Trapping Dynamics Research Articles

An ion trap source of cold atomic hydrogen via photodissociation of the BaH+ molecular ion

I present a novel scheme for producing cold (magnetically trappable) atomic hydrogen, based on threshold photodissociation of the BaH+ molecular ion. BaH+ can be sympathetically cooled using laser cooled Ba+ in an ion trap, before it is photodissociated on the single photon A1Σ+ ← X1Σ+ transition. The small mass ratio between Ba+ and BaH+ ensures a strong overlap within the ion trap for sympathetic cooling, while the large mass ratio between BaH+ and H means that the released hydrogen can be up to 139 times colder than the parent molecular ions. I examine the hydrogen production rate, and describe how the trap dynamics and photodissociation laser detuning influence the achievable energies. The low infrastructure costs and the ion trap nature of the scheme make it suitable for loading hydrogen into an antihydrogen experiment. This would support a direct matter–antimatter comparison, which could provide important clues as to why our Universe contains so little antimatter.

Ultrafine NbN nanoparticle decorated nitrogen-doped carbon nanosheets with efficient polysulfide catalytic conversion for superior Li–S batteries

Lithium-sulfur batteries are considered as one of the most promising energy storage systems beyond commercial lithium-ion batteries, but the practical application of lithium-sulfur batteries is still hindered by the severe polysulfides dissolution and sluggish redox reaction kinetics with low areal capacity. Herein, ultrafine NbN decorated nitrogen-doped porous carbon nanosheets are reported via C 3 N 4 sacrifice template using phenolic resol as carbon precursor. The ultrafine NbN nanoparticles and nitrogen-doped carbons guarantee efficient polysulfides trapping and fast redox reaction kinetics even with a high sulfur content of 75 wt%. In addition, porous carbon nanosheets and NbN nanoparticles provide more active sites for Li 2 S nucleation and serve as a second host for the reuse of sulfur. Hence, the lithium-sulfur cells with NbN@CNS-5 modified multifunctional separator deliver a high initial capacity of 1252 mAh g −1 @ 0.2 C, 683 mAh g −1 @ 4 C, and high capacity retention of 84.5% after 200 cycles at 0.2 C. Furthermore, a high initial capacity of 4.95 mAh cm −2 and 4.01 mAh cm −2 @0.2 C after 200 cycles are achieved at a sulfur loading of 4.2 mg cm −2 . These findings open up a new method for the practical application of lithium-sulfur batteries with superior sulfur utilization and a long lifespan. • Ultrafine NbN decorated N-doped porous carbon nanosheets was successfully prepared. • NbN could enhance the adsorption and accelerate the conversion of polysulfides. • Nitrogen doped porous carbon nanosheets provide more sites for S/Li 2 S deposition. • Li–S battery performance is enhanced using NbN@CNSs decorated PP separator.

Three-Dimensional Dynamic Optical Trapping Using Non-Iterative Computer-Generated Holography

Three-Dimensional Dynamic Optical Trapping Using Non-Iterative Computer-Generated Holography

Orbital Gating Driven by Giant Stark Effect in Tunneling Phototransistors.

Conventional gating in transistors uses electric fields through external dielectrics that require complex fabrication processes. Various optoelectronic devices deploy photogating by electric fields from trapped charges in neighbor nanoparticles or dielectrics under light illumination. Orbital gating driven by giant Stark effect is demonstrated in tunneling phototransistors based on 2H-MoTe2 without using external gating bias or slow charge trapping dynamics in photogating. The original self-gating by light illumination modulates the interlayer potential gradient by switching on and off the giant Stark effect where the dz 2-orbitals of molybdenum atoms play the dominant role. The orbital gating shifts the electronic bands of the top atomic layer of the MoTe2 by up to 100 meV, which is equivalent to modulation of a carrier density of 7.3 × 1011 cm-2 by electrical gating. Suppressing conventional photoconductivity, the orbital gating in tunneling phototransistors achieves low dark current, practical photoresponsivity (3357 AW-1 ), and fast switching time (0.5ms) simultaneously.

