Excess Charge Research Articles

Analyze Strategies for Diversifying the Country's Economy Driven by Tourism Using Pattaya, Chonburi, Thailand as a Case Study. To Reduce Fragility and Increase Economic Stability

Purpose: This study investigates ways to enhance economic stability in tourism-dependent regions, using Pattaya, Chonburi, Thailand, as a case study.
 Theoretical Reference: Thailand's heavy reliance on tourism, constituting about 17% of its GDP, sets the context. The study gathers insights from SMEs in Chonburi Province through in-depth interviews.
 Method: In-depth interviews with SMEs reveal challenges faced by small hotel businesses, including high taxation and substantial expenses, with a focus on labor costs and pre-existing issues like excessive charges.
 
 Results and Conclusion: Prioritizing the hotel industry over attracting new tourists is key. Post-COVID-19 economic stability in Pattaya's tourism industry requires a comprehensive approach involving industry revitalization, diversification, support for local businesses, sustainable practices, infrastructure investments, marketing, and government-industry collaboration.
 Implications of Research: This research underscores the importance of addressing challenges in tourism-driven regions during crises and offers practical insights for safeguarding economic stability.
 Originality/Value: The study's unique focus on Pattaya provides valuable insights for similar regions, offering strategies to mitigate vulnerabilities caused by external shocks like pandemics.

First-principles study of the magnetic anisotropy of ultrathin B-, C-, and N-doped FeCo films

Iron-based layered systems are of great interest because of their ability to tune effective material parameters such as magnetic anisotropy energy (MAE). The influence of the crystallographic structure of Fe, its thickness, and the presence of other layers above and below the Fe layer on magnetic parameters, such as the MAE of the studied system, is an intriguing and important topic from an application point of view. Here, we present a density functional theory (DFT) study of the magnetic anisotropy of nine-monolayer Fe, FeCo, and FeCo films with B, C, and N dopants placed in octahedral interstitial positions. The theoretical study is based on calculations using the full-potential local-orbital code FPLO and the generalized gradient approximation. The chemical disorder in the FeCo layers was modeled using the virtual crystal approximation. The structures of the layers were subjected to optimization of the geometry of the interlayer spacings and the neighborhood of the dopant sites. We determined the local magnetic moments and the excess charge at each layer position. We also identified the influence of dopant atoms on the magnetic properties of FeCo layers, such as magnetization and magnetic anisotropy.

Electroviscous effects in pressure-driven flow of electrolyte liquid through an asymmetrically charged non-uniform microfluidic device

BackgroundMicro-scale systems depict a different flow behavior from the macro-scale systems due to more vital surface forces such as surface tension, electrical charges, magnetic field, etc., which significantly affect the micro-scale flow. Further, among others, electrokinetic phenomena play a significant role at the micro-scale for controlling practical microfluidic applications. Therefore, it is essential to understand the fluid dynamics in micron-sized channels to develop efficient and reliable microfluidic devices. MethodsThe electroviscous effects in pressure-driven flow of electrolyte liquid through an asymmetrically charged contraction-expansion (4:1:4) slit microfluidic device have been investigated numerically. The mathematical model (i.e., Poisson's, Navier-Stokes, and Nernst-Planck equations) is solved using the finite element method to obtain the electrical potential, velocity, pressure, ion concentration fields, excess charge, an induced electric field strength for the following ranges of parameters: Reynolds number (Re=0.01), Schmidt number (Sc=1000), inverse Debye length (2≤K≤20), top wall surface charge density (4≤St≤16), surface charge density ratio (0≤Sr≤2) and contraction ratio (dc=0.25). Significant FindingsResults show that the charge asymmetry (Sr) at the different walls of the microfluidic device plays a significant role on the induced electric field development and microfluidic hydrodynamics. The total potential (|ΔU|) and pressure drop (|ΔP|) maximally increase by 197.45% and 25.46%, respectively with asymmetry of the charge. The electroviscous correction factor (ratio of apparent to physical viscosity) maximally changes by 20.85% (at K=2, St=16 for 0≤Sr≤2), 34.16% (at St=16, Sr=2 for 2≤K≤20), and 39.13% (at K=2, Sr=2 for 0≤St≤16). Thus, charge asymmetry (0≤Sr≤2) remarkably influences the fluid flow in the microfluidic devices, which is used for controlling the microfluidic processes, such as, mixing efficiency, heat, and mass transfer rates. Further, a simpler analytical model is developed to predict the pressure drop in electroviscous flow considering asymmetrically charged surface, based on the Poiseuille flow in the individual uniform sections and pressure losses due to orifice, estimates the pressure drop 1–2% within the numerical results. The robustness of this model enables the use of present numerical results for design aspects in the microfluidic applications.

