Spatial Distribution Of Electric Field Research Articles

The Influence of Temperature on Charging Effects in Mask During Plasma Etching

ABSTRACTThis research examines the correlation between temperature effects and surface charging problems on a silicon dioxide mask using simulation techniques. The findings of this study validate the significance of considering electron–solid interactions, especially when influenced by varying temperatures. The impacts of temperature changes on the spatial distributions of net charge deposition, electric potential, and electric field are examined. It was noted that the temperature rise leads to an increase in the concentration of positively charged holes near the surface of the mask, thereby diminishing the spatial dispersion of positive potential. This results in a less conspicuous alteration of the mask profile as the temperature increases. This investigation is anticipated to possess substantial significance and offer valuable insights for optimizing mask design.

Array hollow-anode microsecond-pulsed plasma jets at atmospheric pressure: mode transition and influencing factors

Abstract Hollow cathode plasma jets are commonly utilized across various fields, yet there is limited research on hollow anode discharge, particularly on array hollow anode plasma jets. This letter presents the novel design of a array hollow anode discharge device excited by microsecond pulse. Systematical investigations about the discharge characteristics and mode transition process of the device are examined from the perspectives of electricity and space-time distribution to get insights into the formation mechanisms of array hollow anode plasma jets. Results show that three distinct discharge modes when the array hollow anode plasma jets interacting with ITO plate are identified based on the number and location of the discharged hollow anodes: Mode A involves all 16 hollow anodes discharging, Mode B entails 12 hollow anodes discharging, and Mode C comprises 4 hollow anodes discharging at the four vertices of the device. It is observed that experimental outcomes are influenced by the distance from the hollow anode tube port to the plate. The formation mechanism is determined by an increase in distance impacting spatial electric field distribution and facilitating mode transition. Furthermore, the impacts of pulse voltage, pulse frequency, and flow rate on the variation of interval length under different modes are investigated. The results indicate that voltage has the most significant effect on interval length, followed by frequency, while flow rate has a minimal effect. These findings hold significant implications for enhancing understanding of mode transition and influencing factors of array hollow anode plasma jets.

Electric Field Features and Charge Behavior in Oil-Pressboard Composite Insulation under Impulse Voltage

Oil-pressboard/paper insulation materials are essential in transformers for ensuring their safe and stable operation, primarily due to their roles in spatial electric field distribution and charge migration mechanisms. Current spatial distribution analyses rely on computational methods that lack empirical validation, particularly for oil-pressboard/paper composites. This study leverages the principles of the Kerr electro-optic effect to develop a rapid measurement platform for electric fields within oil-pressboard/paper insulation under impulse voltage conditions, which measures the spatial electric field characteristics using Cu-Cu and Al-Al electrodes under various scenarios: with asymmetric and symmetric pressboard coverage and different numbers of insulating paper layers. Findings indicated: (1) In asymmetric pressboard models, Cu-Cu electrodes exhibit a consistent peak electric field of approximately 16 kV/mm, while Al-Al electrodes show peak values of 18.13 kV/mm and −14.98 kV/mm. Charge density patterns are similar, with Cu-Cu at about 68 μC/m2 and Al-Al at 11.2 μC/m2 and −124.8 μC/m2. (2) Symmetric models present consistent peak electric fields and charge densities for both polarities. (3) Increasing insulating paper layers elevates electric field strengths. Both electrodes show the similar peak field of about 17 kV/mm with differing paper layers due to higher charge injection from the Al electrode. (4) Utilizing the Schottky effect and field emission principles, the study clarifies charge generation and migration mechanisms. These insights could provide a theoretical foundation for designing and verifying oil-pressboard/paper insulation structures in transformers.

Kerr Electro-Optic Effect-Based Methodology for Measuring and Analyzing Electric Field Distribution in Oil-Immersed Capacitors