A rational design of V2O3/VN heterostructures with high-efficient chemisorption and electrocatalytic activity for polysulfides in lithium-sulfur batteries

Polysulfide shutting between cathode and anode and sluggish redox of solid-liquid-solid conversion largely impede the commercial applications of lithium-sulfur (Li–S) batteries. Herein, a novel V2O3/VN heterostructure has been designed as an efficient adsorbent and catalyst to promote polysulfide trapping and redox kinetics. Such synchronous advantages of each part of V2O3/VN can efficiently alleviate shuttling and accelerate polysulfide conversion, thus improve electrochemical performances. Benefited from this synergistic effect, the assembled full cells with V2O3/VN heterostructure exhibit an initial capacity of about 1100 mAh g−1 at 0.1C and an outstanding rate performance of 612 mAh g−1 at 2C. After 100 cycling tests at 0.2C, the specific capacity still maintains about 670 mAh g−1. Our approach would provide a new viewpoint of designing efficient sulfur additives to improve the redox kinetics for high-performance lithium-sulfur batteries.

Particle-in-cell techniques for the study of space charge effects in an electrostatic ion beam trap.

We developed a simulation technique to study the effect of space charge interaction between trapped ions in the electrostatic ion beam trap (EIBT). The importance of space charge is demonstrated in both the dispersive and the self-bunching regime of the ion trap. The simulation results provide an estimate for the space charge effect on the trapping efficiency. They also allow for a better understanding of the enhanced diffusion and the self-bunching effect and provide a better characterization of the EIBT as a mass spectrometer, where peak coalescence is important. The numerical results reproduce all experimental data, demonstrating the critical importance of including space charge effects, even at low ion density, to understand the ion trap dynamics.

The role of light-harvesting complex I in excitation energy transfer from LHCII to photosystem I in Arabidopsis.

Photosynthesis powers nearly all life on Earth. Light absorbed by photosystems drives the conversion of water and carbon dioxide into sugars. In plants, photosystem I (PSI) and photosystem II (PSII) work in series to drive the electron transport from water to NADP+. As both photosystems largely work in series, a balanced excitation pressure is required for optimal photosynthetic performance. Both photosystems are composed of a core and light-harvesting complexes (LHCI) for PSI and LHCII for PSII. When the light conditions favor the excitation of one photosystem over the other, a mobile pool of trimeric LHCII moves between both photosystems thus tuning their antenna cross-section in a process called state transitions. When PSII is overexcited multiple LHCIIs can associate with PSI. A trimeric LHCII binds to PSI at the PsaH/L/O site to form a well-characterized PSI–LHCI–LHCII supercomplex. The binding site(s) of the “additional” LHCII is still unclear, although a mediating role for LHCI has been proposed. In this work, we measured the PSI antenna size and trapping kinetics of photosynthetic membranes from Arabidopsis (Arabidopsis thaliana) plants. Membranes from wild-type (WT) plants were compared to those of the ΔLhca mutant that completely lacks the LHCI antenna. The results showed that “additional” LHCII complexes can transfer energy directly to the PSI core in the absence of LHCI. However, the transfer is about two times faster and therefore more efficient, when LHCI is present. This suggests LHCI mediates excitation energy transfer from loosely bound LHCII to PSI in WT plants.

Demonstration of a p-Type Ferroelectric FET With Immediate Read-After-Write Capability

In this letter, p-type ferroelectric field-effect-transistors (FeFETs) based on HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and embedded in GlobalFoundries 28 nm bulk high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k}$ </tex-math></inline-formula> metal gate (HKMG) technology (28SLPe) are systematically investigated and compared to their n-type counterparts. We show that the two device types, based on Si channel, exhibit a symmetric memory window (MW) and very similar switching behavior, yet profoundly different trapping kinetics. In contrast to n-FeFETs, p-FeFETs display a full MW immediately after the write operation and apparently no parasitic electron trapping. Based on this, we demonstrate an immediate read-after-write operation. Finally, we illustrate how slight structural changes of the gate stack, such as the introduction of the SiGe channel material, can enhance charge trapping and nullify the above-mentioned advantages.

