Accumulation Of Positive Charge Research Articles

Moderation of the Electronic Structure of Phosphamides to Execute the Catalytic Appel Reaction Bypassing Phosphine.

A set of structurally analogous, albeit electronically distinct, phosphamides (1aa-10aa) is prepared, and the effect of the electronic amendment due to p-substitution has been tested for the conversion of alcohols to halides via the Appel reaction. The -OMe-substituted diphosphamide (8aa) remains the most active, providing ∼96% conversion of alcohols to halides with a TON of 11 in moderate reaction conditions with a large substrate scope. Halide formation follows a pseudo-first-order rate with a constant rate (kobs) of 7.13 × 10-5 s-1. Temp-dependent kinetics and Eyring analyses reveal the activation parameters ΔH‡ of 28.95 (±1.6) kcal mol-1, ΔS‡ of -70.02 (±0.4) cal K-1 mol-1, and ΔG‡298 of 49.81 (±1.2) kcal mol-1. The deuterium labeling study highlights the O-H dissociation of the alcohol as the rate-determining step, while the Hammett analysis with p-substituted benzyl alcohols indicates a positive charge accumulation at the phosphorus center during the Appel reaction. The HOMO-LUMO energy and NPA analyses show that p-OMe substitutions in 8aa make the "P═O" bond more ionic and corresponding aminophosphine is nucleophilic, which are favorable for the Appel reaction. In situ detection of the Appel salt, [R3PX]CX3 and alkoxy phosphonium cation [R3POR]X, validates the reaction pathway mediated by the phosphamides.

Ski S. V. Influence of gamma irradiation on the reverse current-voltage characteristics of silicon photomultipliers

The study investigated the effect of Co60 gamma-quanta on the reverse current-voltage characteristic (IV) of silicon photomultiplier (SiPMs) with 1004 cells, which themselves were optically isolated from each other n+ –p–p+ -structures. The cells were optically isolated from each other by trenches filled with tungsten after passivation of the walls with SiO2 and Si3N4 layers. Two variants of structural design of SiPMs were studied. Two variants were tested for the trench metal connection in the SiPMs: variant BI connected the trench metal to the n+-region of the cell through a quenching polysilicon resistor, while variant BII connected it to the p+-region. The breakdown voltage of the investigated SiPMs was Ubr = 34 ± 1.0 V. The samples were irradiated in both the active electrical mode (avalanche breakdown mode) and the passive mode (reverse bias Ub = 0 V). It was discovered, that at dose of D = 106 rad, the dark current for SiPM (BI) and (BII) increased by 6–7 times when irradiated in passive mode and by 15–16 times for SiPM (BII) when irradiated in active mode. For SiPM (BI) irradiated in the avalanche breakdown mode, the dark current increased by 104 times at D = 105 rad. The research demonstrates that the radiation-induced degradation of the dark current in the SiPMs under study is due to an increase in the generation and, primarily, surface components. This is a result of the accumulation of positive charge in the insulating layer of the separating trenches.

Modified nanoporous zeolites on a biodegradable polymer film with excellent hydrophobicity, ethylene gas adsorption, and antibacterial activity through surface charge accumulation

The high specific surface area and large pore volume of nanoporous zeolites (NZs) were utilized to impart a biodegradable polymer film with superhydrophobicity, ethylene gas adsorption capability, and active antibacterial activity. NZs were synthesized by using organic silanes via a sol–gel method. They were then dispersed on a biodegradable blended PPP [poly(lactic acid) (PLA)/poly butylene succinate (PBS)/poly butylene adipate terephthalate (PBAT)] film to enhance its mechanical properties and control water repellent. The hydrophobicity of the organic silanes on the zeolite surface gradually increased according to their length. The film prepared by utilizing octadecyltriethoxysilane (ODTES) was superhydrophobic with a contact angle 142.6°. The porous structure of the PPP with attached ODTES-NZs impeded the release of accumulated charges generated through friction, thereby yielding excellent output voltage when applying friction periodically. The output performance of the PPP-ODTES-NZs film was measured to be 723 V when a positive charge was injected into the film, which was about 3.1 times higher than the output performance of the PPP film without surface modification. The accumulated positive charges provided excellent antibacterial efficacy against externally introduced bacteria. Our approach of attaching ODTES-NZs to a blended polymer provides a multifunctional biodegradable film (ethylene gas adsorption, water repellent, and antibacterial activity via positive charge accumulation) with excellent food-storage capability.

