Nonuniform Charge Distribution Research Articles

Regulation of d-band center of TiO2 through fluoride doping for enhancing photocatalytic H2O2 production activity

Titanium dioxide (TiO2) has received extensive attention for photocatalytic hydrogen peroxide (H2O2) production, with the d-band center related to the adsorption performance, which affects the photocatalytic reaction process. Herein, an ingenious strategy to lower the antibonding-orbital occupancy in the Ti 3d orbital by fluoride ion (F−) doping is proposed, with density functional theory calculations predicting that F-doping into TiO2 induces a non-uniform charge distribution and enables an upshift of the d-band center in F/TiO2. This manipulation provides accessible active centers with favorable d-band energy levels, which can improve the charge-transfer behavior, strengthen the interaction between the adsorbed oxygen and the photocatalyst, and reduce the adsorption energy of oxygen, eventually promoting the photocatalytic H2O2 production rate. The experimental results further confirm that a lower antibonding-orbital occupancy can intensify the adsorption of atomic oxygen at the Ti sites. Electron paramagnetic resonance experiment reveals that the presence of F− ions in the lattice induces the formation of Ti3+ centers that localize the extra electron needed for charge compensation. Femtosecond transient absorption (fs-TA) spectroscopy suggests that photogenerated electrons are transferred from the conduction band of F/TiO2 to the Ti3+ surface states and surface F− ions, expediting the separation of electrons and holes. Consequently, with F− doping in TiO2, the photocatalytic H2O2 production yields improved from 277 to 467 μmol·g−1·h−1, with ethanol as a sacrificial reagent. This study provides a new strategy for regulating the d-band center to optimize the adsorption strength between the photocatalyst and oxygen atoms and achieve enhanced photocatalytic H2O2 production performance.

Influence of interface on the domain polarization orientation in ferroelectric Hf0.5Zr0·5O2 thin films

Ferroelectric HfO2-based materials have attracted extensive attention in the research of next-generation nonvolatile memories and logic devices due to their superior scaling properties and compatibility with the CMOS process. However, forming the ferroelectric metastable phase in the thin films of a few nanometers requires clamping of the top and bottom electrodes. As a result, the interface can significantly impact domain structure and polarization, leading to imprinting effects and non-uniform space charge distribution. Here, we have demonstrated how the interface affects the ferroelectric polarization in Hf0.5Zr0·5O2 (HZO) thin films produced by ALD and the physical mechanisms behind it. We found that by regulating the quantity of oxygen vacancy content at the top and bottom interfaces of TiN/HZO/TiN ferroelectric capacitors, it is possible to achieve inversion of polarization orientation. By using a spherical aberration-corrected transmission electron microscope and first-principles calculation, we identified that the internal electric field generated by the accumulation of oxygen vacancies at an interface and the asymmetrical electrostatic energy of the interfacial T-phase layer jointly play a role in the ferroelectric polarization orientation. Our results will significantly help the interface engineering of HfO2-based ferroelectric thin films and devices.

Protein Deceleration and Sequencing Using Si3N4-CNT Hybrid Nanopores.

Protein sequencing is crucial for understanding the complex mechanisms driving biological functions and is of utmost importance in molecular diagnostics and medication development. Nanopores have become an effective tool for single molecule sensing, however, the weak charge and non-uniform charge distribution of protein make capturing and sensing very challenging, which poses a significant obstacle to the development of nanopore-based protein sequencing. In this study, to facilitate capturing of the unfolded protein, highly charged peptide was employed in our simulations, we found that the velocity of unfolded peptide translocating through a hybrid nanopore composed of silicon nitride membrane and carbon nanotube is much slower compared to bare silicon nitride nanopore, it is due to the significant interaction between amino acids and the surface of carbon nanotube. Moreover, by introducing variations in the charge states at the boundaries of carbon nanotube nanopores, the competition and combination of the electrophoretic and electroosmotic flows through the nanopores could be controlled, we then successfully regulated the translocation velocity of unfolded proteins through the hybrid nanopores. The proposed hybrid nanopore effectively retards the translocation velocity of protein through it, facilitates the acquisition of ample information for accurate amino acid identification.

