Impact Ionization Research Articles

Martian Crustal Magnetic Field Effects on the Ionospheric Main Peak

Planetary magnetic fields can affect ionospheric plasma transport and coupling with the solar wind. In contrast to the terrestrial global magnetic field, there are only weaker and sporadic crustal magnetic fields on Mars. Many studies have indicated that Martian crustal fields can still modulate the topside ionosphere and its coupling with the solar wind. Nevertheless, it is unclear whether the crustal fields can affect the ionospheric main peak, which does not directly interact with the solar wind and is dominated by photochemical processes. In this study, the crustal field effect was identified from ionospheric measurements over unevenly distributed crustal fields. Both the intensity and configuration of the crustal fields were found to be capable of affecting the ionospheric main peak. The ionospheric peak electron density tends to decrease in the strong horizontal crustal field region. The results suggest that the crustal fields may affect the ionospheric main peak through modulating solar wind energetic particle precipitation; strong horizontal magnetic fields can partially prevent energetic particle precipitation and thus weaken impact ionization.

Hints to lightning breakdown enhancement for synthetic ester insulating oil: Unraveling the impact of molecular chain length on electron structural parameters under electric field stress

The high flash point and biodegradability of synthetic ester insulating oil offer transformers both operational stability and environmental protection. However, its poor lightning breakdown characteristics under long oil gaps and inhomogeneous electric field often lead to rapid streamer discharges, posing challenges and limits to the use of synthetic ester insulating oil and hinders the development of low-carbon, eco-friendly high voltage power transformers. To address this issue, we propose improving the lightning breakdown characteristics through molecular chain length design. Using density functional theory, time-dependent density functional theory, and wave function analysis, we investigate how microscopic factors like molecular polarity, discharge active sites, frontier orbitals, traps, ionization and electron affinity, and excitation processes influence macroscopic discharge characteristics. Our findings show that under an electric field, chain length is positively correlated with electron transfer, enhancing charge polarization. Chain length also correlates positively with dipole moment, facilitating the formation of space charge centers. While chain length minimally affects discharge active sites, the electric field can intensify their formation. Additionally, a longer chain length decreases the energy gap, increasing electron trap levels more than hole trap levels, thus capturing charges longer. Chain length is negatively correlated with ionization energy, promoting electron impact ionization, and has little effect on the excitation energy of S(0) → S(1), making excitation under high electric fields unlikely.

Thermographic observation of fast ion impact areas in the NBI ducts of TJ-II

Infrared thermography has been used to study the fast ion impact areas in the Co and Counter NBI ducts of TJ-II. Statistical results of the distribution of accumulated impacts on the walls of the duct have been obtained with an ion trajectory code. A more realistic description is obtained by coupling a beam simulation code to produce the ion birth point distribution. In this way, the main interception areas for both injectors have been found. Those areas constitute the Regions of Interest (ROI's) for the IR thermography system. The up-graded IR system, with its high definition MIR camera, enlarged window, and precision support and displacement mechanisms for camera and mirror, allows such ROI's to be captured. The optimal alignment parameters of the camera and mirror have been obtained with the optical simulation code ZEMAX, and the feasibility of the mechanical configuration in the crowded window environment has been checked with a CAD program, also used to simulate the field of view inside the ducts. Finally, infrared images of the ducts during beam pulses without magnetic field and with magnetic field have been compared, to obtain highlighted images of the fast ion impact areas in both ducts, showing the expected stellarator symmetry.

Low excess noise HgCdTe e-SWIR avalanche photodiode operating at high gain and temperature

The Hg1−xCdxTe material can exhibit a pure electron avalanche when the composition of the Cd is below 0.6. This hole-to-electron impact ionization ratio close to zero results in noiseless gain. In this paper, we present the results on the gain and noise characteristics of the extended short wavelength infrared (e-SWIR) HgCdTe electron-initialed avalanche photodiodes (e-APDs). The e-APD has a Cd composition of 0.4 and a cutoff wavelength of 3.1μm. At 80 K with a bias voltage of −18.5 V, the device achieves a remarkable gain of 1080, with an excess noise factor below 1.6. Furthermore, the device maintains a gain of 550 and an excess noise below 1.6 at 220 K. Notably, this work reports for the first time the low noise performance of the device at high temperatures and high gain. Moreover, we investigate the responsivity and detectivity of the device when operating at the unit gain point.

