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The measurement for the surface electric field intensity of insulators based on electroluminescent effect is a non-contact measurement. By spraying a coating of epoxy paint mixed with ZnS:Cu electroluminescence powder on the surface of insulators, the part with high surface electric field intensity would be the first to glow. As the applied voltage increases, the area of luminous and the brightness increase. Therefore, the surface electric field distribution can be deduced by photographing and analyzing the luminescence of insulator surface coating. This method has successfully measured the surface electric field intensity distribution of disc insulators in GIL. Without the use of electric field probe, this method eliminates the electric field distortion caused by the probe completely. Besides, the permittivity of the coating can be decided according to the permittivity of the insulator material, and so eliminate the electric field distortion caused by the coating. The measure results of this method are in good agreement with reality.

The surface discharge development processes of polluted porcelain insulators for power transmission lines are tightly related with the development of leakage current (LC), the characteristics of LC, the insulating condition, and discharge intensity of the insulator surface have an important significance for revealing the contamination discharge state of insulators. In order to analyze the LC characteristics of porcelain insulators in the process of pollution flashover, artificial pollution flashover tests on porcelain insulators were conducted in the artificial fog cabinet, and the characteristics of LC waveforms in time-domain and frequency-domain were simultaneously measured and analyzed during the tests. The results indicated that the amplitude of LC, fundamental harmonic, the third harmonic, and fifth harmonic had a strong correlation, the maximum of LC(Im), the rate of total harmonics (THD), and the phase difference of fundamental harmonic (θ) were used for the representation of the characteristics of the LC waveform. The LC has the characteristics of high amplitude, low proportion harmonic, and small phase difference between the fundamental harmonic and voltage before the flashover occurrence. The test results provide effective reference for porcelain insulators in pollution flashover forecasting.

In this paper, the heat balance integral method was employed to solve the internal temperature of ice layer and the position of melting interface by stages, due to its main advantage of converting the governing partial differential equation to an ordinary differential one, which can effectively reduce numerical efforts. Then the deicing time of hot water for insulator was calculated and analyzed. Taking LXY-120 insulator as the verification object, after natural icing at Xuefeng mountain natural icing test base, the validation experiments of deicing time were carried out in the natural environment. The initial water temperature and outlet pressure were optimized for deicing efficiency. Finally, the leakage current of water jet was measured. The research results indicate that the deicing rate increases and the energy consumption gradually decreases as the initial temperature of hot water increases. As the outlet pressure increases, the deicing rate increases. For the deicing condition of 1.2 mm nozzle, ambient temperature of -1 °C, wind speed of 3 m/s, ice weight of 2 kg/piece and deicing distance of 2 m, when the initial temperature of hot water and outlet pressure are 85.21 °C and 3.35 MPa respectively, the comprehensive deicing efficiency is the highest. The leakage current through water jet decreases with the increasing distance. The leakage current increases with the increase of water conductivity and outlet pressure. Hot water deicing for insulator in 110 kV system can be carried out according to the safety distance of the existing regulation.

In recent years, the electrical performance of polluted suspension insulators operating in coastal foggy regions has attracted wide attention because of the occurrence of flashover. Surface wetting by salt fog accretion increases the surface conductivity and degrades the flashover voltage of insulators. Normally, the effect of conductivity under fog condition and pre-contamination on the flashover of polluted insulators are analyzed separately. Therefore, this does not reveal the flashover characteristic in salt fog, which requires further research. This paper describes salt fog experiments with an AC test voltage conducted using suspension insulators in a 110-kV power system. The electrical strength performance of insulators with salt fog treatments is analyzed, and the effects of salt deposit density (SDD) and the fog water conductivity (FWC) on the flashover of three types of suspension insulators are studied. The concept of additional SDD is proposed to quantify analyze the effects of salt fog. The results show that there is less dependence on FWC at higher pollution levels than at lower pollution levels. That is, the effect of FWC on 50% AC flashover voltage ($U_{50}$ ) can be neglected for SDD >0.15 mg/cm2, whereas FWC has a strong effect on $U_{50}$ for SDD 2. FWC has a greater influence on $U_{50}$ of ceramic insulators than on that of silicone rubber insulator. A model for calculating the critical flashover voltage of insulators is proposed by considering the combined effect of FWC and pre-polluting SDD.

The electrical performance of insulators under comprehensive conditions including low air pressure, pollution and icing, is an important basis for the selection of external insulation. However, the problem of cold wet deposition has not attracted extensive and considerable interest in research. Based on flashover tests of suspension insulators in field test station, the AC flashover performance of insulators was studied. The results show that the duration of existence of the arc throughout the composite insulator surface in case of condensation was significantly lower than that in case of freezing fog flashover because of a change of the sheds surface roughness, which leads the arc melt the frozen fog droplets on the sheds surface and extends its flashover time. Compared with the flashover characteristics of the hydrophilic insulators in frost fog, the composite insulators exhibited clear arc extinguishing and arc starting phenomena. Moreover, the wind velocity has affected the flashover performance of suspension insulators in cold fog. Studying flashover characteristics of suspension insulators can contribute to the design of the external insulation of transmission lines and substations under natural cold fog and wet deposition regions.

Insulator failure generally occurs due to improper design, and if there exists sharp edges over the insulator surface. There is a need to detect the fragile parameters in the insulator design as they can cause large electrical stress, leading to insulation failure. In this paper, machine learning based approach is used to identify the fragile design parameter and thus determine an optimized design of the insulator, which will eventually decrease the voltage stress over it. A 220 kV insulator is designed and electric field intensity and potential distribution for an assembly of live, ground and insulator is calculated for different geometries. The design parameters of the insulator are considered and varied. The electric field is calculated for the whole assembly of insulator to generate the most optimized design. The optimized design reduces the overall stress by 13.12 %.