Probiotic spore-derived multifunctional nanoparticles for enhanced ulcerative colitis treatment by activating metabolic pathways and repairing epithelial barrier

Ulcerative colitis is an agnogenic and refractory intestinal disease. Probiotic therapy has gained prevalence in medical research. Particularly, the probiotic spore coat has shown effectiveness in delivering oral drugs or probiotics for colitis treatment. Nevertheless, challenges persist in understanding the exact mechanism of the spore coat for optimal anti-inflammatory efficacy. Consequently, we develop a type of multifunctional spore coat nanoparticles (CN) derived from probiotic spore coat to comprehensively investigate its mechanisms of action in alleviating inflammation. Surprisingly, our research findings demonstrate that CN exhibits remarkable resistance to the harsh gastric acid environment and possesses the ability to selectively target inflammatory colonic sites characterized by an accumulation of positive charges. Additionally, CN effectively maintains the normal expression levels of zonula-1, occludin, and claudin-1 while simultaneously enhancing the small intestinal mucin 2 to ensure the integrity of intestinal barriers. Furthermore, the metabolomics analysis identifies 88 potential biomarkers that are enriched in three metabolic pathways, including tyrosine metabolism, tryptophan metabolism, and biosynthesis of valine, leucine, and isoleucine. These pathways are associated with Nrf2 signaling pathway activation, NF-κB and Nrf2 signaling pathways regulation, and metabolic disorders regulation. Collectively, our work provides a multifunctional nanomaterial CN and elucidates its anti-inflammatory mechanisms for ulcerative colitis treatment.

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.

Effects of co-60 gamma-ray irradiation on the DC and RF characteristics of SiGe HBTs

This study investigates the effects of Co-60 gamma-ray irradiation on the DC and RF characteristics of the SiGe HBTs, with a total dose of up to 4000 krad(Si). The degradation of the forward base current is primarily attributed to surface recombination due to the induced interface traps. The ideality factor of the forward excess base current is affected by the positive oxide-trapped charges at the interface of the emitter-base spacer oxide. TCAD simulation results indicate that the effective integral region of the surface recombination rate is associated with the positive oxide-trapped charge density. The accumulation of positive oxide-trapped charges in the shallow trench isolation oxide has an impact on the potentials of the interface and epi-collector region, subsequently affecting the base diffusion current. Therefore, the ideality factor of the reverse excess base current depends on the device geometry. The RF characterization suggests that the depletion capacitance of the base-emitter junction is more susceptible to gamma-ray irradiation compared to the base-collector junction. And the cut-off frequency experiences a slight degradation as the total dose increases.

Surface charge accumulation of functionalized carbonized polymer dots selectively induces lysosomal membrane permeabilization of breast cancer cells

Lysosomal membrane permeabilization (LMP) has become an attractive strategy in tumor therapy. However, non-specific cytotoxicity caused by LMP remains a challenge; whether lysosomal-dependent autophagy process affected by lysosomal damage is still unclear. Here, we provide a carbonized polymer dots (CPDs)-based lysosomal targeted nano-strategy that mediates specific cytotoxicity to breast cancer cells by inducing LMP and disruption of autophagy degradation. CPDs functionalized via covalent conjugation with PpIX modified cathepsin D (CTSD) specific substrate peptide (CPDs-PP) were designed to achieve the selectivity to breast cancer cells. The effects and underlying mechanism of CPDs-PP on lysosomal membrane integrity and autophagic flux were determined. CPDs-PP with pH-dependent protonation and CTSD-responsive surface positive charge accumulation property at specific pH were obtained. Conversion of CPDs-PP to CPDs-P and ratiometric green–red fluorescence switching were observed in breast cancer cells with high expression of CTSD. It has been confirmed that CPDs-PP induced LMP and autophagic flux blockage of breast cancer cells. Lysosomal lipid accumulation was demonstrated to be the potential mechanism. CPDs-PP-induced LMP exhibited selective cytotoxicity to adherent tumor cells and tumor spheres, which was furtherly enhanced by spatiotemporal controlled lysosomal specific photodamage. This strategy offers promise for utilization of lysosome-targeting nanocarriers for anti-cancer pro-drugs and drug delivery systems.