High power impulse magnetron sputtering of a zirconium target

High power impulse magnetron sputtering (HiPIMS) discharges with a zirconium target are studied experimentally and by applying the ionization region model (IRM). The measured ionized flux fraction lies in the range between 25% and 59% and increases with increased peak discharge current density ranging from 0.5 to 2 A/cm2 at a working gas pressure of 1 Pa. At the same time, the sputter rate-normalized deposition rate determined by the IRM decreases in accordance with the HiPIMS compromise. For a given discharge current and voltage waveform, using the measured ionized flux fraction to lock the model, the IRM provides the temporal variation of the various species and the average electron energy within the ionization region, as well as internal discharge parameters such as the ionization probability and the back-attraction probability of the sputtered species. The ionization probability is found to be in the range 73%–91%, and the back-attraction probability is in the range 67%–77%. Significant working gas rarefaction is observed in these discharges. The degree of working gas rarefaction is in the range 45%–85%, higher for low pressure and higher peak discharge current density. We find electron impact ionization to be the main contributor to working gas rarefaction, with over 80% contribution, while kick-out by zirconium atoms and argon atoms from the target has a smaller contribution. The dominating contribution of electron impact ionization to working gas rarefaction is very similar to other low sputter yield materials.

ВИЗНАЧЕННЯ ВПЛИВУ ВНУТРІШНІХ ЕНЕРГІЙ КРИСТАЛІЧНОЇ РЕШІТКИ НА ОТРИМАННЯ НАНОСТРУКТУР У ПОВЕРХНЕВИХ ШАРАХ АЛЮМІНІЄВИХ СПЛАВІВ

The paper presents the results of calculating the crystallization energy and examines its influence on the size of the nanostructured grain during ion-plasma treatment of aluminum (VD17) with oxygen and nitrogen ions. To address this task, we employ a previously proposed model, which considers the impact of individual ions on thermal conductivity and thermoelasticity in the affected area, taking into account their energy, charge, and type. Initially, we estimate the potential number of particles in the nanostructure. Then, we compute the energy required for atomizing the grain from atoms and chemical compounds. By determining the total atomization energy of the grain (Eas), we establish the necessary energy for its formation (Es = 1.1Eas). This energy enables the determination of all characteristics in the ion's action area, such as temperature, temperature rise rate, thermal stresses, strain rate, grain size, volume, and depth of the nanostructure, as well as the actual number of particles in the nanostructure. The calculations demonstrate that the crystallization energy increases the ion energy required to obtain nanostructures. At energies close to 3∙102 eV, it ranges from 0.1 to 7 eV, which can be disregarded, while at energies close to 1.6∙104 eV, crystallization energy ranges from 2.1∙102 to 1.2∙104 eV, with higher values for oxygen ions. Additionally, the calculations show that ion charge significantly affects crystallization energy; for large ion charges, it increases. All of this underscores the necessity of considering crystallization energy only at energies of 2∙103 – 2∙104 eV, allowing refinement of the technological parameters of ion-plasma treatment of aluminum alloys to increase the likelihood of obtaining nanostructures. Furthermore, the ability to determine the sizes of nanostructures allows predicting the physical and mechanical characteristics of surface layers of processed materials. These studies may be of interest to specialists involved in surface strengthening of aluminum alloy surfaces and further research into nanostructures

Enhancement of Electrical Safe Operation Area of 60 V nLDMOS by Engineering of Reduced Surface Electrical Field in the Drift Region.

To enhance the electrical safe operation area (eSOA) of laterally diffused metal oxide semiconductor (LDMOS) transistors, a novel reduced surface electric field (Resurf) structure in the n-drift region is proposed, which was fabricated by ion implantation at the surface of the LDMOS drift region and by drift region dimension optimization. Technology computer-aided design (TCAD) simulations show that the optimal value of Resurf ion implantation dose 1 × 1012 cm-2 can reduce the surface electric field in the n-drift region effectively, thereby improving the ON-state breakdown voltage of the device (BVon). In addition, the extended n-drift region length of the Ld design also improves device BVon significantly, and is aimed at reducing the current density and the electric field, and eventually suppressing the n-drift region impact ionization. The results show that the novel 60 V nLDMOS has a competitive BVon performance of 106.9 V, which is about 20% higher than that of the conventional one. Meanwhile, the OFF-state breakdown voltage of the device (BVoff) of 88.4 V and the specific ON-resistance (RON,sp) of 129.7 mΩ⋅mm2 exhibit only a slight sacrifice.