Porcelain insulators have a long history and wide application range in power systems, but just like any other insulator, they can fail. A number of pole fires occurred on lines utilising porcelain suspension insulators. In some cases, the insulators appeared to be visually intact with no external signs of degradation or abnormal stress. This prompted a comprehensive assessment to identify the mechanism that leads to the permanent loss of insulating properties while retaining external physical characteristics. A single test is not sufficient to determine the underlying cause of conduction as results may produce contradictory conclusions. Electrical tests were able to identify samples with poor dielectric strength. Nevertheless, these same samples exhibited excellent mechanical properties. Despite successfully passing numerous porosity tests, scanning electron microscopic analysis revealed porosity and multiple microscopic punctures in the porcelain dielectric. Only upon complete dissection of samples, the conduction mechanism was revealed. This article discusses the challenges associated with establishing the root failure mechanism for the investigated porcelain insulators that allows visually sound samples to lose their insulating properties without experiencing catastrophic failure.

Starting with twisted bilayer graphene, graphene-based moir\'e materials have recently been established as a new platform for studying strong electron correlations. In this paper, we study twisted graphene monolayers on trilayer graphene and demonstrate that this system can host flat bands when the twist angle is close to the magic angle of $1.{16}^{\ensuremath{\circ}}$. When monolayer graphene is twisted on ABA trilayer graphene, the flat bands are not isolated, but are intersected by a Dirac cone with a large Fermi velocity. In contrast, graphene twisted on ABC trilayer graphene (denoted AtABC) exhibits a gap between flat and remote bands. Since ABC trilayer graphene and twisted bilayer graphene are known to host broken-symmetry phases, we further investigate the ostensibly similar magic-angle AtABC system. We study the effect of electron-electron interactions in AtABC using both Hartree theory and an atomic Hubbard theory to calculate the magnetic phase diagram as a function of doping, twist angle, and perpendicular electric field. Our analysis reveals a rich variety of magnetic orderings, including ferromagnetism and ferrimagnetism, and demonstrates that a perpendicular electric field makes AtABC more susceptible to magnetic ordering.

A conductive metallic particle in a gas-insulated metal-enclosed system can charge through conduction or induction and move between electrodes or on insulating surfaces, which may lead to breakdown and flashover. The charge on the metallic particle and the charging time vary depending on the spatial electric field intensity, the particle shape, and the electrode surface coating. The charged metallic particle can move between the electrodes under the influence of the spatial electric field, and it can discharge and become electrically conductive when colliding with the electrodes, thus changing its charge. This process and its factors are mainly affected by the coating condition of the colliding electrode. In addition, the interface characteristics affect the particle when it is near the insulator. The charge transition process also changes due to the electric field strength and the particle charging state. This paper explores the impact of the coating material on particle charging characteristics, movement, and discharge. Particle charging, movement, and charge transfer in DC, AC, and superimposed electric fields are summarized. Furthermore, the effects of conductive particles on discharge characteristics are compared between coated and bare electrodes. The reviewed studies demonstrate that the coating can effectively reduce particle charge and thus the probability of discharge. The presented research results can provide theoretical support and data for studying charge transfer theory and design optimization in a gas-insulated system.

Significance Micrometer-sized uniform four-layer (ABCA) rhombohedral graphene is realized by introducing a small twist angle between two bilayers of Bernal graphene. By means of scanning tunneling spectroscopy we observe an extremely sharp van Hove singularity of 3–5-meV half-width and a correlated many-body gap of 9.5 meV at neutrality, thus making small twisted double-bilayer graphene a unique platform to realize electronic correlations in the absence of a moiré potential. Furthermore, ABCA graphene domain walls display tunable topological edge states, of great interest in Floquet engineering., Atomically thin van der Waals materials stacked with an interlayer twist have proven to be an excellent platform toward achieving gate-tunable correlated phenomena linked to the formation of flat electronic bands. In this work we demonstrate the formation of emergent correlated phases in multilayer rhombohedral graphene––a simple material that also exhibits a flat electronic band edge but without the need of having a moiré superlattice induced by twisted van der Waals layers. We show that two layers of bilayer graphene that are twisted by an arbitrary tiny angle host large (micrometer-scale) regions of uniform rhombohedral four-layer (ABCA) graphene that can be independently studied. Scanning tunneling spectroscopy reveals that ABCA graphene hosts an unprecedentedly sharp van Hove singularity of 3–5-meV half-width. We demonstrate that when this van Hove singularity straddles the Fermi level, a correlated many-body gap emerges with peak-to-peak value of 9.5 meV at charge neutrality. Mean-field theoretical calculations for model with short-ranged interactions indicate that two primary candidates for the appearance of this broken symmetry state are a charge-transfer excitonic insulator and a ferrimagnet. Finally, we show that ABCA graphene hosts surface topological helical edge states at natural interfaces with ABAB graphene which can be turned on and off with gate voltage, implying that small-angle twisted double-bilayer graphene is an ideal programmable topological quantum material.

The induction of unconventional superconductivity by twisting two layers of graphene a small angle was groundbreaking1, and since then has attracted widespread attention to novel phenomena caused by lattice or angle mismatch between two-dimensional (2D) materials2. While many studies address the influence of angle mismatch between layered 2D materials3-5 , the impact of the absorption alignment on the physical properties of planar molecules on 2D substrates has not been studied in detail. Using scanning probe microscopy (SPM) we show that individual cobalt phthalocyanine (CoPc) molecules adsorbed on the layered superconductor 2H-NbSe2 change drastically their charge and spin state when the symmetry axes of the molecule and the substrate are twisted with respect to each other. The CoPc changes from an effective spin-1/2 as found in gas-phase6 to a molecule with non-magnetic ground-state. On the latter we observe a singlet-triplet transition originating from an antiferromagnetic interaction between the central-ion spin and a distributed magnetic moment on the molecular ligands. Because the Ising superconductor 2H-NbSe2 lacks inversion symmetry and has large spin-orbit coupling7 this intramolecular magnetic exchange has significant non-collinear Dzyaloshinskii-Moriya (DM)8, 9 contribution., 4 figures

