Surface Electric Field Research Articles

Analysis On Surface Enhanced Infrared Absorption Characteristics of Multi-Resonance Optical Antenna

Infrared spectroscopy is an important detection technique. Because each functional group of different molecules has a fixed vibration mode, the molecules can be detected by infrared spectroscopy in the mid-infrared region. Metal nano-optical antennas can be used to construct high-sensitive sensors to detect different molecules. A structure with multi-band plasmon resonance is designed, which is composed of one gold nanorod and two symmetrical opening frames in order to detect the different target molecules simultaneously. In this study, the surface electric field distribution of the optical antennas is simulated by using finite difference time domain method (FDTD). In addition, the effects of the optical antenna structure on the surface enhanced infrared absorption (SEIRA) characteristics of the antenna are investigated. The different modes can be coupled, which brings new plasmon resonance peaks. It has been analyzed by the localized surface plasmons theory. These results provide a theoretical reference for the application of the new infrared sensing technology and shed light on guiding further exploration of infrared detectors.

Simulation studies of secondary electron yield with electron transport from Cu (110) surfaces containing C2, N2, CO2, or NO2 adsorbates

Secondary electron yields of (110) copper surfaces, covered with either carbon, nitrogen, or their dioxides, have been studied by employing combined first principles methods for the material properties and Monte Carlo simulations for electron transport. Furthermore, by studying electron transport inside the Cu system and modeling the power loss taking account of the inelastic electron scattering within the material, changes in the thermal energy of the system have been modeled. The physical reasons behind the increase and decrease of the yield for each system from an electronic perspective are discussed. In agreement with results observed in studies of secondary electron emission, it is shown that the formation of C2 and N2 monolayers reduce the secondary electron yields, while CO2 and NO2 increase the yield significantly. It is demonstrated that in the case of C2 and N2 formation, changes in the surface electronic barrier reduce the probability of electron escape from the Cu surface, resulting in lower secondary electron emission. Formation of CO2 and NO2, on the other hand, reduce the electronic barrier effects. In addition, due to weak bonding of the CO2 layer with the Cu host, the surface provides an additional source of secondary electrons resulting in higher electronic emission yield. Moreover, the NO2 adsorbate creates a surface electric field that changes the surface electron energy and increases the electron escape probability. Additionally, it is verified that thermal change in the system is negligible and so during secondary electron emission measurements, negligible (if any) surface adsorption or desorption could occur.

Voltage-Dependent FTIR and 2D Infrared Spectroscopies within the Electric Double Layer Using a Plasmonic and Conductive Electrode.

Strong electric fields exist between the electric double layer and charged surfaces. These fields impact molecular structures and chemistry at interfaces. We have developed a transparent electrode with infrared plasmonic enhancement sufficient to measure FTIR and two-dimensional infrared spectra at submonolayer coverages on the surface to which a voltage can be applied. Our device consists of an infrared transparent substrate, a 10-20 nm layer of conductive indium tin oxide (ITO), an electrically resistive layer of 3-5 nm Al2O3, and a 3 nm layer of nonconductive plasmonic gold. The materials and thicknesses are set to maximize the surface number density of the monolayer molecules, electrical conductivity, and plasmonic enhancement while minimizing background signals and avoiding Fano line shape distortions. The design was optimized by iteratively characterizing the material roughness and thickness with atomic force microscopy and electron microscopy and by monitoring the plasmon resonance enhancement with spectroscopy. The design is robust to repeated fabrication. This new electrode is tested on nitrile functional groups using a monolayer of 4-mercaptobenzonitrile as well as on CO and CC stretching modes using 4-mercaptobenzoic acid methyl ester. A voltage-dependent Stark shift is observed on both monolayers. We also observe that the transition dipole strength of the CN mode scales linearly with the applied voltage, providing a second way of measuring the surface electric field strength. We anticipate that this cell will enable many new voltage-dependent infrared experiments under applied voltages.