Particle-in-cell simulations of EUV-induced hydrogen plasma in the vicinity of a reflective mirror

Particle-In-Cell (PIC) simulations were performed in this work to study the dynamics of the EUV-induced hydrogen plasma. The Monte-Carlo Collision (MCC) model was employed to deal with the collisions between charged particles and background gas molecules. The dynamic evolution of the plasma sheath, as well as the flux and energy distribution of ions impacting on the mirror surface, was discussed. It was found that the emission of secondary electrons under the EUV irradiation on the ruthenium mirror coating creates a positively charged wall and then prevents the ions from impacting on the mirror and therefore changes the flux and energy distribution of ions reaching the mirror. Furthermore, gas pressure has a notable effect on the plasma sheath and the characteristics of the ions impinging on the mirrors. With greater gas pressure, the sheath potential decreases more rapidly. The flux of ions received by the mirror grows approximately linearly and at the same time the energy corresponding to the peak flux decreases slightly. However, the EUV source intensity barely changes the sheath potential, and its influence on the ion impact is mainly limited to the approximate linear increase in ion flux.

On surface binding of serum albumin by harmane: An in vitro spectroscopic and theoretical analysis

Harmane, a naturally occurring beta-carboline alkaloid found in plants and animals, has sparked interest due to its potential biological impacts, specifically its neuro-pharmacological properties and its link with neurodegenerative ailments. This work studies the interaction between the bovine serum albumin (BSA) and the Harmane via multi-spectroscopic and computational analyses. Spectroscopic titrations at different temperatures and concentrations of the salt showed that Harmane forms a stable ground-state complex revealed by a static quenching of the fluorescence spectra. Thermodynamic characteristics of the binding show that BSA and Harmane have a 1:1 binding stoichiometry. The negative change in the Gibbs free energy (ΔG) indicates that the interaction is spontaneous, whereas the positive values of the change in entropy (ΔS) and the change in enthalpy (ΔH) indicate that hydrophobic forces predominate in the binding. The protein surface hydrophobicity index confirms significant surface hydrophobicity. The study also demonstrates the impact of metal ions on protein structure. According to molecular docking studies, Harmane binds to BSA in site II, domain III, subdomain IIIA. Molecular Dynamic (MD) modeling was used to reconfirm the perturbation in the stability and structure of the protein due to Harmane binding at different time frames.

Laser desorption mass spectrometry of rubrene and photodissociation of its cation

Laser desorption mass spectrometry was employed to study rubrene using three different sample preparation methods. Pressed-pellet and films drop-cast from solution were investigated with a laser-desorption time-of-flight spectrometer. Jet-cooled rubrene cations were produced in a supersonic molecular beam by laser desorption from a film-coated metal rod and detected with time-of-flight mass spectrometry. The films for this process were produced by vacuum sublimation of powder samples. The mass spectra from each of these samples contained the parent molecular ion and fragments resulting from phenyl ring elimination - a pattern similar to that produced by electron impact ionization. The amount of fragmentation varied with sample preparation and desorption laser wavelength. The rubrene cation was mass selected and studied with UV laser photodissociation at 355 nm. The resulting fragmentation mass spectrum indicated the loss of one or two phenyl groups, but no more than this. Computational studies of the ion energetics were used to investigate the stable fragment ion structures and understand the energetics of the dissociation process.