In recent years, the notion of Quantum Materials has emerged as a powerful unifying concept across diverse fields of science and engineering, from condensed-matter and cold atom physics to materials science and quantum computing. Beyond traditional quantum materials such as unconventional superconductors, heavy fermions, and multiferroics, the field has significantly expanded to encompass topological quantum matter, two-dimensional materials and their van der Waals heterostructures, Moire materials, Floquet time crystals, as well as materials and devices for quantum computation with Majorana fermions. In this Roadmap collection we aim to capture a snapshot of the most recent developments in the field, and to identify outstanding challenges and emerging opportunities. The format of the Roadmap, whereby experts in each discipline share their viewpoint and articulate their vision for quantum materials, reflects the dynamic and multifaceted nature of this research area, and is meant to encourage exchanges and discussions across traditional disciplinary boundaries. It is our hope that this collective vision will contribute to sparking new fascinating questions and activities at the intersection of materials science, condensed matter physics, device engineering, and quantum information, and to shaping a clearer landscape of quantum materials science as a new frontier of interdisciplinary scientific inquiry., Comment: 93 pages, 27 figures

A TCAD approach for the investigation of charge transport in thick amorphous silicon dioxide is presented for the first time. Thick oxides are investigated representing the best candidates for integrated galvanic insulators in future power applications. The large electric fields, such devices experience and the preexisting defects in the amorphous material, give rise to a leakage current, which leads to degradation and failure. Hence, it is crucial to have a complete understanding of the main physical mechanisms responsible for the charge transport in amorphous silicon oxide. For this reason, metal–insulator–metal structures have been experimentally characterized at different high-field stress conditions and a TCAD approach has been implemented in order to gain insight into the microscopic physical mechanisms responsible for the leakage current. In particular, the role of charge injection at contacts and charge build-up due to trapping–detrapping mechanisms in the bulk of the oxide layer has been investigated and modeled to the purpose of understanding the oxide behavior under dc- and ac-stress conditions. Numerical simulations have been compared against experiments to quantitatively validate the proposed approach.

Charge transport in thick amorphous silicon dioxide capacitors for integrated galvanic insulators is experimentally investigated and analyzed through numerical simulations carried out with a commercial TCAD tool. The material intrinsic defectivity and the large biases applied to such devices give rise to a leakage current which is responsible of degradation and failure. Hence it is crucial to have a complete understanding of the charge-transport main physical mechanisms in amorphous silicon oxide. For this reason, constant-current time dependent dielectric breakdown measurements have been performed on thick metal-insulator-metal structures and, in order to gain insight on the role of defects on breakdown, numerical simulations have been compared to experiments.

International audience; This paper presents the application of the equivalent electrical circuit for the predictive modeling of the dynamic of surface discharge and flashover of solid insulators. Both of dry insulator and polluted insulator models and application are presented. The results show that this model is useful for a better understanding of the flashover mechanism and the design of the insulation level for high voltage electrical equipment.

The rate of heat loss is analyzed for three materials: glass, brick and wood. To do this, the initial and final temperatures are set to 75℉ and 100℉, respectively, and the dimensions of each material are chosen to be 5ft by 5ft with a thickness of 2 inches. The objective of this paper is to see which material is best for insulating heat, thus enhancing the thermal performance of a building. Results from this study suggest that glass and brick have a higher rate of heat loss (high thermal conductance values and low thermal resistance values) compared to wood and are therefore poor insulators whereas wood, with a lower rate of heat loss (low thermal conductance value and a high thermal resistance value) serves as a better insulator.

In this paper, factors that account for the disc brake noise were explored with a bench test to fix the methods of reducing the brake squeal noise. The influence of the stiffness and damping of insulator on the noise of the braking system was analyzed by establishing a mathematical model for the 6-DOF braking system with internal and external insulators. It is proposed that the insulator with a multilayered structure of different materials has a better restraining effect on brake squeal. Four different insulator schemes were designed, the test results of which were compared with those of the original scheme. The comparative analysis shows that the stiffness and damping of insulator have an important influence on the braking system noise, which can be reduced by improving the material parameters of the structure layer of the insulator. The test results show that the insulator with one layer of rubber and one layer of steel has a good effect on restraining the low-frequency noise, while the insulator with two layers of rubber and one layer of steel has a good inhibition on the high-frequency noise around 7~8 kHz. The final conclusion shows that a rubber-steel-rubber structure insulator made of a 0.5-mm-thickness steel sheet can reduce the overall incidence of the brake system noise from 19.27% to 1.27%. An appropriate selection of material structure parameters of the insulator can minimize the occurrence of brake squeal.

In this paper, based on insulation coordination and simulation, a lightning protection composite insulator is proposed, made up of an insulation part and an arrester part connected in series, whose length is close to that of the standard composite insulator, which met the window size requirements of the tower. The arrester part contains zinc oxide resistors and an internal core rod, which has good explosion-proof performance and tensile strength, in the meantime overcomes the problem that arresters cannot bear the tensile load of transmission lines. Electrical simulations and experiments have shown that the shielding failure current can be released through the proposed lightning protection insulator to the ground and the counterattack current can be prevented from entering the line. The dry-arc distances of the arrester part and the insulation part are 2.4 and 2.2 m respectively, and the grading ring distance is 1.8 m. The maximum AC withstanding voltage reaches 700 kV, and the switching overvoltage impulse withstanding voltage reaches 1200 kV. The proposed insulator can prevent lightning accidents from happening. Moreover, its length, tensile load, and installation mode are the same as existing line insulators, which has the advantages of low cost and ease of installation and maintenance.

