grid. The effect of grid aperture ratio on the electron transmission efficiency was tested. The simulation results and optimized structure can provide a reference for the grid design of cold cathode emission X-ray tubes.

Influence of the electron field emission on the magnetized direct current high-pressure discharge

The influence of electron field emission on the sub-normal mode of a magnetized direct current high-pressure helium discharge is analyzed using the two-dimensional axisymmetric fluid model. It is observed that in spite of accounting for a more intense electron emission mechanism, discharge still operates in the sub-normal mode. However, the field emission driven discharge is characterized by a smaller discharge voltage and a larger discharge current. For large values of the electric field enhancement factor, the discharge voltage can be as low as ∼40 V, and the discharge current is a few amperes. It is also seen that for large values of the field enhancement factor and small values of the ballast resistor, rather dense plasma (density ∼ 1017 m−3) can be generated on the nanosecond time scale.

Tunable light trapping in the graphene metasurface.

Graphene metasurfaces based on surface plasmon resonance can greatly enhance the interaction between light and matter at the nanoscale. At present, the resonance of graphene metasurfaces is widely used to enhance the absorption of atomic layer graphene, but little work has focused on the light field trapping capabilities it brings. In this paper, we numerically study the light trapping and manipulation of an asymmetric graphene metasurface. The designed device supports two resonant modes, and the multipole decomposition confirms that the electric dipole response dominates them. The calculated average electric field enhancement factor (EF) can reach 1206 and 1779, respectively. The near-field distribution indicates that the electric field is mainly localized in the graphene nanodisks. When the Fermi energy changes, the intensity and peak position of EF can be effectively regulated. In addition, when the polarization of the incident light is adjusted, the light field capture of the two modes is independently regulated. These results reveal that the graphene metasurface has significant light field capture and regulation ability, which provides a new idea for the realization of active regulation of high-performance low-dimensional optical devices.

Mid-infrared chalcogenide slot waveguide plasmonic resonator sensor embedded with Au nanorods for surface-enhanced infrared absorption spectroscopy

The problem of a traditional waveguide plasmonic resonator sensor is that part of the near-field intensity enhanced area is confined in the waveguide dielectric layer, which decreases the interaction effect between light and analyte. In order to solve this problem, a novel mid-infrared (MIR) chalcogenide (ChG) slot waveguide plasmonic resonator (SWGPR) sensor embedded with Au nanorods was proposed, where Au nanorods were used as antenna for enhancing mode coupling with the waveguide through resonance at the absorption wavelength of the analyte. The antenna parameters were optimized to make the resonance wavelength align with the absorption wavelength of the analyte. The proposed waveguide structure provides a sufficient sensing area and increases the electric field enhancement factor to > 6400. Polymethyl methacrylate (PMMA) and styrene were adopted as the analyte for sensing performance evaluation. The normalized absorption reaches 23.31 when the maximum extinction coefficient of PMMA is 0.08, which is at least 7 times higher than other silicon-on-insulator (SOI) waveguide plasmonic resonator sensors. The proposed waveguide structure provides a new idea for the design of other waveguide plasmonic resonator sensors with high sensing performance and has the potential for biochemical sensing.

Emission Properties and Dielectric Strength of a Nanostructured Tungsten Field-Emissive Cathode

Research of the tungsten “fuzz” emission properties and dielectric strength was carried out. A “fuzzy” sample was made through He+ ion exposure of an initially polished tungsten surface using an inductively coupled plasma (ICP) facility. The eventual He+ ion fluence was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 1.7\times 10^{25}\,\,\text{m}^{-2}$ </tex-math></inline-formula> . The induced nanostructured layer thickness was estimated to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 1~\mu \text{m}$ </tex-math></inline-formula> . The measurements were performed with an automated experimental setup developed. The setup was operated under the control of the programmable DAC/ADC module “LCard E20-10.” As a result, the untypical behavior of a nanostructured cathode in comparison with an ordinary field emissive cathode was registered. Instability of the W “fuzz” emission properties was demonstrated. Typical values of the electric field enhancement factor were found to be in the range of ~120–200 both before a single breakdown and after it. These values are in agreement with the estimations of the enhancement factor performed with taking into account the geometry of protrude cathode structures. Stabilization of the emission properties after the breakdown was observed. The conditioning effect of the nanostructured cathode was found to take place after approximately five breakdowns. After conditioning, an asymptotic value of a breakdown electric field strength was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 8.5\times 10^{7}$ </tex-math></inline-formula> V/m, which is in agreement with the one for an ordinary tungsten cathode. The conditioning effect and the emission current stabilization are believed to be due to the destruction of the nanostructure under the impact of the breakdowns.