Impact ionization coefficients and excess noise in Al0.55Ga0.45As0.56Sb0.44 lattice matched to InP

The avalanche multiplication and noise characteristics of Al0.55Ga0.45As0.56Sb0.44p–i–n and n–i–p structures grown lattice matched on InP have been investigated. From measurements undertaken using 530 nm illumination on several devices, the electron (α) and hole (β) impact ionization coefficients have been determined. While α only shows a relatively small increase compared to the higher Al composition alloys of AlxGa1−xAsSb, β is found to increase significantly. Although the β/α ratio is increased to ∼0.125–0.2, higher than the ∼0.003–0.02 seen in the higher-Al alloys, a relatively low excess noise factor of 2.2 was measured in the p-i-n with electron-initiated multiplication of 20. This noise performance is significantly lower than that predicted using a local-field model and comparable to some commercial silicon APDs. This avalanching material with a bandgap of ∼1.24 eV will have the advantages of a smaller band discontinuity with the absorber region and should also operate at a lower voltage.

The impact of seawater ions on urea decomposition and calcium carbonate precipitation in the MICP process

As an environmentally friendly biotechnology, the microbial induced calcium carbonate precipitation (MICP) provides a new approach to repair concrete cracks. Most existing studies focused on finding a suitable environment for bacteria to induce as much calcium carbonate as possible, but the effect of actual concrete service environment on the repair of concrete cracks was usually ignored. This work compared the repair quality of cracked specimens via MICP with the original Sporosarcina (Sp.) pasteurii strain and salt-tolerant Sp. pasteurii strain in the deionized water and simulated seawater. Then the adverse effects of seawater ions on the MICP process was investigated. The results showed that the permeability coefficient of repaired specimens was 175.7 % higher, and the bond strength between the calcium carbonate and concrete surface was lower in the simulated seawater as compared with the deionized water environment. The high concentration of sodium, chloride, magnesium, and sulfate ions in the seawater led to the decrease of the urea decomposition rate and calcium carbonate yield rate, which further induced the decreased super-saturation of calcium carbonate and the conversion of the calcium carbonate crystal form from calcite to vaterite. Besides, the salt-tolerant strain with a high salt adaptability showed a higher repair ability in the simulated seawater as compared with the original strain.

Investigating the addition of Fe for improving contaminant removal and regulating microbes in a simulated coastal wetland.

Contaminants from wastewater of aquaculture are increasing the risks of red tides in coastal areas. Such types of contaminants are difficult to remove by using conventional biological and ecological treatment methods because of the relatively low C/N ratios and the high salinity in coastal water ambience. Fe is considered a key element in natural chemical cycling and promotes the growth of animals and plants as well. The cycling of Fe ion combined with carbon, nitrogen, and phosphorus stimulates bacterial growth. As a result, it acts as a microbial carbon pump in coastal areas, such as natural wetlands, which have been activated and adapted to be salinity resistant and insufficient energy supply. Along these lines, in this work, constructed wetlands (CWs) with high ecological benefits and low cost of maintenance were used to treat aquaculture wastewater. The impact of Fe ion recycling on multiple contaminants was also systematically investigated. The two types of Fe dosage were pure ferrous ions and a mixture of iron powder and ferrous ions. After the application of a 3-day treatment, the dosage of iron powder/ferric ions (1:1 m/m) at a concentration of 15 mg L-1 showed a better effect, where the total nitrogen, total phosphorus, and chemical oxygen demand removal rates were increased by 2.95%, 2.16%, and 9.76%, respectively. From the microbial analysis, it was indicated that Fe ion affected the abundance and functions of the microbial communities in the CWs. The significant enrichment of Proteobacteria promoted the removal of multiple contaminants under saline stress and fixed carbon, and affected the whole microbe distribution and diversity in CWs. The implementation of such an environmentally friendly and economical approach arises as a promising candidate for the efficient removal of multiple contaminants from aquacultural wastewater in coastal zones.

Performance parameters estimation of high speed Silicon/Germanium/InGaAsP avalanche photodiodes wide bandwidth capability in ultra high speed optical communication system