Electric field optimization is a critical technique to ensure the compact structure and reliable operation for AC gas insulated power apparatus. To obtain a more uniform electric field distribution, this paper proposes the concept of the d-SFGM insulator, i.e., applying the surface functionally graded material (SFGM) with a designed thickness (d) distribution of high permittivity along the insulator surface. The magnetron sputtering technique was used to fabricate the d-uniform insulator and the d-SFGM insulator by depositing BaTiO3 layers. The theoretical analysis indicates that the electric field distribution is optimized using the d-SFGM insulator, followed by the d-uniform insulator. The finite element simulations were employed to investigate the electric field distributions and dielectric losses of different insulators. The results show that for the case of the d-uniform insulator, a higher permittivity or larger thickness of the sputtering layer results in a more uniform electric field distribution. With the application of the d-SFGM insulator, the maximum electric field strength and dielectric loss are both significantly reduced compared to the d-uniform insulator. Finally, experimental tests were conducted to further verify the feasibility of SFGM. The AC flashover voltage of the d-SFGM insulator is much higher than those of the conventional insulator and the d-uniform insulators. Therefore, the d-SFGM insulator has great potential for improving the reliability of the AC gas insulated power apparatus.

The proven reliability of ceramic cap-and-pin insulators for high voltage (HV) and extra-high voltage (EHV) overhead lines suffers in the presence of harsh industrial or strong salt pollution [1]. In these cases, apart from the countermeasures such as increasing creepage distance, washing, and applying greases, insulators with a silicone rubber surface have demonstrated better performance [2]. The two alternatives for having insulators with a polymeric surface are (1) composite insulators, which consist of an inner fiberglass rod and an outer silicone rubber housing, and (2) precoated toughened glass cap-and-pin insulators with room temperature vulcanized (RTV) silicone rubber coating, hereafter referred to as RTV insulators.

© The Royal Society of Chemistry. Mechanically exfoliated two-dimensional (2D) black phosphorus (bP) is epitaxially terminated by monolayers and multilayers of tetracosane, a linear alkane, to form a weakly interacting van der Waals heterostructure. Atomic force microscopy (AFM) and computational modelling show that epitaxial domains of alkane chains are ordered in parallel lamellae along the principal crystalline axis of bP, and this order is extended over a few layers above the interface. Epitaxial alkane multilayers delay the oxidation of 2D bP in air by 18 hours, in comparison to 1 hour for bare 2D bP, and act as an electrical insulator, as demonstrated using electrostatic force microscopy. The presented heterostructure is a technologically relevant insulator-semiconductor model system that can open the way to the use of 2D bP in micro-and nanoelectronic, optoelectronic and photonic applications.

The complex interplay among electronic, magnetic and lattice degrees of freedom in Mott-Hubbard materials leads to different types of insulator-to-metal transitions (IMT) which can be triggered by temperature, pressure, light irradiation and electric field. However, several questions remain open concerning the quantum or thermal nature of electric field-driven transition process. Here, using intense terahertz pulses, we reveal the emergence of an instantaneous purely-electronic IMT in the Mott-Hubbard vanadium sequioxide (V2O3) prototype material. While fast electronics allow thermal-driven transition involving Joule heating, which takes place after tens of picoseconds, terahertz electric field is able to induce a sub-picosecond electronic switching. We provide a comprehensive study of the THz induced Mott transition, showing a crossover from a fast quantum dynamics to a slower thermal dissipative evolution for increasing temperature. Strong-field terahertz-driven electronic transition paves the way to ultrafast electronic switches and high-harmonic generation in correlated systems., Thermal effects limit the speed of the electrically driven insulator-metal transition in V2O3 to tens of picoseconds. Here the authors show that under an intense THz-electric-field excitation the thermal regime can be overcome, achieving a purely electronic transition on ultrafast timescales.

High voltage transmission line design requires careful insulator selection to ensure good operational performance. This paper reports on the in-situ measurements of leakage current (LC) on composite and glass insulators of the Cahora Bassa high voltage direct current (HVDC) transmission line in South Africa over a 6 - month period. The influence of temperature, humidity, dew, rain and the HVDC line's voltage and current on LC are investigated. The results show that the composite and glass insulator LC behaviour is similar, except in cases of high humidity or rain. At the commencement of rainfall and humidity (>90%), elevated LC levels are observed on glass insulators, while composite insulators demonstrate lower LC levels under these conditions. Under nominal weather conditions of no rain and low humidity, the LC measurements exhibit an almost square-wave behaviour with LC switching between lower (≈20 μA) and higher values (≈60 μA) with relatively short transitions on a daily basis. This phenomenon can be ascribed to condensation on the insulators, which is a primary determinant of the LC levels on contaminated insulators. The line current and voltage fluctuations do not influence the LC level.

A converter valve unit, which converts Alternating Current (AC) to Directing Current (DC) and DC to AC, is one of the key elements of high voltage direct current (HVDC) transmission. The insulation design of a converter valve unit should be considered for air clearance according to the DC superimposed overvoltage and the insulator that maintains the insulation performance and the corona shield to suppress DC corona discharge. There is no prescribed standard for the insulation design of a converter valve unit. Moreover, insulation performance under an applied DC voltage has not yet been thoroughly investigated. Therefore, it is necessary to study the insulation design method of the converter valve unit. In this paper, consideration of the insulation design method on a ±200 kV converter valve unit in an HVDC converter hall is performed. The finite element method (FEM) is used to simulate the 3D model. Additionally, the safety factor (SF) is applied in accordance with the dielectric test in IEC 62271-1. As a result, an insulation design process on the converter valve unit is proposed and the insulation design is carried through the design factors. It is confirmed that design factors on the air clearance, insulator and corona shield have a significant effect on a highly reliable insulation design.