Approaching Theoretical Limits in the Performance of Printed P-Type CuI Transistors via Room Temperature Vacancy Engineering.

Development of a novel high performing inorganic p-type thin film transistor could pave the way for new transparent electronic devices. This complements the widely commercialized n-type counterparts, indium-gallium-zinc-oxide (IGZO). Of the few potential candidates, copper monoiodide (CuI) stands out. It boasts visible light transparency and high intrinsic hole mobility (>40 cm2 V-1 s-1 ), and is suitable for various low-temperature processes. However, the performance of reported CuI transistors is still below expected mobility, mainly due to the uncontrolled excess charge- and defect-scattering from thermodynamically favored formation of copper and iodine vacancies. Here, a solution-processed CuI transistor with a significantly improved mobility is reported. This enhancement is achieved through a room-temperature vacancy-engineering processing strategy on high-k dielectrics, sodium-embedded alumina. A thorough set of chemical, structural, optical, and electrical analyses elucidates the processing-dependent vacancy-modulation and its corresponding transport mechanism in CuI. This encompasses defect- and phonon-scattering, as well as the delocalization of charges in crystalline domains. As a result, the optimized CuI thin film transistors exhibit exceptionally high hole mobility of 21.6 ± 4.5 cm2 V-1 s-1 . Further, the successful operation of IGZO-CuI complementary logic gates confirms the applicability of the device.

An Improved Model of Single-Event Transients Based on Effective Space Charge for Metal-Oxide-Semiconductor Field-Effect Transistor.

In this paper, a single-event transient model based on the effective space charge for MOSFETs is proposed. The physical process of deposited and moving charges is analyzed in detail. The influence of deposited charges on the electric field in the depletion region is investigated. The electric field decreases in a short time period due to the neutralization of the space charge. After that, the electric field increases first and then decreases when the deposited charge is moved out. The movement of the deposited charge in the body mainly occurs through ambipolar diffusion because of its high-density electrons and holes. The derivation of the variation in electric field in the depletion region is modeled in the physical process according to the analysis. In combination with the ambipolar diffusion model of excessive charge in the body, a physics-based model is built to describe the current pulse in the drain terminal. The proposed model takes into account the influence of multiple factors, like linear-energy transfer (LET), drain bias, and the doping concentration of the well. The model results are validated with the simulation results from TCAD. Through calculation, the root-mean-square error (RMSE) between the simulation and model is less than 3.7 × 10-4, which means that the model matches well with the TCAD results. Moreover, a CMOS inverter is simulated using TCAD and SPICE to validate the applicability of the proposed model in a circuit-level simulation. The proposed model captures the variation in net voltage in the inverter. The simulation result obviously shows the current plateau effect, while the relative error of the pulse width is 23.5%, much better than that in the classic model. In comparison with the classic model, the proposed model provides an RMSE of 7.59 × 10-5 for the output current curve and an RMSE of 0.158 for the output voltage curve, which are significantly better than those of the classic model. In the meantime, the proposed model does not produce extra simulation time compared with the classic double exponential model. So, the model has potential for application to flow estimation of the soft error rate (SER) at the circuit level to improve the accuracy of the results.