Molecular simulation on CO2 adsorption heterogeneity in montmorillonite nanopores with different surface charges in presence of water

Understanding the CO2 adsorption mechanism in clay nanopores is crucial for enhancing carbon capture and storage in shale reservoirs. Nonetheless, the impact of surface charge on the heterogeneity of CO2 adsorption and its subsequent effects on adsorption capacity within clay nanopores are not fully understood. By employing molecular dynamics simulations and grand canonical Monte Carlo techniques, we examine the effects of surface charge, pressure, and nanopore water on the adsorption capacity, density distribution, and free energy profile of CO2 in montmorillonite (Mt) nanopore. Utilizing density entropy as an innovative metric for adsorption heterogeneity, we shed light on how isomorphous substitution, which results in a non-uniform distribution of negative charges within Mt layers, triggers heterogeneous distribution of CO2 and water in Mt nanopore. Our findings highlight a unique correlation between the density entropy of CO2 and its adsorption capacity. The maximum adsorption capacity is strongly associated with surface charge heterogeneity in dry Mt nanopores and is governed by the heterogeneity of water distribution in wet Mt nanopores. We find that a greater heterogeneity in the CO2 distribution within the Mt nanopore system aligns with an increased maximum adsorption energy for CO2, consequently resulting in an enhanced overall adsorption capacity.

Utilizing the Complexity of Transition Metal Phosphide Surfaces to Tune Nitrate Reduction Selectivity

Electrocatalytic nitrate reduction (NO3RR) is one exciting method of upcycling nitrate in wastewater by conversion to ammonia, an essential component in fertilizers and a potential liquid fuel. Nitrate reduction to NH3 is impeded by the formation of other products such as NO2 - or H2 via the hydrogen evolution reaction (HER). Transition metal phosphide (TMP) nanocrystals have a non-uniform surface charge distribution due to their binary compositions, which leads to a variety of active sites with different binding affinities. We hypothesize that the diversity of active sites on Ni2P can be leveraged to perform complex electrocatalytic reactions such as the NO3RR. Specifically, a diversity of surface sites can create local active site motifs that promote the adsorption of different intermediates, e.g., *NO3 - and *H, that can readily react for the NO3RR. We prepare 5 nm Ni2P and Ni nanocrystals using colloidal syntheses and deposit them onto a carbon support to compare the simpler catalytic surface of Ni with the more complex Ni2P surface. We compare their NO3RR activities with cyclic voltammetry in neutral, buffered aqueous conditions. We also investigate the selectivity between the NO3RR and HER with bulk electrolysis coupled with a colorimetric assay, where Ni2P on carbon shows higher selectivity toward NH3 over NO2 - and H2. With these experiments, we evaluate our hypothesis that the surface complexity of Ni2P will lead to enhanced NO3RR selectivity relative to Ni. This work sets the stage for developing selective electrocatalysts by utilizing ensembles of active sites to drive electrocatalytic selectivity.

An improved magnetic dipole model for MFL testing based on non-uniform magnetic charge distribution

ABSTRACT Magnetic flux leakage (MFL) signal prediction is important in ferromagnetic defect evaluation and reconstruction. At present, the magnetic dipole model (MDM) is the most widely applied method because of its high efficiency. However, it has low accuracy when applied to analysing complex defects (complex in profile and magnetic permeability) due to the original setting of uniform magnetic charge distribution. To solve the issue, this paper proposes an improved MDM method for MFL inspection of ferromagnetic materials by calculating the non-uniform magnetic charge distribution. It partly applies the finite volume method (FVM) to derive the magnetic charge distribution on the defect surface, which makes it able to take into account the defect’s profile and magnetic permeability distribution. The new magnetic charge distribution can increase the MDM’s accuracy for complex defect MFL field prediction with little extra cost. Experimental results show that, when compared with traditional MDM, the proposed one can achieve a maximum 69% decrease in root mean squared error when analysing complex defects. Compared with the numerical method, the computation time could reach a great reduction.

