Electrostatic Confinement Research Articles

Electrostatic Confinement‐Induced Excited Charge Transfer in Ionic Covalent Organic Framework Promoting CO2 Reduction

We demonstrate an electrostatic confinement‐induced charge transfer pathway in a supramolecular photocatalyst comprising of an ionic covalent organic framework (COF) and cationic metal complexes. The dynamic electrostatic interactions not only attract cations around the COF to accept photogenerated electrons, but also allows for a retention of homogeneous catalytic characters of complexes, making a subtle balance. Accordingly, the electrostatic confinement effect facilitates the forward electron transfer from a photoexcited COF to cationic Co complex, realizing a remarkable photocatalytic CO2 reduction performance. Its catalytic efficiency is far superior to the supramolecular counterparts with Van‐der‐Waals or hydrogen bonding interactions. This work presents an insight for enhancing charge transfer in supramolecular systems, and provides an effective approach for construction of highly efficient photocatalysts.

Effect of electrostatic confinement on the dome-shaped superconducting phase diagram at the LaAlO3/SrTiO3 interface

The two-dimensional electron gas (2DEG) at the LaAlO\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document}/SrTiO\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document} (LAO/STO) interface exhibits gate-tunable superconductivity with a dome-like shape of critical temperature as a function of electron concentration. This behavior has not been unambiguously explained yet. Here, we develop a microscopic model based on the Schrödinger–Poisson approach to determine the electronic structure of the LAO/STO 2DEG, which we then apply to study the principal characteristics of the superconducting phase within the real-space pairing mean-field approach. For the electron concentrations reported in the experiment, we successfully reproduce the dome-like shape of the superconducting gap. According to our analysis such behavior results from the interplay between the Fermi surface topology and the gap symmetry, with the dominant extended s-wave contribution. Similarly as in the experimental report, we observe a bifurcation effect in the superconducting gap dependence on the electron density when the 2DEG is electrostatically doped either with the top gate or the bottom gate. Our findings explains the dome-shaped phase diagram of the considered heterostucture with good agreement with the experimental data which, in turn, strongly suggest the appearance of the extended s-wave symmetry of the gap in 2DEG at the LAO/STO interface.

Influence of electrode transparency on the plasma properties of a cylindrical IEC plasma source

This study investigates the influence of cathode and anode grid transparency on the plasma properties of a Cylindrical Inertial Electrostatic Confinement plasma source. The primary focus is to elucidate how variations in the transparency of the electrodes impact plasma characteristics and the operational performance of the source, particularly during spray jet mode. Employing optical emission spectroscopy (OES) and Langmuir probe diagnostics, the plasma behavior is analyzed comprehensively. The results demonstrate that cathode transparency has a pronounced effect on discharge current and plasma density within the cathode. Conversely, the transparency of the anode has only a little influence the ignition characteristics and operational stability of the plasma source. The findings highlight the importance of utilizing cathode transparency to adjust both the pressure and voltage operating ranges of the IEC source in spray jet mode, optimizing its performance for various applications.

Investigation of the Effects of Ion Sources and RF Power on the Neutron Production Rate at SNRTC-IEC Fusion Device

Studies on an inertial electrostatic confinement (IEC) device are generally focused on increasing particle production. One way to achieve this is to increase the number of ion sources. In this study, the deuterium-deuterium fusion reaction was carried out in the IEC Saraykoy Nuclear Research and Training Center (SNRTC-IEC) fusion device (previously at the Turkish Atomic Energy Authority, now reestablished as the Turkish Energy, Nuclear and Mineral Research Agency) at cathode voltage of 85 kV and pressure of 5 × 10−4 mbars, and the effect of ion sources and radio-frequency (RF) power on the neutron production rate was investigated. To ensure a high concentration of ions in the center of the cathode, three inductively coupled plasma deuterium ion sources were added to this device. As the number of ion sources increased from one to three, the neutron production rate increased from 2.3 × 104 to 3.6 × 105n/s. Two ion source configurations were used to examine the effect of RF power. It was observed that when the RF power was increased from 40 to 200 W, the neutron production rate increased linearly from 4.6 × 104 to 1.7 × 105 n/s.