In the current design and verification processes of insulation structures for high-voltage oil-immersed capacitors, there is a heavy reliance on electric field simulation calculations using idealized models that lack empirical validation of spatial electric fields. This study employs the Kerr electro-optic effect to establish a non-contact optical remote sensing system for measuring the spatial electric field distribution in the insulating liquid dielectric (benzyltoluene) between the capacitor’s element and the case under various temperatures and main insulation distances. The findings reveal that the measured spatial electric field stress can be up to 15% higher than the simulated values. The electric field stress measured in the Y1 direction (up toward the capacitor top) is comparable to that measured in the Y2 direction (down toward the capacitor end). Furthermore, when varying the main insulation distance, the electric field stress consistently shows a negative correlation with increasing measurement distance. Specifically, at a main insulation distance of 1.5 mm, the electric field stress is 1.81 times that at 5.5 mm. As the temperature rises, the spatial electric field stress increases gradually, and the electric field distribution becomes more uneven at higher temperatures. At 80 °C, the field stress is approximately 1.57 times that at 20 °C, with the measured field stress at 80 °C being 19% higher than the simulated value. Finally, this paper undertakes a comprehensive theoretical analysis and experimental validation to elucidate the discrepancies between simulated and measured spatial electric fields. Leveraging these insights, it proposes advanced optimization strategies for the insulation structures of capacitor elements. The outcomes of this study furnish substantial technical and theoretical support, significantly enhancing the design, verification, and optimization processes for insulation in oil-immersed capacitors.

A Closed Formalism for Anatomy-Independent Projection and Optimization of Magnetic Stimulation Coils on Arbitrarily Shaped Surfaces.

Transcranial magnetic stimulation (TMS) is a popular method for the noninvasive stimulation of neurons in the brain. It has become a standard instrument in experimental brain research and has been approved for a range of diagnostic and therapeutic applications. These applications require appropriately shaped coils. Various applications have been established or approved for specific coil designs with their corresponding spatial electric field distributions. However, the specific coil implementation may no longer be appropriate from the perspective of available material and manufacturing opportunities or considering the latest understanding of how to achieve induced electric fields in the head most efficiently. Furthermore, in some cases, field measurements of coils with unknown winding or a user-defined field are available and require an actual implementation. Similar applications exist for magnetic resonance imaging coils. This work aims at introducing a complete formalism free from heuristics, iterative optimization, and ad-hoc or manual steps to form practical stimulation coils with individual turns to either equivalently match an existing coil or produce a given field. The target coil can reside on practically any sufficiently large or closed surface adjacent to or around the head. The method derives an equivalent field through vector projection exploiting the well-known Huygens' and Love's equivalence principle. In contrast to other coil design or optimization approaches recently presented, the procedure is an explicit forward Hilbert-space vector projection or basis change. For demonstration, we map a commercial figure-of-eight coil as one of the most widely used devices and a more intricate coil recently approved clinically for addiction treatment (H4) onto a bent surface close to the head for highest efficiency and lowest field energy. The resulting projections are within ≤4% of the target field and reduce the necessary pulse energy by more than 40%.

A bird droppings flashover analysis method based on the combination of electric field distortion and spatial electric field distribution

To study the flashover of air gap caused by bird droppings shorting air gap and the influence of space electric field change on it, the distortion electric field simulation, space electric field simulation, and related flashover test of transmission line bird droppings falling process were carried out. By analyzing the specific influencing factors of bird droppings flashover fault, it is pointed out that the electric field distortion caused by bird droppings will affect the spatial electric field distribution around the insulator and thus affect the air gap flashover. This study analyzes the specific causes of bird dropping flashover of transmission line insulators, reduces the number of bird damage trips of transmission lines, reduces the cost of operation and maintenance of transmission lines, improves the intrinsic safety of transmission lines, and ensures the safe and reliable operation of power grids.

Advanced characterization of SiC devices by optical beam induced current (OBIC): Experimental and simulation results

Wide-bandgap semiconductors, such as silicon carbide (SiC), gallium nitride (GaN), and diamond (C), have proven to outperform traditional silicon (Si) based power electronic devices. However, the peripheral protection of these wide-bandgap devices requires careful design to handle high voltage effectively. This article highlights the potential of using the Optical Beam Induced Current (OBIC) technique to analyze the effectiveness of different protection methods and provide valuable feedback to device designers regarding peripheral termination efficiency. Designers need simulations representative of the measurement, In this article a finite element simulation is used to determine the induced current as a function of the position of the optical beam.Firstly a theoretical approach will be presented to introduce the OBIC method. Subsequently, the electro-optical characterization technique is applied to a PiN diode protected by narrow field rings.The article also showcases new results obtained from components with new-generation peripheral protection, demonstrating the continuous progress in this field.Overall, this article highlights the significance of the OBIC technique in evaluating the effectiveness of peripheral protection methods for wide-bandgap semiconductors, particularly SiC devices. By providing valuable insights into the electric field's spatial distribution, this technique aids in optimizing device design and improving overall performance. Finite element simulations in relation to the characteristics of the UV beam and its scanning across the surface of the component help to assess the geometric parameter impact on the electrical results.