Analytical model of non-uniform charge distribution within the gated region of GaN HEMTs

A physics-based analytical expression that predicts the charge, electrical field and potential distributions along the gated region of the GaN HEMT channel has been developed. Unlike the gradual channel approximation (GCA), the proposed model considers the non-uniform variation of the concentration under the gated region as a function of terminal applied voltages. In addition, the model can capture the influence of mobility and channel temperature on the charge distribution trend. The comparison with the hydrodynamic (HD) numerical simulation showed a high agreement of the proposed model with numerical data for different bias conditions considering the self-heating and quantization of the electron concentration. The analytical nature of the model allows us to reduce the computational and time cost of the simulation. Also, it can be used as a core expression to develop a complete physics-based transistor Ⅳ model without GCA limitation.

Tuning of internal electric field and diffusion distance boosting the charge separation for photocatalytic electricity generation

Solar-light driven electricity generation from organic molecule oxidation emerges as a green technology for energy conversion and sewage recycling. However, low charge separation efficiency severely restricts the photocatalytic electricity generation and photooxidation. Herein, we introduce a novel monolayered Sb-BiOCl nanosheets fabricated via injecting Sb ions and hydrophobic chains of cetyltrimethylammonium (CTA+) for photocatalytic electricity generation. By visible light irradiation and addition of organic molecule fuel to artificially construct the photo fuel cell system, the BiOCl with 10% Sb dopant converts electricity with 3.9-fold increase compared to the bulk BiOCl. The enhanced electrical output is primarily attributed to their efficient charge separation facilitated by the boosted internal electric field (IEF) and reduced diffusion distance. DFT calculation and electrochemical test demonstrate that the nonuniform charge distribution between [Bi2O2] and [Cl] slices resulting from the electron donor Sb doping contributes to 92-fold increase of IEF parallel to [010] zone. Significantly, the shortened transport channel of charge carriers further promotes the photogenerated charge anisotropic separation. This work proves that the cooperative effect of IEF and diffusion distance tuning can boost the charge separation of photocatalysts, which offers a useful strategy for constructing effective solar-light driven electricity generation system.

Research on the Forward Solving Method of Defect Leakage Signal Based on the Non-Uniform Magnetic Charge Model.

Pipeline magnetic flux leakage inspection is widely used in the evaluation of material defect detection due to its advantages of having no coupling agent and easy implementation. The quantification of defect size is an important part of magnetic flux leakage testing. Defects of different geometrical dimensions produce signal waveforms with different characteristics after excitation. The key to achieving defect quantification is an accurate description of the relationship between the magnetic leakage signal and the size. In this paper, a calculation model for solving the defect leakage field based on the non-uniform magnetic charge distribution of magnetic dipoles is developed. Based on the traditional uniformly distributed magnetic charge model, the magnetic charge density distribution model is improved. Considering the variation of magnetic charge density with different depth positions, the triaxial signal characteristics of the defect are obtained by vector synthesis calculation. Simultaneous design of excitation pulling experiment. The leakage field distribution of rectangular defects with different geometries is analyzed. The experimental results show that the change in defect size will have an impact on the area of the defect leakage field distribution, and the larger the length and wider the width of the defect, the more sensitive the impact on the leakage field distribution. The solution model is consistent with the experimentally obtained leakage signal distribution law, and the model is a practical guide by which to improve the quality of defect evaluation.

A comparative investigation for identification of N-(4-dimethylamino 3,5-dinitrophenyl)maleimide

This study has identified the characteristic behaviors of N-(4-dimethylamino 3,5-dinitrophenyl)maleimide molecule using ab initio Hartree-Fock (HF) and density functional theory (DFT) based on Becke’s three-parameter hybrid exchange functional combined with Lee-Yang-Parr non-local correlation function (HF/B3LYP and DFT/B3LYP) at 6-311G++(d,p) level of theory for the first time. On this basis, the optimized molecular structures, some thermodynamic features at 300 K, function groups of structures, charge distributions-dipole moments, molecular charge transfer regions, spectroscopic characteristic properties, vibrational frequencies, nuclear magnetic resonance chemical shifts of 13C-NMR and 1H-NMR spectra, and corresponding vibrational assignments have been investigated in detail. Comparisons between some experimental findings and theoretical results are performed to test the reliability of the calculation method preferred in the study. The comparison results in high correlation parameters such as R2 =0.976 and R2 =0.985 for the molecular structures and vibrational frequencies in the DFT and HF calculation levels, respectively. Moreover, the obtained vibrational frequencies and calculated results are in good agreement with the experimental data. Additionally, the simulations of highest/lowest occupied/unoccupied molecular orbital (HOMO and LUMO), molecular electrostatic potential (MEP), and electrostatic potential (ESP) maps have shown that there appear strong non-uniform intra-molecular charge distributions (ICT), electron engagements, lone pairs of electrons, π-π* conjugative effects based on the bond weakening, and intermolecular hydrogen bonding in the compound. Correspondingly, the molecule with the electrophilic reactive and nucleophilic regions has been noted to exhibit kinetical chemical stability. All the discussions have been confirmed by means of the findings of optimized molecular structures and vibrational frequencies belonging to the molecule.

