Accumulation Of Negative Charge Research Articles

Underlying Mechanism of Electrolyte Compositional Engineering Based on Additive Solvation-Structure Governing Solid Electrolyte Interphase Formation in Lithium-Ion Batteries.

Substantial efforts are dedicated to optimizing the additive dosage in the electrolyte and studying its effect on solid electrolyte interphase (SEI) formation in Li-ion batteries (LIBs). This study reveals that the decomposition characteristics of the additive based on its lithium-ion solvation nature significantly contribute to controlling SEI formation. During SEI formation, the strong lithium-ion solvating additive spontaneously migrates to the negative electrode due to negative charge accumulation on the surface, and SEI reinforcement is feasible by increasing the additive dosage. In contrast, population-based SEI formation occurs with a weaker solvating additive, so dosage-dependent modification of the SEI is not effective. These findings demonstrate that compositional electrolyte engineering based on the solvation properties of the additive can be more effective than empirical and experimental studies based on trial and error.

Physicochemical Properties of Water in Contact with Nanobubbles Generated by CO2‐Hydrate Dissociation: An Investigation from Experiment and Molecular‐Dynamics Simulation

AbstractThe study investigates CO2‐nanobubbles (NBs) generated from gas‐hydrate dissociation, exploring their impact on the physicochemical properties of liquid water. Raman spectroscopy evidenced a slight increase in the Raman‐band intensity, suggesting enhanced total hydration‐layer water‐dipole moment and polarity without affecting water molecule structuring. Furthermore, an overall decreasing trend for the zeta potential of NB solution can be observed due to the strong electron affinity on the surface of CO2 bulk NBs, probably caused by a negative charge accumulation. These findings are in good qualitative accord with molecular‐dynamics (MD) simulation results, wherein water can induce a small dipole moment of about 0.16 D for CO2 NBs, thereby increasing the polarity of the system. Due to the interaction between water molecules, the Coulombic or electrostatic forces increase in the presence of NBs compared to pure water, which can reflect the increase in the dipole moment of water molecules in the presence of NBs. The presence of NBs strengthens the local hydrogen‐bond network, leading to higher‐frequency vibrations. Additionally, NBs amplify the intrinsic electric field of the aqueous solution, causing the gas‐water interface to exhibit negatively charged characteristics, dependent on NB size. Molecular simulations agree qualitatively with experiments, emphasizing their utility in studying NB evolution in water.

Zinc Assisted Thermal Etching for Rich Edge-Located Fe-N4 Active Sites in Defective Carbon Nanofiber for Activity Enhancement of Oxygen Electroreduction.

Single-atom catalysts (SACs) with edge-located metal active sites exhibit superior oxygen reduction reaction (ORR) performance due to their narrower energy gap and higher electron density. However, controllably designing such active sites to fully reveal their advantages remains challenging. Herein, rich edge-located Fe-N4 active sites anchored in hierarchically porous carbon nanofibers (denoted as e1-Fe-N-C) are fabricated via an in situ zinc-assisted thermal etching strategy. The e1-Fe-N-C catalyst demonstrates superior alkaline ORR activity compared to counterparts with fewer edge-located Fe-N4 sites and commercial Pt/C. Density functional theory calculations show that the accumulation of more negative charges near the Fe-N and the formation of partially reduced Fe state in the edge-located Fe-N4 sites reduce the energy barrier for the ORR process. Additionally, the unique hierarchically porous structures with mesopores and macropores facilitate full utilization of the active sites and enhance long-range mass transfer. The zinc-air battery (ZAB) assembled with e1-Fe-N-C has a peak power density of 198.9mWcm-2, superior to commercial Pt/C (152.3mWcm-2). The present strategy by facile controlling the amount of the zinc acetate template systematically demonstrates the superiority of edge-located Fe-N4 sites, providing a new design avenue for rational defect engineering to achieve high-performance ORR.