Chemical modification of the GaP(0 0 1) surface electric field with sulfide solutions

The surface electric field in GaP(001) passivated with aqueous and alcoholic sulfide solutions is studied by reflectance anisotropy spectroscopy using data on the surface chemical and electronic structure obtained by synchrotron-radiation X-ray photoelectron spectroscopy. Treatment of n-GaP(001) surface with a sulfide solution decreases the surface electric field depending on sulfide solution composition. In particular, passivation with the solution of ammonium sulfide in 2-propyl alcohol turns the total surface electric field almost to zero, while passivation with the aqueous ammonium sulfide solution reduces the surface electric field in a lesser extent. On the other hand, sulfide treatment of p-GaP(001) surface enhances the surface electric field dramatically and this enhancement is nearly independent of the sulfide solution composition. Such changes in the surface electric field can be related to the modification of the dipole associated with chemical bonds in the passivating layer.

Influence of substrate impurity concentration on sub-threshold swing of Si n-channel MOSFETs at cryogenic temperatures down to 4 K

The sub-threshold swing (SS) of Si n-MOSFETs is experimentally and systematically evaluated in a temperature range of 4–300 K with varying the substrate impurity concentration (N sub) from ~1016 to ~1018 cm−3, to obtain a physical understanding of SS at cryogenic temperatures. It is clarified that the temperature and drain current dependencies of SS in n-MOSFETs are well represented by a model composed of mobile tail states and localized interface states, irrespective of N sub. The densities of these states are found to increase with increasing N sub. A physical origin of band tail states is studied by experimentally examining the impact of substrate bias on these states, which can separate the effects of the N sub and the surface electric field. It has been clarified, as a result, that the band tail states can be explained by the impurity-induced model.

Effects of the electromagnetic power coupling on vacuum breakdown

Vacuum breakdown is a key factor limiting the performance of applications that utilize vacuum for insulation. The surface electric field has been regarded in previous studies as the only parameter that determines the occurrence of a vacuum breakdown, for a given surface condition. However, several recent works indicated that the ultimate limit for a vacuum breakdown also depends strongly on the electromagnetic power available in the system to be delivered at the breakdown site. In this work, we study this dependence both experimentally using a pulsed DC system and by numerical simulations using a particle-in-cell (PIC) model. By varying the circuit impedance which includes resistance and capacitance, we controllably limit the power coupled to the vacuum discharge gap. The experimental results show that the breakdown voltage increases with increasing impedance, i.e. with increasing circuit resistance and decreasing capacitance; The PIC results showed that a minimum current is required besides the critical voltage during the initiation of the breakdown plasma, and the breakdown voltage is defined by the circuit impedance and the critical power loaded to the gap just before the breakdown, which is in agreement with the experimental results.

Frequency Dependence of the Electric Field Grading of End-Winding of Generator Bars

To reduce the electric field stresses in the end-winding in hydropower generator bars, a field dependent grading tape is applied in the transition zone from outer corona protection (OCP) to bare insulation. The design is typically optimized for 50/60 Hz with both low heat generation and optimal electric field distribution. The introduction of power electronic converters (PECs) with high switching frequencies and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{d}{U}/\text{d}{t}$ </tex-math></inline-formula> for controlling the generators changes the optimal design requirements. This work investigated experimentally the effect of higher voltage-frequencies on the conductivity in three field grading tapes (FGTs) from the same manufacturer with different field grading properties. The experimentally determined material parameters were then applied as inputs to finite element method (FEM) models to evaluate the electric field distribution at different voltage-frequencies. Measurements showed that the dc conductivity was highly nonlinear and strongly dependent on the electric field. This strong nonlinearity decreased at low electric fields as the frequency increased. The ac conductivity had a transition from a strong nonlinear material at line frequency to a less nonlinear material at 10 kHz. Simulations of the surface electric field and temperature using the dc conductivity for different voltage frequencies showed minor differences from simulations using the apparent ac conductivity. This indicates that the low field conductivity is of minor importance as it varied by two decades between dc and 10 kHz without resulting in a significant difference in either electric field, or temperature. The measured and simulated surface temperature increased linearly with applied voltage frequency. The simulated surface electric field was well distributed at line frequency, whereas it was greatly enhanced above 1 kHz.

