Space Charge Research Articles

Unequal {110} Facets: The Potential Role of Intraparticle Heterogeneity and Facet Termination in Photoelectrochemical Activity of Single BiVO4 Particles.

BiVO4 photoanodes are promising for solar water splitting, with photogenerated electrons and holes preferentially reacting at top {010} and lateral {110} facets, respectively. However, the mechanisms driving this facet-dependent reactivity remain unclear. Here, we investigate facet-dependent photocurrent and material heterogeneity using correlative scanning photoelectrochemical microscopy (SPCM), electron beam induced current (EBIC) mapping, and mid-IR scattering scanning near-field optical microscopy (s-SNOM). SPCM measurements of 62 BiVO4 particles confirmed higher photocurrents at lateral {110} facets compared to top {010} facets, but unexpectedly revealed variations in photocurrent among lateral facets within the same particle. Variations in lateral facet surface termination could explain the intraparticle-level reactivity heterogeneity, consistent with theoretical predictions. Nano-FTIR spectroscopy and Raman microspectroscopy indicated significant materials chemistry heterogeneity within individual particles and facets that could be attributed to variations in lattice vibration distortions that enhance the overlap between Bi 6s and O 2p orbitals. The increased orbital overlap is significant as it potentially increases hole mobility in the valence band and potentially explains the lateral facet-dependent charge separation efficiency observed in photocurrent maps. Facet-dependent electrical and EBIC measurements showed no space charge regions at interfacet junctions or metal-BiVO4 contacts under vacuum, suggesting that photogenerated holes beneath top {010} facets are unlikely to transport to lateral {110} facets to drive water/sulfite oxidation. These findings indicate the potential influence of distinct bulk properties and surface termination chemistries across different particles and facets, highlighting the importance of carefully controlling defects and surface chemistry during sample growth to optimize photocatalytic performance.

Balancing the Mechanical Toughness and Electrical Insulation of Polypropylene by Blending and Grafting Modifications

AbstractBalancing the mechanical toughness and electrical insulation of polypropylene (PP) for recyclable cable insulation application has attracted increasing attention. Due to the different molecular conformation, isotactic polypropylene (IPP) always delivers excellent electrical insulation but poor mechanical toughness, while block polypropylene (BPP) has been dramatically opposed properties. Blending IPP with BPP at an appropriate content may be beneficial to reconcile the toughness and insulation. In this study, the blending ratio of IPP and BPP is first investigated, and it is found that 60: 40 wt.% is the optimized ratio for achieving outstanding overall performance. Furthermore, polyolefin elastomer (POE) and styrene‐grafted POE (POE‐g‐St) are incorporated into IPP/BPP blends respectively to intensify the toughness as well as the insulation property. The microstructure, electrical properties, mechanical properties, and thermal properties of the composites are systematically analyzed and discussed. The results demonstrate that the composite with a grafting ratio of 1.21 wt.% styrene exhibits superior overall performances, the enhanced breakdown field strength of 314.02 kV mm−1, and reduced elastic modulus of 352.54 MPa are achieved. Additionally, the modified composites also possess a high melting temperature, high volume resistivity, and excellent space charge suppression capability, achieving the synergistic improvements of the electrical, mechanical, and thermal properties.

Space Charge and Conduction Characters of PP/POE Composites and Their Influence on the Aging Lifetime Under DC Voltage

Space Charge and Conduction Characters of PP/POE Composites and Their Influence on the Aging Lifetime Under DC Voltage

The Space Charge Measurement by Pulsed Electroacoustic Method up to 200 ∘C

The Space Charge Measurement by Pulsed Electroacoustic Method up to 200 ^∘C

A novel insulation space charge non-contact measurement method based on elasto-optical sensing and ellipsometric detection

A novel insulation space charge non-contact measurement method based on elasto-optical sensing and ellipsometric detection

Influence of Sample Surface Oil on the Accuracy of Space Charge Measurement in Oil-Paper

Influence of Sample Surface Oil on the Accuracy of Space Charge Measurement in Oil-Paper

High Dimensionless Figure of Merit and Efficiency Thermoelectrics for Operation below Sub-250 °C─Origin of Colossal Seebeck Coefficient with Phonon Assisting, Coexistence with Electrical Conductivity, and Device Application for Their Multilayered Structure.