Photodetector array for measuring the spatial–temporal distribution characteristics of electric field in oil–pressboard insulation based on the Kerr electro‐optic effect

AbstractAccurate measurement and effective analysis of the space electric field and charge characteristics within the oil–pressboard insulation structure of converter transformer are essential for achieving precise insulation structure design. Presently, most electric field measurement methods relying on the Kerr electro‐optical effect are limited to single‐point measurements. Given the complexity of converter transformer insulation structures, including their large scale and the use of various materials, existing technologies and findings struggle to provide comprehensive electric field observations within the oil–pressboard region. After leveraging the Kerr electro‐optic effect, a high‐precision 32‐unit photodetector array has been developed to achieve regional measurements of spatial‐temporal electric field in oil–pressboard insulation. The array boasts a measurement spatial resolution of 1.4 mm2 and a sensitivity of 0.15 kV/mm, ensuring measurement accuracy exceeding 96.50%. Through practical measurements of the spatial electric field distribution within the oil–pressboard insulation under direct current voltage, the non‐uniform distribution of the electric field is effectively captured in oil. Notably, the maximum deviation in field strength at different positions within the transformer oil can reach 18.5%. Moreover, as the applied voltage increases, the unevenness coefficient of the field strength gradually rises, peaking at 1.19, which signifies a progressive expansion in the area affected by electric field distortion. By conducting tests to assess the dispersion of volume resistivity in samples from various positions within large sheets of pressboard, the variation in volume resistivity of materials is posited as one of the contributing factors to the non‐uniform distribution of electric field within the oil. The detailed accomplishments aim to provide essential technical and theoretical support for optimising insulation structure design of converter transformers.

Performance improvement of enhancement-mode GaN-based HEMT power devices by employing a vertical gate structure and composite interlayers*

In this work, p-n junction vertical gate (JVG) and polarization junction vertical gate (PVG) structures are for the first time proposed to improve the performance of GaN-based enhancement-mode (E-mode) high electron mobility transistor (HEMT) devices. Compared with the control group featuring the vertical gate structure, a highly improved threshold voltage (V th) and breakdown voltage (BV) are achieved with the assistance of the extended depletion regions formed by inserting single or composite interlayers. The structure dimensions and physical parameters for device interlayers are optimized by TCAD simulation to adjust the spatial electric field distribution and hence improve the device off-state characteristics. The optimal JVG-HEMT device can reach a V th of 3.4 V, a low on-state resistance (R on) of 0.64 mΩ cm2, and a BV of 1245 V, while the PVG-HEMT device exhibits a V th of 3.7 V, an R on of 0.65 mΩ cm2, and a BV of 1184 V, which could be further boosted when an additional field plate design is employed. Thus, the figure-of-merit value of JVG- and PVG-HEMT devices rise to 2.4 and 2.2 GW cm−2, respectively, much higher than that for the VG-HEMT control group (1.0 GW cm−2). This work provides a novel technical approach to realize higher-performance E-mode HEMTs.

Time-dependent model of temperature distribution in continuous flow pulsed electric field treatment chambers

A key component of a continuous flow pulsed electric field (PEF) system is the treatment chamber, where the product is exposed to electric pulses. Determination of the temperature distribution in the chamber during PEF treatment is important since high local increases in temperatures can affect the quality of the product. Coupled simulations of electric field, fluid flow, and heating in the existing literature do not model each individual electric pulse, but rather employ a “duty cycle” approach, which does not account for transient variations in treatment intensity and temperature changes in the medium. We present a time-dependent approach to modelling PEF treatment in continuous flow treatment chambers, which can model each pulse separately, and thus enables a more accurate study of temporal and spatial distributions of electric field and temperature. The model has been validated on laboratory scale treatment chambers of parallel plate or colinear design and using realistic protocols. Industrial relevance textThe paper is relevant to all pulsed electric field (PEF) applications either on laboratory or industrial scale that implement a continuous flow treatment chamber. It presents an improved modelling approach which allows for an analysis of the electrical current, electric field, and temperature distribution in the chamber during, at the end, and in between application of electrical pulses. The model can be used to predict the peak temperature at the end of each pulse in the hot spots, which if large enough could potentially lead to thermal damage of the product or in extreme cases even potential local boiling of the medium, resulting not only in degradation of the treated product, but also in accelerated electrode fouling, oxidation, and dissolution (etching), as well as arcing. This would not only affect the quality of the treated product but would also affect the wear and lifetime of electrodes/chambers, and of the pulse generator. The model can also be used to avoid expensive trial-and-error optimization of the PEF protocols and chamber geometries in situ.

