Local Charge Research Articles

Secure and energy-efficient inter- and intra-cluster optimization scheme for smart cities using UAV-assisted wireless sensor networks.

In recent years, lightweight sensors have become essential for advancing technologies, particularly in wireless sensor networks (WSNs). A persistent challenge in WSNs is maintaining continuous operation while achieving balanced energy consumption across sensor nodes. Wireless mobile energy transmitters (WMETs) provide a promising solution by wirelessly recharging sensor nodes. However, most existing approaches fail to optimize WMET charging locations, resulting in energy imbalance and reduced network coverage. Furthermore, conventional clustering systems often overlook both inter- and intra-cluster energy balancing, degrading overall network performance. Security issues, such as insufficient data encryption, further exacerbate these challenges, leaving WSNs vulnerable to attacks. To address these gaps, we propose the secure and energy-efficient inter- and intra-cluster optimization scheme (SEI2), a novel WMET-based framework that ensures balanced energy utilization among cluster heads (CHs) and member nodes (MNs) while securing data transmission. The SEI2 system incorporates UAVs to dynamically recharge sensor nodes, determining optimal charging locations within clusters to maximize energy efficiency. Additionally, robust data encryption mechanisms are applied at both the CH and base station (BS) levels to safeguard transmitted data. Key parameters considered include node energy levels, data transmission rates, optimal charging locations, and encryption overhead. Experimental evaluations demonstrate that SEI2 improves network lifetime by 35%, reduces compromised data packets by 19%, enhances coverage time by 15%, and significantly minimizes energy variance by 62% for CHs and 88% for MNs. These results highlight SEI2's potential as a comprehensive solution for extending WSN lifetimes, enhancing energy efficiency, and strengthening data security, making it particularly suitable for smart city applications.

Tight Binding Simulation of the MgO and Mg(OH)2 Hydration and Carbonation Processes.

Magnesium, the lightest engineering metal, has MgO and Mg(OH)2 as its common corrosion products, which can also be used for CO2 storage due to their chemical reactivity. In this study, we developed a DFTB model with monopole, dipole, and quadrupole electrostatics for magnesium compounds containing oxygen, hydrogen, and carbon and applied it in both static and molecular dynamics (DFTB-MD) calculations of the MgO and Mg(OH)2 hydration and carbonation processes. With our new model, the Electron Localization Function (ELF) and Charge Density Difference (CDD) were computed as part of the electronic structure analysis, providing insights into the electronic mechanism of MgO and Mg(OH)2 hydration and carbonation processes. The geometry for the brucite-water bulk system was analyzed, including the reconstruction of near-surface water molecules which may influence the dissolution, hydration, and carbonation processes. By comparing experimental, DFT, classical MD results and the results from other parameter set, the accuracy of the model was assessed. A strong covalent bond between CO2 and the (001) surface of MgO leads to the formation of a CO3 group, while no such CO3 group forms on the (101̅1) surface of Mg(OH)2. Defect sites, however, are more favorable for the formation of the CO3 group. In contrast, covalent bonds are not found for either surface when water interacted with them. This work provides new insights into the behavior of magnesium compounds interacting with water and carbon dioxide using our model, and it introduces a tool for effectively analyzing chemical electronic structures and bonding mechanisms.

Role of Superlattice Phonons in Charge Localization Across Quantum Dot Arrays.

Understanding charge transport in semiconductor quantum dot (QD) assemblies is important for developing the next generation of solar cells and light-harvesting devices based on QD technology. One of the key factors that governs the transport in such systems is related to the hybridization between the QDs. Recent experiments have successfully synthesized QD molecules, arrays, and assemblies by directly fusing the QDs, with enhanced hybridization leading to high carrier mobilities and coherent band-like electronic transport. In this work, we theoretically investigate the electron transfer dynamics across a finite CdSe-CdS core-shell QD array, considering up to seven interconnected QDs in one dimension. We find that, even in the absence of structural and size disorder, electron transfer can become localized by the emergent low-frequency superlattice vibrational modes when the connecting neck between QDs is narrow. On the other hand, we also identify a regime where the same vibrational modes facilitate coherent electron transport when the connecting necks are wide. Overall, we elucidate the crucial effects of electronic and superlattice symmetries and their couplings when designing high-mobility devices based on QD superlattices.