The Electrical properties of Bi0.7Dy0.3FeO3 (BDFO) thin films deposited by pulsed laser deposition (PLD) on ZnO/Si films and its potential applications are discussed in this paper. MIS (metal/insulator/semiconductor) Capacitors of Cr-Au/BDFO/ZnO/p-Si structures have been fabricated and their interface traps and electrical properties have been investigated. To obtain the information about the interface trap states, systematic studies on the frequency-dependent capacitances and conductance measurement were performed. Frequency dependent analysis of the device was made in the frequency range of 10kHz-500kHz. It was observed that dispersion of the oxide capacitance was 2% per decade within this frequency range. When the sweeping voltage changes from -3 to +4V the memory aperture was found to be increased from 300 to 850mV. This significant hysteresis property in the C-V characteristics may be attributed to the slight ferroelectric behaviour of BDFO/ZnO film, which is essential for a memory device. It was also observed that density of trap state (Dit) is found approximately 9?1011cm-2eV-1 while increasing the frequency from 10kHz to 500kHz, the thickness of the oxide layer was 300nm in this experiment. The calculated dielectric constant of device (~190) is much higher than that of BDFO (>30). The dielectric loss tangent of the device was found to initially increase with voltage then decrease, whereas the ac conductivity depicted an opposite trend. Multiferroic BDFO is promising material shows the good coupling between ferroelectric and ferromagnetic properties and ideal behaviour at room temperature. Integration of BDFO films with ZnO piezoelectric can be used directly as electricity generator with enhanced output in MEMS applications as well as in Memory devices. Display Omitted Frequency dependent analysis of the device was made in the frequency range of 10kHz-500 kHz.Memory aperture was found to be increased from 300 to 850 mVDensity of trap state (Dit) is found approximately 9?1011 cm-2 eV-1 for all frequenciesDielectric constant of device (~190) is much higher than that of BDFO (>30)Dielectric Loss tangent of the device was found to initially increase with voltage then decrease

The spacer is a challenging part of high voltage direct current (HVDC) gas-insulated switchgear (GIS) and gas- insulated transmission lines (GILs). Based on the charge adaptively controlling strategy verified by our previously published papers, this paper serves as an important step towards further industrialization of charge adaptively controlling spacers. The insulation compounding scheme based on previous researches is focused in this paper. Spacers composed of insulating regions and charge adaptive control regions with different mass fractions of nonlinear materials were prepared. The mechanical properties, as well as the DC and AC surface flashover performance of these spacers were investigated. The results show that the DC surface flashover voltage is greatly reduced using spacers with a pure insulating region and with a doped charge adaptive region. As the doping ratio of the nonlinear material in the insulating region increases, the surface flashover voltage increases remarkably. However, the mechanical stress decreases dramatically when the mass ratio of nonlinear material is beyond 35%. The different doping ratios of nonlinear materials does not make a difference in AC surface flashover voltage. However, these surface flashover values obtained by bowl shaped spacers are much more stable and higher than that of the values measured from traditional cone type spacers at AC. The results in this paper can be a key step and are helpful in further determining the preferred option of the industrial spacer that can be potentially used in HVDC GIS/GILs. Meanwhile, based on the advanced performance, the idea of the novel bowl shape has potentially possibility in the application field of AC GIS/GILs.

Predicting the electrical breakdown of polymers is critical for certifying the endurance and lifetime of high voltage power equipment. Since various factors contribute nonlinearly to the breakdown phenomena of polymer insulators, it is difficult to assess the impact of each factor independently. In this study, we numerically analyzed the breakdown phenomenon because of the ramp rate of the DC voltage applied to a polymer insulator, low-density polyethylene (LDPE), using the finite element method (FEM). To predict the breakdown initiation, we analyzed the relaxation time of the conduction current through the insulator as a significant indicator. The bipolar charge transport (BCT) model was used to analyze the charge behavior within the LDPE, and the breakdown voltage was predicted by incorporating the molecular displacement model. This analysis was conducted for a wide range of ramp rates from 10 to 1500 V/s. The current density was calculated using two different methods, namely the energy and average methods, and the results were compared with each other. The results of the numerical model were further verified by comparing with those from experiments reported in the literature.

International audience; SU-8 photoresist was applied to the gate insulator of a-IGZO TFT. The hard bake temperature of SU-8 is important and was varied from 95 to 185 A degrees C. The FTIR showed that hard-bake temperature higher than 125 A degrees C is necessary for complete polymerization. The leakage current and breakdown voltage were improved as increasing hard bake temperatures to 155 A degrees C. However, the crack was generated at 185 A degrees C degrading the electrical characteristics of insulator. The SU-8 insulator was successfully applied to a-IGZO TFT where the on-off ratio was highest for hard-bake temperature of 155 A degrees C.

Icing can adversely influence electric power system security. Two main issues are caused by icing: the overload of transmission lines, and the reduction in the insulation ability of the insulators. Most previous research has focused on the flashover characteristics of ice-covered insulators, but research on the icing process of the insulator is seriously lacking. Considering the effect of icing shape, the outer airflow field of an insulator was calculated and the local collision efficiencies of water droplets (β1) were investigated according to the Lagrange algorithm. The simulation showed that the values of β1 on the insulator edge and rod are much higher than on the insulator surface, and both were significantly influenced by the wind speed and median volume diameter (MVD) of the water droplets. Based on thermal balance equations, a dynamic dry-growth icing model was established. Using the natural icing conditions of Xuefeng Mountain (China) as an example, validation experiments were conducted on a composite insulator and the climate parameters measured by multi-cylinders were used to model the icing shape and mass. The results indicate that high wind speed and low temperature increase icing rate; the icing was mainly concentrated on the windward side and the greatest horizontal thickness was generally on the insulator edge. The dry-growth model had an average error lower than 25% for icing thickness and an average error lower than 20% for icing mass, which were affected by icing roughness.