Topography and localized charge of steps on CeO2(111) investigated by AFM/KPFM

The configuration of step edges on metal oxide surface is significant for understanding fundamental reactivity and predicting the performance in catalysis. In this work, the topography feature and charge of steps on CeO2(111) are investigated by atomic force microscopy /kelvin probe force microscopy combined with density functional theory. Hexagonal islands and pits containing step I edge and step II edge have been observed at annealing 1100 K. The irregular structures with the addition of step III edge have been found at 1200 K. The measurement of contact potential difference reveals that step II displays the strongest localized charge state, followed by step III, and step I with the weakest localized charge state. The calculations of density functional theory have confirmed that step II possesses a stronger localized charge state. In addition, the Ce atoms at the step II edge exhibit greater positive and negative charge accumulation. These results provide the surface structure and electrical potential of three step edges on the CeO2(111), and establish both experimental and theoretical foundations for subsequent investigations on adsorption and catalysis.

Mechanisms of interface electrostatic potential induced asphalt-aggregate adhesion

The electrostatic potential at the interface of the asphalt molecular and aggregate oxides is the primary factor generating the adhesion between the asphalt-aggregate contact surfaces. However, the route of electrostatic potential affecting the asphalt-aggregate adhesion is yet to be determined at the molecular level. This study proposed that the electron accumulation at the interface of the asphalt molecular and aggregate oxides generates a significant electrostatic potential hence to induce the adhesion between the asphalt and aggregate in asphalt pavement. A microscopic molecular dynamics (MD) simulation incorporated with macroscopic adhesion work experiments is conducted to analyze the interface adhesive performance between the asphalt and aggregate. The adhesion work experiment demonstrated the effect of aggregate surface oxides on asphalt adhesion at the macro level and further verified the simulation results. The result demonstrated that a notable electron accumulation can be observed by MD at the interface of asphalt molecular and multiple oxides which generates the electrostatic potential. The strong electrostatic attractions and hydrogen bonds between alkaline oxides (MgO, CaO, CaCO3) and asphalt molecules enhance the relative concentration distribution, diffusion coefficient, and adhesion of asphalt on the aggregate surface. The significant electrostatic potential difference at the interface of the asphalt molecular and the oxide enables a strong adhesion between them due to the near-surface failure potential. Besides, the negative charge accumulation on both the benzene ring structure and oxygen atoms in the asphalt molecules results in poor adhesion at the interface of asphalt molecules and multiple oxides. It was found that a high correlation exists between the MD prediction and experimental testing results. Thus, this research provides a valuable tool for guiding the pairing and selection of asphalt with various minerals for pavement design, construction, and maintenance agencies.

Exploring electron energy dependencies in the formation of surface charge on ZnO crystals

This study delves into the phenomena surrounding the emergence of negative charge accumulation on the surface of zinc oxide (ZnO) crystals upon exposure to low-energy electron irradiation within the range of E = 0 ÷ 600 eV. We demonstrate the critical significance of the primary electron energy in dictating the initial processes initiated at the ZnO surface. Energy thresholds governing both the genesis and elimination of surface charge, along with the formation of oxygen vacancies on the ZnO surface, are elucidated. Our findings reveal that irradiation instigates distinct dissociative pathways contingent upon electron energy, engendering diverse physical and chemical transformations via bond dissociation, desorption, and atomic and molecular restructuring of the surface. These insights serve as pivotal groundwork towards advancing the fabrication of epitaxial films, facilitating the controlled generation of two-dimensional structures predicated on surface potential modulation.