Thermoelectric (TE) devices recycle high-temperature waste-heat efficiently, but waste-heat below sub-250 °C remains uncaptured. As promoting full autonomy for the Internet of Things (IoT), we present a TE generator using multilayered pseudo-p-type GaN/TiN/GaN and n-type TiO2/TiN/TiO2 TE one-leg devices, where heterozygous of outer/inner layers demonstrates the functions of a colossal Seebeck coefficient (S = +15,000 μV K-1) with phonon-assist hopping, controlling by the porosity for reducing thermal conductivity (κ), a high electric conductivity (σ) with reducing κ by outer layers, and σ-S coexistence over singular curve by the asymmetric electrode configuration. S is elucidated hopping among inner grains and the space charge (SC) grain boundary (GB) of 100 μm regions within Debye length. By assisting phonon, SC capturing, hopping-up (recoiling, pseudo-p-type) or -down (n-type) over potential barriers at GBs are investigated. The devices showed high ZT (∼2.2), low κ (15.2 W m-1 K-1), and outputs at sub-250 °C, which is promising for waste heat recycling (predicted efficiency: 12.5%).

Research on the Accumulative Damage of Flywheels Due to In-Space Charging Effects

High-speed rotating flywheel bearings, designed for space applications, generate a high-resistance hydrodynamic lubrication film, which isolates the rotor, transforming it into a conductor. This phenomenon introduces a novel failure mode—flywheel bearing electrical damage caused by space charging effects. This paper first reviews the sources of common shaft voltages in flywheels and the mechanisms of electrical damage and improves the principle of deep charge causing shaft voltages in flywheel bearings, proposing that surface charge is another source of shaft voltages. The quantified analysis model of flywheel bearing electrical damage in relation to rotational speed and high-energy electron flux is derived, indicating that the damage caused by space charge–discharge to the bearing is of small magnitude and only becomes apparent after long-term accumulation, thus being easily overlooked. Based on the causal chain of electrical damage, a correlation analysis model consistent with physical principles is constructed, and the correlation between on-orbit anomalies of the flywheel and high-energy electron flux is confirmed through the use of big data. Preliminary experiments are conducted to validate all of the research results. Finally, suggestions are given for the reliable design, application, and testing of flywheels.

Nanoscale nonlocal thermal transport and thermal field emission in high-current resonant tunnel structures

We present a nonlinear model of thermal field emission in resonant tunneling nanostructures with multiple barriers and potential wells, based on an accurate determination of the quantum potential shape and a rigorous solution of the Schrödinger equation, while considering thermal balance. The model applies to vacuum and semiconductor resonant tunnel diode and triode structures with two and three electrodes and to the general case of two-way tunneling with electrode heating. The complete balance of heat release and transfer is accounted for, with heat transport considered ballistic. This approach can also be extended to the non-stationary case, incorporating the influence of space charge. The short flight time of electrons in such structures makes them promising for the fabrication of THz devices.

Fabrication of Highly Ordered Macropore Arrays in p-Type Silicon by Electrochemical Etching: Effect of Wafer Resistivity and Other Etching Parameters

Macroporous silicon is a promising substrate in the field of optics, electronics, etc. In this paper, highly ordered macropore arrays were fabricated in p-type silicon wafers by electrochemical etching using a double-tank cell. The effect of the silicon resistivity, etching voltage and etching time on the pore morphology was investigated and the influence mechanism was analyzed. The pore diameter would decrease with the increase in the silicon resistivity and the decrease in the etching voltage, due to the increase in the space charge region width (SCRL). The pore depth would increase with the resistivity and the voltage. However, too high resistivity would cause insufficiency at the pore tips and too high voltage would cause pore splitting, which may cause a decrease in the pore depth. Then, the aspect ratio of 21 can be obtained on the silicon wafer with a resistivity of 50–80 Ω·cm at the etching voltage of 5 V with a maximum etching rate of about 0.92 μm/min.