Epitaxial Growth of Li2O2 Achieved by a Rational Designed Fe3O4@N‐doped Carbon Nanoflower Structure for Improving the Performance of Li−O2 Batteries

AbstractThe insulated and insoluble discharge product Li2O2 can cause excessive charge overpotential, eventually leading to the deactivation of the Li−O2 battery. Here, a nanoflower structure (Fe3O4@NC) fabricated by coating Fe3O4 with N‐doped carbon was used as an effective catalyst for Li−O2 cathode. The N‐doped defective carbon layer provides sufficient active sites for the formation of discharge intermediates and exhibits a coating effect on Fe3O4, thereby facilitating the maintenance of structural stability. The hierarchical structure of Fe3O4 can effectively mitigate the agglomeration of the carbon layer, thus promoting a homogeneous distribution and optimal utilization of active sites on the carbon layer. As a result, the synergistic effect of Fe3O4 combined with the N‐doped carbon layer enhances the Li+/e− transfer rate and effectively accelerates the kinetic of oxygen reduction/evolution reaction (ORR/OER). Furthermore, the unique functionality of Fe3O4@NC induces the epitaxial growth of Li2O2 into uniform nanosheets, thereby increasing the utilization of cathode space and ultimately promoting the energy release of Li−O2 batteries. The Li−O2 battery with Fe3O4@NC cathode exhibits remarkable full discharge capacity of 16495 mAh g−1 and significantly improved round‐trip performances for 120 cycles at a cutoff capacity of 1000 mAh g−1 with a current density of 200 mA g−1.

Assessing a Tourism City from an Ecosystem Services Perspective: The Evaluation of Tourism Service in Liyang, China

Tourism is an important industry that promotes national economic and social progress. All-for-one tourism is a new concept of regionally coordinated development that uses the tourism industry as an engine to boost resource integration, industrial integration, and social sharing. Tourism service is the main embodiment of cultural ecosystem services for all-for-one tourism cities. Taking the city of Liyang in China as an example, this paper used a combination of GIS spatial analysis and big data text mining to evaluate tourism service from three aspects: the quality of tourism resources, the comprehensiveness of tourism service facilities, and the satisfaction of tourists. The results show that (1) tourism service is better in the northwestern and eastern areas of the city, while it is lower in the northeastern and southwestern parts; (2) the hotspot areas should focus on improving tour routes, transport capacity, and excessive charges; the cold spot areas should work on ecological restoration and creating new tourism attractions by combining the local industries; and (3) rural tourism integrating agriculture and visitation should be highlighted as a key growth point to improve the city’s tourism service function.

Recommendations for improving the experimental protocol for the determination of photocatalytic activity by nitric oxide oxidation measurements.

The photocatalytic nitric oxide (NO) oxidation reaction is used as a standard diagnostic tool for photocatalytic activity according to the well-defined protocol described by ISO Standard 22197-1-2007. This protocol identifies the negative peak showing a NOx concentration drop during a gas flow switch from the calibration bypass to the reactor as adsorption of NOx on the surface. Evidence is provided for this first transient to be due to a dilution effect in the gas phase within the reactor. With proper models of residence time distribution analysis, this transient revealed the internal hydrodynamics and it can be used to determine the internal volumes of the system. The second transient occurs immediately after the light is switched on. The conversions strongly depend on the time constant of this transient. Controlled measurements of the effect of illumination intensity revealed that at higher light intensities the transient takes longer to reach steady state. The longer transient was attributed to the time needed to reach a thermal steady state of the hot spots generated by the recombination of excess charge carriers. When the catalyst amount was investigated as a parameter, a saturation effect was observed. This saturation effect was correlated with the gas phase concentrations of NOx and moisture and their ratios to the available specific surface area. Hence, additional constraints with respect to the illumination intensity and catalyst amounts are recommended for accurate measurements of photocatalytic activity by NO oxidation.

Limit Efficiency of a Silicon Betavoltaic Battery with Tritium Source.