A method for identifying the operating state of deteriorated insulators based on partial discharge signal reconstruction algorithm and spatial electric field distribution law

In order to improve the accuracy of identifying the working status of degraded insulators and thereby contribute to preventive maintenance and repair, this proposes a method for identifying the operating status of deteriorated insulators based on a partial discharge signal reconstruction algorithm and spatial electric field distribution law. Firstly, the partial discharge signal of the deteriorated insulator is obtained through capacitive sensor technology and clustering analysis algorithm. Then, the mapping features between the partial discharge signal and the electric field distribution are extracted using the SN-EMD algorithm to determine the spatial electric field distribution on the surface of the insulator. Finally, a state recognition model is established based on the hidden Markov model to identify the operating status of deteriorated insulators. The experimental results show that the method designed in this paper has superior performance in terms of accuracy.

Design of a microwave spectrometer for high-precision Lamb shift spectroscopy of antihydrogen atoms

We have developed a microwave spectrometer for a measurement of the 2S1/2-2P1/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{2S_{1/2}-2P_{1/2}}$$\\end{document} Lamb shift of antihydrogen atoms towards the determination of the antiproton charge radius. The spectrometer consists of two consecutive apparatuses, of which the first apparatus, Hyperfine Selector (HFS), filters out 2S1/2(F=1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{2S_{1/2}(F=1)}$$\\end{document} hyperfine states and pre-selects the 2S1/2(F=0)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{2S_{1/2}(F=0)}$$\\end{document} state, and the second apparatus, MicroWave Scanner (MWS), sweeps the frequency around the target transition to obtain the spectrum. We optimized the geometry of the apparatuses by evaluating the S-parameter that represents the ratio of the reflected microwave signal over the input, utilizing microwave simulations based on the finite element method. The HFS was designed to obtain a resonant property at 1.1 GHz for an efficient removal of the 2S1/2(F=1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{2S_{1/2}(F=1)}$$\\end{document} hyperfine states, and the MWS was designed to realize weak frequency-dependency in the signal reflection. Also, the spatial distributions of microwave electric field were simulated. We report the design of the spectrometer and discuss an expected precision of the first measurement.

Electrochemotherapy for head and neck cancers: possibilities and limitations.

Head and neck cancer continues to be among the most prevalent types of cancer globally, yet it can be managed with appropriate treatment approaches. Presently, chemotherapy and radiotherapy stand as the primary treatment modalities for various groups and regions affected by head and neck cancer. Nonetheless, these treatments are linked to adverse side effects in patients. Moreover, due to tumor resistance to multiple drugs (both intrinsic and extrinsic) and radiotherapy, along with numerous other factors, recurrences or metastases often occur. Electrochemotherapy (ECT) emerges as a clinically proven alternative that offers high efficacy, localized effect, and diminished negative factors. Electrochemotherapy involves the treatment of solid tumors by combining a non-permeable cytotoxic drug, such as bleomycin, with a locally administered pulsed electric field (PEF). It is crucial to employ this method effectively by utilizing optimal PEF protocols and drugs at concentrations that do not possess inherent cytotoxic properties. This review emphasizes an examination of diverse clinical practices of ECT concerning head and neck cancer. It specifically delves into the treatment procedure, the choice of anti-cancer drugs, pre-treatment planning, PEF protocols, and electroporation electrodes as well as the efficacy of tumor response to the treatment and encountered obstacles. We have also highlighted the significance of assessing the spatial electric field distribution in both tumor and adjacent tissues prior to treatment as it plays a pivotal role in determining treatment success. Finally, we compare the ECT methodology to conventional treatments to highlight the potential for improvement and to facilitate popularization of the technique in the area of head and neck cancers where it is not widespread yet while it is not thecase with other cancer types.