Manipulating Charge Distribution at Organic‐inorganic Interface via Optimizing Substituents for Sustainable Water Electrolysis

AbstractThe space charge effect induced by high‐quality heterojunctions is essential for efficient electrocatalytic processes. Herein, we delicately manipulate intermolecular charge transfer by modifying substituents (−g=‐CH3, ‐H, ‐NO2) with various electron donating/withdrawing capabilities in CoPc‐g/CoS organic–inorganic heterostructures. CoPc‐CH3, as a typical electron donor, transfers more electrons to CoS due to the presence of ‐CH3, forming the strongest space electric field and thus regulating the dual active sites at the interface. Furthermore, oxygen‐containing intermediates preferentially adsorb on the positively charged CoPc‐CH3 side, and the rapid accumulation of electrons on the CoS side decelerates catalyst dissolution at the oxygen evolution reaction (OER) potential, ensuring the stable OER process under the optimized adsorbate evolution mechanism. As a result, CoPc‐CH3/CoS catalyst exhibits the lowest overpotential and remains stable for 150 h at 0.5 A cm−2 in the membrane electrode assembly electrolyzer. The method provides a novel strategy for accurately regulating the space electric field of heterojunctions.

Overcoming the thermal limits of photon counting CT resolution using focal spot multiplexing: A feasibility study.

The spatial resolution of new, photon counting detector (PCD) CT scanners is limited by the size of the focal spot. Smaller, brighter focal spots would melt the tungsten focal track of a conventional X-ray source. To propose focal spot multiplexing (FSM), an architecture to improve the power of small focal spots and thereby enable higher resolution clinical PCD CT. In FSM, the source rapidly alternates between multiple focal spot locations. The dwell time at each focal spot location is much shorter than the readout interval of the PCD, and each location is visited many times during the readout interval so that heat can be effectively distributed over a larger surface area. The PCD accumulates recorded events on the detector (prior to slip ring transmission) into multiple spatial bins, as a second dimension to conventional energy bins. We estimated the maximum power permissible for a square, 0.2 mm focal spot assuming a maximum allowed surface temperature of 2900 K and a maximum transient temperature increase at the focal spot of 1400 K. This was performed using two separate thermal simulation codes: first, a commercial finite element method (FEM) was used to estimate bulk heating; second, a custom solver linearizing the heat equation was used to estimate track heating. FSM was simulated assuming that focal spot locations lay on parallel focal tracks, that instantaneous switching between tracks was possible, and that the space charge limit was never reached. We assumed a focal track velocity of 100 m/s and a 1 mm tungsten focal track layer with TZM alloy backing. The tube power was constant over a 4 s acquisition period. Without FSM, the 0.2 mm focal spot could attain a maximum power output of 17 kW before reaching the thermal limit. FSM required a minimum switching frequency of 0.5 MHz to produce benefit. With two focal tracks and a switching frequency of 4 MHz, the power could be increased to 28 kW, and with eight focal tracks and a switching frequency of 16 MHz, the power could be increased to 98 kW. In all cases, the 1400 K transient increase thermal limit was reached before the 2900 K maximum surface temperature constraint. The relationship between maximum power, switching frequency, and number of focal tracks is discussed in relation to the underlying physics of heat transport. Focal spot multiplexing is an architecture that exploits the digital nature of photon counting to improve the power of high-resolution CT X-ray sources. With fast switching and several parallel focal tracks, it may be possible to halve the size of the focal spot while maintaining source power. This work motivates the development of new source technologies that can achieve fast electronic switching.

Wave‐Interference Photonic Crystals and Space Charge Engineering Enable Efficient Broadband Faint Light Detection in Organic/Inorganic Hybrid Photodetectors

AbstractNoise current, detectivity, quantum efficiency, and response speed are critical metrics in evaluating organic/inorganic photodiodes. Herein, these metrics are simultaneously advanced in poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/native SiOx/n‐Si hybrid photodetectors, achieving excellent performance in detecting broadband faint light. Wave‐interference photonic crystals, comprising periodic microstructured inverse pyramids with nanometer‐scale mesa widths, are integrated into the Si absorber to effectively couple incident light for increased absorption, thereby balancing optics and conformal contact coverage. The developed photodetector comprises a deep depletion region and interfacial SiOx layer, enabling diffusion‐mitigated broadband photocarrier transport and effective charge collection, and suppressing carrier tunneling processes for low‐noise. An ultralow reverse dark current density of ≈2.46 × 10−8 A cm−2 at −0.4 V is realized for nanowatt‐level light detection. The photodetector showcases superlative properties among reported PEDOT:PSS–based inorganic heterojunctions, including a broadband external quantum efficiency of >≈80% from 340 to 960 nm (internal quantum efficiency of >≈90% from 380 to 840 nm), detectivity of >≈1012 Jones from 300 to 1140 nm, and microsecond response speed. This study provides practical insight for combining high‐absorption microstructures with space charge engineering for the development of high‐performance organic/inorganic hybrid photodetectors.

