Charge Buildup Research Articles

Origin of Rapid Coalescence and Active Unstable Fluctuation of Au Nanoparticles under TEM Observation: Electron Bombardment Versus Charge Buildup

Origin of Rapid Coalescence and Active Unstable Fluctuation of Au Nanoparticles under TEM Observation: Electron Bombardment Versus Charge Buildup

Monte-Carlo simulation and experimental study of the effect of internal charging on the electron emission yield of amorphous SiO2 thin films

A Monte-Carlo code has been developed for the transport of low energy electrons and the simulation of the internal charge buildup induced by the electron irradiation in thin films of amorphous SiO2. The code is validated with time resolved experimental Electron Emission Yield (EEY) data on 20 nm SiO2 thin films for incident electrons of 300 eV and 1 keV. As the EEY is greater than 1, this corresponds to the case of positive charging. In order to assess the impact of the charge buildup on the electron emission yield, the samples have been negatively polarized to suppress the positive external charging effects, and irradiated with a defocused beam (mm²). A direct correlation is found between the value of the EEY and the density of holes created in the material. This clearly shows that the recombination of the secondary electrons with trapped holes significantly affects the EEY of insulators.

Analysis of Load-Bearing Electrical Properties of Composite Materials Based on Homogenization Theory

In this study, the broadband dielectric spectrum of polyimide composites was examined using the homogenization theory. The findings demonstrate that the addition of boron nitride nanosheets (BNNSs) and silver nanoparticles (AgNPs) causes an increase in conductivity, dielectric constant, and dielectric loss of the composites but does not result in a surge in the three parameters; the results also demonstrate that an increase in temperature causes an increase in dielectric constant and dielectric loss of the composites. In addition, temperature has a bigger impact on the dielectric loss than it does on the dielectric constant. An increase in the amount of polarized charges and a shallower bulk trap depth can result from the addition of nanomaterials, according to research on thermally stimulated current in composite materials. The presence of the interfacial region, which made it simple to cause charge accumulation and simple to form conduction current, is primarily responsible for the significant increase in bulk conductivity of the composites at 50 Hz that occurred with the addition of more nanomaterials. The large rise in bulk conductivity of the composites at 50 Hz that happened with the addition of more nanomaterials is mostly due to the existence of the interfacial region, which made it simple to produce charge buildup and simple to form conduction current. The variation in volume conductivity when the doping ratio is less than 10 vol% is not significant due to AgNPs’ low concentration and ambiguous contribution to the conduction current. As the polarization temperature rises, the amount of polarization charges increases, but it has minimal effect on the bulk trap depth of the composites.

Correlating Thermodynamic and Kinetic Hydricities of Rhenium Hydrides.

The kinetics of hydride transfer from Re(Rbpy)(CO)3H (bpy = 4,4'-R-2,2'-bipyridine; R = OMe, tBu, Me, H, Br, COOMe, CF3) to CO2 and seven different cationic N-heterocycles were determined. Additionally, the thermodynamic hydricities of complexes of the type Re(Rbpy)(CO)3H were established primarily using computational methods. Linear free-energy relationships (LFERs) derived by correlating thermodynamic and kinetic hydricities indicate that, in general, the rate of hydride transfer increases as the thermodynamic driving force for the reaction increases. Kinetic isotope effects range from inverse for hydride transfer reactions with a small driving force to normal for reactions with a large driving force. Hammett analysis indicates that hydride transfer reactions with greater thermodynamic driving force are less sensitive to changes in the electronic properties of the metal hydride, presumably because there is less buildup of charge in the increasingly early transition state. Bronsted α values were obtained for a range of hydride transfer reactions and along with DFT calculations suggest the reactions are concerted, which enables the use of Marcus theory to analyze hydride transfer reactions involving transition metal hydrides. It is notable, however, that even slight perturbations in the steric properties of the Re hydride or the hydride acceptor result in large deviations in the predicted rate of hydride transfer based on thermodynamic driving forces. This indicates that thermodynamic considerations alone cannot be used to predict the rate of hydride transfer, which has implications for catalyst design.