Cationic Polyhedral Chalcogenaboranes: Activation without breaking Wade's Rules.

Wade's rules are a well-established tool for the description of the geometry of inorganic clusters. Among others, they state that a decrease or increase in charge is always accompanied by a change in the number of skeletal electron pairs (SEPs). This work reports the synthesis of the first cationic chalcogenaboranes closo-[12-X-2-IPr-1-EB11H10]BF4 (X = H, I; E = S, Se 3a/b, 4a/b) featuring the same SEP count as their neutral precursors, EB11H11, but bearing a positive charge. This ionisation significantly enhances the activity towards the electrophiles. It unlocks reactivity with very weak bases and offers the control of the regioselectivity towards hard/soft bases by the modulation of LUMO. The localisation of the positive charge within the borane cluster has been confirmed experimentally, spectroscopically and theoretically.

Cationic Polyhedral Chalcogenaboranes: Activation without breaking Wade’s Rules

Wade’s rules are a well‐established tool for the description of the geometry of inorganic clusters. Among others, they state that a decrease or increase in charge is always accompanied by a change in the number of skeletal electron pairs (SEPs). This work reports the synthesis of the first cationic chalcogenaboranes closo‐[12‐X‐2‐IPr‐1‐EB11H10]BF4 (X = H, I; E = S, Se 3a/b, 4a/b) featuring the same SEP count as their neutral precursors, EB11H11, but bearing a positive charge. This ionisation significantly enhances the activity towards the electrophiles. It unlocks reactivity with very weak bases and offers the control of the regioselectivity towards hard/soft bases by the modulation of LUMO. The localisation of the positive charge within the borane cluster has been confirmed experimentally, spectroscopically and theoretically.

Fluorine-Free Ion-Selective Membrane with Enhanced Mg2+ Transport for Mg-Organic Batteries.

Magnesium batteries offer a safer alternative for next-generation battery technology due to their insusceptibility to dendrite deposition. Selective membranes tailored for magnesium-ion conduction will unlock further technological advancement. Herein, we demonstrate fluorine-free magnesiated sulfonated poly(ether ether ketone) (Mg-SPEEK) selective membranes capable of facilitating magnesium-ion conduction while effectively rejecting soluble organic species. These membranes demonstrate a reversible Mg plating and stripping Coulombic efficiency (CE) of 85.4% and an ionic conductivity of 3.3 × 10-4 S cm-1 at room temperature, surpassing those for a Mg-Nafion selective membrane. Theoretical density functional theory (DFT) calculations reveal that SPEEK possesses more localized charge centers along its backbone compared with Nafion, potentially facilitating enhanced ion conduction. Full cells assembled with Mg-SPEEK coupled with the organic cathode pyrene-4,5,9,10-tetraone (PTO) and Mg metal demonstrated significantly improved capacity retention as compared to those assembled with conventional nonselective separators.

Light‐induced Enhancement of Energetic Charge Carrier Extraction and Modulation of Local Charge Density to Impact Selectivity in Plasmonic Nanometals