Charge dynamic behavior under high-frequency stress considering coupled effect of temperature-frequency interaction

Abstract Space charge behavior under combined high-frequency electrothermal stress is an important causative factor for insulation failure in high-voltage power electronic equipment. In this research, a novel charge transport model adapted to the high-frequency stress environment is developed. Modifications are implemented in the model to address the high-frequency stress characteristics, namely for the electrothermal coupled stress environment, high-frequency injection, flexible migration, and interfacial features. The study examines the evolution of space charge influenced by polarisation parameters, including frequency, duty cycle, and polarisation polarity. The results indicate a disparity in charge accumulation polarity under uni/bipolar stress. The electric field distortion induced by heteropolar charge accumulation under bipolar stresses poses a great challenge to the insulating properties of the interface. Furthermore, both the quantity and depth of charge accumulation exhibit an inverse association with frequency. The minimum accumulation depth is merely 6μm at a polarisation frequency of 1kHz. Conversely, the extent of charge accumulation escalates exponentially with an increase in the duty cycle (stress power). Finally, the model reliability is validated by comparing with the high-frequency charge measurement under the relevant parameter. The pertinent research can offer a viable technical approach to elucidate the dynamic behaviour of space charge under high-frequency stress.

Grain-Boundary Corrosion in UO2+δ from a Defect Chemical Perspective: A Case Study of the Σ5(310)[001] Grain Boundary.

We combine atomistic and continuum simulation methods to study the defect chemistry of a model grain boundary in UO2+δ. Using atomistic methods, we calculate the formation energies of oxygen interstitials, uranium vacancies, and hole polarons (U5+ ions) across the Σ5(310)[001] symmetric tilt grain boundary. This information is then used as input in a continuum model of point-defect concentrations at the grain boundary and in its vicinity, taking into account electrostatic (space-charge) effects. Two scenarios are modeled: one in which oxygen interstitials are the majority ionic defect and one in which uranium vacancies are the majority ionic defect, with bulk charge neutrality being maintained by hole polarons in both cases. Our results indicate that, irrespective of the majority ionic defect, the Σ5(310)[001] grain boundary in UO2+δ is negatively charged, with positively charged adjacent space-charge zones in which the hole-polaron concentration is enhanced. We propose that the enhanced U5+ concentration at the grain boundary and within the space-charge zones renders grain-boundary regions more susceptible to oxidative corrosion, an effect that could be counteracted by acceptor doping.

Structural, elastic, electronic, magnetic and thermal properties of X3FeO4 (X = mg, ca and Sr) materials

This prediction evaluates the different physical characteristics of magnetic materials X3FeO4 (X = Mg, Ca and Sr) by using density functional theory (DFT). The generalized gradient approximation (GGA) approach is chosen to define the exchange and correlation potential. The structural study of the compounds X3FeO4 (X = Mg, Ca and Sr) shows that the ferromagnetic phase is the more stable ground state, where all the parameters of the network are given at equilibrium. The calculated elastic constants confirm their stability in the cubic structure. The electronic characteristics calculated using the GGA and GGA + U approaches prove that all these compounds are semi-metallic with a wide band gap (EHM) and a high Curie temperature (TC). Furthermore, the magnetic moments of the studied compounds are calculated in order to claim their half-metallicity behavior. The p-d hybridization between the 3d-Fe and 2p-O states generates weak magnetic moments in the non-magnetic X and O sites, and decreases the Fe atomic moment relative to its free space charge of 4 µB. The thermal parameters including the thermal expansion coefficient, the heat capacity at constant volume and the Debye temperature were calculated for these compounds.

Space charge behaviors and electrical insulation characteristics in EPDM/micro‐SiC composite with surface‐modified nano‐SiC for HVDC insulation

Space charge behaviors and electrical insulation characteristics in <scp>EPDM</scp>/micro‐<scp>SiC</scp> composite with surface‐modified nano‐<scp>SiC</scp> for <scp>HVDC</scp> insulation

Enhancing ionic conductivity and expanding the electrochemical window in polymer electrolytes via ferroelectric-metal-organic-frameworks to manipulate charge spatial distribution.

