Local Electron Density Research Articles

Global Distribution of Electron Temperature Enhancement at Mid‐Low Latitudes Observed by DMSP F16 Satellite

AbstractThis study investigates the global distribution of electron temperature enhancement observed by Defense Meteorological Satellite Program F16 satellite and its dependence on the season and solar activity for the solar maximum (2014) and minimum (2018) years during geomagnetic quiet times (maximum per day ap <10). Electron temperature enhancements occurred mainly over the North American‐Atlantic (260°–360°E) and Eurasia (0°–160°E) (Southern Oceania (80°–280°E)) sector in the Northern (Southern) Hemisphere and are prominent in the winter hemispheres and solar maximum year. They have obvious longitude characteristics. Interestingly, they could extend to geomagnetic equatorial regions in the North American‐Atlantic sector from high to low latitudes in the December Solstice, further crossed the magnetic equator, and merged into the Southern Hemisphere in 2014, where the maximum temperature reached ∼3500 K. Our analysis indicates that low‐energy electrons (<100 eV) associated with photoelectron from the conjugate sunlit hemisphere, can contribute to these enhancements. Furthermore, the local geomagnetic declination, magnetic equator position, and terminator position at magnetic conjugate points together can impact the global distribution of photoelectrons of different energies and therefore the electron temperature enhancement distribution. Other processes (including local electron density variation) may play certain roles as well.

Simulation of localized electron density enhancement caused by high-pressure H2O gas release in ionosphere

Based on the continuity and momentum equations, a self-consistent simulation model is developed for describing the localized electron density enhancement caused by high-pressure H2O gas release in the ionosphere. The chemical reaction and momentum exchange process between the neutral gas and ionospheric plasma species are considered in the theoretical simulation model. The finite element method is used to solve the simulation model for H2O gas release, and the expansion and ionospheric disturbance process at the early stage of high-pressure gas release are studied. It is shown that the space expansion of the released gas is mainly dominated by the pressure difference between the H2O gas and the ionospheric plasma at the early stage of release. Then the diffusion process becomes the dominant process of the space transport of H2O molecules. An electron depletion region forms near the center of the release region due to the chemical reaction and collision process with H2O molecules. Meanwhile, an electron density enhancement region forms on both sides along the magnetic field direction due to the electron snowplow effect. With the increase in the released mass of H2O gas, the intensity and duration of the electron density enhancement increase gradually. With the release position rising, it is found that the intensity of the electron density enhancement has a peak near 380 km and the duration increases slightly with the increasing release height.

Visible-light-induced self-propelled nanobots against nanoplastics

The accumulation of plastic debris in aquatic organisms has raised serious concerns about the potential health implications of their incorporation into the food chain. However, conventional water remediation techniques are incapable of effectively removing nanoplastics (NPs) smaller than 200 nm, which can have harmful effect on animal and human health. Herein, we demonstrate the “on-the-fly” capture of NPs through their enlargement (approximately 4,100 times) using self-propelled nanobots composed of a metal-organic framework. Under visible-light irradiation, the iron hexacyanoferrate (FeHCF) nanobot exhibits fuel-free motion by electrostatically adsorbing NPs. This strategy can contribute to reducing plastic pollution in the environment, which is a significant environmental challenge. Light-induced intervalence charge transfer in the FeHCF nanobot lattice induces bipolarity on the nanobot surface, leading to the binding of negatively charged NPs. The local electron density in the lattice then triggers self-propulsion, thereby inducing agglomeration of FeHCF@NP complexes to stabilize their metastable state. The FeHCF nanobot exhibits a maximum removal capacity of 3,060 mg∙g−1 and rate constant of 0.69 min−1, which are higher than those recorded for materials reported in the literature.