Direct Cation Stabilization Effects of CO Dimerization for Boosting C2 Pathways of CO2 Reduction on Noble Metal Surfaces

The carbon dioxide reduction reaction (CO2RR) is one of the most promising solutions for realizing carbon neutralization via converting the emitted CO2 into value‐added chemicals. The CC coupling step for CO dimerization is the rate‐determining step for C2 pathways, which have not been thoroughly investigated. Herein, the direct cation stabilization effects on CO dimerization for *OCCO formation on the representative Cu(100) and Pt(100) surfaces are investigated. Density functional theory calculations show that the presence of alkali metal ions plays a vital role in promoting the coupling of *CO monomers on both metal surfaces, where Cu shows a stronger stabilization effect. More importantly, a strong linear correlation (R2 ≈ 0.9) between the dimer stabilization energy and the reaction energy is revealed for the first time, which is a promising indicator for the selectivity of C2 pathways. Further investigations on electronic structures reveal that the promoting effect on *OCCO formation is strongly related to the negative charges of the molecules, in which the negative charge accumulation is favored by the directional electron transfer due to the chemisorption of *OCCO on Cu(100) surface. This work offers insights into the understanding of CC coupling reactions for CO2RR mechanisms.

The atomic configuration and metallic state of extrinsic defects in Nb-doped BiFeO3 thin films

Defects in ferroelectric materials can cause microscopic strain and electron doping, which opens up new possibilities for unique physical properties in nanoelectronics. However, comprehending the relationship between these deep-buried defect configurations and the resulting physical properties is a long-term challenge. Here, utilizing the integrated differential phase imaging technique equipped in scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy, we show the full element-resolved atomic configuration of characteristic extrinsic defects in Nb-doped epitaxial BiFeO3 thin films. Atomic-resolution characterization reveals that the Nb doping substitutes Fe at the center of an oxygen octahedron and creates Fe vacancies near the defect core, leading to the formation of one perovskite cell-wide BiNbO3 chain that is expanded by 19 % in perovskite cell volume and rotated by 45° relative to the matrix lattice. Further quantitative analysis of the defect demonstrates that the ferroelectric polarization distribution around the dopant-induced defects displays a “head-to-head” configuration, indicating the accumulation of negative charges. Supported by electron energy loss spectroscopy and density functional theory calculations, the linear defect leads to one-dimensional metallic channels embedded within the ferroelectric BiFeO3 matrix. These atomic-scale findings establish the structure-functionality relationship of extrinsic defect in Nb-doped BiFeO3 thin films, providing new insight into their fundamental understanding and potential use in low-dimensional nanoelectronics devices.

Integrative modeling of guanylate binding protein dimers.

Guanylate-binding proteins (GBPs) are essential interferon-γ-activated large GTPases that play a crucial role in host defense against intracellular bacteria and parasites. While their protective functions rely on protein polymerization, our understanding of the structural intricacies of these multimerized states remains limited. To bridge this knowledge gap, we present dimer models for human GBP1 (hGBP1) and murine GBP2 and 7 (mGBP2 and mGBP7) using an integrative approach, incorporating the crystal structure of hGBP1's GTPase domain dimer, crosslinking mass spectrometry, small-angle X-ray scattering, protein-protein docking, and molecular dynamics simulations. Our investigation begins by comparing the protein dynamics of hGBP1, mGBP2, and mGBP7. We observe that the M/E domain in all three proteins exhibits significant mobility and hinge motion, with mGBP7 displaying a slightly less pronounced motion but greater flexibility in its GTPase domain. These dynamic distinctions can be attributed to variations in the sequences of mGBP7 and hGBP1/mGBP2, resulting in different dimerization modes. Unlike hGBP1 and its close ortholog mGBP2, which exclusively dimerize through their GTPase domains, we find that mGBP7 exhibits three equally probable alternative dimer structures. The GTPase domain of mGBP7 is only partially involved in its dimerization, primarily due to an accumulation of negative charge, allowing mGBP7 to dimerize independently of GTP. Instead, mGBP7 exhibits a strong tendency to dimerize in an antiparallel arrangement across its stalks. The results of this work go beyond the sequence-structure-function relationship, as the sequence differences in mGBP7 and mGBP2/hGBP1 do not lead to different structures, but to different protein dynamics and dimerization. The distinct GBP dimer structures are expected to encode specific functions crucial for disrupting pathogen membranes.