AbstractLocalized surface plasmon resonance (LSPR) metals exhibit remarkable light‐absorbing property and unique catalytic activity, attracting significant attention in photocatalysts recently. However, the practical application of plasmonic nanometal is hindered by challenge of energetic electrons extraction and low selectivity. The energetic carriers generated in nanometal under illumination have extremely short lifetimes, leading to rapid energy loss. In this work, silver nanometals modified with five distinct sulfhydryl ligands (re‐Ag‐S‐R) were synthesized via photoreduction of superlattice precursors. Modified surface efficiently extracts and preserves excited state electrons of plasmonic nanometals. By modulation the local charge density at catalytic active sites through substituents with varying electron‐donating and electron‐withdrawing properties, the selectivity of the photocatalytic carbon dioxide reduction reaction and hydrogen evolution reaction was influenced. The results demonstrated opposite selectivity between methoxy‐modified re‐Ag‐S‐OCH3 (CO selectivity of 96.73 %) and amino‐modified re‐Ag‐S‐NH2 (H2 selectivity of 96.66 %) despite their similar structures. The changes in excited states and surface contact potentials induced by LSPR were monitored using femtosecond transient absorption (fs‐TA) spectroscopy and Kelvin probe force microscopy (KPFM). Meanwhile, the detailed discussion of the LSPR mechanism in plasmonic nanometals will serve as valuable references and foundational elements for future research in this area.

Solvent Mediated Interfacial Microenvironment Design for High-Performance Electrochemical CO2 Reduction to C2+ Products.

Electrochemical CO2 reduction (CO2RR) in membrane electrode assembly (MEA) represents a viable strategy for converting CO2 into value-added multi-carbon (C2+) compounds. Therefore, the microstructure of the catalyst layer (CL) affects local gas transport, charge conduction, and proton supply at three-phase interfaces, which is significantly determined by the solvent environment. However, the microenvironment of the CLs and the mechanism of the solvent effect on C2+ selectivity remains elusive. Herein, a tailored interfacial structure is designed by introducing a solvent-mediated catalyst-ionomer-solvent microenvironment. The acetone surface promotion strategy is beneficial for the unfolded ionomers to uniformly coat the catalysts, which contributes to enhancing interfacial hydrophobicity and inhibiting hydrogen evolution. Furthermore, molecular dynamics (MD) simulation and in situ ATR-SEIRAS are employed to elucidate the appropriate interfacial network with a balanced distribution of CO2 and H2O. The uniform and continuous network in acetone is advantageous for CO2-to-C2+. The optimized structure favors the production of C2+ products in Cu-based MEA, exhibiting a high C2+ faradaic efficiency (FE) of 80.27% at 400mA cm-2.

Probing the Active Nitrogen Species in Nitrogen-Doped Carbon Nanozymes for Enhanced Oxidase-Like Activity.

Nitrogen doping emerges as a potent approach to enhance the oxidase-like activity of carbon nanozymes. However, the unclear knowledge of the active nitrogen species within nitrogen-doped carbon nanozymes hinders the advancement of high-performance carbon nanozymes. Herein, a group of nitrogen-doped carbon (N/C) nanozymes with controllable nitrogen dopants are successfully synthesized via a dicyandiamide-assisted pyrolysis method. The intrinsic connection between different nitrogen configurations (pyridinic N, pyrrolic N, and graphitic N) in N/C nanozymes and the oxidase-like performance are experimentally investigated. The results confirm pyridinic N is the active nitrogen species in N/C nanozymes for enhanced oxidase-like activity. Theoretical calculations further reveal the potential regulatory mechanism is pyridinic N can increase the local charge density of neighboring carbon atoms and accelerate the adsorption and activation of molecular oxygen. Notably, the optimized N/C nanozyme with the highest pyridinic N ratio presents impressive oxidase-like performance, surpassing most of the previously reported oxidase-like materials. Moreover, the optimized N/C nanozyme exhibits excellent antibacterial properties and can be easily incorporated into common medical and hygiene products to give them spontaneous antibacterial properties. The work will facilitate the rational design of carbon nanozymes with high-performance oxidase-like activity for applications in the antibacterial field.

MEDOC: A Fast, Scalable, and Mathematically Exact Algorithm for the Site-Specific Prediction of the Protonation Degree in Large Disordered Proteins.