Quantum Mechanical Study of the Dielectric Response of V2C-ZnO/PPy Ternary Nanocomposite for Energy Storage Application

With the proliferation of electronic gadgets and the internet of things comes a great need for lightweight, affordable, sustainable, and long-lasting power devices to combat the depletion of fossil fuel energy and the pollution produced by chemical energy storage. The use of high-energy-density polymer/ceramic composites is generating more curiosity for future technologies, and they require a high dielectric constant and breakdown strength. Electric percolation and Interface polarization are responsible for the high dielectric constant. To create composite dielectrics, high-conductivity ceramic particles are combined with polymers to improve the dielectric constant. In this work, ternary nanocomposites with better dielectric characteristics are created using a nanohybrid filler of V2C Mxene-ZnO in a polypyrrole (PPy) matrix. Then, the bonding and the uneven charge distribution in the ceramic/ceramic contact area are investigated using quantum mechanical calculations. This non-uniform distribution of charges is intended to improve the ceramic/ceramic interface’s dipole polarization (dielectric response). The interfacial chemical bond formation can also improve the hybrid filler’s stability in terms of structure and, consequently, of the composite films. To comprehend the electron-transfer process, the density of state and electron localization function of the ceramic hybrid fillers are also studied. The polymer nanocomposite is suggested to provide a suitable dielectric response for energy storage applications.

Study of MFL signal identification in pipelines based on non-uniform magnetic charge distribution patterns

Magnetic flux leakage (MFL), a pipeline internal detection, is the mainstream technology for international oil and gas pipeline safety maintenance. To address the problem of large errors in the assessment of defects in pipeline inspection by existing theoretical analysis models, this paper introduces the charge density parameter to establish a mathematical model of non-uniform magnetic charge for pipeline leakage detection and calculates the non-uniform distribution pattern of magnetic charge on the defect side wall. The contour plot method is proposed to visually analyze the size of defects. To compare the error between uniform and non-uniform models, and verify the correctness of the theoretical model, experiments were systematically conducted on the X70 pipeline with internal MFL technology. The results show that: the magnetic charge distribution curve is symmetrically shaped at the center of the defect, with a valley at the center and two peaks at the defect edge. As the defect depth and width increase, the magnetic charge density increases sharply near the surface and edge. The peak-to-valley spacing and peak-to-valley values in the contour map of the MFL signal can directly reflect the location and size of defects. The signal characteristic values follow the trend of a first-order decreasing exponential function as the value of the lift-off increases. The first-order derivative of the signal characteristic value tends to decrease and then increase as the mesh size decreases, and the extreme point of the derivative curve is the best mesh size.

Tau and tubulin protein aggregation characterization by solid-state nanopore method and atomic force microscopy

In this study, a silicon nitride nanopore-based sensing system was used to measure tau and tubulin monomers and their aggregations in salt solution at a single molecule level. Nanopores (6–30 nm) were fabricated on silicon nitride membranes supported by silicon substrates using a combination of focused ion beam milling and ion beam sculpting. When a charged protein molecule in the salt solution passes through a nanopore driven by an applied voltage, the protein molecule increases pore resistivity, which induces an ionic current drop that can be measured. The current drop amplitude is directly proportional to the local excluded volume of the protein molecule in the nanopore. We measured the monomers and aggregations of tau and tubulin proteins at biased voltages from 60 to 210 mV in a solution of pH 7.0–10. Our results showed that (1) the nanopore method was able to differentiate tau and tubulin proteins in their monomer and aggregated forms by their excluded volumes; (2) the most probable aggregation form was dimer for α- and β-tubulin and pentamer for αβ tubulin plus tau under experimental conditions; (3) the protein excluded volumes measured by the nanopore method depended on the applied voltage, and this observation could be explained by the nonuniform charge distribution of proteins. The monomer and aggregated proteins were further analyzed using atomic force spectroscopy (AFM), and protein volumes estimated by AFM were consistent with nanopore results.