Multi-layer phenomena in petawatt laser-driven acceleration of heavy ions

Laser-accelerated high-flux-intensity heavy-ion beams are important for new types of accelerators. A particle-in-cell program (Smilei) is employed to simulate the entire process of Station of Extreme Light (SEL) 100 PW laser-accelerated heavy particles using different nanoscale short targets with a thickness of 100 nm Cr, Fe, Ag, Ta, Au, Pb, Th and U, as well as 200 nm thick Al and Ca. An obvious stratification is observed in the simulation. The layering phenomenon is a hybrid acceleration mechanism reflecting target normal sheath acceleration and radiation pressure acceleration, and this phenomenon is understood from the simulated energy spectrum, ionization and spatial electric field distribution. According to the stratification, it is suggested that high-quality heavy-ion beams could be expected for fusion reactions to synthesize superheavy nuclei. Two plasma clusters in the stratification are observed simultaneously, which suggest new techniques for plasma experiments as well as thinner metal targets in the precision machining process.

Ultrahigh efficiency and enhanced discharge energy density at low loading of nanofiller in trilayered polyvinylidene fluoride‐Ba0.8Sr0.2TiO3 nanocomposites

AbstractPoly(vinylidene)fluoride‐Ba0.8Sr0.2TiO3 (PVDF‐BST) trilayered nanocomposites (with different vol% loading of BST nanoparticles, i.e. 0.75%, 1.50%, 2.25% and 3.00%) has been processed by the tape casting technique. The upper and lower layers of the nanocomposites are casted in the same direction, whereas the middle layer is casted in the opposite direction. The trilayered PVDF‐BST nanocomposite consisting of 3.00 vol% of BST nanoparticles exhibited high dielectric permittivity (~25), low tangent loss (~0.03) and moderately high breakdown strength (BDS ~282 MV/m). Moreover, it also possesses a high discharge energy density (~7.8 J/cc at 1400 kV/cm) and efficiency (~93%). A mechanism for the excellent energy storage behavior and dielectric properties has been proposed. Where, moderately high BDS and low tangent loss are associated with the spatial distribution of the local electric field at interlayer interfaces of PVDF‐BST trilayered nanocomposites, which restricts the conduction of charge carriers at high electric field. The ultrahigh efficiency and enhanced discharge energy density is attributed to the formation of interfacial dipoles at various interfaces such as interlayer, intralayer (PVDF/PVDF), and PVDF/BST interfaces. These investigations would be adopted as a futuristic strategy for developing excellently efficient polymer‐ceramic nanocomposites for the high energy density capacitors used in pulsed power applications.Highlights PVDF‐BST trilayered nanocomposites exhibit high ε′ ~25 and low tanδ ~0.03. Nanocomposite shows ultra‐high energy efficiency ~93% and enhanced UD ~ 7.8 J/cc. Mechanism for the excellent energy storage and dielectric properties Relies on the interfacial dipoles and distribution of the local electric field.

Thermal switch for localized heating based on spatial electric field distribution regulation

At present, the thermal switch for localized heating is becoming a hot research topic in MEMS packaging technology. A method of using a liquid-based thermal switch is proposed in this paper. A plate local heating device based on electric field distribution control is constructed, where a thermal liquid column can be formed under the action of the electric field. The electric field controls the formation and dissipation of the liquid column to realize the on-off and off-on function of the thermal switch. Through the control of the different conductive substrates in the plate, the localized heat transfer can be further realized, and the heat transfer position is precisely regulated. Furthermore, due to the fluidity of the liquid, the prepared thermal switch can also realize movable heating. The experimental results show that the heating time and speed can be controlled precisely by adjusting the driven voltage and the conductive area of the upper substrate.

Improved Breakdown Strength and Restrained Leakage Current of Sandwich Structure Ferroelectric Polymers Utilizing Ultra-Thin Al2O3 Nanosheets.

Flexible capacity applications demand a large energy storage density and high breakdown electric field strength of flexible films. Here, P(VDF-HFP) with ultra-thin Al2O3 nanosheet composite films were designed and fabricated through an electrospinning process followed by hot-pressing into a sandwich structure. The results show that the insulating ultra-thin Al2O3 nanosheets and the sandwich structure can enhance the composites' breakdown strength (by 24.8%) and energy density (by 30.6%) compared to the P(VDF-HFP) polymer matrix. An energy storage density of 23.5 J/cm3 at the ultrahigh breakdown strength of 740 kV/mm can be therefore realized. The insulating test and phase-field simulation results reveal that ultra-thin nanosheets insulating buffer layers can reduce the leakage current in composites; thus, it affects the electric field spatial distribution to enhance breakdown strength. Our research provides a feasible method to increase the breakdown strength of ferroelectric polymers, which is comparable to those of non-ferroelectric polymers.