Study on Pseudospark Switch Triggered by 532-nm Focused Laser

The influence of laser energy, irradiation position, photoelectric material, and anode voltage on the trigger characteristics of a pseudospark switch triggered by a 532-nm nanosecond focused laser is studied. The parameters of the seed electrons induced by the interaction between the focused laser and metal are measured. It is found that the increase of laser energy and anode voltage can increase the current density of seed electrons, reduce the time of electrons diffusion to the cathode hole, and thus reduce the trigger delay. When the irradiation position is close to the cathode hole, the surface electric field is larger, which is conducive to achieving a smaller trigger delay and jitter under low laser energy. The seed electron current induced by the focused laser has two peaks. The first peak mainly corresponds to the thermal emission, with a short time delay and narrow pulsewidth, contributing to the trigger. The second peak mainly corresponds to the electrode surface ablation, with a long time delay and large pulsewidth, contributing little to the trigger. In this case, the electrode surface temperature is more important than the work function, so Cu has better electron emission characteristics than Mg. With the increase of laser energy, the number of electrons in high-energy components increases.

Electric field detection method of 500 kV porcelain deteriorated insulator based on Combination Neural Network

The operation state of insulators is closely related to the safety and reliability of the power network. Affected by the environment, the insulator strings will gradually age and become low-value or zero-value in insulators. Therefore, it is of great engineering significance to correctly and timely detect whether there are faults in insulators. It has a good engineering application prospect to evaluate the insulation condition of insulators by detecting the surface electric field value of insulators. In this paper, the external axial electric field value of the insulator skirt is obtained through finite element simulation, and the combined neural network model is used. Finally, the effectiveness of the model is verified by the measured data. The experimental results show that this method can effectively identify whether the insulator has deteriorated.

Temperature‐dependent adaptive conductivity coating for surface charge release and electric field control under electro‐thermal coupling field

AbstractSurface charge accumulation is the potential criminal for surface insulation failure on spacers under direct current (DC) voltages. The existence of thermal gradient posing the difficulty of surface charge regulation. This study proposes a temperature‐dependent adaptive conductivity coating technique for surppressing surface charge accumulation under electro‐thermal coupling field. A two‐dimensional axis‐symmetrical simulation model regrading surface charge computation is established. The effects of thermal gradients and coating conductivity on surface charge and electric field distribution are investigated. The results show that the thermal gradient increases the bulk conductive current, therefore aggravating surface charge accumulation. The effects of the coating condcutivity on surface charge and electric field contains three stages. The lower coating conductivity leads to aggravated homo‐polarity charge accumulation. By increasing the coating conductivity, the surface charge and electric field are significantly suppressed at the obtained optimal conductivity, where the bulk and surface conductive current reach a balance stage. Continuously increasing the coating conductivity results in aggravated hetero‐polarity charges. Besides, the increase of thermal gradient to an appropriate extent contributes to the further suppression of surface charge on coated spacers. It is hoped that this study could provide some references for designing highly reliable DC GIL under electro‐thermal coupling field.

A novel LDMOS with circular drift region for uniform electric field distribution

In this paper, a lateral double diffused MOS which features a circular drift region (Cir-LDMOS) is proposed and investigated by numerical simulation. The circular drift region in Cir-LDMOS introduces a curvature effect on the electric field, which can neutralize the effect of ionized dopants on electric field and optimize the electric field distribution. Our investigations prove that the Cir-LDMOS can achieve uniform electric field distribution when the drift region doping concentration (Ndrift) is appropriate designed to balance with the curvature effect of electric field. Moreover, it is found that the curvature effect of the electric field in Cir-LDMOS is proportional to the critical electric field (Ec) and is inversely proportional to the radius of curvature. Since the curvature effect of electric field is proportional to Ec, the Cir-LDMOS exhibits a larger Ndrift as well as better performance in the field of wide bandgap semiconductor materials. Our simulation results show that, for silicon carbide (SiC), the performance of Cir-LDMOS is better than that of LDMOS based on reduced surface electric field techniques and can reach the one-dimensional SiC limit. Therefore, this work revealed the affecting factors of curvature effect of electric field and proposed a promising LDMOS structure for wide bandgap semiconductor materials.