Fabrication of In–S-co-doped two-dimensional BiOCl coupling with surface hydroxylation toward simultaneously efficient charge separation and redox capability for photocatalytic water remediation

Tailoring energy band structure of bismuth oxychloride (BiOCl)-based photocatalysts by virtue of the metal and/or non-metal elements is one of the promising strategy to address environmental issues, especially plays a crucial role in water remediation. However, it still remains a great challenge to balance the light-harvesting and charge carriers separation. Herein, a feasible strategy was proposed for the simultaneous integration of energy-band modulation and surface hydroxylation to alleviate the as-mentioned contradiction and long-standing issues. By using a simple one-pot hydrothermal method, In–S-co-doped BiOCl photocatalyst coupling with surface hydroxylation (denoted as In/BOC-S-OH) was prepared by the simultaneous co-precipitation and ripening process and exhibited a good photocatalytic activity for removing tetracycline (TC) under visible light-irradiation than the counterparts of In-doped BiOCl (In/BOC), S-doped BiOCl (In/BOC-S) or surface –OH modification BiOCl (In/BOC-OH). Such satisfied photocatalytic efficiency benefits from the synergistic effect on the visible light capture, charge migration and separation associated with the introduction of intermediate energy levels and surface defect, respectively. Accompanying with the introduction of In and S hetero-atoms intercalation, both the potentials of valence and conduction bands were adjusted and the reduction of the bandgap could promote the capture of photons. Meanwhile, the powerful polarization effect associated with the non-uniform charge distribution could promote the special separation of carriers. More importantly, the surface defects induced by hydroxylation could act as traps for photogenerated electrons to stimulate the rapid separation of carriers, thereby causing the cleavage of antibiotics on the catalytic surface. This research offers a reliable strategy and promising scheme via effective solar energy conversion and charge carrier separation to advance photocatalytic wastewater remediation.

Localized Charge on Surfactant-Wrapped Single-Walled Carbon Nanotubes

As-synthesized, semiconducting single-walled carbon nanotubes (SWCNTs) are nominally charge neutral. However, ionic surfactants that are commonly used to disperse SWCNTs in solution can lead to significantly charged aggregates adsorbed to the nanotube. Here, electrostatic force microscopy (EFM) was used to characterize the static-charge interactions between individual SWCNTs and the local environment. We report nonuniform spatial charge distributions with highly varying magnitudes ranging between ±15 e associated with surfactant coverage on long SWCNTs (>1.5 μm). EFM images acquired after resonant photoexcitation demonstrate charge carrier localization due to electrostatic interactions with charged surfactant aggregates. Charge densities as measured by EFM are used to estimate the depth of this electrostatically induced potential well, calculated to be on the order of hundreds of millielectronvolts, suggesting that surfactant charges heterogeneously covering SWCNTs provide traps for excitons potentially leading to their localization.

Improved circuit model for plasmonic resonance of single split-ring resonators

In this work, an improved circuit model is presented for the single split ring resonator (SRR), taking into account non-uniform distribution of conduction current and surface charges. To determine the circuit elements of the SRR, the electron kinetic, electric, and magnetic energy have been derived theoretically. Moreover, in addition to gap and surface capacitances, coupling capacitance is introduced to characterize the electric coupling effect between them. A formula for the fundamental resonance wavelength has been obtained, which shows good agreement with numerical simulations in both optical and microwave frequency ranges. The model will be instructive for engineering resonant properties of the SRRs and provide valuable insight into other complex plasmonic structures.