Mechanism insights into photo–assisted peroxymonosulfate activation on oxygen vacancy–enriched nolanites via an electron transfer regime

The utilization of photo–assisted persulfate activation for the removal of organic contaminants in water has garnered significant research interest in recent times. However, there remains a lack of clarity regarding specific contributions of light irradiation and catalyst structure in this process. Herein, a photo–assisted peroxymonosulfate (PMS) activation system is designed for the highly efficient degradation of organic contaminants on oxygen vacancy–enriched nolanites (Vo–FVO). Results suggest that the degradation of bisphenol A (BPA) in this system is a nonradical–dominated process via an electron transfer regime, in which VO improves the local electron density and thus facilitates the electron shuttling between BPA and PMS. During BPA degradation, PMS adsorbed at the surface of FVO–180 withdraws electrons near VO and forms FVO–PMS* complexes. Upon light irradiation, photoelectrons effectively restore the electron density around VO, thereby enabling a sustainable electron transfer for the highly efficient degradation of BPA. Overall, this work provides new insights into the mechanism of persulfate activation based on defects engineering in nolanite minerals.

Multifractal Conductance Fluctuations of Helical Edge States.

Two-dimensional topological insulators are characterized by the bulk gap and one-dimensional helical states running along the edges. The theory predicts the topological protection of the helical transport from coherent backscattering. However, the unexpected deviations of the conductance from the quantized value and localization of the helical modes are generally observed in long samples. Moreover, at millikelvin temperatures significant mesoscopic fluctuations are developed as a function of the electron energy. Here we report the results of an experimental study of the transport in a HgTe quantum well with an inverted energy spectrum that reveal a multifractality of the conductance fluctuations in the helical edge state dominated transport regime. We attribute observed multifractality to mesoscopic fluctuations of the electron wave function or local density of states at the spin quantum Hall transition. We have shown that the mesoscopic two-dimensional topological insulator provides a highly tunable experimental system in which to explore the physics of the Anderson transition between topological states.

Modulating Electron Density of Ni-N-C Sites by N-doped Ni for Industrial-level CO2 Electroreduction in Acidic Media.

Electro-chemically reducing CO2 in a highly acidic medium is promising for addressing the issue of carbonate accumulation. However, the hydrogen evolution reaction (HER) typically dominates the acidic CO2 reduction. Herein, we construct an efficient electro-catalyst for CO formation based on a core-shell structure, where nitrogen-doped Ni nanoparticles coexist with nitrogen-coordinated Ni single atoms. The optimal catalyst demonstrates a significantly improved CO faradaic efficiency (FE) of 96.7 % in the acidic electrolyte (pH=1) at an industrial-scale current density of 500 mA cm-2 . Notably, the optimal catalyst maintains a high FE of CO exceeding 90 % (current density=500 mA cm-2 ) in the electrolyte with a wide pH range from 0.67 to 14. In-situ spectroscopic characterization and density functional theory calculations show that the local electron density of Ni-N-C sites is enhanced by N-doped Ni particles, which facilitates the formation of *COOH intermediate and the adsorption of *CO. This study demonstrates the potential of a hybrid metal/Ni-N-C interface in boosting acidic CO2 electro-reduction.

First principles study of hydrogen induced the grain boundaries decohesion in fcc Ag

Hydrogen embrittlement (HE) is a pervasive but harmful physical (chemical) phenomenon, and it has a profound effect on the mechanical properties of metals. Although the study of HE began as early as the near century and a half ago, the essential mechanism of HE still cannot be completely figured out yet. The metallic-H atoms interaction at the atomistic scale is considered the essence of the HE. Especially the interaction of interstitial H and host atoms at grain boundaries is crucial for revealing the HE mechanism. Here, the first principles simulation is applied to study the effect of the trapped H atoms on the grain boundaries (GBs) cleavage behavior. We construct the GBs with different orientations of the face-cantered cubic (fcc) Argentum (Ag) and conduct the ab initio tensile test for all the GBs. The strength of GBs during cleavage, the distortion of GBs structure, and the electronic structure variation induced by trapped H atoms are analyzed. We find the GBs cleavage strength is generally decreased by trapping H atoms at GBs. The decohesion mechanism is the GBs distortion induced by the local electron density variation of the GBs trapping H atoms.

Computational Study into the Effects of Countercations on the [P8W48O184]40- Polyoxometalate Wheel.