Direct visualization of the drug release process of non-conductive polymeric implants via molecular imaging

Long-acting parenteral (LAP) implant has garnered the attraction as a drug delivery technique in recent years. Understanding the drug release process is critical for the study of underlying release mechanism. In this paper, we present a novel application of matrix-assisted laser desorption/ionization-mass spectrometry imaging (MADLI-MSI) for the direct visualization of the drug release process from non-conductive polymeric based LAP implants at molecular level. Custom-made sample holders were designed for LAP sample introduction in place of traditional conductive glass slides. The main technical obstacles of applying MALDI-MSI to study non-conductive materials are surface conductivity which can lead to charge build-up. In order to obtain homogeneous imaging of non-conductive sample surfaces, we developed a new sample surface treatment procedure, which is a critical control step to ensure the data reliability and accuracy in understanding kinetics of drug release process of LAP. Overall, this is the first comprehensive report of a sample preparation methodology tailored for imaging LAP at molecular level, allowing for the direct chemical identification and 2D mapping of an active pharmaceutical ingredient (API) distribution during LAP release process. Furthermore, this work has established the foundation to apply MALDI-MSI to the understanding of LAP implant formulation homogeneity, chemical composition, and degradation. More importantly, this work enabled the extension of MALDI-MSI technique to study a wide range of non-conductive materials.

Study protocol: Effects of active versus passive recharge burst spinal cord stimulation on pain experience in persistent spinal pain syndrome type 2: a multicentre randomized trial (BURST-RAP study)

BackgroundSpinal cord stimulation (SCS) has shown to be an effective treatment for patients with persistent spinal pain syndrome type 2 (PSPS Type 2). The method used to deliver electrical charge in SCS is important. One such method is burst stimulation. Within burst stimulation, a recharge pattern is used to prevent buildup of charge in stimulated tissues. Two variations of burst waveforms are currently in use: one that employs active recharge and one that uses passive recharge. It has been suggested that differences exist between active and passive recharge paradigms related to both efficacy of pain relief and their underlying mechanism of action. Active recharge has been shown to activate both the medial spinal pathway, engaging cortical sensorimotor areas involved in location and intensity of pain, and lateral pathway, reaching brain areas involved with cognitive-emotional aspects of pain. Passive recharge has been suggested to act via modulation of thalamic neurons, which fire in a similar electrical pattern, and thereby modulate activity in various cortical areas including those related to motivational and emotional aspects of pain. The objective of this randomized clinical trial is to assess and compare the effect of active versus passive recharge Burst SCS on a wide spectrum of pain in PSPS Type 2 patients.MethodsThis multicentre randomized clinical trial will take place in 6 Dutch hospitals. PSPS Type 2 patients (n=94) will be randomized into a group receiving either active or passive recharge burst. Following a successful trial period, patients are permanently implanted. Patients complete the Pain Catastrophizing Scale (PCS) (primary outcome at 6 months), Numeric Pain Rating Scale (NRS), Patient Vigilance and Awareness Questionnaire (PVAQ), Hospital Anxiety and Depression Scale (HADS), Quality of Life (EQ-5D), Oswestery Disability Index (ODI), Patient Global Impression of Change (PGIC) and painDETECT questionnaires (secondary outcomes) at baseline, after trial, 1, 3, 6 and 12 months following implantation.DiscussionThe BURST-RAP trial protocol will shed light on possible clinical differences and effectivity of pain relief, including emotional-motivational aspects between active and passive burst SCS in PSPS Type 2 patients.Trial registrationClinicalTrials.gov registration: NCT05421273. Registered on 16 June 2022. Netherlands Trial Register NL9194. Registered on 23 January 2021.