This paper describes the R&D work performed in support of the design of the alumina insulators for the MITICA Neutral Beam Injector. The ceramic insulators are critical elements, both from the structural and electrical point of view, of the 1 MV electrostatic accelerator of the MITICA injector, as they are required to sustain both the mechanical loads due to the cantilevered weight of the ion source and the high electric field between the accelerator grids. This paper presents the results of numerical simulations and experimental tests on prototypes that have been carried out to validate the insulator design under realistic operating conditions.

Engineering the properties of quantum electron systems, e.g., tuning the superconducting phase using low driving bias within an easily accessible temperature range, is of great interest for exploring exotic physical phenomena as well as achieving real applications. Here, the realization of continuous field-effect switching between superconducting and non-superconducting states in a few-layer MoS2 transistor is reported. Ionic-liquid gating induces the superconducting state close to the quantum critical point on the top surface of the MoS2, and continuous switching between the super/non-superconducting states is achieved by HfO2 back gating. The superconducting transistor works effectively in the helium-4 temperature range and requires a gate bias as low as approximate to 10 V. The dual-gate device structure and strategy presented here can be easily generalized to other systems, opening new opportunities for designing high-performance 2D superconducting transistors.

Submerged membrane bioreactor (MBR) is currently believed to be an efficient biological treatment for reusing and recovering wastewater to extenuate the ever increasing water scarcity crisis. To mitigate the main problem, membrane fouling, in MBR systems, we propose a solution that avoids usage of chemicals, and allows uninterrupted operation using a novel concept of obstacle dielectrophoresis (oDEP). The utilization of obstacles, insulator or metal (floating) electrodes, between electrically excited electrodes, can extend the DEP force field to move suspended particles away from membranes without having to increase voltage, for suppressing fouling with low energy consumption. Experimental investigation verified our theoretical simulation prediction and demonstrated that insulator membrane modules provide longer membrane service time for maintaining normalized permeate flux of 55% than those by floating electrode membrane modules, with a maximum intensification factor of 7.8 when applied 220 V voltage and 50 Hz as well as the transmembrane pressure of 0.1 bar. Although stronger DEP force and hence better performance of fouling suppression can be generated by higher voltage, 50 V insulator membrane module demonstrated to be the most energy efficient process with a specific energy consumption of 0.295 kWh/m3 product and 13 times higher efficient factor than the 220 V. - 2017 This research is made possible by NPRP award ( NPRP7-089-2-044 ) from Qatar National Research Fund (QNRF). The statements made herein are solely the responsibility of the authors. Scopus

Picosecond-pulse III-V-on-silicon mode-locked lasers based on linear and ring extended cavity geometries are presented. In passive mode-locked operation a 12 kHz -3dB linewidth of the fundamental RF tone at 4.7 GHz is obtained for the linear cavity geometry and 16 kHz for the ring cavity geometry. Stabilization of the repetition rate of these devices using hybrid mode-locking is also demonstrated.

Insulating films are essential in multiple electronic devices because they can provide essential functionalities, such as capacitance effects and electrical fields. Two-dimensional (2D) layered materials have superb electronic, physical, chemical, thermal, and optical properties, and they can be effectively used to provide additional performances, such as flexibility and transparency. 2D layered insulators are called to be essential in future electronic devices, but their reliability, degradation kinetics, and dielectric breakdown (BD) process are still not understood. In this work, the dielectric breakdown process of multilayer hexagonal boron nitride (h-BN) is analyzed on the nanoscale and on the device level, and the experimental results are studied via theoretical models. It is found that under electrical stress, local charge accumulation and charge trapping/detrapping are the onset mechanisms for dielectric BD formation. By means of conductive atomic force microscopy, the BD event was triggered at several locations on the surface of different dielectrics (SiO2, HfO2, Al2O3, multilayer h-BN, and monolayer h-BN); BD-induced hillocks rapidly appeared on the surface of all of them when the BD was reached, except in monolayer h-BN. The high thermal conductivity of h-BN combined with the one-atom-thick nature are genuine factors contributing to heat dissipation at the BD spot, which avoids self-accelerated and thermally driven catastrophic BD. These results point to monolayer h-BN as a sublime dielectric in terms of reliability, which may have important implications in future digital electronic devices. Fil: Jiang, Lanlan. Soochow University; China Fil: Shi, Yuanyuan. Soochow University; China. University of Stanford; Estados Unidos Fil: Hui, Fei. Soochow University; China. Massachusetts Institute of Technology; Estados Unidos Fil: Tang, Kechao. University of Stanford; Estados Unidos Fil: Wu, Qian. Soochow University; China Fil: Pan, Chengbin. Soochow University; China Fil: Jing, Xu. Soochow University; China. University of Texas at Austin; Estados Unidos Fil: Uppal, Hasan. University of Manchester; Reino Unido Fil: Palumbo, Félix Roberto Mario. Comisión Nacional de Energía Atómica; Argentina. Universidad Tecnológica Nacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Lu, Guangyuan. Chinese Academy of Sciences; República de China Fil: Wu, Tianru. Chinese Academy of Sciences; República de China Fil: Wang, Haomin. Chinese Academy of Sciences; República de China Fil: Villena, Marco A.. Soochow University; China Fil: Xie, Xiaoming. Chinese Academy of Sciences; República de China. ShanghaiTech University; China Fil: McIntyre, Paul C.. University of Stanford; Estados Unidos Fil: Lanza, Mario. Soochow University; China

We formulate an analytical recursive method to generate the wave function of doped short-range resonating valence bond (RVB) states as a tool to efficiently estimate multisite entanglement as well as other physical quantities in doped quantum spin ladders. We prove that doped RVB ladder states are always genuine multipartite entangled. Importantly, our results show that within specific doping concentration and model parameter regimes, the doped RVB state essentially characterizes the trends of genuine multiparty entanglement in the exact ground states of the Hubbard model with large onsite interactions, in the limit which yields the $t$-$J$ Hamiltonian., Comment: 11 pages, 6 figures, RevTex 4-1, accepted in Phys. Rev. B

In this study, we have an insulator is subjected to high voltage under various atmospheric condition. Without porcelain and asbestos coatings to judge the performance and with porcelain and asbestos coatings to judge the performance of electrical insulation materials, upto 44 KV during various atmospheric condition. And for porcelain insulating material, upto 41 KV.