Study on the Formation and Controllable Movement of Polymer Liquid Columns Based on Dynamic Control of Spatial Electric Field Distribution.

Liquid deformation and motion are very common natural phenomena and of great value in various practical applications. In this study, a dielectric fluid column formation and directional flow phenomenon are presented. Dielectric fluid can grow upward to form a liquid column through a spatial electric field and realize directional and controllable operation of the liquid column by regulating spatial electric field distribution. First, the adjustable electric field space is constructed by connecting the two parallel electrodes to the high-voltage DC power supply. Then, the regional electric field distribution was adjusted by the upper plate graphic and power supply regulation to drive the polymer liquid on the lower plate electrode to form a liquid column at different positions. The results show that the polymer liquid column can be driven by the spatial electric field distributed dynamic control method and that the height and the narrowest width of the liquid column are directly controlled by the voltage. With the experiment conditions that the distance between two parallel electrodes is 5-15 mm, the formation of liquid columns with a height of 5-15 mm can be controlled. In addition, the liquid column can be driven by adjusting the on-states of different conductive regions. When the voltage is 10 kV, the liquid column directional movement speed can reach 1 mm/s. The higher the voltage, the faster the directional movement. The research results can be used as producing polydimethylsiloxane stamp, localized heating and temperature control, fabricating a pulsating heat pipe, and so on.

Lattice constant and polarization-independent high transmission in tellurium-based dielectric metasurfaces

High-refractive-index dielectric metasurfaces give rise to unprecedented control of light manipulation, such as control of phase, polarization and amplitude, giving rise to interesting properties, such as directional beam steering, polarization detectors and sensors. Dielectric metasurfaces of sub-wavelength dimensions have tremendous applications in the field of optics, such as negative refractive index, cloaking, perfect absorbers and reflectors. The study of light–matter interactions in such materials has gained impetus due to the formation of novel states, such as anapoles, and transparent states obtained by interference between resonant electric, magnetic and higher-order modes. In this article, we investigate the light–matter interaction of an array of periodic dielectric metasurfaces made from high-refractive-index tellurium in cubic geometries and study its electromagnetic response as a function of the lattice constant, angle of incidence and angle of polarization. More specifically, we observe a non-resonant transparent state at 60.69 THz, which is independent of both the lattice constant and polarization of the input radiation. Moreover, this state shows high transmission for a broad range of incident angles with potential applications as optical filters. It also depends on the incident polarization, thus acting as a perfect polarization detector. Detailed investigations of scattering parameters, the spatial distribution of electric and magnetic fields in the near- and far-field regions and detailed multipole analysis are carried out to analyze the electromagnetic response of the metasurface.

Moiré Superlattice Structure of Pleated Trilayer Graphene Imaged by 4D Scanning Transmission Electron Microscopy.

Moiré superlattices in graphene arise from rotational twists in stacked 2D layers, leading to specific band structures, charge density and interlayer electron and excitonic interactions. The periodicities in bilayer graphene moiré lattices are given by a simple moiré basis vector that describes periodic oscillations in atomic density. The addition of a third layer to form trilayer graphene generates a moiré lattice comprised of multiple harmonics that do not occur in bilayer systems, leading to nontrivial crystal symmetries. Here, we use atomic resolution 4D-scanning transmission electron microscopy to study atomic structure in bilayer and trilayer graphene moiré superlattices and use 4D-STEM to map the electric fields to show subtle variations in the long-range moiré patterns. We show that monolayer graphene folded into an S-bend graphene pleat produces trilayer moiré superlattices with both small (<2°) and larger twist angles (7-30°). Annular in-plane electric field concentrations are detected in high angle bilayers due to overlapping rotated graphene hexagons in each layer. The presence of a third low angle twisted layer in S-bend trilayer graphene, introduces a long-range modulation of the atomic structure so that no real space unit cell is detected. By directly imaging trilayer moiré harmonics that span from picoscale to nanoscale using 4D-STEM, we gain insights into the complex spatial distributions of atomic density and electric fields in trilayer twisted layered materials.