Evidence‐Based Understanding of Lateral Hole Transport During OFF‐State Stress Completing Dynamic GaN‐on‐Si Buffer Charging Model

Gallium nitride (GaN)‐on‐Si high electron mobility transistors require insulating GaN buffers, which are prone to charge trapping and result in dynamic ON‐state resistance (dR DS,on) that negatively impacts performance and reliability. Herein, simultaneous measurements of threshold voltage shift (dV TH) and dR DS,on during OFF‐state stress with microsecond time resolution are employed. Ohmic p‐GaN gate contacts enable the use of dV TH to probe charge accumulation under the gate, while dR DS,on probes charge accumulation in the gate‐drain access region. Comparison of dV TH and dR DS,on provides direct evidence of lateral hole transport in the GaN buffer when exposed to a lateral electric field in OFF‐state. This lateral hole transport causes positive charge accumulation in the buffer under the gate and triggers a newly proposed electron injection mechanism into the same region. Only by considering the combination of lateral hole transport and electron injection under the gate the observed up to fivefold dR DS,on increase in OFF‐state stress compared to back‐gating at low biases can be explained. Furthermore, another electron spillover mechanism is introduced that occurs for large positive charge accumulation under the gate and limits the maximum negative dV TH. All known and newly introduced processes during OFF‐state are summarized in a concise dynamic buffer charging model.

Strain regulation of bond length in single Ru sites via curving support surface for enhanced hydrogen evolution reaction

The intrinsic activity of single-atom catalysts is influenced by the local electronic structures of metal centers, with existing modulation strategies limited to adjacent atomic coordination. However, the impacts of support surface geometry on local bonding environment, and thus electronic structures of single-atom centers have rarely been known. Here, we prepared highly curved B,N co-doped carbon-supported ruthenium catalyst with an ultra-low Ru loading of 0.4 wt%, which exhibited an ultrahigh turnover frequency (TOF) of 10 H2 s−1 (38 times that of Pt/C) and superior stability in alkaline hydrogen evolution reaction (HER). We found that curving support surface induced the strain, resulting in 1.5% compressed Ru-N and 4% stretched Ru-B bonds, leading to the accumulation of positive charge and quenching of spin polarization at Ru sites, thereby achieving the optimal binding of H* and enhanced performance for HER. This work highlights the significant support effects upon the structural design of active sites.

Characterization of program and erase speed of memory capacitors with nanolaminated HfO2/Al2O3 stacks for application in non-volatile memories

The programming and erase performance of atomic layer deposited HfO2/Al2O3 memory stacks is investigated depending on the thickness of the tunnel oxide and the annealing of the structures. The as-grown stacks require applying of voltage pulses with duration of about 10-3 s for a measurable electron trapping (programming). The time dependence of the electron trapping process is quite sharp initially - the increase of the charging time from 4×10-4 s to 4×10-3 s provides more than 80% of the saturation value of the trapped charge obtained at durations above 1 s. The annealing increases the time needed for the onset of the electron trapping. For the chosen voltage amplitudes the programming characteristics does not depend on the tunnel oxide thickness. The electron detrapping (erase) is observed even at durations of ~10-7 s, but with a low efficiency. The erase characteristics is more gradual then the program one, and shows some dependence on tunnel oxide and annealing. The complete erase is achieved for times comparable to those for programming the cell. Erase pulses with duration > 10-2 s results to accumulation of positive charge in the capacitors.

Delay of the potential-induced degradation of n-type crystalline silicon photovoltaic modules by the prior application of reverse bias

We investigated the influence of the pre-application of reverse bias on the potential-induced degradation (PID) of n-type front-emitter (n-FE) crystalline Si (c-Si) photovoltaic modules. Applying a prior positive reverse bias to n-FE cells delays charge-accumulation-type PID (PID-1), decreases in short-circuit current density (J sc) and open-circuit voltage (V oc). The prior positive bias accumulation may accumulate negative charges in the SiN x , which leads to an increase in a duration for the positive charge accumulation by the PID test applying a negative bias. We also found that sufficiently long prior positive bias application results in the delay of PID-2, a fill factor reduction by the incursion of Na ions into the depletion region of the p–n junction of n-FE cells.