Porous metal oxide materials have been obtained from a ring-shaped macrocyclic polyoxometalate (POM) structural building unit, [P8W48O184]40-. This is a tungsten oxide building block with an integrated "pore" of 1 nm in diameter, which, when connected with transition metal linkers, can assemble frameworks across a range of dimensions and which are generally referred to as POMzites. Our investigation proposes to gain a better understanding into the basic chemistry of this POM, specifically local electron densities and locations of countercations within and without the aforementioned pore. Through a rigorous benchmarking process, we discovered that 8 potassium cations, located within the pore, provided us with the most accurate model in terms of mimicking empirical properties to a sufficient degree of accuracy while also requiring a relatively small number of computer cores and hours to successfully complete a calculation. Additionally, we analyzed two other similar POMs from the literature, [As8W48O184]40- and [Se8W48O176]32-, in the hopes of determining whether they could be similarly incorporated into a POMzite network; given their close semblance in terms of local electron densities and interaction with potassium cations, we judge these POMs to be theoretically suitable as POMzite building blocks. Finally, we experimented with substituting different cations into the [P8W48O184]40- pore to observe the effect on pore dimensions and overall reactivity; we observed that the monocationic structures, particularly the Li8[P8W48O184]32- framework, yielded the least polarized structures. This correlates with the literature, validating our methodology for determining general POM characteristics and properties moving forward.

A computational approach for screening carbazole based organic dyes as potential photosensitizers for DSSCs application

The scientific community has shown significant interest in organic materials due to their potential applications in optoelectronics. In this study, we present the design and theoretical investigation of a new class of carbazole-based organic chromogens (R1-6). These chromogens consist of a heteroaromatic carbazole unit as an electron-rich donor, connected to a substituted phenyl ring carrying various electron acceptor groups. Specifically, we analyse the structural impact of electron withdrawing moieties such as carboxylic acid (–COOH), cyano (–CN), and nitro (–NO2) on the photophysical properties of these chromogens. To gain insights into the electron density localization and charge transfer characteristics, we perform DFT, TD-DFT, and MESP calculations. The computational studies indicate that these materials exhibit promising potential as sensitizers for applications in dye-sensitized solar cells (DSSCs).

Vliyanie primesey na adsorbtsiyu kisloroda na poverkhnosti Ti5Si3(0001)

The influence of simple and transition metal impurities, as well as interstitial impurities (B, C, and N), on the oxygen adsorption on the Ti5Si3 titanium silicide surface has been studied using the of projector augmented wave method within the electron density functional theory. It has been shown that titanium-substituting impurities belonging to the latter halves of the 3d–5d periods cause most significant changes in the adsorption energy. In addition, simple metals and interstitial impurities reduce the oxygen–surface interaction. By analyzing local electron densities of states, charge density difference distribution, charge transfer, and the overlap population of oxygen bonds to nearest-neighbor atoms, we have revealed special aspects of impurity influence on chemical bonding between the titanium silicide surface and oxygen. Factors responsible for an increase/decrease in the adsorption energy of oxygen on the doped surface are discussed. A correlation between the change in adsorption energy and the electronegativity of impurities has been found.

Positive and negative magnetoresistance and charge transport anisotropy in RB12 (R - Ho, Er, Tm) antiferromagnets with dynamic charge stripes

Magnetization M and magnetoresistance Δρρ(H,T) (MR) were studied and MR analyzed quantitatively in the complicated low temperature Néel phase of RB12 (R - Ho, Er and Tm) antiferromagnets with structural (originating from cooperative Jahn-Teller effect) and electronic (coming from dynamic charge stripes) instabilities. It is shown, that well below the Néel field (HN) the magnetoresistance is determined by the concurrence of carriers' scattering by spin-density waves (leading to a linear positive contribution Δρρ(H) ∼ H) from one side, and by ferromagnetic nanoscale clusters (leading to a linear negative MR) from the other. The development of different kind instabilities in the critical region just below HN results into the emergence of an additional negative quadratic MR term, attributed to the carriers’ scattering on 4f-5d local electron density fluctuations. The anisotropy of both two linear and one quadratic MR components is analyzed in detail and compared for RB12 compounds with different magnetic structure.