Analytical solution to the Poisson–Nernst–Planck equations for the charging of a long electrolyte-filled slit pore

We study the charging dynamics of a long electrolyte-filled slit pore in response to a suddenly applied potential. In particular, we analytically solve the Poisson–Nernst–Planck (PNP) equations for a pore for which λD≪H≪L, with λD the Debye length and H and L the pore’s width and length. For small applied potentials, we find the time-dependent potential drop between the pore’s surface and its center to be in complete agreement with a prediction of the celebrated transmission line model. For moderate to high applied potentials, prior numerical work showed that charging slows down at late times; Our analytical model reproduces and explains such biexponential charge buildup.

Influence of LDD spacers on total ionizing dose response of the transconductance for bulk MOSFETs working at cryogenic temperatures

In this work, the radiation responses of 0.25 μm bulk transistors irradiated up to 300 krad are discussed. The electricals characteristics shown are measured after irradiation at 95 K, 150 K, and 300 K. The transconductance improves significantly with total ionizing dose (TID) at low temperature and does not vary at room temperature. The impact of incomplete ionization of impurities introduced into the Lightly Doped Drain extensions is examined. Since the transconductance increase is more pronounced for the shortest transistors, positive charges trapped in spacer oxides are likely to constitute the source of this increase. The Technology Computer-Aided Design simulations help us to discuss the influence of charge build-up at the spacers' locations on the drain to source resistance. By the means of a resistivity analysis, the influence of LDD doping level and operating temperature on the TID response of devices is analyzed. Its potential evolution with technological integration is investigated.

Threshold-voltage bias-instability in SiC MOSFETs: effects of stress temperature and level on oxide charge buildup and recovery

In this study we performed slow and fast bias temperature instability (BTI) measurements on n-channel silicon carbide (SiC) metal-oxide-SiC field effect transistors. Threshold voltage (V th) shifts as well as recovery observed during and after stress applied at different temperatures and stress levels were used to understand the dynamics of charge trapping/capture and detrapping/emission at gate oxide defects. It is deduced from the results that no new defects are created by the stress at the levels used in this study and V th shifts are due to the injected electron capture and trapping at existing oxide border traps. Positive gate-voltage BTI induced V th shift is observed to follow a power law on stress time with an exponent, n, dependent on stress temperature and level, such that 0.03 ⩽ n ⩽ 0.09. Electron emission and/or defect interactions are found to proceed with a low activation energy of the order of 0.01 eV and are suggested to be responsible for oxide charge reduction and, consequently, V th recovery.

Atomic Layer Deposition Coating on the Surface of Active Pharmaceutical Ingredients to Reduce Surface Charge Build-Up.

Active pharmaceutical ingredients (APIs) typically consist of solid therapeutic particles that may acquire electrostatic charge during milling and grinding operations. This may result in the agglomeration of particles, thereby reducing the flowability and affecting the homogeneity of the drug formulation. Electrostatic charge build-up may also lead to fire explosions. To avoid charge build-up, APIs are often coated with polymers. In this paper, atomic layer deposition (ALD) using metal oxides such as Al2O3 and TiO2 on APIs, namely, palbociclib and pazopanib HCl, has been utilized to demonstrate a uniform coating that results in a significant reduction in the surface charge of the drug particles. Kelvin probe force microscopy (KPFM) shows a 4-fold decrease in the surface contact potential of uncoated pazopanib HCl (2.3 V) to 0.52 and 0.82 V in TiO2-and Al2O3-coated APIs, respectively. Also, the ζ potential indicated a 4-fold decrease in the surface charge on coating pazopanib HCl, i.e., from -32.9 mV to -7.51 and -8.51 mV in Al2O3 and TiO2, respectively. Surface morphology, thermal stability, dissolution studies, and cytotoxicity of the drug particles after coating were also examined. Thermal analysis indicated no change in the melting temperature (Tm) after coating. ALD coating was found to be uniform and conformal as observed in images obtained from scanning electron microscopy (SEM) and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS). The rate of dissolution was found to be delayed by the coating, and thus ALD offers slower drug release. Coating APIs with TiO2 and Al2O3 did not induce statistically significant cytotoxicity compared to the uncoated samples. The results presented in this study demonstrate that ALD coating can be used to reduce surface charge build-up and enhance the bulk properties of the drug particles without affecting their physicochemical properties.