Construction of an OCP-ATR-FTIR Spectroscopy Device to In Situ Monitor the Interfacial Reaction of Contaminants: Competitive Adsorption of Cr(VI) and Oxalate on Hematite.

The comprehensive understanding of contaminant interfacial behavior strongly depends on the in situ characterization technique, which is still a great challenge. In this study, we constructed a device integrated with open-circuit potentialand attenuated total reflectance Fourier transform infrared (OCP-ATR-FTIR) spectroscopy to simultaneously monitor the electrochemical and infrared spectral information on the interfacial reaction for the process analysis, taking the competitive adsorption of hexavalent chromium (Cr(VI)) and oxalate on hematite nanocubes (HNC) as an example. The synchronous OCP and infrared results revealed that Cr(VI) interacted with HNC via bidentate binuclear inner-sphere coordination, accompanied by electron transfer from HNC to Cr(VI), while oxalate was adsorbed on HNC through bidentate mononuclear side-on inner-sphere coordination with electron transfer from HNC to oxalate, and also outer-sphere coordination with negative charge accumulation. When oxalate was added to HNC with preadsorbed Cr(VI), oxalate would occupy the inner-sphere adsorption sites and thus cause the detaching of preadsorbed Cr(VI) from HNC. This study provides a promising in situ characterization technique for real-time interfacial reaction monitoring and also sheds light on the competitive adsorption mechanism of oxalate and Cr(VI) on the mineral surface.

Perturbations of JUICE/JDC Ion Measurements Caused by Spacecraft Charging in the Jovian Magnetosphere and the Ionosphere of Ganymede

AbstractSpacecraft charging is a well‐known effect that occurs when a spacecraft is located in a charged environment such as plasma. In this process, the surface of the spacecraft acquires an electrostatic potential through the accumulation and emission of positive and negative charges. In addition to causing severe electrostatic discharges, it also significantly affects low‐energy particle measurements performed by instruments onboard the spacecraft as it causes a change in energy and a distortion of the Field Of View (FOV) of the instrument by modifying the trajectory of measured particles. Spacecraft charging is therefore an important aspect to consider for Jovian plasma Dynamics and Composition analyzer (JDC), an instrument which aims to perform cold plasma measurements around the Galilean moons onboard JUpiter ICy moons Explorer (JUICE). In this study we use SPIS to perform simulations to study the FOV distortion of JDC for positive ions caused by spacecraft charging in two environments of the JUICE mission: the ionosphere of Ganymede and the Jovian magnetosphere. We show that the resulting distortion of the instrument FOV is highly space dependent and varies in shape and intensity from a pixel to another. However, we show that in both environments the complexity of the interactions between measured positive ions and the spacecraft can be decomposed and described as a superposition of a finite number of elementary interactions (i.e., modes). We show that each mode is caused by a specific element of the spacecraft and leads to a characteristic distortion of the instrument FOV. This study constitutes a first step toward necessary spacecraft potential corrections of the measurements performed by JDC.

Experimental study of transient surface charging during dielectric barrier discharges in air gap in needle-to-plane geometry

Motivated by a deeper understanding of plasma–surface interactions, this study presents experimental investigations into the transient surface charging process during dielectric barrier discharges (DBDs) in an air gap in a needle-to-plane geometry based on a combination of the Pockels method and a custom-designed ultrafast multi-frame imaging system. We realized three-frame observations of transient surface charge distributions, with a remarkable temporal resolution of 3 ns, during positive primary discharges and negative reverse discharges when applying a positive square-wave pulse. During the positive primary discharges at the rising voltage front, following the circular expansion of the streamer over the surface, multiple streamer filaments bifurcate simultaneously from the center, resulting in a branched positive surface charge distribution. Gradient surface charge densities are observed along the channel with higher charge densities at the head, which gradually evolve into a uniform distribution along the channel as the streamers approach stagnation. No lateral expansion of positive charges is observed across the channel under the present condition. In the case of negative reverse discharges occurring at the falling edge of the voltage pulse, the neutralization of residual positive surface charges and the accumulation of negative surface charges occur simultaneously in the central region. The deposited negative surface charges exhibit a progressively expanding circular distribution characterized by increasing charge density and radius. The propagation dynamics of surface streamers and the fields induced by surface charges are investigated and discussed based on the spatio-temporal surface charge measurements. Further study suggests that the surface streamer is not driven by the over-accumulation of surface charges, but rather by the space charge field above the dielectric. The presented quantitative measurements can be used for detailed validation of DBD simulations and offer deeper insights into plasma–surface interactions.