A Computational Characterization of 2,2′-bis(trifluoromethyl)-[1,1′-biphenyl]-4,4′-diamine Iodine Dopant for Improving Power-Conversion Efficiency of Perovskite Solar Cells

The paper presents ongoing density-functional theory (DFT) computational support to research of hybrid perovskite solar cells to facilitate their understanding at molecular level. Very recently, doping by a iodine salt, namely 2,2′-bis(trifluoromethyl)-[1,1′-biphenyl]-4,4′-diamine iodine BFBAI2, has been described that improves the power conversion efficiency and enhances device stability. As structural characteristics of BFBAI2 are not well known, they are supplied here through DFT calculations for both BFBAI2 monomer and dimer. The geometry optimizations are performed at the M06-2X/3-21G level, and energetics is refined with the M06-2X/Def2QZVP treatment. The dimerization potential-energy change is calculated as −6.2 kcal/mol. BFBAI2 exhibits highly non-uniform charge distribution, i.e., it is a clearly polar system that can strongly modulate surface conditions when adsorbed. The adsorption-energy gain for BFBAI2 on CsPbI3 perovskite is DFT evaluated as −13.2 kcal/mol.

In‐Situ‐Generated MoO2 on MoS2/ZnO Heterostructures with Enriched S,O‐Vacancies for Enhanced Electrocatalytic Reduction of N2 to NH3

AbstractElectrocatalytic nitrogen reduction reaction (NRR) is a green method for synthesis ammonia under mild condition compared to energy‐intensive Haber‐Bosch process. Herein, a novel heterojunction material (MMZ‐900) is prepared as an excellent electrocatalyst for NRR at 900 °C, which is composed of MoS2, MoO2 and ZnO with nonuniform charge distribution of rich S and O vacancies. As a result, MMZ‐900 exhibits about 8 times higher Faradaic efficiency and 5 times higher NH3 yields for NRR than pure MoS2, respectively. These new insights may open up opportunities for exploiting efficient NRR electrocatalysts by simultaneously improving sulfur and oxygen vacancies on heterojunction material.

Radar Cross-section of a target and attenuation of electromagnetic waves in sandstorms

The sand particles suspended in the atmosphere can cause the attenuation of electromagnetic waves (EWs) and affect the electromagnetic scattering properties of a target during sandstorms. In this study, a theoretical analysis is offered for the prediction of the EWs attenuation and the radar cross section (RCS) of a target in sandstorms. In the model, an equivalent medium approximation is performed by considering the non-uniform charge distribution on the sand particles, and the effect of the charged sand particles on the scattering characteristics of a target is also taken into account. Numerical results show that the RCS of a target is severely affected in sandstorms. Besides, the charged sand particles have a much greater effect on the target's RCS than the case of the uncharged sand particles. It can be found that the average variation value of the target's RCS decreases nearly exponentially with the increase of visibility, and increases nearly linearly with the distance between the target and incident wave source. Finally, an empirical formula is presented to calculate the RCS of an arbitrarily shaped metal target in a homogeneous lossy medium. These investigations will be of significant benefit to radar detection technology in sandstorms.

Distribution of Charges on a Flat Disk as the Application of Far-Ranging Mathematics

The foremost grail of this academic indagation is to delineate a mathematical expression of the normalised charge density over a flat disk. Aiming to ensue, firstly, 2 different frameworks have been dealt with to formulate the potential distribution which allows stability of a non-uniform charge distribution. At first, a logical but mathematically toilsome integral method has been approached. Out of the unyielding territory, we reduced the expression into algebraical functions using the Bessel coefficient and Green’s theorem, eventually inferring a new mathematical equivalence. Subsequently, this paper explores beta function as a solving tool of complete elliptic integral so that the normalization of charge apportion leads to 0 gradients of potential. Finally, the article deduces an integral equation whose implicit solution brings into the required charge distribution. The write-up also encounters finding a proximate graphical illustration of the assortment following the CAS system and direction fields. Beyond the conventional approach of real analysis, it facilitates proving the convergence of an acclaimed series. Consequently, it conceives a discussion on image charges for a flat disk. Even a short view of the article’s impact on practical fields of biology and engineering sciences has been included as the denouement. So, it might be of interest to the wide-ranged audience of research scholars in both the fields of physical and mathematical sciences.
 HIGHLIGHTS
 
 Expression of potential at any arbitrary 3D space point due to uniformly charged disk
 Natural unconstrained normalisation of charge density
 Implicating trigonometric solution in complete elliptic integral
 Proving the convergence of a bivariate divergent series
 Results can be of interest to electrostatic and condensed matter physicist including mathematicians of real analysis
 
 GRAPHICAL ABSTRACT