Investigation of electron trapping in AlGaN/GaN HEMT with Fe-doped buffer through DCT characterization and TCAD device simulations

The electron trapping in AlGaN/GaN high-electron mobility transistors (HEMTs) with iron (Fe)-doped buffer is investigated through Drain Current Transient (DCT) measurements and TCAD physics-based 2D device simulations. The DCT characterization reveals two prominent deep-level electron traps E1 (∼0.5 eV) and E2 (∼0.6 eV) in the AlGaN/GaN HEMT. The measured DCT spectrum is analyzed at different trap-filling pulse durations (10 µs–100 ms) to obtain the information of trapping kinetics. As the first step in the simulation, the TCAD physical model parameters are calibrated by matching the simulated DC characteristics with the experimental data. It is shown that the TCAD model incorporating the acceptor-type trap at EC – 0.5 eV in the GaN buffer quantitatively reproduces the measured DCT spectra over the temperature range of 25–100 °C. To explore the buffer trapping effects, the simulated DCT is inspected by varying the activation energy, capture cross section, and concentration of the buffer trap.

Potential gross nitrogen mineralization and its linkage with microbial respiration along a forest transect in eastern China

Nitrogen (N) mineralization in soils generally controls biological N availability in terrestrial ecosystems. As the pivotal first step in the overall N mineralization process, gross N mineralization (GNM, defined as the production of ammonium from microbial mineralization of organic N) is inherently coupled with microbial mineralization of soil organic carbon (C) which is commonly referred to as microbial respiration (MR), and that has often been used as a proxy of C availability. However, the pattern of GNM and its underlying mechanisms at a regional scale, and its linkage with MR remain unclear. By analyzing 100 soil samples collected across different forest types along a 3800 km long north-south transect in eastern China, we simultaneously measured the potential GNM using a 15N pool dilution method and MR using a dynamic CO2 trapping technique. We conducted a structural equation model (SEM) to examine the interactive effects of climate, soil pH, microbial substrate availability, and microbial biomass on potential GNM along the forest transect. Furthermore, we conducted a non-linear regression analysis between potential GNM and MR. We found that both potential GNM and MR varied largely, from 0.55 to 16.14 mg N kg−1 soil d−1 and from 3.64 to 24.30 mg C kg−1 soil d−1, respectively, but were not significantly affected by forest type. The SEM analysis showed that 51% of the variation in potential GNM was explained, with microbial substrate availability being the most important influencing factor. There was a positive non-linear relationship between potential GNM and MR (R2 = 0.52, P < 0.0001). Notably, MR alone exerted a comparable role in explaining the variation in potential GNM compared to the interactive effects between multiple factors used in the SEM. Our findings confirm the dominant control of C availability to microbes on potential GNM, and necessitate the incorporation of MR for better modeling GNM in forest soils.

CoSn Alloy-based three-dimensional ordered multistage porous composite towards effective polysulfide confinement and catalytic conversion in lithium‐sulfur batteries

Reasonable design of porous sulfur cathode can inhibit shuttle effect of lithium polysulfide (LiPS), accelerate redox kinetic and enhance the cycling stability, which is important to the development of lithium-sulfur (Li-S) battery. In this work, a multistage porous composite with three-dimensionally ordered macroporous (3DOM) CoSn alloy and embedded microporous Co decorated N-doped carbon (Co-NC) is rationally designed. The conductive CoSn alloy skeleton exhibits strong polar adsorption and effective catalytic activity towards polysulfide conversion, as well as fast electron transportation. Meanwhile, the 3DOM structure possesses sufficient volume space for ion migration and sulfur expansion. Additionally, the properly embedded Co-NC derived from ZIF-67 can offer abundant micropores and catalytic sites, promoting polysulfide trapping and LiPS conversion kinetics. Accordingly, the Li-S batteries fabricated with 3DOM Co-NC@CoSn exhibit remarkable stability with an ultralow capacity decay of 0.046% per cycle over 500 cycles at 1 C. An impressive areal capacity of about 5.1 mAh cm−2 under high sulfur loading of 6.8 mg cm−2 is also achieved at 0.2 C, with a high capacity retention of 79% over 100 cycles. The pouch cell maintains stable at 0.05 C, and the capacity decay is only 0.29% per cycle. This design and synthesis strategy of cathodes has great prospects in the practical application of Li-S battery.