Intrinsically disordered regions are found in most eukaryotic proteins and are enriched with positively and negatively charged residues. While it is often convenient to assume that these residues follow their model-compound pKa values, recent work has shown that local charge effects (charge regulation) can upshift or downshift side chain pKa values with major consequences for molecular function. Despite this, charge regulation is rarely considered when investigating disordered regions. The number of potential charge microstates that can be populated through acid/base regulation of a given number of ionizable residues in a sequence, N, scales as ∼2N. This exponential scaling makes the assessment of the full charge landscape of most proteins computationally intractable. To address this problem, we developed "multisite extent of deprotonation originating from context" (MEDOC) to determine the degree of protonation of a protein based on the local sequence context of each ionizable residue. We show that we can drastically reduce the number of parameters necessary to determine the full, analytical Boltzmann partition function of the charge landscape at both global and site-specific levels. Our algorithm applies the structure of the q-canonical ensemble, combined with novel strategies to rapidly obtain the minimal set of parameters, thereby circumventing the combinatorial explosion of the number of charge microstates even for proteins containing a large number of ionizable amino acids. We apply MEDOC to several sequences, including a global analysis of the distribution of pKa values across the entire DisProt database. Our results show differences in the distribution of predicted pKa values for different amino acids and good agreement with NMR-measured pKa values in proteins.

Light-induced Enhancement of Energetic Charge Carrier Extraction and Modulation of Local Charge Density to Impact Selectivity in Plasmonic Nanometals.

Localized surface plasmon resonance (LSPR) metals exhibit remarkable light-absorbing property and unique catalytic activity, attracting significant attention in photocatalysts recently. However, the practical application of plasmonic nanometal is hindered by challenge of energetic electrons extraction and low selectivity. The energetic carriers generated in nanometal under illumination have extremely short lifetimes, leading to rapid energy loss. In this work, silver nanometals modified with five distinct sulfhydryl ligands (re-Ag-S-R) were synthesized via photoreduction of superlattice precursors. Modified surface efficiently extracts and preserves excited state electrons of plasmonic nanometals. By modulation the local charge density at catalytic active sites through substituents with varying electron-donating and electron-withdrawing properties, the selectivity of the photocatalytic carbon dioxide reduction reaction and hydrogen evolution reaction was influenced. The results demonstrated opposite selectivity between methoxy-modified re-Ag-S-OCH3 (CO selectivity of 96.73%) and amino-modified re-Ag-S-NH2 (H2 selectivity of 96.66%) despite their similar structures. The changes in excited states and surface contact potentials induced by LSPR were monitored using femtosecond transient absorption (fs-TA) spectroscopy and Kelvin probe force microscopy (KPFM). Meanwhile, the detailed discussion of the LSPR mechanism in plasmonic nanometals will serve as valuable references and foundational elements for future research in this area.

Individual Assembly of Radical Molecules on Superconductors: Demonstrating Quantum Spin Behavior and Bistable Charge Rearrangement.

High-precision molecular manipulation techniques are used to control the distance between radical molecules on superconductors. Our results show that the molecules can host single electrons with a spin 1/2. By changing the distance between tip and sample, a quantum phase transition from the singlet to doublet ground state can be induced. Due to local screening and charge redistribution, we observe either charged or neutral molecules, which couple in a sophisticated way, showing quantum spin behavior that deviates from the classical spins. Dimers at different separations show multiple Yu-Shiba-Rusinov peaks in tunneling spectroscopy of varying intensity, which are in line with the superconducting two-impurity Anderson model, where singlet (S = 0) and doublet (S = 1/2) ground states are found. The assembly of chains of 3, 4, and 5 molecules shows alternating charge patterns, where the edge molecules always host a charge/spin. The tetramer is observed in two configurations, where the neutral site is moved by one position. We show that these two configurations can be switched by the action of the probing tip in a nondestructive manner, demonstrating that the tetramer is an information unit, based on single-electron charge reorganization.

Mechanistic Understanding of the pH-Dependent Oxygen Reduction Reaction on the Fe-N-C Surface: Linking Surface Charge to Adsorbed Oxygen-Containing Species.