An idealized design of a silicon betavoltaic battery with a tritium source is considered, in which a thin layer of tritiated silicon is sandwiched between two intrinsic silicon slabs of equal width, and the excess charge carriers are collected by thin interdigitated n+ and p+ electrodes. The opposite sides of the device are covered with a reflecting coating to trap the photons produced in radiative recombination events. Due to photon recycling, radiative recombination is almost ineffective, so the Auger mechanism dominates. An analytical expression for the current-voltage curve is obtained, from which the main characteristics of the cell, namely, the open-circuit voltage, the fill factor, and the betaconversion efficiency, are found. The analytical results are shown to agree with the numerical ones with better than 0.1% accuracy. The optimal half-thickness of this device is found to be around 1.5 μm. The maximal efficiency increases logarithmically with the surface activity of the beta-source and has the representative value of 12.07% at 0.1 mCi/cm2 and 14.13% at 10 mCi/cm2.

Ferroelectric Polarization Modulated Facet-selective Charge Separation in Bi4 NbO8 Cl Single Crystal for Boosting Visible-light Driven Bifunctional Water Splitting.

Developing bifunctional water-splitting photocatalysts is meaningful, but challenged by the harsh requirements of specific-facet single crystals with spatially separated reactive sites and anisotropic charge transfer paths contributed by well-built charge driving force. Herein, tunable ferroelectric polarization is introduced in Bi4 NbO8 Cl single crystal nanosheets to strengthen the orthogonal charge transfer channels. By manipulating the in-plane polarization from octahedral off-centering of Nb5+ and out-of-plane polarization from lone pair electron effect of anisotropic Bi3+ , both the fast charge recombination in bulk catalyst and the process of charge trapping into surface states can be effectively modulated. Collaborating with modest polarization electric field and facet junction induced built-in electric field, cooperative charge tractive force is constructed, which reinforces the spatial separation and migration of photogenerated electrons and holes to {110} reductive site facet and {001} oxidation site facet, respectively. While excessive polarization charges impair the facet-selective charge separation characteristics and conversely promote charge recombination on the surface. As a result, polarity-optimized Bi4 NbO8 Cl shows an excellent H2 and O2 evolution rate of 54.21 and 36.08 μmol ⋅ h-1 in the presence of sacrificial reagents under visible light irradiation. This work unveils the function of ferroelectric polarization in tuning the intrinsic facet-selective charge transfer process of photocatalysts.

Ferroelectric Polarization Modulated Facet‐selective Charge Separation in Bi4NbO8Cl Single Crystal for Boosting Visible‐light Driven Bifunctional Water Splitting

AbstractDeveloping bifunctional water‐splitting photocatalysts is meaningful, but challenged by the harsh requirements of specific‐facet single crystals with spatially separated reactive sites and anisotropic charge transfer paths contributed by well‐built charge driving force. Herein, tunable ferroelectric polarization is introduced in Bi4NbO8Cl single crystal nanosheets to strengthen the orthogonal charge transfer channels. By manipulating the in‐plane polarization from octahedral off‐centering of Nb5+ and out‐of‐plane polarization from lone pair electron effect of anisotropic Bi3+, both the fast charge recombination in bulk catalyst and the process of charge trapping into surface states can be effectively modulated. Collaborating with modest polarization electric field and facet junction induced built‐in electric field, cooperative charge tractive force is constructed, which reinforces the spatial separation and migration of photogenerated electrons and holes to {110} reductive site facet and {001} oxidation site facet, respectively. While excessive polarization charges impair the facet‐selective charge separation characteristics and conversely promote charge recombination on the surface. As a result, polarity‐optimized Bi4NbO8Cl shows an excellent H2 and O2 evolution rate of 54.21 and 36.08 μmol ⋅ h−1 in the presence of sacrificial reagents under visible light irradiation. This work unveils the function of ferroelectric polarization in tuning the intrinsic facet‐selective charge transfer process of photocatalysts.

Electrocatalytic Mechanisms for an Oxygen Evolution Reaction at a Rhombohedral Boron Monosulfide Electrode/Alkaline Medium Interface.