The Orbitron: A crossed-field device for co-confinement of high energy ions and electrons

To explore the confinement of high-energy ions above the space charge limit, we have developed a hybrid magnetic and electrostatic confinement device called an Orbitron. The Orbitron is a crossed-field device combining aspects of magnetic mirrors, magnetrons, and orbital ion traps. Ions are confined in orbits around a high-voltage cathode with co-rotating electrons confined by a relatively weak magnetic field. Experimental and computational investigations focus on reaching ion densities above the space charge limit through the co-confinement of electrons. The experimental apparatus and suite of diagnostics are being developed to measure the critical parameters, such as plasma density, particle energy, and fusion rate for high-energy, non-thermal plasma conditions in the Orbitron. Initial results from experimental and computational efforts have revealed the need for cathode voltages on the order of 100–300 kV, leading to the development of a custom high voltage, ultra-high vacuum bushing rated for 300 kV.

Characterization of a radially emitting spray jet in a cylindrical inertial electrostatic confinement plasma source based on particle in cell simulation

This paper investigates the outflow mechanism of a cylindrical inertial electrostatic confinement plasma source using Particle in Cell plasma simulations. Various phenomena such as ion-wall interactions, impact ionization, excitation, and secondary electron generation are considered. Together with a fine time and cell resolution to reveal relevant phenomena. The results indicate a high electron and ion density in front of the cathode at the widest grid opening, which suggests the formation of a cascade-like charge carrier emission, commonly referred to as the “spray jet”. Initially, a virtual anode is formed within the cathode grid and is shifted toward the grid opening as time elapsed. Ions are accelerated in the plasma sheath around the cathode and collide with the cathode grids or oscillate through the grid opening. Electrons are accelerated and ionize the background gas at the plasma sheath edge. While the electron flow is disordered within the cathode it forms a cascade-like quasi-neutral plasma at the outlet of the plasma source. Through the formation of a virtual anode the discharge becomes self-sustained. With this simulation results the working principle of the inertial electrostatic confinement plasma source can be derived.

Improvement in ion confinement time with multigrid configuration in an inertial electrostatic confinement fusion device.

Improvement in the functionality of an inertial electrostatic confinement fusion (IECF) device has been investigated through kinetic simulation. Previously, we achieved a neutron generation rate of 10^{6} neutrons per second, but higher rates and better plasma confinement are necessary for broader applications. We compared a traditional single-grid IECF device with a triple-grid variant to evaluate the benefits of using multiple grids for ion confinement. Our computational models, using the 2D-3V xoopic code, suggest that the triple-grid device, with its optimized potentials, could significantly enhance ion confinement. The models show that the triple-grid design directs ion beams more effectively to the center, in contrast with the more scattered ion distribution in the single-grid design. This results in longer ion lifetimes in the triple-grid system due to its modified electrostatic fields. In the standard single-grid IECF device, the primary reasons for ion loss are chaotic ion trajectories and interactions with residual gases. By operating the triple-grid device under very low background gas pressure and with a focused field structure, we expect to achieve improved ion confinement.

Performance of an inertial electrostatic confinement fusion device having a multi-grid configuration

The aim of this work is to enhance the performance of an inertial electrostatic confinement fusion (IECF) device, addressing the issues with glow discharge voltage, current, and gas pressure while achieving significant fusion reactions at reduced pressure. Previous success involved a fusion rate of 106 n/s in a single-grid IECF system, but broader applications require higher neutron production by improving ion density, ion energy, and plasma confinement. Electrostatic focusing ion beams are proposed for better ion confinement. Comparing a single-grid IECF device with a triple-grid one, computational modeling using a 2D-3 V XOOPIC code suggests significant improvements in ion confinement with tailored potentials in the triple-grid device. The simulation demonstrates that modifying electrostatic fields in the triple-grid setup creates a potential well with humps, guiding ion beams to the central region and enhancing ion density.

Nondestructive and active interrogation system for special nuclear material: proof of principle and initial results

Herein, we employ the threshold energy neutron analysis (TENA) technique to introduce the world's first active interrogation system to detect special nuclear materials (SNMs), including U-235 and Pu-239. The system utilizes a DD neutron generator based on inertial electrostatic confinement (IEC) to interrogate suspicious objects. To detect secondary neutrons produced during fission reactions induced in SNMs, a tensioned metastable fluid detector (TMFD) is employed. The current status of the system's development is reported in this paper, accompanied by the results from experiments conducted to detect 10 g of highly enriched uranium (HEU). Notably, the experimental findings demonstrate a distinct difference in the count rates of measurements with and without HEU. This difference in count rates surpasses two times the standard deviation, indicating a confidence level of more than 96% for identifying the presence of HEU. The paper presents and extensively discusses the proof-of-principle experimental results, along with the system's planned trajectory.