We report magnon spin transport in nickel ferrite (NiFe$_2$O$_4$, NFO)/ platinum (Pt) bilayer systems at room temperature. A nonlocal geometry is employed, where the magnons are excited by the spin Hall effect or by the Joule heating induced spin Seebeck effect at the Pt injector, and detected at a certain distance away by the inverse spin Hall effect at the Pt detector. The dependence of the nonlocal magnon spin signals as a function of the magnetic field is closely related to the NFO magnetization behavior. In contrast, we observe that the magnetoresistance measured locally at the Pt injector does not show a clear relation with the average NFO magnetization. We estimate the magnon spin relaxation length to be 3.1 $\pm$ 0.2 $\mu$m in the investigated NFO samples., Comment: 6 pages, 4 figures

Controlling Chiral Light Emission Circularly polarized light plays important roles in a number of applications such as displays, communication, and sensing. Thus, the ability to produce compact and readily controllable polarized light sources is important, and dichalcogenide materials such as tungsten diselenide may provide a route to such sources. Zhang et al. (p. 725 , published online 17 April; see the Perspective by Zaumseil ) formed an electric-double-layer transistor structure with WSe2 and used a gated ionic liquid to control the carrier density. Electrical control of the output light was achieved with the polarization being switched by reversing the polarity of the applied field and injected charge.

In this letter, we describe the use of a germanium-on- silicon waveguide platform to realize an arrayed waveguide grating (AWG) operating in the 5 mu m wavelength range, which can be used as a wavelength multiplexer for mid-infrared (midIR) light engines or as the core element of a midIR spectrometer. Ge-on-Si waveguide losses in the range 2.5-3.5 dB/cm for TE polarized light and 3-4 dB/cm for TM polarized light in the 5.15-5.4 mu m wavelength range are reported. A 200 GHz channel spacing 5-channel AWG with an insertion loss/crosstalk of 2.5/3.1 dB and 20/16 dB for TE and TM polarization, respectively, is demonstrated.

Recent advances in atomic-scale preparation of ultrathin nano-sheets and efficient field-effect gating mediated by movement of ions have provided a prolific paradigm for creating exotic states at interfaces of a new-type of device called electric-double layer transistors (EDLTs). We present a short review on these liquid/solid interfaces formed on nano-sheets prepared by micro cleaving a bulk layered single crystal, which can be electrostatically doped to a high carrier density of ∼1014 cm−2. Atomically flat surfaces prepared on various layered materials allowed ideal transport when they acted as transistor channels after accumulating dense carriers. The unique system combining these two advantages enabled observations of novel transport phenomena showing quantum phase transition of charge and spin states controlled by electric field. Examples include gate-induced metal-insulator transition, opening of new transport channels, and field-induced interface superconductivity, which present a rapidly growing field with emerging opportunities for science and technology.

Ice flashover threatens the security and reliability of power transmission. However, the ice flashover mechanism of insulators remains poorly understood. This study analyses water droplet freezing and ion distribution in ice layer under alternating electric field. It also investigates ion migration during icing process of insulator string under alternating electric field and its effects on insulator flashover. Results showed that the average freezing time of water droplets was related to electric field strength. The extent of ion migration during freezing decreased with increasing electric field strength. The maximal melting water conductivity of the ice layer and icicle of the insulator formed under energized condition was higher than the corresponding freezing water conductivity but lower than that under non-energized condition. Furthermore, the hanging location of each insulator significantly affected the melting water conductivity of the ice layer. The surface conductivity of the ice layer increased because of the conductive ion migration in freezing water during freezing, which was an important factor that decreased the flashover voltage of the ice-covered insulator. The existence of alternating electric field would impact the extent of ion migration. This study may serve as a reference for updating prediction flashover model of ice-covered insulators during the melting period.

The ITER project requires at least two Neutral Beam Injectors (NBIs), each accelerating to 1MV a 40A beam of negative deuterium ions, to deliver to the plasma a power of about 33 MW for one hour as additional heating. A full-size negative ion source (SPIDER - Source for Production of Ion of Deuterium Extracted from RF plasma) and a prototype of the whole 1 MV ITER injector (MITICA - Megavolt ITER Injector & Concept Advancement) are under construction at PRIMA a new test facility for the ITER neutral beams being built at the Consorzio RFX in Padua, Italy. In SPIDER, the source is housed in a stainless steel vessel maintained in high vacuum. A three grid system is foreseen to extract and accelerate at 100kV the beam. For this reason, the vacuum vessel hosts is equipped with three large alumina feedthroughs, ring shaped insulators (800mm in diameter) to insulate the vessel from the hydraulic and electrical services which supply the source components biased at different potentials in the range between -112 and -100kVdc. These insulators (bushings) are one of the most critical items in the SPIDER experiment and they required a particular effort in designing, manufacturing and identifying the proper test procedure. This paper gives an overview of the design, development, manufacturing activities and presents the results of the high voltage tests for the bushing acceptance.