Effect of Coaxial Electrode Geometry on the Electric Field Enhancement Factor for a High Voltage Vacuum Gap

We present an experimental analysis of the change in the electric field enhancement factor with varying gap size and penetration depth (P.D) of cathode into anode for a coaxial vacuum gap, diagnosed using Fowler–Nordheim analysis and optical imaging via scanning electron microscope (SEM) and time integrated Digital single lens reflex camera (DSLR). Data were collected on the Coaxial Gap Breakdown Machine (240 A, 25 kV, 150 ns, ~0.1 Hz). Experiments using five different gap sizes at nine different P.Ds are compared over runs comprising 50 shots for each case. The results show a strong link between enhancement factor and gap size, with P.D and surface topology. For large gap sizes, 150, 330, and 700 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \mathrm {m}$ </tex-math></inline-formula> , the average enhancement factor value increases with increasing P.D. For smaller gap sizes, 50 and 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \mathrm {m}$ </tex-math></inline-formula> , the average enhancement factor decreases with P.D. SEM imaging before and after plasma formation for each gap size allows for quantifying surface finish, microprotrusion growth, average blast diameter, and an estimation of the surface area breakdowns occupy. Time integrated DSLR imaging analysis of the gap at each shot allows for a determination of the distribution of breakdowns about the circumference of the gap for each case tested. The Fowler–Nordheim analysis allows for a quantitative analysis of the surface roughness of all gap sizes tested. Results show that for large gap sizes, the gap geometry and increasing area of breakdown is the main cause for increasing average enhancement factor. For small gap sizes, the dominant driving factor for small average enhancement factors—that subsequently decrease with P.D—is significant changes in surface topology due to an increased number of breakdowns.

Electric Field Sensor Based on High Q Fano Resonance of Nano-Patterned Electro-Optic Materials

This paper presents theoretical studies of Fano resonance based electric-field (E-field) sensors. E-field sensor based on two electro-optical (EO) materials i.e., barium titanate (BaTiO3, BTO) nanoparticles and relaxor ferroelectric material Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) combined with nanostructure are studied. As for the BTO based E-field sensor, a configuration of filling the BTO nanoparticles into a nano-patterned thin film silicon is proposed. The achieved resonance quality factor (Q) is 11,855 and a resonance induced electric field enhancement factor is of around 105. As for the design of PMN-PT based E-field sensor, a configuration by combining two square lattice air holes in PMN-PT thin film but with one offsetting hole left is chosen. The achieved resonance Q is of 9,273 and an electric field enhancement factor is of around 96. The resonance wavelength shift sensitivity of PMN-PT nanostructured can reach up to 4.768 pm/(V/m), while the BTO based nanostructure has a sensitivity of 0.1213 pm/(V/m). If a spectrum analyzer with 0.1 pm resolution is considered, then the minimum detection of the electric field Emin is 20 mV/m and 0.82 V/m for PMN-PT and BTO based nanostructures, respectively. The nano-patterned E-field sensor studied here are all dielectric, it has therefore the advantage of large measurement bandwidth, high measurement fidelity, high spatial resolution and high sensitivity.

Modeling of High-Performance SPR Refractive Index Sensor Employing Novel 2D Materials for Detection of Malaria Pathogens.

The present work exhibits a novel design of surface plasmon resonance (SPR) biosensor, which comprises CaF2 prism, TiO2, metal (Ag/Au), PtSe2, 2D materials (graphene/transition metal dichalcogenides (MoS2/WS2)) and sensing medium, for point-of-care detection of various stages of malaria diseases. The transfer matrix method (TMM) is employed to examine the angular reflectivity of the proposed structure after judiciously optimizing the layer thicknesses and layer numbers. Phase interrogation technique is utilised to validate the position of occurrence of resonance angles. Additionally, the proposed SPR structure is designed using COMSOL Multiphysics, to assay the electric field intensity and electric field enhancement factor near the edge of 2D material-sensing layer interface. Simulation upshots revealed that the use of new class of 2D materials catapult the sensor performance to a new height compared to the traditional SPR configuration. A maximum sensitivity of 240.10°/RIU, quality factor of 78.46 RIU-1 and detection accuracy of 1.99 is attained for Ag-based SPR configuration with bilayer of WS2. Sensing parameters are compared with previously reported works to prove the superiority of the present research. Moreover, the real-time and label-free detection of malaria diseases makes the suggested sensor worth to fabricate as a SPR chip with the recent nanofabrication technologies.