Nitrogen vacancies regulated the local electron density of iron sites in g-C3N4 to boost the generation of high-valent iron-oxo species in a peracetic acid-based Fenton-like process

Large-scale production of high-valent iron-oxo species (Fe(V)=O) for the efficient removal of organic pollutants has been a challenge due to the high activation energy barrier of the Fe(III)-oxidant complex. Here, we propose a novel heterogeneous system using Fe(III)-doped g-C3N4 with three-coordinate nitrogen vacancies (FNCN) as a catalyst for the activation of peracetic acid (PAA). Our investigations and calculations indicate that Fe(III) is the primary active site, and illustrate a nonradical mechanism of two-electron transfer mechanism to produce Fe(V)=O species. Meanwhile, the abundant nitrogen vacancies (Nvs) strengthen the electron distribution of the Fe(Ⅲ) sites to promote reactivity, and reduce the energy barrier to break the O−O bond of PAA in the Fe(Ⅲ)−PAA complex, to achieve the rapid accumulation of Fe(V)=O species. As a result, this heterogeneous system has excellent selectivity and anti-interference in removal of pollutants. Our work offers a unique viewpoint to strengthen a nonradical pathway in PAA activation.

Localized Electron Density Regulation Effect for Promoting Solid-Liquid Ion Adsorption to Enhance Areal Capacitance of Micro-Supercapacitors.

The development of flexible microelectronic systems requires the construction of high-energy-output planar micro-supercapacitors (MSCs). Herein, the localized electron density, by introducing graphene quantum dots (GQDs) on the surface of electrodes, is regulated. The enhanced local field intensity promotes ion electrostatic adsorption at the solid-liquid interface, which significantly improves the energy density of MSCs in the confined space. Local electronic structure has been investigated from the perspective of the topological analysis of the electron localization function (ELF) and the electron density. Impressively, the edges of the simulated structure exhibit a higher electron density distribution than the CC skeleton. This finding indicates that the introduced GQDs reinforce the intrinsic electrical double-layer capacitance (EDLC) and the oxygen-bearing functional groups at the edge, further increasing the pseudocapacitance performance. Moreover, the edge electron aggregation effect enables the all-carbon-based symmetric MSCs to exhibit ultra-high areal capacitance (21.78mFcm-2 ) and excellent cycle stability (86.74% retention after 25000 cycles). This novel surface local charge regulation strategy is also applied for intensifying ion electrostatic adsorption on Zn-ion hybrid MSCs (polyvalent metal ions) and ion-gel electrolyte MSCs (non-metallic ions). With excellent planar integration, this device demonstrates excellent flexibility and has potential applications in timing and environmental monitoring.

Strongly coupled Fe3O4 quantum dots-3D N-enriched carbon aerogel towards boosting peroxydisulfate activation by electron redistribution of multiple active sites

Simultaneous regulation of electronic environment of active sites and engineering architectures with efficient exposed active sites are crucial to realize efficient persulfate activation for pollutants degradation, which remains a great challenge. This study demonstrated an ingenious platform of 0D/3D nanofibrous N-enriched carbon hybrid with incorporated ultrafine metal oxide quantum dots (QDs, ≈ 3 nm) with abundant oxygen vacancies that enabled efficient PDS activation for pollutants degradation via integrating electron density regulation and morphology modulation. The favorable structure configuration and intimate coupling action between QDs and N-doped carbon matrix promoted PDS activation on the surface of Fe3O4 QDs@NC and simultaneously modified pollutant absorption property towards catalyst, synergistically resulting in excellent TC degradation efficiency. More importantly, electron-rich Fe sites derived from electron redistribution and highly-conductive N-doped carbon matrix synergistically directed PDS activation by non-radical pathway with generation of 1O2. This work provides a fresh insight into improving persulfate activation by engineering architectures and regulating local electronic density of multiple active sites.