Symmetry Breaking and Cooperative Spin Crossover in a Hofmann-Type Coordination Polymer Based on Negatively Charged {FeII(μ2-[MII(CN)4])2}n2n- Layers (MII = Pd, Pt).

We report herein the synthesis and characterization of two unprecedented isomorphous spin-crossover two-dimensional coordination polymers of the Hofmann-type formulated {FeII(Hdpyan)2(μ2-[MII(CN)4])2}, with MII = Pd, Pt and Hdpyan is the in situ partially protonated form of 2,5-(dipyridin-4-yl)aniline (dpyan). The FeII is axially coordinated by the pyridine ring attached to the 2-position of the aniline ring, while it is equatorially surrounded by four [MII(CN)4]2- planar groups acting as trans μ2-bidentate ligands defining layers, which stack parallel to each other. The other pyridine group of Hdpyan, being protonated, remains peripheral but involved in a strong [MII-C≡N···Hpy+] hydrogen bond between alternate layers. This provokes a nearly 90° rotation of the plane defined by the [MII(CN)4]2- groups, with respect to the average plane defined by the layers, forcing the observed uncommon bridging mode and the accumulation of negative charge around each FeII, which is compensated by the axial [Hdpyan]+ ligands. According to the magnetic and calorimetric data, both compounds undergo a strong cooperative spin transition featuring a 10-12 K wide hysteresis loop centered at 220 (Pt) and 211 K (Pd) accompanied by large entropy variations, 97.4 (Pt) and 102.9 (Pd) J/K mol. The breaking symmetry involving almost 90° rotation of one of the two coordinated pyridines together with the large unit-cell volume change per FeII (ca. 50 Å3), and subsequent release of significantly short interlayer contacts upon the low-spin → high-spin event, accounts for the strong cooperativity.

Experimental Study on Critical Parameters Degradation of Nano PDSOI MOSFET under TDDB Stress.

In today's digital circuits, Si-based MOS devices have become the most widely used technology in medical, military, aerospace, and aviation due to their advantages of mature technology, high performance, and low cost. With the continuous integration of transistors, the characteristic size of MOSFETs is shrinking. Time-dependent dielectric electrical breakdown (TDDB) is still a key reliability problem of MOSFETs in recent years. Many researchers focus on the TDDB life of advanced devices and the mechanism of oxide damage, ignoring the impact of the TDDB effect on device parameters. Therefore, in this paper, the critical parameters of partially depleted silicon-on-insulator (PDSOI) under time-dependent dielectric electrical breakdown (TDDB) stress are studied. By applying the TDDB acceleration stress experiment, we obtained the degradation of the devices' critical parameters including transfer characteristic curves, threshold voltage, off-state leakage current, and the TDDB lifetime. The results show that TDDB acceleration stress will lead to the accumulation of negative charge in the gate oxide. The negative charge affects the electric field distribution. The transfer curves of the devices are positively shifted, as is the threshold voltage. Comparing the experimental data of I/O and Core devices, we can conclude that the ultra-thin gate oxide device's electrical characteristics are barely affected by the TDDB stress, while the opposite is true for a thick-gate oxide device.