Electromagnetic design of the transition section between modules of a wakefield accelerator

The electromagnetic design of a transition section consisting of couplers for extracting the 180-GHz ${\mathrm{TM}}_{01}$ accelerating mode and 190-GHz ${\mathrm{HE}}_{11}$ dipole mode of a cylindrical corrugated waveguide used as a collinear wakefield accelerator is presented. Extraction of the high power accelerating mode reduces the power dissipation in the corrugated accelerating structure and allows the much weaker ${\mathrm{HE}}_{11}$ mode to be isolated and used to monitor the stability of the 10-nC electron drive bunch. The final design demonstrates wide bandwidth and high coupling efficiency of two couplers. The design was also optimized to have the surface electric and magnetic fields that do not exceed those in the corrugated waveguide. Finally, coupling between the drive electron bunch and the ${\mathrm{HE}}_{11}$ dipole mode in the corrugated waveguide is considered and the utility of the ${\mathrm{TE}}_{11}$ coupler for detecting the electron beam oscillations in the wakefield accelerator is demonstrated using a few representative examples of oscillations below and above a threshold of the beam breakup instability.

Running streams of a ferroelectric nematic liquid crystal on a lithium niobate surface

ABSTRACTSessile droplets of a ferroelectric nematic liquid crystalline material were exposed to surface electric fields produced by pyroelectric and photogalvanic (photovoltaic) effects in X-cut iron-doped lithium niobate crystals. The resulting dynamic processes were monitored by polarisation optical (video)microscopy (POM). During heating/cooling cycles, at first, the droplets change their shape from spherical to extended ellipsoidal. Then, they start to move rapidly along the surface electric field, i.e. along the crystal’s polar axis (c-axis). During this motion, several droplets merge into running streams (tendrils) extending towards the edges of the top surface area. Finally, practically all liquid crystalline material is transported from the top surface to the side surfaces of the crystal. At stabilised temperatures, laser illumination of the assembly causes dynamic processes that are localised to the illuminated area. Also, in this case, the LC droplets merge into several tendril-like formations that are preferentially oriented along the c-axis of the crystal. The pattern of tendrils fluctuates with time, but it persists as long as the illumination is present. In this case, the LC material is transported between the central and the edge regions of the illuminated area.

Single-event burnout hardening evaluation with current and electric field redistribution of high voltage LDMOS transistors based on TCAD Simulations

—A single-event burnout (SEB) hardened design based on high voltage lateral double-diffused metal-oxide-silicon (LDMOS) devices with an optimal partial buried oxide (BOX) layer and a N-buffer layer is firstly proposed in this paper. By analyzing the response of surface electric field and transient current, the optimal parameters of hardened layers are selected. Simulation results reveal that an optimal buffer layer can suppress the peak electric field from 4.5 MV/cm to 2 MV/cm, recreate the position of peak electric field and an optimal BOX layer can reconstruct the path of electron and hole currents, reducing the risk of parasitic bipolar-junction-transistor (BJT). By contrast, the SEB triggering voltage can be improved from 197 V to 396 V, with an increase of 100%. And the ratio of safe operating area (SOA) with SEB to breakdown voltage (BV) can be increased from 30% to 69%. In the case of heavy-ions with different energies, the SEB hardened LDMOS also has better performance than the conventional one.

Square grid pattern with direction-selective surface discharges in dielectric barrier discharge

A new phenomenon that a filament discharged only once instead of twice in a cycle of the applied voltage is observed in a square grid pattern in a dielectric barrier discharge (DBD) with a larger gas gap, which is named intermittent discharge. Its spatiotemporal dynamics and the formation mechanism are studied by the multiple photomultiplier tubes and an intensified charge-coupled device. Corresponding to the positions of spots in the picture with an exposure time of 40 ms, there are some bright spots (discharge spots) and black spots (non-discharged spots) in the instantaneous image with an exposure time of 10 μs (a half cycle of the applied voltage). There are at least two bright spots around one black spot and vice versa. The surface discharges (SDS) can be observed between any two adjacent spots. The intensity of the SDS between the bright spot and the black spot is 2.5 times greater than that between two adjacent bright spots, which indicates that the SDS are directional-selective. The intermittent discharge with positive (negative) current polarity changes to that with negative (positive) current polarity, after it sustains up to 14 voltage cycles at the longest. The spatial distribution of the electric field component is calculated through COMSOL software to solve the Poisson equation numerically. It is found that the inhomogeneous distribution of surface electric field is caused by the inhomogeneous distribution of wall charges, which leads to direction-selective SDS. The intermittent discharge is formed by the competition between the direction-selective SDS and volume discharges (VDS) in DBD. This is the reason why the intermittent discharge is generated.