Anchoring Ru nanoparticles on Ti3C2Tx for accelerated alkaline hydrogen evolution reaction: The effect of electronic metal-support interaction

Electrocatalytic hydrogen evolution reaction (HER) in the alkaline media is a promising strategy for energy conversion. Nevertheless, the sluggish kinetics of alkaline HER hinders its commercial application. Electronic metal-support interaction (EMSI) is an efficient approach to regulate the electronic state of active sites and enhance the electrocatalytic HER performance. Hence, we demonstrate an efficient alkaline HER catalyst comprising Ruthenium nanoparticles (Ru NPs) homogeneously anchored on Ti3C2Tx (Ru-Ti3C2Tx), resulting in the formation of EMSI effect between Ru and Ti3C2Tx. Spectroscopy characterizations and theoretical calculations demonstrate that EMSI facilitated the charge transfer from Ru NPs to Ti3C2Tx. The regulation of local electron density on Ru NPs directly influenced hydrogen adsorption Gibbs free energy (ΔGH*), which optimized the adsorption of hydrogen intermediates (H*) on Ru NPs and promoted the formation of H2 molecules. Therefore, the obtained 5 % Ru-Ti3C2Tx catalyst displayed an outstanding HER performance with the overpotential of 46 mV and 60 mV at 10 and 200 mA·cm−2 in 1.0 M KOH, respectively. Furthermore, the cathode presented excellent stability during 20 h long-term measurements. This study presents some recommendations and guidance for constructing Ru-based catalysts to accelerate HER kinetics in alkaline media.

A Theoretical Investigation of Chemical Bonding of a Heterometallic Trinuclear Cluster Containing Iridium and Ruthenium: [(Cp*Ir) (CpRu)2 (μ3-H) (μ-H)3] by QTAIM Approach

Numerous integral and local electron density’s topological parameters of significant metal-metal and metal-ligand bonding interactions in a trinuclear tetrahydrido cluster [(Cp* Ir) (Cp Ru)2 (μ3-H) (μ-H)3]1 (Cp = η5 -C5Me5), (Cp* = η5 -C5Me4Et) were calculated and interpreted by using the quantum theory of atoms in molecules (QTAIM). The properties of bond critical points such as the delocalization indices δ (A, B), the electron density ρ(r), the local kinetic energy density G(r), the Laplacian of the electron density ∇2ρ(r), the local energy density H(r), the local potential energy density V(r) and ellipticity ε(r) are compared with data from earlier organometallic system studies. A comparison of the topological processes of different atom-atom interactions has become possible thanks to these results. In the core of the heterometallic tetrahydrido cluster, the Ru2IrH4 part, the calculations showed that there are no bond critical points (BCPs) or identical bond paths (BPs) between Ru-Ru and Ru-Ir. The distribution of electron densities is determined by the position of bridging hydride atoms coordinated to Ru-Ru and Ru-Ir, which significantly affects the bonds between these transition metal atoms. On the other hand, the results confirm that the cluster under study contains a 7c–11e bonding interaction delocalized over M3H4, as shown by the non-negligible delocalization index calculations. The small values for ρ(b) above zero, together with the small values, again above zero, for Laplacian ∇2ρ(b) and the small positive values for total energy density H(b), are shown by the Ru-H and Ir-H bonds in this cluster is typical for open-shell interactions. Also, the topological data for the bond interactions between Ir and Ru metal atoms with the C atoms of the cyclopentadienyl Cp ring ligands are similar. They show properties very identical to open-shell interactions in the QTAIM classification.

Activating coordinative conjugated polymer via interfacial electron transfer for efficient CO2 electroreduction

With tunable local electronic environment, high mass density of MN4 sites, and ease of preparation, metal–organic conjugated coordinative polymer (CCP) with inherent electronic conductivity provides a promising alternative to the well-known M−N−C electrocatalysts. Herein, the coordination reaction between Cu2+ and 1,2,4,5-tetraaminobenzene (TAB) was conducted on the surface of metallic Cu nanowires, forming a thin layer of CuN4-based CCP (Cu-TAB) on the Cu nanowire. More importantly, interfacial transfer of electrons from Cu core to the CuN4-based CCP nanoshell was observed within the resulting CuTAB@Cu, which was found to enrich the local electronic density of the CuN4 sites. As such, the CuTAB@Cu demonstrates much improved affinity to the *COOH intermediate formed from the rate determining step; the energy barrier for C–C coupling, which is critical to convert CO2 into C2 products, is also decreased. Accordingly, it delivers a current density of −9.1 mA cm−2 at a potential as high as −0.558 V (vs. RHE) in H-type cell and a Faraday efficiency of 46.4% for ethanol. This work emphasizes the profound role of interfacial interaction in tuning the local electronic structure and activating the CuN4-based CCPs for efficient electroreduction of CO2.