The Fe-N-C catalyst, featuring a single-atom Fe-N4 configuration, is regarded as one of the most promising catalytic materials for the oxygen reduction reaction (ORR). However, the significant activity difference under acidic and alkaline conditions of Fe-N-C remains a long-standing puzzle. In this work, using extensive ab initio molecular dynamics (AIMD) simulations, we revealed that pH conditions influence ORR activity by tuning the surface charge density of the Fe-N-C surface, rather than through the direct involvement of H3O+ or OH- ions. The acidic environment, combined with an elevated electrode potential, can result in a highly charged Fe-N-C surface. On this surface, the adsorbed *OH will spontaneously convert to *O and remain stable, accompanied by a change in the valence state of the Fe atom. This phenomenon makes the ORR step from *O to *OH the rate-determining step, thereby significantly reducing the corresponding ORR activity. Under fixed pH conditions and electrode potentials, the surface charge density of Fe-N-C can be tuned by changing the coordination environment of the Fe atom. Further calculations reveal that doping a Co4 cluster near the Fe active center or creating an edge-type Fe-N-C structure can effectively reduce the local charge density around the Fe atom. This reduction hinders the transition of *OH to *O, thereby enhancing ORR activity at a high electrode potential in acidic environments. Our work revealed the underlying explanation of the pH-dependent ORR activity for the Fe-N-C catalyst and sheds light on the future design and synthesis of high-performance Fe-N-C catalysts.

Membrane Surface Charge, Phospholipids, and Protein Localization.

Cell membranes contain multiple charged lipids that bind proteins dynamically and their spatial organization on the inner/outer membrane leaflet, or in spatially localized areas has considerable biological importance. Myristoylated alanine-rich C kinase substrate (MARCKS) proteins and their roles as electrostatic switches are one example covered. Cell surface charge needs to be monitored and regulated continually and the roles of lipid flippases and scramblases and their electrical regulation also are considered.

In situ self-cleaning removal of emerging organic contaminants with covalent organic framework armed with arylbiguanide.

An in situ self-cleaning covalent organic framework featuring arylbiguanide arms (Aryl-BIG-COF) was first developed to remove emerging organic pollutants such as propranolol (PRO) from water. The main breakthroughs addressed the scarcity of functional active sites, the impracticality of ex situ regeneration, and the rapid recombination of electronhole pairs in the application of COFs. Owing to the directional capture ability and electronic structure regulation of the arylbiguanide arms, the adsorption capacity and photocatalytic degradation rate of the newly synthesized COF increased by nearly four and seven times, respectively. Its self-cleaning ability, driven by the photocatalytic regeneration of active sites, enabled in situ removal of PRO and sustained over 90 % removal efficiency after six cycles. Moreover, it demonstrated broad applicability for removing PRO and other emerging pollutants, such as bisphenol A (BPA), tetracycline (TC), and norfloxacin (NOR), across various water matrices with less residual toxicity. The coexisting organic matter and ions in natural water promoted the removal of PRO. The enhancement mechanism involved arylbiguanide arms narrowing the band gap and inducing local charge polarization, thereby increasing the separation efficiency of electronhole pairs. This work provides significant insights into the structural design and practical applications of COFs for purifying water.

Combination of atom transfer radical polymerization and alkyne-azide click-chemistry for the synthesis of phosphonic acid cation exchange materials.

Phosphonic acid cation exchange materials (PCX) are synthesized by atom transfer radical polymerization (ATRP) followed by alkyne-azide click-chemistry. ATRP is used to synthesize polymeric chains of diethyl 4-vinylbenzylphosphonate with different chain lengths, which are covalently bonded to the surface of monodisperse polystyrene-divinylbenzene (PS/DVB) particles by click-chemistry. The functionalized particles are characterized by FIB-SEM, IR and Schoeniger combustion followed by chromatographic experiments. The effect of chain length on chromatographic behavior is investigated by comparing four PCX columns with different chain lengths. Polar ionic pesticides and non-polar triazines are used as model analytes for chromatographic characterization. The chain length showed an influence on the retention of doubly charged analytes, which can be explained by the increased local charge density with longer chains. The resolution of the constitutional isomers prometryn and terbutryn increased with the chain length, leading to an isocratic separation of seven triazines in 35 min. They also showed secondary interactions with the polymeric support material that are not influenced by capacity or chain length.