Role of Void Orientation and Shape on The Electric Field Distortion in High Voltage Cable

One of the problems that face the use of XLPE insulators is the appearance of defects. These defects appear during the manufacturing processes of the insulator, and one of these defects is air cavities or voids. The defects presence within the insulators of high voltage cables affects the distribution of the electric field within the cable layers. The distortion of the electric field due to the presence of air cavities is the main reason for the treeing appearance inside the insulator, which eventually leads to the emergence of partial discharges that reduce the life of the cable. In this study, the effect of the presence of an air cavity inside an XLPE insulator was studied by changing the dimensions of the cavity, that is, changing the ratio of the dimensions of the cavity parallel to the electric field and vertical to it and the effect of this on the value of the electric field in the center of the cavity. It was noted that the electric field in the cavity is higher than in the external electric field. The increase in the field in the cavity center does not depend on the cavity size, but rather on the ratio of the cavity dimensions parallel to the electric field to the vertical to it. The electric field enhancement factor was calculated based on the simulation results, which showed a reasonable agreement with the theoretical values.

Investigation on Electrical and Thermal Performance of Glass Fiber Reinforced Epoxy–MgO Nanocomposites

Epoxy nanocomposites reinforced with glass fiber, have been prepared with various weight percentages (1, 3, and 5 wt.%) of MgO nanofillers to improve their electrical and thermal performance. An increase in MgO nanofiller content up to 3 wt.% tends to enhance surface discharge and corona inception voltages measured using fluorescence and UHF methods, under both AC and DC voltage profiles. Reduced initial surface potential along with increased decay rate is observed after inclusion of MgO nanoparticles. Before and after the polarity reversal phenomena, heterocharge formation is observed in the bulk of test specimens. In comparison with other test samples, the 3 wt.% sample had reflected lower electric field enhancement factor. After MgO filler was added to glass fiber reinforced polymer (GFRP) composites, the coefficient of thermal expansion (CTE) has reduced, with the 3 wt.% specimen having the lowest CTE value. TGA measurements revealed an improvement in thermal stability of the GFRP nanocomposites up on the inclusion of MgO nanofillers. Overall, the GFRP nanocomposite sample filled with 3 wt.% nano-MgO outperformed the other test samples in terms of electrical and thermal performance.

Investigation of changes in field electron emission characteristics of industrial fine-grained graphite when operated in an argon atmosphere up to 10–2 Pa

Studying of field electron emission properties of carbon cathodes operating under technical vacuum conditions is a promising scientific field. Massive cathode made of commercial fine-grained graphite of MG (Russian abbreviation) grade is being investigated. Experiments on obtaining current-voltage characteristics and long-term testing are being carried out. The emitter made of fine-grained graphite demonstrates good emission properties under technical vacuum conditions. Carbon cathode is capable of operating at pressures up to 2×10–2 Pa. Increased pressure in the vacuum chamber leads to deterioration of cathode emission properties. Electric field enhancement factors were calculated for all stages of studies. Analysis of experimental data demonstrates decrease in enhancement factor due to ion bombardment of cathode surface during exploitation. This results in higher electric field for operation of investigated graphite cold cathodes.

Decay Rates of Plasmonic Elliptical Nanostructures via Effective Medium Theory.

This paper investigates the spontaneous decay rate of elliptical plasmonic nanostructures. The refractive index was analyzed using the effective medium theory (EMT). Then, the polarizability, spontaneous radiative, non-radiative decay rate, and electric field enhancement factor were characterized for the targeted elliptical nanostructures at different aspect ratios. All of the optical analyses were analyzed at different distances between the excited fluorescent coupled atom and the plasmonic nanostructure (down to 100 nm). This work is promising in selecting the optimum elliptical nanostructure according to the required decay rates for optical conversion efficiency control in energy harvesting for solar cells and optical sensing applications.