Electrostatic Lofting Conditions for Supercharged Dust

Electrostatic dust lofting may be a common occurrence on small bodies in the solar system, whereby the upward electrostatic force on a grain is able to overcome the surface gravity and cohesion binding it to the surface. This electrostatic lofting may serve to redistribute and transport dust across the surface of these bodies to produce features such as dust ponds and lineations found on Eros, or even to rid bodies of small particles completely. Classical models, which distribute charge evenly across a dust grain, have historically predicted electric field strengths that are insufficient to loft dust. However, recent studies have developed grain-scale charging models that account for the buildup of charge in the microcavities of regolith and assume unequal distribution of charge on a dust grain. These models predict electric field strengths orders of magnitude larger than classical models, which may explain how electrostatic dust lofting occurs on small bodies. In this paper, we compare the grain-scale supercharging models developed by Zimmerman et al. and survey how the different parameters affect grain charging—namely, charge separation, grain size, and dielectric breakdown strength. Furthermore, we investigate how each of the charging models can be used to bound initial condition requirements such as charge and velocity for dust lofting to occur on these small bodies. Initial condition requirements are examined for a range of grain sizes, regolith cohesive strengths, and small body sizes.

Ab initio calculation of silicon monovacancy defect in amorphous-SiO2/Si interface

Defects significantly influence the electrical properties of semiconductors and their interfaces. The migration barriers and electrical properties of silicon monovacancy defect in an amorphous-SiO2/Si (a-SiO2/Si) interface are studied in this work. The minimum energy path and kinetics of monovacancy defect in the a-SiO2/Si interface are calculated by the climbing image nudged elastic band method. It is indicated that the a-SiO2/Si interface may be an effective sink for the monovacancies from the Si sublayers due to the unevenly distributed strain; the vacancy defect migrated into a-SiO2/Si interface can trigger structural changes by local distortion. The partial charge density of a monovacancy in the a-SiO2/Si interface shows that the induced defect level is localized around the unpaired Si dangling bonds and extends along the [110] zigzag chains of Si atoms. In addition, the formation energies of a silicon vacancy defect in the a-SiO2/Si interface are calculated with sophisticated corrections applicable to the interface system by combining the density functional theory calculation and finite element simulation. It is suggested that a Si monovacancy can appear in V0, V−, and V2−, and the (−/2−) and (0/−) transition levels lie at 0.15 and 0.2 eV below the CBMSi, respectively. The vacancies generated by displacement damage result in anisotropic migration and charge build-up in the a-SiO2/Si interface; for further dynamics, the ionization radiation can induce cascade reactions of displacement defects by synergistic effect between ionization and displacement radiation damages, and consequently excess base current and gain degradation in transistors.

Microchannel insulating foams comprising a multifunctional epoxy/graphene‐nanoplatelet nanocomposite

AbstractGraphene nanomaterials have demonstrated simultaneous enhancement of both the thermal and mechanical properties of many base polymer systems, but for application as a reinforcement in multifunctional thermally insulating polymer foam the graphene additive must not significantly increase the macroscopic thermal conductivity. In an effort to study and decouple these mechanical and thermal properties, low loadings of reduced graphene oxide nanoplatelets have been added into epoxy formulations to comprise the matrix structure of hollow microchannel nanocomposite foams. Substantial improvements of 226% were achieved in the microchannel foam specific flexural modulus at only 0.15% graphene nanoplatelet loading without compromising the foam flexural strength and while also maintaining the low thermal conductivity of the baseline epoxy foam material. These results support the use of these nanocomposite foams as mechanically reinforced thermal insulation, with the addition of the graphene nanoplatelets potentially providing additional multifunctional improvements to the foam such as reduced UV‐radiation transmittance, improved electrical surface conductivity for diminished static charge buildup, and/or lowering of the coefficient of thermal expansion for enhanced structural stability in extreme environments. This particular combination of multifunctional properties makes these materials well suited as high‐performance structural thermal insulation materials in support of next generation space system applications.