Optimal interplay of charge localization, lattice dynamics and slip systems drives structural softening in dilute W alloys with Re additives

Optimal interplay of charge localization, lattice dynamics and slip systems drives structural softening in dilute W alloys with Re additives

Characterization of an Unexpected μ3 Adsorption of Molecular Oxygen on Ag(100) with Low-Temperature STM.

Precise description of the interaction between molecular oxygen and metal surfaces is one of the most challenging topics in quantum chemistry. In this work, we use low-temperature scanning tunneling microscopy (STM) to identify and characterize an adsorption state of molecular oxygen that coordinates to three Ag atoms (μ3) on Ag(100). Surprisingly, μ3-O2 cannot be identified as a stable configuration with generalized gradient approximation (GGA)-level density functional theory (DFT) calculations. Through inelastic electron tunneling spectroscopy (IETS), we identify three vibrational modes of individual μ3-O2 and assign them to out-of-plane hindered rotation (HR) at 38.0 meV, in-plane HR at 32.4 meV, and in-plane hindered translation (HT) at 22.0 meV. We determine the barrier for rotational isomerization of μ3-O2 to be 69.3 meV from tunneling electrons-induced rotations. The inability of theory to predict the experiment stems most likely from self-interaction errors inherent to GGA-DFT, which leads to an inaccurate description of localized charges. We speculate that the μ3-O2 configuration represents a formal molecular oxygen anion and assign the ±11 meV excitation in the IETS to a transition between spin-orbit states of the surface-bound anion.

Nitrogen-carbon nanotubes as a basis for a new type of semiconductor materials for electronics devices

The use of semiconductor nanomaterials is currently considered to be one of the most promising device optimization methods since those materials allow controlling the electronic properties and possess high mechanical and thermal strength, providing for long device service life without the necessity of replacement or seeking new solutions. The parameters of the electronic and energy structure of new semiconductor nanomaterials based on carbon nanotubes containing substitution atoms have been studied. The test carbon nanotubes contained specific substitution atom concentrations (15, 25 and 50%). A relationship has been drawn between the band gap, conductivity and optical properties of the materials. Data on the band gap and conductivity as functions of substituting nitrogen atom concentration and tube diameter have been reported. The experimental band gap data suggest that the nanotubes in question are narrow-gap semiconductors. One can also conclude that a new semiconductor material has been synthesized on the basis of carbon nanotubes with substitution nitrogen atoms since the test tubes exhibit a redistribution of electron density towards the nitrogen atoms and positive charge localization in the vicinity of the carbon atoms. The results are of utmost importance for the design and fabrication of components and units for nanoelectronics and microsystems: our theoretical study has confirmed the possibility to control the refraction index and conductivity of media by implementing a carbon-for-nitrogen substitution reaction to various concentrations. Thus, a new electronics material has been studied, i.e., carbon nanotubes modified by substitution of nitrogen atoms.

Inelastic Scattering in Weak Localization for Single‐Layer Graphene

Chemical‐vapor‐deposited graphene is used extensively to fabricate devices. However, the charge‐neutral point (CNP) of this material appears at a relatively high back‐gate voltage (VG) because of molecular adsorption and impurities on the graphene surface. In this study, a Ti‐cleaning process is used to remove contaminants from the transferred graphene. Two contributions to the magnetoresistance are investigated: weak localization (WL) and inhomogeneous charge transport near the Dirac point. One of the most important parameters for clarifying the quantum transport properties is the inelastic scattering time. Fitting of the experimental results with a theoretical WL expression is performed to investigate the temperature and VG dependence of the inelastic scattering and intervalley scattering rates. Small momentum transfer due to Nyquist scattering is dominant in the CNP region, while large momentum transfer processes of direct electron–electron interaction dominate the electron and hole‐transport regions.