Abstract This paper has clarified the performance parameters estimation of high speed silicon/germanium/InGaAsP avalanche photodiodes wide bandwidth capability in ultrahigh speed optical communication system. The basic structure configuration of avalanche photodiode is clarified. The basic depletion region configuration schematic view is demonstrated. As well as the maximum electric field is indicated for impact ionization through avalanche photodiode in the presence of load. Various avalanche photo-detectors multiplication factor is clarified versus reverse bias voltage at room temperature. Different avalanche photo-detectors dark current is measured against avalanche photo-detectors volume at room temperature. Various avalanche photo-detectors effective doping concentration is demonstrated against ambient temperature variations. Si/Ge/InGaAsP avalanche photo-detectors excess noise factor is demonstrated versus the ionization ratio at room temperature (T = 300 K) and different ambient temperature (T = 350 K and T = 400 K). Various avalanche photo-detectors excess noise factor is measured clearly versus the multiplication factor at room temperature. Si/Ge/InGaAsP avalanche photo-detectors excess noise factor is demonstrated versus reverse bias voltage at room temperature. Si/Ge/InGaAsP avalanche photo-detectors noise equivalent power is clarified versus multiplication factor at room temperature. Various avalanche photo-detectors noise equivalent power is studied versus temperature variations. Si/Ge/InGaAsP avalanche photo-detectors sensitivity is measured in relation to the temperature variations. Different avalanche photo-detectors sensitivity is demonstrated in relation to reverse bias voltage variations at room temperature.

Regulation of anti-tumor immunity by metal ion in the tumor microenvironment.

Metal ions play an essential role in regulating the functions of immune cells by transmitting intracellular and extracellular signals in tumor microenvironment (TME). Among these immune cells, we focused on the impact of metal ions on T cells because they can recognize and kill cancer cells and play an important role in immune-based cancer treatment. Metal ions are often used in nanomedicines for tumor immunotherapy. In this review, we discuss seven metal ions related to anti-tumor immunity, elucidate their roles in immunotherapy, and provide novel insights into tumor immunotherapy and clinical applications.

Construction of β-Cyclodextrin supramolecular gel and the effect of metal ions on its formation

As a natural cyclic oligosaccharide, β-Cyclodextrin with cavity structure has excellent water solubility and biocompatibility, which makes it highly valuable in the field of supramolecular self-assembly. Although the self-assembly of β-Cyclodextrin into supramolecular gels has been reported by our group, the impact of metal ions on β-Cyclodextrin supramolecular gels has not yet been studied. Herein, a β-Cyclodextrin supramolecular gel was prepared firstly and then the effects of six different metal ions on this gel system were investigated systematically. It was found that tubular stacking induced by hydrogen bond is the main driving force for the self-assembly of β-Cyclodextrin into β-Cyclodextrin supramolecular gels. Moreover, the introduction of metal ions did not hinder the formation of β-Cyclodextrin supramolecular gels. On the contrary, the metal coordination interaction between metal ions and β-Cyclodextrin stabilized the tubular stacking state of β-Cyclodextrin, thereby promoting the formation of β-Cyclodextrin supramolecular gels. This research not only deepens the study of β-Cyclodextrin supramolecular gels but also lays a solid foundation for their application in intelligent materials, drug delivery, and ion channels, among other fields.

Effect of Nanoporous Molecular Sieves TS-1 on Electrical Properties of Crosslinked Polyethylene Nanocomposites.

Crosslinked polyethylene (XLPE) is an important polyethylene modification material which is widely used in high-voltage direct current (HVDC) transmission systems. Low-density polyethylene (LDPE) was used as a matrix to improve the thermal and electrical properties of XLPE composites through the synergistic effect of a crosslinking agent and nanopore structure molecular sieve, TS-1. It was found that the electrical and thermal properties of the matrices were different due to the crosslinking degree and crosslinking efficiency, and the introduction of TS-1 enhanced the dielectric constants of the two matrices to 2.53 and 2.54, and the direct current (DC) resistivities were increased to 3 × 1012 and 4 × 1012 Ω·m, with the enhancement of the thermal conductivity at different temperatures. As the applied voltage increases, the DC breakdown field strength is enhanced from 318 to 363 kV/mm and 330 to 356 kV/mm. The unique nanopore structure of TS-1 itself can inhibit the injection and accumulation in the internal space of crosslinked polyethylene composites, and the pore size effect of the filler can limit the development of electron impact ionization, inhibit the electron avalanche breakdown, and improve the strength of the external applied electric field (breakdown field) that TS-1/XLPE nanocomposites can withstand. This provides a new method for the preparation of nanocomposite insulating dielectric materials for HVDC transmission systems with better performance.