Superlattice Quantum Solid of Dipolar Excitons.

We study dipolar excitons confined at 330mK in a square electrostatic lattice of a GaAs double quantum well. In the dipolar occupation blockade regime, at 3/2 filling, we evidence that excitons form a face-centered superlattice quantum solid. This phase is realized with high purity across 36 lattice sites, in a regime where the mean interaction energy exceeds the depth of the electrostatic lattice confinement. The superlattice solid then closely relates to Wigner crystals.

Bifunctional Zn2+-solvation structure electrolyte for highly reversible zinc anodes

Aqueous zinc batteries exhibit promises for energy storage systems because of their attractive advantages including low cost and high safety. However, Zn anodes often face challenges such as water-induced side reactions and dendritic growth. Here, we present an electrolyte engineering with bifunctional Zn2+-solvation structures to solve these problems. 1) The coordination between anions and Zn2+ neutralizes the Zn2+-solvation structure, creating an electrostatic shielding effect that hinders dendritic growth on the Zn surface. 2) The original H-bond networks between water molecules are replaced by the abundant O-H∙∙∙Cl- H-bond networks through the electrostatic confinement, thus capable of reducing the water activity. Moreover, the electrolyte endows the Zn anode with fast plating/stripping behaviors owing to its enhanced ionic migration kinetics. Consequently, the Zn‖Zn cell maintains a high Coulombic efficiency (99.6 %) after 600 cycles. The assembled Zn‖PANI hybrid capacitor exhibits improved electrochemical reversibility and cycling stability over 2000 cycles. This work offers valuable insights into the development of electrolyte design strategies for advanced aqueous energy-storage devices.

Exploring Electrostatic Confinement Transport in MoS2/WSe2 Heterostructure via Triple‐Gated Point Contact Device

AbstractThe exponential development in quantum phenomena is directly correlated with the decreasing size of nano‐semiconductor transistors. Consequently, the use of a quantum structure that deviates from traditional transistor types becomes imperative. Electrostatically defined nanoscale devices within 2D semiconductor heterostructures serve as foundational elements for diverse quantum electrical circuits. Van der Waals heterostructures, distinguished by atomically flat interfaces and inherent 2D characteristics, offer advantages such as large‐scale uniformity, flexibility, and portability over conventional bulk semiconductor heterostructures. Herein, the intricate electronic behavior of a MoS2/WSe2 encapsulated heterostructure governed by split‐gate and middle‐gate configurations is investigated, revealing a distinctive step‐like current profile at a low temperature of 77 K. The observed four regimes in the current highlight the impact of quantum confinement induced by reduced lateral dimensions, coupled with precise electrostatic confinement controlled by gate voltages. The temperature dependence of the phenomena emphasizes the role of thermal effects on carrier scattering mechanisms. In addition, the pinch‐off characteristics with different temperatures, middle‐gate voltages, and drain biases are explored. This study contributes to a deeper understanding of electrostatic effects in 2D transition metal dichalcogenide heterostructures and holds promise for the development of advanced electronic devices with tailored confinement for enhanced functionalities.

Pulse operation mode of inertial electrostatic plasma confinement devices

The paper discusses the operation features of the inertial electrostatic plasma confinement (IEC) devices in the pulsed high voltage mode. The pulse operation mode offers significant advantages in IEC devices, which are associated with high discharge currents that are inaccessible for continuous operating modes. However, the implementation of such operating modes is associated with a number of physical limitations and technical difficulties.A stand with an IEC chamber powered by a high-voltage pulse transformer and a unit for gas preliminary ionization in the IEC chamber has been developed. In the chamber, ions are accelerated from a background glow discharge. A study of the burning background discharge in the IEC chamber, background discharge current Ipre influence on the duration of current and voltage pulses of the main discharge and the delay between them was carried out. The results of the neutron yield measuring in an IEC chamber operating in pulsed mode are presented at a charging voltage up to 105 kV, a discharge current amplitude of several tens of amperes, a preionization current of 8 mA, and a pulse repetition rate from single to 300 Hz. A stable neutron flux with an energy of 2.5 MeV at a level of 106 neutrons/s was experimentally obtained.