Dynamics of dissolution trapping in geological carbon storage

We report a quantitative study on the dynamics of dissolution trapping occurring during the injection of supercritical CO2 (scCO2) into a brine-filled heterogeneous porous medium, implying an application for the geological storage of CO2 in saline aquifers. We present volume-of-fluid (VOF)-based simulations of integrated two-phase flow and species mass transport at the pore-scale to capture transient dissolution of scCO2 in brine. It becomes evident that CO2 dissolution is not an instantaneous process, as the structural heterogeneity of the porous medium induces incomplete mixing leading to non-equilibrium dissolution. According to our observations, dissolution of scCO2 into brine occurs at an increasing rate at the early stage of the injection period, reaches a peak value, and follows by a declining trend at late stages. The observed trend in the dissolution rate is attributed to the evolution of interfacial area between percolated fingers of CO2 plume and brine. When the system reaches the steady-state, a stabilized interface between scCO2 and brine forms, undermining the scCO2 dissolution and dissolved CO2 mass transfer in brine. The pore-level analysis implies that injection rate and surface wettability are key factors influencing the evolution of the scCO2-brine interfacial area and consequently the mass transfer occurring at the interface during the dissolution trapping of scCO2. According to the results, scCO2 dissolution becomes more pronounced when the injection rate becomes higher and the medium is more wetting to the brine.

Accurate and efficient simulations of Hamiltonian mechanical systems with discontinuous potentials

This article considers Hamiltonian mechanical systems with potential functions admitting jump discontinuities. The focus is on accurate and efficient numerical approximations of their solutions, which will be defined via the laws of reflection and refraction. Despite of the success of symplectic integrators for smooth mechanical systems, their construction for the discontinuous ones is nontrivial, and numerical convergence order can be impaired too. Several rather-usable numerical methods are proposed, including: a first-order symplectic integrator for general problems, a third-order symplectic integrator for problems with only one linear interface, arbitrarily high-order reversible integrators for general problems (no longer symplectic), and an adaptive time-stepping version of the previous high-order method. Interestingly, whether symplecticity leads to favorable long time performance is no longer clear due to discontinuity, as traditional Hamiltonian backward error analysis does not apply any more. Therefore, at this stage, our recommended default method is the last one. Various numerical evidence, on the order of convergence, long time performance, momentum map conservation, and consistency with the computationally-expensive penalty method, are supplied. A complex problem, namely the Sauteed Mushroom, is also proposed and numerically investigated, for which multiple bifurcations between trapped and ergodic dynamics are observed.

Surface-facilitated trapping by active sites: From catalysts to viruses.

Trapping by active sites on surfaces plays important roles in various chemical and biological processes, including catalysis, enzymatic reactions, and viral entry into host cells. However, the mechanisms of these processes remain not well understood, mostly because the existing theoretical descriptions are not fully accounting for the role of the surfaces. Here, we present a theoretical investigation on the dynamics of surface-assisted trapping by specific active sites. In our model, a diffusing particle can occasionally reversibly bind to the surface and diffuse on it before reaching the final target site. An approximate theoretical framework is developed, and its predictions are tested by Brownian dynamics computer simulations. It is found that the surface diffusion can be crucial in mediating trapping by active sites. Our theoretical predictions work reasonably well as long as the area of the active site is much smaller than the overall surface area. Potential applications of our approach are discussed.