Enhanced structural, vibrational, and dielectric properties of (Ba0·95Ca0.05) (Ti0.95Zr0.05)1-x(Zn1/3Nb2/3)xO3 ceramics

The (Ba0·95Ca0.05) (Ti0·95Zr0.05)1-x(Zn1/3Nb2/3)xO3 BCZTxZN compounds, were created using the widely adopted solid-state method. To assess the impact of (Zn, Nb: ZN) co-substitution ions we studied the structural, vibrational, and dielectric characteristics of BCZT. The phase purity was validated by conducting Rietveld refinement of XRD data, indicating the coexistence of orthorhombic and tetragonal phases at ambient temperature in the (Ba0·95Ca0.05) (Ti0·95Zr0.05)0.975(Zn1/3Nb2/3)0.025O3 (BCZT25ZN) composition. Furthermore, Raman spectroscopy confirmed the observed transitions. The presence of Zn2+ and Nb5+ ions resulted in a decrease in cell parameters and cell volume. The real part of the dielectric constant and the tangent loss (tan δ) exhibited values of approximately 3380 and 0.031, respectively, for the sample (Ba0·95Ca0.05)(Ti0·95Zr0.05)0.95(Zn1/3Nb2/3)0.05O3 (BCZT50ZN), obtained by substituting ZN in Ba0·95Ca0·05Ti0·95Zr0·05O3. Incorporation of ZN into Ba0·95Ca0·05Ti0·95Zr0·05O3 presents promising prospects for using the material in various device applications, including energy storage capacitors, sensors, and actuators.

Exploring molecular composition of upgraded pyrolysis bio-oil using GC×GC-(EI/PI)-TOF MS with different column set-ups

Bio-oils produced from the pyrolysis of lignocellulosic biomass are rich in oxygen, which causes instability and corrosion problems. Therefore, dedicated post-pyrolysis treatments such as hydrotreatment are required to increase the H/C ratio of the products to be used as fuel or chemicals. Here, a characterization method based on two-dimensional gas chromatography (GC×GC) was developed to highlight the evolution of the volatile fraction during hydrotreatment. Six samples obtained at different times of the hydrotreatment were analyzed. In this way, information on catalyst deactivation was obtained. The combination of information from normal and reversed phase GC×GC analysis provides a detailed characterization of the hydrotreated bio-oils. Furthermore, the use of soft photoionization (PI), in addition to conventional electron impact ionization (EI), yields a better understanding of the compound structures present in the sample. Identification and semi-quantification of the sample components indicate that the concentration of paraffins, cycloalkanes, and monoaromatics have largely decreased during hydrotreatment, while the concentration of oxygenated species and polycyclic aromatic hydrocarbons have increased. Using complementary GC methods highlights changes in the molecular composition of volatile species that correlate with catalyst performance. This approach can be used to follow the decrease in hydrodeoxygenation activity as a function of time on stream to estimate the catalyst aging during the hydrotreating process.

3D Simulation of an Extreme SAID Flow Channel

AbstractSpace‐based observations of the signatures associated with STEVE show how this phenomenon might be closely related to an extreme version of a SAID channel. Measurements show high velocities (>4 km/s), high temperatures (>4,000 K), and very large current density drivers (up to 1 μA/m2). This phenomena happens in a small range of latitudes, less than a degree, but with a large longitudinal span. In this study, we utilize the GEMINI model to simulate an extreme SAID/STEVE. We assume a FAC density coming from the magnetosphere as the main driver, allowing all other parameters to adjust accordingly. We have two main objectives with this work: show how an extreme SAID can have velocity values comparable or larger than the ones measured under STEVE, and to display the limitations and missing physics that arise due to the extreme values of temperature and velocity. Changes had to be made to GEMINI due to the extreme conditions, particularly some neutral‐collision frequencies. The importance of the temperature threshold at which some collision frequencies go outside their respective bounds, as well as significance of the energies that would cause inelastic collisions and impact ionization are displayed and discussed. We illustrate complex structures and behaviors, emphasizing the importance of 3D simulations in capturing these phenomena. Longitudinal structure is emphasized, as the channel develops differently depending on MLT. However, these simulations should be viewed as approximations due to the limited observations available to constrain the model inputs and the assumptions made to achieve sensible results.