Fast spacecraft charging induced by a high-power electron beam emission and its mitigation through a plasma contactor

Active sounding experiments, including tracing magnetic field lines and magnetospheric sounding, may be accomplished in the GEO environment by the active emission of high-power electron beams. The continual emission of electron beam pulses during such experiments may result in the accumulation of positive charges on the spacecraft surface and a rise in the spacecraft potential, which might prohibit the normal emission of succeeding pulses. The plasma contactor has been shown to be a reliable method for neutralizing the spacecraft potential. But as the active charging effect brought on by the high-current electron beam manifests itself more quickly, it is still unknown whether the plasma contactor can reliably control the spacecraft potential in this circumstance. In this study, a two-dimensional PIC model is used to examine the active charging effect brought on by high-power electron beam emission. Findings indicate that the potential neutralization process may be affected by the ion sheath that forms close to the emitting surface of the plasma contactor, which cuts the electrical connection between the spacecraft and plasma in space. By evaluating the quantities and growth speeds of different particles during active charging, we discover that lowering the particle density or pre-emission time of the plasma contactor may bring the spacecraft potential to the equilibrium state. Additionally, the high-current electron beam raises the peak potential, making it more difficult to launch the electron beam properly before the spacecraft potential reaches equilibrium. In contrast, the high-energy electron beam is less susceptible to the active charging effect.

PHYSICAL MODEL OF TEMPORARY CURRENT INSTABILITY IN ION- SELECTIVE FIELD-EFFECT TRANSISTORS WITH SILICON OXIDE/NITRIDE DIELECTRIC LAYERS

The work is devoted to the study of the instability (drift) of the threshold voltage of p-channel ion selective field- effect transistors (ISFET) with an induced channel, caused by the long-term effect of a negative voltage applied to the channel section of the transistor through a double- layer dielectric SiO2/Si3N4. Based on the obtained experimental data, a physical model of the observed instability is proposed, according to which it is caused by the process of accumulation of an unbalanced positive charge in the near-surface layer of silicon nitride. The mechanisms of Pool–Frenkel superbarrier ionization and multiphonon ionization of deep centers are involved in the quantitative calculation of model parameters. Design and technological improvements are outlined that can improve the stability of ISFET sensors for long-term continuous measurements in solutions.

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.

Radiation-Induced Degradation Mechanism of X-Ray SOI Pixel Sensors With Pinned Depleted Diode Structure

The X-ray Silicon-On-Insulator (SOI) pixel sensor named XRPIX has been developed for the future X-ray astronomical satellite FORCE. XRPIX is capable of a wide-band X-ray imaging spectroscopy from below 1 keV to a few tens of keV with a good timing resolution of a few tens of μs. However, it had a major issue with its radiation tolerance to the total ionizing dose (TID) effect because of its thick buried oxide layer due to the SOI structure. Although new device structures introducing pinned depleted diodes dramatically improved radiation tolerance, it remained unknown how radiation effects degrade the sensor performance. Thus, this paper reports the results of a study of the degradation mechanism of XRPIX due to radiation using device simulations. In particular, mechanisms of increases in dark current and readout noise are investigated by simulation, taking into account the positive charge accumulation in the oxide layer and the increase in the surface recombination velocity at the interface between the sensor layer and the oxide layer. As a result, it is found that the depletion of the buried p-well at the interface increases the dark current, and that the increase in the sense-node capacitance increases the readout noise.

Improvement of surface insulating performance for polytetrafluoroethylene film by atmospheric pressure plasma deposition

The surface flashover phenomenon across a vacuum-dielectric interface severely limits the service life and operational reliability of high voltage electrical equipment. Surface modification by atmospheric pressure plasma treatment is a promising method to improve the surface insulating performance of polymers. In order to explore the mechanism of plasma processing on the vacuum flashover characteristics of polymer materials, atmospheric pressure plasma deposition was used to treat polytetrafluoroethylene (PTFE) film. The surface parameters under different processing conditions, such as surface chemical composition, surface resistivity, surface charge decay and trap distribution, were tested and analyzed. The space charge distribution of PTFE and the flashover voltage in vacuum were measured. The results show that Si–O–Si and Si–OH groups are introduced on the surface of PTFE, and the characteristic peaks of PTFE are gradually weakened with the increase of processing time. The surface trap density increases and more traps with lower energy level arise with longer processing time. The plasma deposition changes the space charge distribution in PTFE body, and leads to positive charge accumulation inside the sample. The flashover field strength respectively increases by 15% and 70% in direct current (DC) voltage and microsecond pulse voltage after plasma deposition. The rapid dissipation of surface charge is the main reason for pulse flashover voltage enhancement, while the increase of surface leakage current due to lower surface resistivity and space charge accumulation in PTFE body make the DC flashover voltage reach the saturation point. Therefore the surface insulating and body performance of polymer materials after plasma modification processing should be considered comprehensively based on different applications.