Presence of Maximal Characteristic Time in Photoluminescence Blinking of MAPbI3 Perovskite

AbstractPhotoluminescence (PL) blinking is a common phenomenon in nanostructured semiconductors associated with charge trapping and defect dynamics. PL blinking kinetics exhibit very broadly distributed timescales. The traditionally employed analysis of probability distribution of ON and OFF events suffers from ambiguities in their determination in complex PL traces making its suitability questionable. Here, the statistically correct power spectral density (PSD) estimation method applicable for fluctuations of any complexity is employed. PSDs of the blinking traces of submicrometer MAPbI3 crystals at high frequencies follow power law with excitation power density dependent parameters. However, at frequencies less than 0.3 Hz, the majority of the PSDs saturate revealing the presence of a maximal characteristic timescale of blinking in the range of 0.5–10 s independently of the excitation power density. Super‐resolution optical microscopy shows the characteristic timescale to be an inherent material property independent of polycrystallinity. Thus, for the first time the maximum timescale of the multiscale blinking behavior of nanoparticles is observed demonstrating that the power law statistics are not universal for semiconductors. It is proposed that the viscoelasticity of metal‐halide perovskites can limit the maximum timescale for the PL fluctuations by limiting the memory of preceded deformations/re‐arrangements of the crystal lattice.

Non-monotonic threshold voltage variation in 4H-SiC metal–oxide–semiconductor field-effect transistor: Investigation and modeling

We propose an analytical model to reproduce the non-monotonic instability of the threshold voltage in 4H-SiC MOSFETs submitted to a positive gate stress bias. Experimental analysis of the threshold voltage transients indicates that both electron and hole trappings take place in the gate dielectric or at the dielectric/semiconductor interface, responsible for a VTH increasing–decreasing–increasing pattern. At low/moderate stress fields (&amp;lt;7 MV/cm), the electron trapping kinetics responsible for a positive VTH shift are modeled by a rate equation considering a trapping-inhibition model, which explains the logarithmic degradation kinetics. In the high field regime (&amp;gt;8 MV/cm), we propose that electrons can tunnel through the SiO2, be accelerated by the high field, and generate holes through impact ionization (II) or anode hole injection. These holes are then trapped in the oxide, thus generating a negative VTH shift. This second process has an exponential time-dependency, as found through the analysis of the corresponding rate equations. The time constant of the positive VTH shift is evaluated as a function of stress voltage and temperature. The results indicate that the time constant is strongly dependent on the electric field (that accelerates electrons to generate holes), and not thermally activated, in agreement with theoretical considerations.

Positive and negative charge trapping GaN HEMTs: Interplay between thermal emission and transport-limited processes

This paper investigates the kinetics of buffer trapping in GaN-based normally-off high-voltage transistors. The analysis was carried out on transfer-length method (TLM) structures.By means of a custom setup, (i) we investigated the trapping and de-trapping processes induced by a large vertical bias and identified different mechanisms, responsible for the storage of negative and positive charge in the buffer. (ii) temperature-dependent analysis was carried out to evaluate the time constants associated to negative and positive charge build-up. Remarkably, the results indicate that the activation energy for negative charge trapping is ~0.3 eV, which is much lower than the ionization energy of carbon acceptors (0.8–0.9 eV). This result is explained by considering that trapping and de-trapping are not dominated by thermal processes (thermal emission from acceptors), but by transport mechanisms, that limit the transfer of charge to trap states. (iii) in the recovery experiments, after low stress bias negative charge trapping dominates. After high stress bias, also the effect of positive charge generation is detected, and the related activation energy is evaluated.The results presented within this paper clearly indicate that the trapping and de-trapping kinetics of normally-off GaN HEMTs are the results of the interplay of transport-limited conduction processes, that result in a low thermal activation (Ea ~ 0.3 eV), compared to that of CN acceptors.