Poly (ethylene oxide) (PEO)-based polymer electrolytes have promising applications in all-solid-state lithium metal batteries. However, their wide range of practical applications is severely limited by their relatively low room temperature lithium ion conductivity and narrow electrochemical window. In this paper, based on the ability of spontaneous polarization of ferroelectric materials to generate polarization field under applied electric field and the characteristics of Metal-Organic-Frameworks (MOFs) materials with regular adjustable pore structure, a Nano material combining ferroelectric materials and MOF (NUS-6(Hf)-MOF) was first proposed to be added to PEO polymer electrolyte as a filler. NUS-6(Hf)-MOF can provide rapid transport channel for lithium ion, born under the applied electric field of the latter's consistent dipole polarization field can adjust the interface of the space charge distribution, the composite polymer electrolyte (NUSCPE) modified with NUS-6(Hf)-MOF has high ionic conductivity (1.16×10-3Scm-1) and lithium ion mobility (0.33) at 60°C. Simultaneously, the phenomenon of self-polarization causes the surface electronization, this results in a higher susceptibility to oxidation compared to PEO, thereby expanding the electrochemical window to 4.7V, and when paired with commercial LiNi0.8Co0.1Mn0.1O2 cathode, the capacity is maintained at 85% after 50 stable cycles at 0.2C at 60°C. The polymer electrolyte NUSCPE modified by NUS-6(Hf)-MOF provides a novel design idea for all solid-state lithium batteries with excellent electrochemical performance.

Interactive Coupling Relaxation of Dipoles and Wagner Charges in the Amorphous State of Polymers Induced by Thermal and Electrical Stimulations: A Dual-Phase Open Dissipative System Perspective.

This paper addresses the author's current understanding of the physics of interactions in polymers under a voltage field excitation. The effect of a voltage field coupled with temperature to induce space charges and dipolar activity in dielectric materials can be measured by very sensitive electrometers. The resulting characterization methods, thermally stimulated depolarization (TSD) and thermal-windowing deconvolution (TWD), provide a powerful way to study local and cooperative relaxations in the amorphous state of matter that are, arguably, essential to understanding the glass transition, molecular motions in the rubbery and molten states and even the processes leading to crystallization. Specifically, this paper describes and tries to explain 'interactive coupling' between molecular motions in polymers by their dielectric relaxation characteristics when polymeric samples have been submitted to thermally induced polarization by a voltage field followed by depolarization at a constant heating rate. Interactive coupling results from the modulation of the local interactions by the collective aspect of those interactions, a recursive process pursuant to the dynamics of the interplay between the free volume and the conformation of dual-conformers, two fundamental basic units of the macromolecules introduced by this author in the "dual-phase" model of interactions. This model reconsiders the fundamentals of the TSD and TWD results in a different way: the origin of the dipoles formation, induced or permanent dipoles; the origin of the Wagner space charges and the Tg,ρ transition; the origin of the TLL manifestation; the origin of the Debye elementary relaxations' compensation or parallelism in a relaxation map; and finally, the dual-phase origin of their super-compensations. In other words, this paper is an attempt to link the fundamentals of TSD and TWD activation and deactivation of dipoles that produce a current signal with the statistical parameters of the "dual-phase" model of interactions underlying the Grain-Field Statistics.

Manipulating Charge Distribution at Organic-inorganic Interface via Optimizing Substituents for Sustainable Water Electrolysis.

The space charge effect induced by high-quality heterojunctions is essential for efficient electrocatalytic processes. Herein, we delicately manipulate intermolecular charge transfer by modifying substituents (-g = -CH3, -H, -NO2) with various electron donating/withdrawing capabilities in CoPc-g/CoS organic-inorganic heterostructures. CoPc-CH3, as a typical electron donor, transfers more electrons to CoS due to the presence of -CH3, forming the strongest space electric field and thus regulating the dual active sites at the interface. Furthermore, oxygen-containing intermediates preferentially adsorb on the positively charged CoPc-CH3 side, and the rapid accumulation of electrons on the CoS side decelerates catalyst dissolution at the oxygen evolution reaction (OER) potential, ensuring the stable OER process under the optimized adsorbate evolution mechanism. As a result, CoPc-CH3/CoS catalyst exhibits the lowest overpotential and remains stable for 150 h at 0.5 A cm-2 in the membrane electrode assembly electrolyzer. The method provides a novel strategy for accurately regulating the space electric field of heterojunctions.