Rhombohedral boron monosulfide (r-BS) with a layer stacking structure is a promising electrocatalyst for an oxygen evolution reaction (OER) within an alkaline solution. We investigated the catalytic mechanisms at the r-BS electrode/alkaline medium interface for an OER using hybrid solvation theory based on the first-principles method combined with classical solution theory. In this study, we elucidate the activities of the OER at the outermost r-BS sheet with and without various surface defects. The Gibbs free energies along the OER path indicate that the boron vacancies at the first and second layers of the r-BS surface (VB1 and VB2) can promote the OER. However, we found that the VB1 is easily occupied by the oxygen atom during the OER, degrading its electrocatalytic performance. In contrast, VB2 is suitable for the active site of the OER due to its structure stability. Next, we applied a bias voltage with the OER potential to the r-BS electrode. The bias voltage incorporates the positive excess surface charge into pristine r-BS and VB2, which can be understood by the relationship between the OER potential and potentials of zero charge at the r-BS electrode. Because the OH- ions are the starting point of the OER, the positively charged surface is kinetically favorable for the electrocatalyst owing to the attractive interaction with the OH- ions. Finally, we qualitatively discuss the flat-band potential at a semiconductor/alkaline solution interface. It suggests that p-type carrier doping could promote the catalytic performance of r-BS. These results explain the previous measurement of the OER performance with the r-BS-based electrode and provide valuable insights into developing a semiconductor electrode/water interface.

재건축부담금 산정 방식의 개선을 위한 합리적 방안에 관한 연구

The purpose of this study is to examine how excessive the reconstruction levy is in the reconstruction maintenance project, what the cause of such excessive charge is calculated, and to study the solution. The development levy and reconstruction levy of the development levy system, which became the basis of the reconstruction levy system, are very similar in purpose, nature, and calculation method, but the difference in actual burden is excessive, raising concerns about equity and balance. In this regard, this study examines the contents of unreasonable charges through literature analysis and case analysis of reconstruction project areas in Seoul and Gyeonggi-do, where reconstruction charges are scheduled to be imposed recently, and proposes solutions from various aspects. The reconstruction levy is generally high regardless of regional factors, such as Seocho, Gangnam, and non-Gangnam areas, complex size, and apartment price level. It needs to be rationally improved. In order to reasonably calculate the reconstruction levy, various measures were proposed to ensure objectivity and fairness by matching the calculation standards and market price reflection rate of the housing price at the start and end of the reconstruction, and by calculating through a specialized institution. In the current real estate market, which is suffering from serious side effects due to the lack of supply of newly built apartments, we hope to achieve the goals of stabilizing real estate prices, sound development of the national economy, and social integration through institutional improvements.

Are High-Temperature Molten Salts Reactive with Excess Electrons? Case of ZnCl2.

New and exciting frontiers for the generation of safe and renewable energy have brought attention to molten inorganic salts of fluorides and chlorides. This is because high-temperature molten salts can act both as coolants and liquid fuel in next-generation nuclear reactors. Whereas research from a few decades ago suggests that salts are mostly unreactive to radiation, recent experiments hint at the fact that electrons generated in such extreme environments can react with the melt and form new species including nanoparticles. Our study probes the fate of an excess electron in molten ZnCl2 using first-principles molecular dynamics calculations. We find that on the time scale accessible to our study, an excess electron can be found in one of three states; the lowest-energy state can be characterized as a covalent Zn2Cl5•2- radical ion, the other two states are a solvated Zn•+ species (ZnCl3•2-) and a more delocalized species that still has some ZnCl3•2- character. Since for each of these, the singly occupied molecular orbital (SOMO) where the excess charge resides has a distinct and well-separated energy, the different species can in principle be characterized by their own electronic spectra. The study also sheds light onto what is commonly understood as the spectrum of a transient radical species which can be from the SOMO onto higher energy states or from the melt to pair with the excess electron leaving a hole in the liquid.