Effect of surface modification on the photoluminescent properties of γ-Ga2O3 nanocrystals

Ga2O3 nanocrystals with compelling optical properties attract broad attention from the scientific and industrial community. However, the influence of surface modification on the photoluminescent properties of Ga2O3 NCs remains unexplored. Here, we report comparative investigations of the photoluminescent properties of oleylamine-capped and ligand-free γ-Ga2O3 nanocrystals. The removal of oleylamine ligand on the Ga2O3 nanocrystal surface via a post-synthesis reaction is accompanied by the accumulation of positive surface charges and a reduction of oxygen vacancies. The change of nanocrystal surface leads to an appreciable red shift of emission spectrum along with a substantial increase in photoluminescence lifetime. Modeling the photoluminescence decay dynamics of Ga2O3 nanocrystals indicate the change of photoluminescent property is correlated to the decrease of the number density of donors and donor Bohr radius resulting from the change of nanocrystal surface.

Boosting Electroreduction Kinetics of Nitrogen to Ammonia via Atomically Dispersed Sn Protuberance.

Atomically dispersed metal catalysts show potential advantages in N2 reduction reaction (NRR) due to their excellent activity and efficient metal utilization. Unfortunately, the reported catalysts usually exhibit unsatisfactory NRR activity due to their poor N2 adsorption and activation. Herein, we report a novel Sn atomically dispersed protuberance (ADP) by coordination with substrate C and O to induce positive charge accumulation on Sn site for improving its N2 adsorption, activation and NRR performance. The extended X-ray absorption fine structure (EXAFS) spectra confirmed the local coordination structure of the Sn ADPs. NRR activity was significantly promoted via Sn ADPs, exhibiting a remarkable NH3 yield (RNH3 ) of 28.3 μg h-1 mgcat -1 (7447 μg h-1 mgSn -1 ) at -0.3 V. Furthermore, the enhanced N2 Hx intermediates was verified by in situ experiments, yielding consistent results with DFT calculation. This work opens a new avenue to regulate the activity and selectivity of N2 fixation.

Boosting Electroreduction Kinetics of Nitrogen to Ammonia via Atomically Dispersed Sn Protuberance

AbstractAtomically dispersed metal catalysts show potential advantages in N2 reduction reaction (NRR) due to their excellent activity and efficient metal utilization. Unfortunately, the reported catalysts usually exhibit unsatisfactory NRR activity due to their poor N2 adsorption and activation. Herein, we report a novel Sn atomically dispersed protuberance (ADP) by coordination with substrate C and O to induce positive charge accumulation on Sn site for improving its N2 adsorption, activation and NRR performance. The extended X‐ray absorption fine structure (EXAFS) spectra confirmed the local coordination structure of the Sn ADPs. NRR activity was significantly promoted via Sn ADPs, exhibiting a remarkable NH3 yield (RNH3) of 28.3 μg h−1 mgcat−1 (7447 μg h−1 mgSn−1) at −0.3 V. Furthermore, the enhanced N2Hx intermediates was verified by in situ experiments, yielding consistent results with DFT calculation. This work opens a new avenue to regulate the activity and selectivity of N2 fixation.

KPFM visualisation of the Schottky barrier at the interface between gold nanoparticles and silicon.

Gold nanoparticles (AuNPs) deposited on a doped silicon substrate induce a local band bending and a local accumulation of positive charges in a semiconductor. Unlike the case of planar gold-silicon contacts, working with nanoparticles results in reduced values for the built-in potential and lower Schottky barriers. Here, AuNPs of 55 nm diameter were deposited on several silicon substrates that were previously functionalized with aminopropyltriethoxysilane (APTES). The samples are characterized by Scanning Electron Microscopy (SEM) and the nanoparticle surface density is assessed with dark-field optical microscopy. A density of 0.42 NP μm-2 was measured. Kelvin Probe Force Microscopy (KPFM) is used to measure the contact potential differences (CPD). The CPD images exhibit a ring-shaped pattern ("doughnut-shape") centred on each AuNP. The built-in potential is measured at +34 mV for n-doped substrates and it decreased to +21 mV for p-doped silicon. These effects are discussed using the classical electrostatic approach.