Radiation shielding for inertial electrostatic confinement fusion system utilizing concrete and water

In this investigation, the impact of water thickness and various types of concrete materials, each characterized by different densities and elemental compositions, is examined for their role in shielding a radiation generator based on Inertial Electrostatic Confinement Fusion (IECF) device. The study focuses on assessing several vital parameters, including the effective removal cross-section (∑Rt) for fast neutrons, total mass attenuation coefficients (μmt), linear attenuation coefficients (μl), half-value layer (HVL), and mean free path (MFP) for X-rays across different concrete types. Different water thicknesses around the IECF chamber, ranging from 0.5 to 10.0 cm, are investigated, and five concrete types are evaluated: Ilmenite-magnetite Concrete (IMC), Ordinary Concrete-1 (OC1), Barite-containing Concrete (BC), Ordinary Concrete-2 (OC2), and Serpentine-containing Concrete (SC). The results indicate that, among these materials, SC requires the least thickness to attenuate 2.45 MeV generated from IECF to 1/100th of its initial intensity across varying water thicknesses (6.5 cm in case of 5 cm water thickness). The values of μmt, HVL, and MFP are also calculated for different water thicknesses and X-ray energies (ranging from 0.2 to 3.0 MeV). These calculations highlight BC as the material requiring the least thickness to attenuate X-rays to 1/100th of their initial intensity. Moreover, neutron dose rate measurements are conducted on a commercial IECF system shielded with 50 cm of water and operated at a neutron intensity of 105 ns−1, which was ∼12 nSv/h on average, approximately 0.002% of the initial intensity. This underscores the efficacy of water shielding in attenuating the outcomes of IECF.

A systematic approach to the modelling and comparison of the geometries of spherical electrodes in inertial electrostatic confinement fusion devices

Inertial electrostatic confinement fusion (IECF) devices often use two concentric spherical electrodes to converge ions in a plasma electrostatically. Using a highly transparent inner cathode, the ions can move through the cathode and collide at the center to undergo fusion reactions. This is a simple method to build a neutron source. Past research has focused chiefly on cathode “grids” manufactured by joining metal wire loops or disc-shaped elements via spot welding. There are two common geometries: “Globe” grids with a distinct latitude-longitude structure and “symmetric” grids with even-sized triangular-shaped apertures. Recent advances in additive manufacturing have opened the way to manufacturing a third class of grids in which the apertures are evenly distributed over the grid surface and have either circular or polygonal shaped apertures - here called “regular” grids. These three types are analyzed and compared based on a set of metrics, including transparency, homogeneity of aperture size, and the regularity of aperture distribution. It is shown that every type of grid comes with different advantages and disadvantages. The analysis focuses on grid geometries with 6 to 120 apertures.

Tunable p–n junction barriers in few-electron bilayer graphene quantum dots

Graphene quantum dots provide promising platforms for hosting spin, valley, or spin-valley qubits. Taking advantage of their electrically generated bandgap and their ambipolar nature, high-quality quantum dots can be defined in bilayer graphene using natural p–n junctions as tunnel barriers. In these devices, demonstrating the electrical tunability of the p–n junction barriers and understanding its physical mechanism, especially in the few-electron regime, are essential for further manipulating electrons' quantum degrees of freedom to encode qubits. Here, we show the electrostatic confinement of single quantum dots in bilayer graphene using natural p–n junctions. When the device is operated in the few-electron regime, the electron tunneling rate is found to be monotonically tuned by varying gate voltages, which can be well understood from the view of manipulating the p–n junction barriers. Our results provide an insightful understanding of electrostatic confinement using natural p–n junctions in bilayer graphene, which is beneficial for realizing graphene-based qubits.

Investigating the effect of changing parameters in the IEC device in comparative study

Kinetic simulations have been performed on an Inertial Electrostatic Confinement Fusion (IECF) device. These simulations were performed using the particle-in-cell (PIC) method to analyze the behavior of ions in an IEC device and the effects of some parameters on the Confinement Time (CT). CT is an essential factor that significantly contributes to the IEC's performance as a nuclear fusion device. Using the PIC method, the geometry of a two-grided device with variable grid radius, the number of cathode grid rings, variable pressure and different dielectric thickness for the feed stalk was simulated. In this research, with the development of previous works, the interaction of particles was simulated and compared with previous results. The simulation results are in good agreement with the previous results. In these simulations, it was found that with the increase of the dielectric thickness of the feed stalk, the electric field was weakened and as a result, the confinement time was reduced. On the other hand, with the increase of the cathode radius, the confinement time increased. Using the results, an IEC device can be designed with higher efficiency and more optimal CT for ions.