Impact of single-defects on the variability of CMOS inverter circuits

Variations in the operational behavior of seemingly identical transistors pose a remarkable challenge for application engineers as integrated circuits have to be designed to be resilient against process and aging-related error sources. In small-area transistors, electrically active defects give rise to considerable device-to-device variations for instance of the threshold voltage. With the ongoing reduction of device dimensions, the impact of a single-defect becomes more and more relevant for the device behavior. While in circuit simulations, typically changes of mean values are considered, we thoroughly investigate the impact of variations of defect distributions on the signal propagation delay of an inverter circuit from the perspective of single oxide and interface defects. For this, the charge trapping kinetics of each defect is described using our stochastic charge trapping model. The impact of these single defects on the device behavior is extracted from detailed experimental studies. We demonstrate that the variation of the defect distributions between devices can lead to a signal propagation delay of several picoseconds for an inverter circuit. This can become a critical issue for circuits employing nanoscale transistors intended to operate at several hundreds of megahertz.

Preventative pest management in field crops influences the biological control potential of epigeal arthropods and soil-borne entomopathogenic fungi

• This study examined how pesticides influence beneficial biota in field crops. • Pesticidal seed treatments and sprays decreased total predator activity-density. • In year one, seed treatments and sprays decreased spider activity-densities. • In year three, spider activity-density increased with seed treatments alone. • Overall, the use of pesticides did not improve crop yield in maize or soybean. Field crop growers in the United States have adopted prophylactic pest management strategies to control sporadic crop pests that are spatially and temporally difficult to predict. While evidence shows these preventative management practices, specifically pesticidal seed treatments, can be important in regions with predictable pest pressures, employing them ubiquitously in field crops across the northeastern U.S. can have variable returns on productivity. Further, prophylactics may also limit the potential of integrated pest management (IPM). A three-year field experiment (2017–2019) was conducted in a maize-soybean cropping system to compare the influence of a preventative pest management practice and a scouting-based IPM practice on biological control organisms. Aboveground predator densities were measured via pitfall trapping and predation temporal dynamics were assessed using a standard sentinel-bait assay at two time points per year. Belowground biological control potential was determined using a sentinel-bait bioassay to quantify the abundance of soil-borne entomopathogenic fungi (EPF). The variable responses of beneficial communities to pesticide inputs were strongly influenced by season and time of application, underscoring the importance of applying pesticides only when necessary. Compared with no pesticide use, pesticidal seed treatments and foliar sprays together in a maize-soybean production system suppressed total predator activity-density, spider activity-density, predation, and infection potential of soil-borne entomopathogenic fungi in one out of three years of the field study. In the third year, the activity-density of spiders increased across all fields in preventative plots that included seed treatments only. Overall, the use of pesticides did not improve crop yield in either maize or soybean. These findings highlight that the use of a prophylactic pesticide program may not always be necessary for maximum crop productivity and that this management approach can occasionally have unintended negative consequences on above- and belowground soil biota and the ecosystem services they provide.

Potential of Vasoprotectives to Inhibit Non-Enzymatic Protein Glycation, and Reactive Carbonyl and Oxygen Species Uptake.

Reactive carbonyl species (RCS) such as methylglyoxal (MGO) or glyoxal (GO) are the main precursors of the formation of advanced glycation end products (AGEs). AGEs are a major factor in the development of vascular complications in diabetes. Vasoprotectives (VPs) exhibit a wide range of activities beneficial to cardiovascular health. The present study aimed to investigate selected VPs and their structural analogs for their ability to trap MGO/GO, inhibit AGE formation, and evaluate their antioxidant potential. Ultra-high-performance liquid chromatography coupled with an electrospray ionization mass spectrometer (UHPLC-ESI-MS) and diode-array detector (UHPLC-DAD) was used to investigate direct trapping capacity and kinetics of quenching MGO/GO, respectively. Fluorimetric and colorimetric measurements were used to evaluate antiglycation and antioxidant action. All tested substances showed antiglycative effects, but hesperetin was the most effective in RCS scavenging. We demonstrated that rutin, diosmetin, hesperidin, and hesperetin could trap both MGO and GO by forming adducts, whose structures we proposed. MGO-derived AGE formation was inhibited the most by hesperetin, and GO-derived AGEs by diosmetin. High reducing and antiradical activity was confirmed for quercetin, rutin, hesperetin, and calcium dobesilate. Therefore, in addition to other therapeutic applications, some VPs could be potential candidates as antiglycative agents to prevent AGE-related complications of diabetes.