Characterization and numerical analysis of breakdown in thick amorphous SiO2 capacitors

Charge transport in thick amorphous silicon dioxide capacitors for integrated galvanic insulators is experimentally investigated and analyzed through numerical simulations carried out with a commercial TCAD tool. The material intrinsic defectivity and the large biases applied to such devices give rise to a leakage current which is responsible for degradation and failure. Hence it is crucial to have a complete understanding of the charge-transport main physical mechanisms in amorphous silicon oxide. In particular, charge injection at contacts and charge build-up due to trapping/de-trapping mechanisms in the bulk of the oxide are expected to play a crucial role and their complex coupled interaction needs to be investigated via a TCAD-based approach. For this reason, time-dependent dielectric breakdown measurements at constant-current stresses and voltage-ramp stresses up to breakdown have been performed on thick metal-insulator–metal structures, and numerical simulations have been carried out so to predict the failure mechanisms. To this purpose, special attention has been devoted to the physical modeling of defects and impact-ionization generation.

The effect of particle size and relative humidity on triboelectric charge saturation

Triboelectric charging is present in numerous technologies and everyday processes, providing both problems and opportunities. Despite this, there is no generalised model for the amount of charge that will build up on surfaces in contact. Here, we develop a new model for the saturation charge on triboelectrically charged spherical insulators, accounting for both equalisation of surface potentials and electrical breakdown of the surrounding medium. Experiments are conducted under controlled temperature and humidity using two independent methods, measuring the saturation charge on polymer spheres contacting grounded stainless steel. The results verify our equalisation of surface potentials model which describes how saturation charge density increases for smaller particle sizes. Key triboelectric properties are calculated: The estimated saturation charge on a flat surface and the equalisation potential between different materials, which can be used to predict charge saturation and quantify a triboelectric series. The transition radius below which electrical breakdown will cause saturation of charge is also calculated theoretically. Limitations to the model are demonstrated experimentally. As particle size reduces, a point is reached at which the electrostatic adhesion of particles to the grounded charging surface prevents further charge build-up. Furthermore, it is found that the saturation charge for smaller particles in humid conditions is greatly reduced. These calculations, and the demonstrated procedure, can serve as a tool for the design of technologies and processes influenced by triboelectric charge build-up, including triboelectric nanogenerators and electrostatic mineral separators.

Understanding water structure and hydrogen association on platinum–electrolyte interface

Abstract Platinum (Pt) is a benchmarked catalyst for several electro-catalytic processes, although the complex nature of heterogeneous charge transfer processes at the Pt–electrolyte interface hinders an atomistic-level understanding of the electrodics. In this study, we aim to capture the chemical changes of Pt surfaces brought on by an applied potential, which can probe the catalytic efficacy under varying applied bias. Through a combined experimental and reactive molecular dynamics (MD) simulation approach, we uncover the effect of charge buildup on the surface of the Pt electrode, which can be directed toward capacitive and faradaic processes. In the case of a moderately acidic pH shown here, the potential dependence of simulated electrodic processes aligns well with the experimental results from electrochemistry and in situ surface-enhanced Raman spectroscopy (SERS). Using reactive MD- and SERS-based studies, we are able to probe into the interfacial water structure and the formation of the Helmholtz layer. At reductive potentials of ∼0.3–0.0 V vs. RHE, we simulate phenomena such as under potential hydrogen adsorption and hydrogen evolution/oxidation reaction. Together, the investigation establishes a framework for quantitative exploration of catalytic processes in electrolytes at very high spatial and temporal resolution.

Computational Exploration of Anomalous Regioselectivities in Cycloadditions of Ketenes to Oxazolines.