Acceleration of Stepwise Carbon-Polygold Bonding Cleavage in Hypercoordinated Carbon-Centered Gold(I) Clusters

Hypercoordinated carbon-centered organometallic clusters extensively exist in polymetallic and metal surface catalysis. The investigation on their electronic structures and transformations is crucial for mechanistic studies. Herein, we try to clarify the reactivity difference between a hypercoordinated tetrametalated species [PA-C-Au4]+ and a classical trimetalated one [(PA-C-Au3) + H]+ based on experimental and theoretical studies. Under a protonolysis condition, the hypercoordinated carbon species [PA-C-Au4]+ experiences a sequential cleavage process of carbon-polymetal bonding through the trinuclear [(PA-C-Au3) + H]+ intermediate to end up with a methyl group. Theoretical studies indicate that the high symmetry of five-center bonding in [PA-C-Au4]+ promotes the delocalization of negative charges, finally resulting in less nucleophilicity of the central hypercarbon atom. In contrast, the low C3V triangular arrangement of gold atoms in the [(PA-C-Au3) + H]+ structure causes the decrease in orbital interaction between the Aun moiety and the central carbon atom and the increase in the negative charge on the central carbon atom. Along with the gradual cleavage of the carbon-polymetal bonding, the accumulation of negative charges and the reduction of steric hindrance around the central carbon atom jointly contribute to the synergistic multi-step protodeauration process. This work not only illustrates the reactivity difference of RC-Mn species in different degrees of metalation but also provides an essential structural basis for the design of synergistic polymetallic catalysts.

Capacitance–voltage modeling of mid-wavelength infrared nBn detectors

Capacitance–voltage measurements are a powerful technique to determine doping profiles of semiconductor pn junctions and Schottky barrier diodes. The measurements were recently extended to III-V-based mid-wavelength nBn infrared detectors, and absorber doping densities have been extracted using the widely accepted Schottky approximation, where the potential drop across the device is assumed to be across the depleting absorber layer. However, this approach is limited to when the absorber region of the nBn is under high reverse bias and thus is only able to extract the absorber region doping profile. Here, we introduce a semi-analytical model that is capable of extracting barrier dopant polarity, doping concentration, and thickness, as well as contact and absorber layer doping concentrations, all from a capacitance–voltage measurement. Rather than solely considering the potential drop across the depleting layers, it considers the potential drop across the accumulating layer as well. This negative charge accumulation occurs for the contact and absorber layers in the case of reverse and forward biases, respectively. This allows for a single model to be applied to a capacitance–voltage curve at forward and reverse biases and it can provide regions of bias where the absorber transitions from depletion to accumulation. We compare the agreement of the semianalytical model with modeling results from commercially available finite element method software and experimental capacitance–voltage data. Finally, we show that the method is consistent with the Schottky approximation of extracting absorber doping densities at high reverse bias and discuss the model's limitations.

Modeling plasma-induced surface charge effects on CO2 activation by single atom catalysts supported on reducible and irreducible metal oxides

The accumulation of negative surface charge on catalytic surfaces in the presence of low-temperature plasma (LTP) could influence catalytic performance. However, it is difficult to disentangle the role of surface charging and other LTP catalytic effects in experiment. Herein, we use density functional theory (DFT) modeling to understand the effect of plasma-induced surface charging on CO2 activation by atomically dispersed single atom (SA) catalysts on both reducible and irreducible metal oxide supports. We model CO2 adsorption strength and CO2 dissociation barriers for Co1, Ni1, Cu1, Rh1, Pd1, and Ag1 SAs on both reducible and irreducible supports, namely, CeO2(100), TiO2(101), and γ-Al2O3(110), to elucidate trends. We find that accumulated surface charge on the SA increases the CO2 adsorption strength and decreases the CO2 dissociation barrier for all studied SA/support combinations. For both charged and uncharged (neutral) systems, SAs on the reducible CeO2(100) support generally adsorb CO2 more weakly compared to when on irreducible supports like γ-Al2O3(110). SAs on γ-Al2O3(110) typically have larger barriers for CO2 dissociation for both charged and uncharged systems compared to TiO2(101) and CeO2(100). The magnitude of surface charging effects on CO2 binding energies and dissociation barriers depends sensitively on both the SA and the support. In some cases, the CO2 activation trends qualitatively change between neutral and charged systems for a fixed SA across different supports. This DFT modeling study demonstrates that surface charging should be considered in strong electric fields because it can have a large effect on molecule adsorption and bond-breaking on catalytic surfaces.