Quantum-information theory of magnetic field influence on circular dots with different boundary conditions

Influence of the transverse uniform magnetic field B on position (subscript ρ) and momentum (γ) Shannon quantum-information entropies S ρ,γ Fisher informations I ρ,γ and informational energies O ρ,γ is studied theoretically for the 2D circular quantum dots (QDs) whose circumference supports homogeneous either Dirichlet or Neumann boundary condition (BC). Comparative analysis reveals similarities and differences of the influence on the properties of the structure of the surface interaction with the magnetic field. A conspicuous distinction between the two spectra are crossings at the increasing induction of the Neumann energies with the same radial quantum number n and adjacent non-positive angular indices m. At the growing B, either system undergoes Landau condensation when its characteristics turn into their uniform field counterparts. It is shown that for the Dirichlet system this transformation takes place at the smaller magnetic intensities; e.g. the Dirichlet sum on its approach from above to a fundamental limit is at any B smaller than the corresponding Neumann quantity what physically means that the former geometry provides more total information about the position and motion of the particle. It is pointed out that the widely accepted disequilibrium uncertainty relation , with d being a dimensionality of the system, is violated by the Neumann QD in the magnetic field. Comparison with electrostatic harmonic confinement is performed; in particular, contrary to the hard-wall QDs, for this configuration the sums S ρ + S γ and the products I ρ I γ and O ρ O γ do not depend on the field. Physical interpretation is based on the different roles of the two BCs and their interplay with the field: Dirichlet (Neumann) surface is a repulsive (attractive) interface.

3D to 2D perspectives - Traditional and new doping and metrology challenges at the nanoscale

In this perspectives paper we will explore the doping state-of-the-art as it evolves for 3D to 2D structures and materials, and the following impact on the metrology methods needed to characterise them. Historically, silicon devices for logic complementary metal-oxide-semiconductor (MOS) are built in bulk monocrystalline substrates. In this context bulk silicon substrates are 3D, as there is not the electrostatic confinement associated with more technologically advanced device structures. The determination of technology figures-of-merit such as sheet resistance, impurity concentration and activation profiles versus depth, and reverse bias leakage current to track crystal quality post-doping process, have been the typical methods for evaluation. Since the emergence of FinFET, gate-all-around (GAA) for logic, and layered 2D materials such as transition-metal-dichalcogenides (TMDs) for MOS channel active areas, these figures-of-merit are more awkward to extract, or simply do not apply in the usual sense. Logic devices, like MOS transistors, depend on doping processes to lower access resistance and thus drive performance, traditionally relied on ion implantation to introduce impurities to the substrate, which is a physical bombardment that damages the target material. Gentler doping processes that rely on in-diffusion are an emerging category, and most recently the concept of terminating or functionalising the (near-) surface of the semiconductor is growing in popularity, at least in research labs. Likewise, methods to characterise these require evolution to adapt to the times, from the conventional high-throughput techniques to the more exploratory, albeit lower throughput, methods. Metrology relies upon high-sensitivity, large dynamic range of detection, spatial resolution, as well as time- and cost-efficient sample preparation and post-analysis data interpretation. Driven primarily by the continued development of novel, scaled-down, truly unique device architectures and the introduction of novel materials in the nano-fabrication technology, the portfolio of dopant characterisation methods is unremittingly enlarging its numbers. Herein, we focus our discussion onto dopant profiling for fin and nanowire FETs, and relate these to analysis of test vehicles such as arrays of fin structures with varying dimensions. Although reports detailing correlative use of the dopant characterisation methods are only a few, we present examples that provided unique new information, in absence of which the overall description of the dopant process is inconclusive and, in some cases, misleading.

Effect of Positive Polarity in an Inertial Electrostatic Confinement Fusion Device: Electron Confinement, X-Ray Production, and Radiography

The conventional inertial electrostatic confinement fusion (IECF) operation is based on the application of high negative voltage to the central grid, which results in the production of neutrons due to the fusion of lighter ions. The device can also be used as an X-ray source by altering the polarity of the central grid. In this work, electron dynamics during the positive polarity of the central grid are studied using the object-oriented particle-in-cell code XOOPIC. The simulated trapped electron density inside the anode is found to be on the order of 1016 m when 10 kV is applied to the anode. The recirculatory characteristics of the electrons are also studied from the velocity distribution function. A scintillator-based photomultiplier tube is used to detect the produced X-ray. The X-ray-emitting zones of the device are investigated by pinhole imaging techniques. Last, the radiography of metallic as well as biological samples are reported in the later part of this paper. This study shows the utilization of the IECF device when the polarity of the central grid is reversed.