Thermal (2 + 2) cycloadditions of several N-carboalkoxy (R)-2-tert-butyldihydrooxazoles with ketenes have been studied experimentally by the Ghosez group. Contrary to results from Seebach and co-workers that the electrophilic addition of acylating agents occurs β to dihydrooxazole nitrogen, Ghosez found major cycloadducts resulting from an attack of ketene carbonyl carbon β to oxygen. We investigate the potential energy surface for the cycloaddition of diphenyl- and phenylchloroketenes to two (R)-2-tert-butyldihydrooxazoles with ωB97X-D and mPW1PW91 density functional theory and DLPNO-CCSD(T) wave function theory. These (2 + 2) cycloadditions are concerted but highly asynchronous, and the selectivity trends in ketene addition cases are in good agreement with the experiment. We propose a model based on the buildup of charge in oxazoline to reconcile the regiochemical differences between Ghosez and Seebach's observations.

Coulomb explosion imaging of small polyatomic molecules with ultrashort x-ray pulses

Ultrashort x-ray pulses from free-electron lasers can efficiently charge up and trigger the full fragmentation of molecules. By coincident detection of up to five ions resulting from rapid Coulomb explosion of highly charged iodomethane, we show that the full three-dimensional equilibrium geometry of this prototypical polyatomic system can be determined from the measured ion momenta with the help of a charge buildup model. Supported by simulations of how the ion momenta would reflect specific changes in molecular bond lengths and angles, we demonstrate that Coulomb-explosion imaging with ultrashort x-ray pulses is a promising technique for recording movies of multidimensional nuclear wave packets, including hydrogen motions.Received 18 January 2021Revised 22 September 2021Accepted 23 September 2021DOI:https://doi.org/10.1103/PhysRevResearch.4.013029Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAtomic & molecular processes in external fieldsAtomic & molecular structureLight-matter interactionSingle- and few-photon ionization & excitationUltrafast phenomenaX-ray beams & opticsAtomic, Molecular & Optical

Space Charge Redistribution in Epoxy Mold Compounds of High-Voltage ICs at Dry and Wet Conditions: Theory and Experiment

Space charge profile plays an important role in defining the charge transport and breakdown field of an insulator. Non-destructive experimental techniques (e.g., PEA measurement) have recently been used to track in-situ the time-evolution of space charge profiles within complex insulators, such as epoxy mold compounds. Unfortunately, the published results are often inconsistent (both positive and negative charge build-up have been reported), and the discrepancy remains unexplained. In this paper, we (i) derive a physics-based compact analytical model of homocharge injection, (ii) explain the time-and voltage-dependent redistribution of homo- and heterocharge, (iii) investigate experimentally and explain theoretically the importance of moisture ingress regarding space charge redistribution, and finally, (iv) summarize strategies to suppress space-charge related instability in modern ICs encapsulated by epoxy mold compounds.

Instability of a planar fluid interface under a tangential electric field in a stagnation point flow

The interface between two immiscible fluids can become unstable under the effect of an imposed tangential electric field along with a stagnation point flow. This canonical situation, which arises in a wide range of electrohydrodynamic systems including at the equator of electrified droplets, can result in unstable interface deflections where the perturbed interface gets drawn along the extensional axis of the flow while experiencing strong charge build-up. Here, we present analytical and numerical analyses of the stability of a planar interface separating two immiscible fluid layers subject to a tangential electric field and a stagnation point flow. The interfacial charge dynamics is captured by a conservation equation accounting for Ohmic conduction, advection by the flow and finite charge relaxation. Using this model, we perform a local linear stability analysis in the vicinity of the stagnation point to study the behaviour of the system in terms of the relevant dimensionless groups of the problem. The local theory is complemented with a numerical normal-mode linear stability analysis based on the full system of equations and boundary conditions using the boundary element method. Our analysis demonstrates the subtle interplay of charge convection and conduction in the dynamics of the system, which oppose one another in the dominant unstable eigenmode. Finally, numerical simulations of the full nonlinear problem demonstrate how the coupling of flow and interfacial charge dynamics can give rise to nonlinear phenomena such as tip formation and the growth of charge density shocks.