Impact of Hydrogen in Ga‐Doped Silicon on Maximum LeTID Defect Density

Many studies suggest that hydrogen is an important factor for light and elevated temperature‐induced degradation (LeTID) in p‐type c‐Si solar cells. The exact mechanism of this defect is still unknown. Here, Ga‐doped Si wafers fired with an SiN x :H layer present were used to establish a correlation between the initial concentration of GaH pairs and H2 dimers on one and the maximum defect density evolving during degradation on the other hand. Degradation of all samples is performed at constant excess charge carrier injection. The correlation to LeTID defect density is found to be linear in the case of [H2], hence, a direct involvement of H2 in the defect formation is expected. In contrast, the correlation between GaH pairs and defects is found to scale with the fraction of GaH on total hydrogen concentration. This fraction is not constant but rather decreases with an increase in total hydrogen concentration. In addition, changes in [GaH] and lifetime are examined under different degradation conditions with either fixed injection up to and temperatures up to 180 °C. Under these conditions, LeTID evolves but no dissociation of [GaH] takes place. The effective activation energy of LeTID defect formation is determined to be 0.76(17) eV.

Optimal battery charge with safe exploration

Li-ion batteries have become the standard power source for electric vehicles (EVs) as the alternative of choice to reduce CO2 emissions. But before becoming a reliable technology, Li-ion batteries must deal with two significant challenges: undesirable electrochemical reactions caused by excessive charging rates and considerable time for an EV to get charged. It is necessary to employ balanced current profiles that prevent both serious battery degradation effects and the inconvenience to end users. In this work, the authors propose a safe exploration deep reinforcement learning (SDRL) approach in order to determine optimal charging profiles under variable operating conditions. One of the main advantages of RL techniques is that they can learn from interaction with the real or simulated system while incorporating the nonlinearity and uncertainty derived from fluctuating environmental conditions. However, since RL techniques must explore undesirable states before obtaining an optimal policy, no safety guarantees are provided. The proposed approach aims at maintaining zero-constraint violations throughout the learning process through the integration of a safety layer that corrects the action if a constraint is likely to be violated. The proposed method is tested in the equivalent circuit of a Li-ion battery under varying conditions. Results reveal that with the integration of this safety layer, SDRL is able to find safe optimized charging policies while considering a trade-off between the charging speed and the battery lifespan, including a 30% reduction in charging time while still maintaining temperatures within permissible limits and up to 38% of battery life conservation, compared with benchmark methods. Moreover, our approach does not experience episodes demonstrating restriction violations throughout the pre-training, training, and evaluation phases.

Electronic and Photochemical Passivation by a Classic Sunscreen Material Leading to Reduced Voc Losses and Enhanced Stability in Organic Solar Cells.

Organic solar cells (OSCs) have been a popular topic of research for a long time. As a well-known electron transport layer (ETL) material for inverted device architecture, sol-gel-derived zinc oxide (ZnO) displays certain defective surfaces that cause excessive charge recombination and lower device performance. While ultraviolet (UV)-light soaking is sometimes necessary for the ZnO layer to function properly, the latter can also cause the photodegradation of conjugated organic semiconductors. The photostability of OSCs has always been a hot research topic, as the radiation of UV light may cause changes in the material's properties, and that, in turn, may cause rapid attenuation of the devices. Herein, ZnO is modified by inserting the commonly used sunscreen ingredient benzophenone-3 (BP-3) between the photoactive layer, consisting of a PM6:Y6 blend, and ZnO to reduce the impact of UV radiation on the photosensitive layer. The addition of BP-3 successfully enhances the photovoltaic parameters, and a remarkable open-circuit voltage (Voc) value of 0.887 V is obtained for PM6:Y6-based inverted solar cells, corresponding to a Voc loss as small as 0.547 V. Finally, the application of this strategy increases the device's power conversion efficiency from 12.44 to 13.71% and provides improved UV stability.

Protein–lipid charge interactions control the folding of outer membrane proteins into asymmetric membranes

Biological membranes consist of two leaflets of phospholipid molecules that form a bilayer, each leaflet comprising a distinct lipid composition. This asymmetry is created and maintained in vivo by dedicated biochemical pathways, but difficulties in creating stable asymmetric membranes in vitro have restricted our understanding of how bilayer asymmetry modulates the folding, stability and function of membrane proteins. In this study, we used cyclodextrin-mediated lipid exchange to generate liposomes with asymmetric bilayers and characterize the stability and folding kinetics of two bacterial outer membrane proteins (OMPs), OmpA and BamA. We found that excess negative charge in the outer leaflet of a liposome impedes their insertion and folding, while excess negative charge in the inner leaflet accelerates their folding relative to symmetric liposomes with the same membrane composition. Using molecular dynamics, mutational analysis and bioinformatics, we identified a positively charged patch critical for folding and stability. These results rationalize the well-known ‘positive-outside’ rule of OMPs and suggest insights into the mechanisms that drive OMP folding and assembly in vitro and in vivo.