Acupoints sensitization in people with and without chronic low back pain:A matched-sample cross-sectional study.

Acupoints are considered a dynamic functional area, which can reflect the internal condition of the body. In pathological states, disease-related acupoints are believed to be activated, which is known as acupoint sensitization. This study aimed to investigate the major manifestations of acupoint sensitization in patients with chronic low back pain (cLBP) to provide better understanding of acupoint sensitization phenomena in the context of cLBP. This study was a matched-sample cross-sectional study 16 participants diagnosed with cLBP and 16 healthy controls matched in age, sex, and ethnicity were included. The following aspects of sensitization phenomena of targeted points were compared: pressure pain threshold (PPT), skin temperature, surface electrical conductance, receptive field, and morphological change of skin. PPT at points of interest were significantly lower in cLBP participants compared with healthy controls (P< 0.05); in addition, receptive field was found to be larger at left BL 23 in cLBP participants (P< 0.05). There was no statistically significant difference in skin temperature, electrical conductance, or morphology between the two groups. Reduced PPT at all detected points and enlarged receptive field at left BL 23 were found in cLBP participants. These two features appear key in defining acupoint sensitization in cLBP, and provide evidence for selecting and locating acupuncture points in future clinical studies.

Construction of surface electron island by a simple organic molecule adsorption strategy: tuning the energy band structure and boosting the photocatalytic performance

A surface electric field was constructed on commercial P25 by a simple adsorption strategy utilizing PEG-400 to optimize the energy band structure and significantly enhance photocatalytic hydrogen evolution performance.

Пленение излучения и субзонный пик в спектрах квантового выхода фотоэмиссии из p-GaAs(Cs,O)

In the spectra of the photoemission quantum yield of p-GaAs(Cs,O) measured in the reflection geometry, a peak was found at a photon energy lower than the band gap of GaAs. It is shown that the appearance of the peak is due to the trapping of weakly absorbed radiation, which scatters diffusely on the rough back face of the epitaxial structure. Possible microscopic mechanisms of the appearance of the peak are discussed: the Franz-Keldysh effect in the surface electric field and adsorption-modified optical transitions in cesium adatoms.

Light trapping and subbandgap maximum in photoemission quantum yield spectra of p-GaAs(Cs,O)

In the spectra of the photoemission quantum yield of p-GaAs(Cs,O) measured in the reflection geometry, a peak was found at a photon energy lower than the band gap of GaAs. It is shown that the appearance of the peak is due to the trapping of weakly absorbed radiation, which scatters diffusely on the rough back face of the epitaxial structure. Possible microscopic mechanisms of the appearance of the peak are discussed: the Franz-Keldysh effect in the surface electric field and adsorption-modified optical transitions in cesium adatoms. Keywords: photoemission, GaAs, negative electron affinity, quantum yield spectra.

Performance Investigation of a Dielectric Stacked Triple Material Cylindrical Gate All Around MOSFET (DSTMCGAA) for Low Power Applications

This paper presents an analysis of gate stacked triple material dual-halo cylindrical MOSFET. The surface potential and electric field have been plotted for the proposed device using TCAD Silvaco at various channel lengths. The analytical model of surface potential, field and subthreshold current is also present. A comparative analysis has been accomplished for the proposed device with Asymmetric gate stack triple metal gate all around (AGSTMGAA), dual dielectric triple metal surrounding gate (DDTMSG) and Triple metal surrounding gate MOSFET. The performance metric of the device has been investigated in terms of Drain Induced Barrier Lowering (DIBL), Subthreshold swing and threshold-voltage roll-off. Furthermore, the analog behaviour of the device has been evaluated by determining transconductance, early voltage and intrinsic gain. The proposed device shows much better performance when compared to its counterpart. The mitigation in DIBL and leakage current indicates the cut back in the SCEs. The proposed device shows 8% improvement in SS, 36.2% improvement in DIBL and 13.5% improvement in threshold voltage roll-off as compared to AGSTMGAA. Hence, it can be used for low power applications.