Tunable and Efficient Photoluminescence of Lanthanide-Doped Cs2NaScCl6 Double Perovskite Single Crystals toward Multifunctional Light-Emitting Diode Applications.

Lead-free halide double perovskite, as one of the promising candidates for lead halide perovskite materials, shows great potential in light-emitting diodes (LEDs), benefiting from its environmental friendliness and high chemical stability. However, the poor regulation of the emission spectra severely limits its application range. Herein, various lanthanide ions were successfully doped in Cs2NaScCl6 double perovskite single crystals (DPSCs) to yield effective and stable emissions spanning from visible to near-infrared (NIR) regions. Notably, efficient energy transfer from the host to the dopants enables tunable emissions with good chromaticity, which is rarely reported in the field of lead-free double perovskite. Moreover, density functional theory calculations reveal that the high local electron density around the [LnCl6]3- octahedron in DPSCs plays a key role in the improvement of photoluminescence quantum yields (PLQYs). The optimal PLQYs are up to 84%, which increases around 3 times over that of the undoped sample. Finally, multicolor and NIR LEDs based on Ln3+-doped Cs2NaScCl6 DPSCs were fabricated and had different application functions. Specifically, the single-composite white LED shows adjustable coordinates and correlated color temperatures, while the NIR LED shows good night vision imaging. This work provides new inspiration for the application of efficient multifunctional LEDs based on lead-free double perovskite materials.

Tuning counterion chemistry to reduce carrier localization in doped semiconducting carbon nanotube networks

Understanding and controlling the impact that electrostatic interactions have on the transport of injected charge carriers is important for the utilization of pi-conjugated semiconductors in opto-electronic applications. Here, we explore the impact of dopant chemical and electronic structure on the doping efficacy and charge carrier transport in semiconducting single-walled carbon nanotube (s-SWCNT) networks using molecular charge-transfer dopants based on functionalized icosahedral dodecaborane (DDB) clusters. Calculations indicate that localization of electron density on the DDB core reduces the coulombic interactions that contribute to hole localization in the s-SWCNTs, thereby improving charge carrier transport. The enhanced delocalization produces an increase in the electrical conductivity and thermopower at lower charge carrier densities, yielding enhanced thermoelectric transport and a thermoelectric power factor that surpasses the previous best in class for enriched s-SWCNT thin-film networks. This strategy can be applied broadly across pi-conjugated semiconductors to tune and enhance performance in a variety of energy harvesting devices.

Photocatalytic Cascade Reaction Driven by Directed Charge Transfer over VS -Zn0.5 Cd0.5 S/GO for Controllable Benzyl Oxidation.

Photocatalysis is an important technique for synthetic transformations. However, little attention has been paid to light-driven synergistic redox reactions for directed synthesis. Herein, the authors report tunable oxidation of benzyl to phenylcarbinol with the modest yield (47%) in 5h via singlet oxygen (1 O2 ) and proton-coupled electron transfer (PCET) over the photocatalyst Zn0.5 Cd0.5 S (ZCS)/graphene oxide (GO) under exceptionally mild conditions. Theoretical calculations indicate that the presence of S vacancies on the surface of ZCS/GO photocatalyst is crucial for the adsorption and activation of O2 , successively generating the superoxide radical (• O2 - ) and 1 O2 , attributing to the regulation of local electron density on the surface of ZCS/GO and photogenerated holes (h+ ). Meanwhile, accelerated transfer of photogenerated electrons (e- ) to GO caused by the π-π stacking effect is conducive to the subsequent aldehyde hydrogenation to benzyl alcohol rather than non-selective oxidation of aldehyde to carboxylic acid. Anisotropic charge transport driven by the built-in electric field can further promote the separation of e- and h+ for multistep reactions. Promisingly, one-pot photocatalytic conversion of p-xylene to 4-methylbenzyl alcohol is beneficial for reducing the harmful effects of aromatics on human health. Furthermore, this study provides novel insights into the design of photocatalysts for cascade reactions.