Tuning Electrochemical Stability of 5,10-Ditolylphenazine-Based Antiaromatic Materials for Unipolar Memristor toward Artificial Synapses Application.

Three organic conjugated small molecules, DTA-DTPZ, Cz-DTPZ, and DTA-me-DTPZ comprising an antiaromatic 5,10-ditolylphenazine (DTPZ) core and electron-donating peripheral substituents with high HOMOs (-4.2 to -4.7 eV) and multiple reversible oxidative potentials are reported. The corresponding films sandwiched between two electrodes show unipolar and switchable hysteresis current-voltage (I-V) characteristics upon voltage sweeping, revealing the prominent features of nonvolatile memristor behaviors. The numerical simulation of the I-V curves suggests that the carriers generated by the oxidized molecules lead to the increment of conductance. However, the accumulated carriers tend to deteriorate the device endurance. The electroactive sites are fully blocked in the dimethylated molecule DTA-me-DTPZ, preventing the irreversible electrochemical reaction, thereby boosting the endurance of the memristor device over 300 cycles. Despite the considerable improvement in endurance, the decrement of on/off ratio from 105 to 101 after 250 cycles suggests that the excessive charge carriers (radical cations) remains a problem. Thus, a new strategy of doping an electron-deficient material, CN-T2T, into the unipolar active layer was introduced to further improve the device stability. The device containing DTA-me-DTPZ:CNT2T (1:1) blend as the active layer retained the endurance and on/off ratio (∼104) upon sweeping 300 cycles. The molecular designs and doping strategy demonstrate effective approaches toward more stable metal-free organic conjugated small-molecule memristors.

Atomic-Scale Engineering of Grain Boundary Chemistry and Potential for Li-Garnet Solid-State Electrolytes

With increasing demands to replace flammable liquid electrolytes, solid-state electrolytes have sparked interests both in academic and industrial sectors. In particular, Li-garnet LLZO (Li7La3Zr2O12) exhibits outstanding electrical, chemical, and mechanical properties. Despite the promise, LLZO suffers from the formation of lithium (Li) dendrites at high current operations, thereby limiting the safety and performance of garnet-based solid-state batteries. Li metal nucleation and growth reportedly initiate and grow along the locality of grain boundaries (GBs) in such polycrystalline electrolytes, due either to low ionic or high electronic conductivity of the boundaries. However, limited understanding yet exists on the origins of the local GB conductivity mismatch. The mechanistic understanding should be an important prerequisite to develop engineering strategies of the failing GB interfaces. In this work, we first apply grain boundary core-space charge layer model to understand the basis of Li metal nucleation at GBs. Grain boundary core of LLZO is modeled to have excess negative charge potential, leading to the subsequent Li ionic carrier depletion and electronic carrier accumulation in the adjacent space charge layers. The carrier concentration variations then drive the local electronic conductivity surge and detrimental Li metal nucleation at the GBs. Both electrochemical and microscopic characterization techniques are employed to investigate the atomic-level composition and space charge potential at the GBs. This understanding offers us new strategies for controlling Li nucleation. First, sintering atmosphere is selectively chosen to reduce the potential barrier by suppressing intrinsic defect accumulation at the GB core. Second, an aliovalent dopant, with net-positive charge, is introduced to segregate to GB and mitigate the negative core potential. Both approaches are shown effective in lowering the electronic conductivity and to impede Li metal penetration. We successfully achieve critical current densities (CCD) of ~ 1 mA cm-2,a two-fold increase over prior reports. Our theoretical understanding and the engineering approaches will aid in interpreting the failure origin of the garnet electrolytes, and provide a blueprint on how to engineer GBs for improved safety and performance of all-solid-state Li metal batteries.