We present the design, fabrication and characterization of efficient fiber-to-chip grating couplers on a Germanium-on-Silicon (Ge-on-Si) and Germanium-on-silicon-on-insulator (Ge-on-SOI) platform in the 5 µm wavelength range. The best grating couplers on Ge-on-Si and Ge-on-SOI have simulated coupling efficiencies of -4 dB (40%) with a 3 dB bandwidth of 180 nm and -1.5 dB (70%) with a 3 dB bandwidth of 200 nm, respectively. Experimentally, we show a maximum efficiency of -5 dB (32%) and a 3 dB bandwidth of 100 nm for Ge-on-Si grating couplers, and a -4 dB (40%) efficiency with a 3 dB bandwidth of 180 nm for Ge-on-SOI couplers.

The Monte Carlo simulations of charged particle transport are used to investigate the effects of exposing ultra-thin layers of insulators (commonly used in integrated circuits) to beams of protons, alpha particles and heavy ions. Materials considered include silicon dioxide, aluminum nitride, alumina, and polycarbonate - lexan. The parameters that have been varied in simulations include the energy of incident charged particles and insulating layer thickness. Materials are compared according to both ionizing and non-ionizing effects produced by the passage of radiation. [Projekat Ministarstva nauke Republike Srbije, br. 171007]

This study reports the fabrication of polymer field-effect transistors operating under a bias of |1 V| in which the insulator and semiconductor are gravure-printed on plastic at the high speed of 0.7 m s−1. Remarkably, the process does not necessitate any surface modification and relies solely on the careful selection and optimization of formulations based on solvent blends. In addition to demonstrating high-throughput fabrication, this study fulfills another requirement for organic electronics and achieves low-voltage operation in ambient air by using a polyelectrolyte insulator, poly(4-styrenesulfonic acid) (PSSH). PSSH is a proton conductor that forms electrical double layers at the interfaces with the gate electrode and the semiconductor channel upon application of a small gate voltage (≤ |1 V|). Printed PSSH exhibits a high capacitance of 10 µF cm−2, leading to a printed poly(3-hexylthiophene) hole mobility above 0.1 cm2 V−1 s−1 in a bottom-gate, top-contact configuration.

Natural polluted insulator surfaces are always coated with various kinds of soluble constituents, and those constituents affect flashover performance differentially. Currently, this fact is not considered either in laboratory experiments or field pollution degree measurements, causing the existing insulation selection method to be deficient. In this paper, a systematic study on insulator flashover voltage gradient correction involving different types of soluble pollution constituents is presented. Using a typical type glass insulator as the sample, its flashover tests, polluted by typical soluble chemicals (NaCl, NaNO3, KNO3, NH4NO3, MgSO4, Ca(NO3)2 and CaSO4), were carried out. Then, the flashover gradient correction was made by combining the flashover performance of each soluble constituent, the equivalent salt deposit density (ESDD) contribution of the seven constituents, and the saturation performance of CaSO4. The correction agreed with the flashover test results of insulator polluted by three types of soluble mixture. Research results indicate that the flashover gradient correction method proposed in this paper performs well in reducing the calculating error. It is recommended to carry out component measurements and flashover gradient correction to better select outdoor insulation configuration.

International audience; A novel hard material, orthorhombic BCN3 based on the intergrowth of non-centrosymmetric wurtzite CN+ and centrosymmetric pyrite BN2− motifs alike in fully characterized AlSiP3 ternary is proposed from calculations within DFT methodology. BCN3 is identified as a “nitride-dinitride” related with Zintl phases. The ground state structure exhibits significantly short interatomic distances: d(C-N) = 1.47 Å and d(N-N) = 1.43 Å as compared to d(Si-P) = 2.24 Å and d(P-P) = 2.18 Å in the phosphide, resulting into high magnitude bulk modulus obtained from E,V equation of state (EOS) with B0 = 371 GPa versus B0 = 97 GPa in the phosphide. The complete set of elastic constants complies with the mechanical stability conditions of the new system and equally produces high hardness magnitude (384 GPa). Ratio of bulk/shear modules of 0.85 characterizes a brittle material. Electronic band structures identify small indirect gap semi-conducting AlSiP3 and large band gap insulator BCN3 with direct gap ΓV-ΓC ∼ 4 eV.

We study the fate of the surface states of Bi$_2$Se$_3$ under disorder with strength larger than the bulk gap, caused by neon sputtering and nonmagnetic adsorbates. We find that neon sputtering introduces strong but dilute defects, which can be modeled by a unitary impurity distribution, whereas adsorbates, such as water vapor or carbon monoxide, are best described by Gaussian disorder. Remarkably, these two disorder types have a dramatically different effect on the surface states. Our soft x-ray ARPES measurements combined with numerical simulations show that unitary surface disorder pushes the Dirac state to inward quintuplet layers, burying it below an insulating surface layer. As a consequence, the surface spectral function becomes weaker, but retains its quasiparticle peak. This is in contrast to Gaussian disorder, which smears out the quasiparticle peak completely. At the surface of Bi$_2$Se$_3$, the effects of Gaussian disorder can be reduced by removing surface adsorbates using neon sputtering, which, however, introduces unitary scatterers. Since unitary disorder has a weaker effect than Gaussian disorder, the ARPES signal of the Dirac surface state becomes sharper upon sputtering., Comment: 5+2 pages. 4 figures

We report an innovative technique for growing the silicon carbide-on-insulator (SiCOI) structure by utilizing polycrystalline single layer graphene (SLG) as a buffer layer. The epitaxial growth was carried out using a hot-mesh chemical vapor deposition (HM-CVD) technique. Cubic SiC (3C-SiC) thin film in (111) domain was realized at relatively low substrate temperature of 750 °C. 3C-SiC energy bandgap of 2.2 eV was confirmed. The Si-O absorption band observed in the grown film can be caused by the out-diffusion of the oxygen atom from SiO2 substrate or oxygen doping during the cleaning process. Further experimental works by optimizing the cleaning process, growth parameters of the present growth method, or by using other growth methods, as well, are expected to realize a high quality SiCOI structure, thereby opening up the way for a breakthrough in the development of advanced ULSIs with multifunctionalities.