Defect self-propulsion in active nematic films with spatially varying activity.

We study the dynamics of topological defects in active nematic films with spatially varying activity and consider two set-ups: (i) a constant activity gradient and (ii) a sharp jump in activity. A constant gradient of extensile (contractile) activity endows the comet-like +1/2 defect with a finite vorticity that drives the defect to align its nose in the direction of decreasing (increasing) gradient. A constant gradient does not, however, affect the known self-propulsion of the +1/2 defect and has no effect on the -1/2 that remains a non-motile particle. A sharp jump in activity acts like a wall that traps the defects, affecting the translational and rotational motion of both charges. The +1/2 defect slows down as it approaches the interface and the net vorticity tends to reorient the defect polarization so that it becomes perpendicular to the interface. The -1/2 defect acquires a self-propulsion towards the activity interface, while the vorticity-induced active torque tends to align the defect to a preferred orientation. This effective attraction of the negative defects to the wall is consistent with the observation of an accumulation of negative topological charge at both active/passive interfaces and physical boundaries.

Insulation Properties and Interfacial Quantum Chemical Analysis of Cross-Linked Polyethylene Under Different Degassing Time for HVDC Cable Factory Joint Applications

Degassing treatment is critical to remove cross-linking by-products in cross-linked polyethylene (XLPE) cable factory joints and prevent early insulation deterioration. In this article, 500-kV high-voltage direct-current (HVDC) cable factory joint samples were prepared, and the physicochemical and temperature-dependent electrical properties of the samples under different degassing times were investigated. The results show that prolonged degassing treatment increases the crystallinity and reduces the tensile properties of the XLPE samples. The samples without degassing have visible micropores near the interface, and these micropores can be eliminated after a longer degassing time. In addition, degassing treatment can reduce the current density, increase the threshold field strength, and enhance the breakdown strength of the samples. A significant negative charge accumulation appears at the interface of the sample without degassing, which dramatically distorts the electric field. Long-term degassing treatment can improve this phenomenon, and the accumulated charge at the interface at elevated temperatures is significantly reduced. Furthermore, a model of the molecular chain microstructure at the interface before and after degassing is proposed. The molecular chain’s energy band structure and electron cloud distribution at the interface are analyzed based on quantum chemical calculation. It is found that cable makers can improve the insulation properties of cable factory joints by appropriately extending the degassing time to avoid interface deterioration.

Effect of hydrogen atoms on potassium-ion electrets used in vibration-powered generators

Potassium-ion electrets, which are mainly composed of amorphous silica and potassium atoms, can accumulate negative charges and are expected to be useful for future vibration powered generators. According to previous research, the origin of the accumulation of negative charges was revealed to be related to the presence of SiO5 structures in amorphous silica. In general, Si–O bonds are so stable that potassium-ion electrets are expected to retain a high electric potential longer than previously studied materials and are therefore being studied intensively for practical use. However, charge decay phenomena were observed in previous experiments, and this presents serious problems. In this study, we focus on the role of hydrogen which is considered to be one of the origins of charge decay and have investigated the behavior of hydrogen in potassium-ion electrets and the mechanism of the charge decay using first-principles calculations. As a result, we found that hydrogen atoms can create a positively charged characteristic local structure or break SiO5 structures and therefore cause degradation of the negative charge storing ability of potassium-ion electrets.