Charge Transfer Model Research Articles

Computational algorithms for a one-dimensional MEP model of charge transfer in semiconductors

Subject of research: hydrodynamic model describing charge transfer in semiconductor devices in the one-dimensional case.
 Purpose of research: to develop computational algorithms for finding a numerical solution of a ballistic diode problem.
 Methods and objects of research: the object of research is the ballistic diode problem. The developed computational algorithms are based on the use of the method of lines, the method of establishment, various non-stationary regularizations and schemes without saturation.
 Main results of the research: computational schemes were developed based on the use of the spline function technique, on reducing the problem to integral equations and using the predictor-corrector scheme.

Electronic coarse-graining of long conjugated molecules: Case study of non-fullerene acceptors.

By considering only one electronic state per molecule, charge transport models of molecular solids neglect intramolecular charge transfer. This approximation excludes materials with quasi-degenerate spatially separated frontier orbitals, such as non-fullerene acceptors (NFAs) and symmetric thermally activated delayed fluorescence emitters. By analyzing the electronic structure of room-temperature molecular conformers of a prototypical NFA, ITIC-4F, we conclude that the electron is localized on one of the two acceptor blocks with the mean intramolecular transfer integral of 120meV, which is comparable with intermolecular couplings. Therefore, the minimal basis for acceptor-donor-acceptor (A-D-A) molecules consists of two molecular orbitals localized on the acceptor blocks. This basis is robust even with respect to geometry distortions in an amorphous solid, in contrast to the basis of two lowest unoccupied canonical molecular orbitals withstanding only thermal fluctuations in a crystal. The charge carrier mobility can be underestimated by a factor of two when using single site approximation for A-D-A molecules in their typical crystalline packings.

Charge transfer interactions exist in extracellular polymeric substances: Comparison with natural organic matter

Extracellular polymeric substances (EPS) and natural organic matter (NOM) are widely present in the environment. While the molecular basis of NOM's optical properties and reactivity after treatment with sodium borohydride (NaBH4) has been successfully explained by the charge transfer (CT) model, the corresponding structure basis and properties of EPS remain poorly understood. In this work, we investigated the reactivity and optical properties of EPS after NaBH4 treatment, comparing them to the corresponding changes in NOM. After reduction, EPS exhibited optical properties and a reactivity with Au3+ similar to NOM, manifesting an irreversible loss of visible absorption (≥70%) associated with blue-shifted fluorescence emission (8–11 nm) and a lower rate of gold nanoparticles formation (decreasing by ≥ 32%), which can be readily explained by the CT model as well. Furthermore, the absorbance and fluorescence spectra of EPS were solvent polarity dependent, contrary to the superposition model. These findings contribute to an original understanding of the reactivity and optical properties of EPS and facilitate further cross-disciplinary studies.

Increasing the conductivity of V2O5-TeO2 glass by crystallization: structure and charge transfer studies

In the present paper, V2O5-TeO2 glass was prepared by the melt-quenching technique. Crystallization of glass with a vanadium content higher than 35%mol results in an increase in electrical conductivity by a few orders of magnitude and a decrease in activation energy from ~0.40 to ~0.12 eV. In this work, a critical review of existing charge transfer models was presented on the example of V2O5-TeO2 glass and glass–ceramics. Schnakenberg’s and Friedman-Triberis’ charge transfer models were found to be applicable to both glass and glass–ceramics. Optical phonon frequencies obtained from Schnakenberg’s model are in agreement with FTIR studies. Values of activation energies obtained from the Schnakenberg model decrease after crystallization. Friedman-Triberis’ model shows an increase in the density of states near the Fermi level from 1019 eV−1 cm−3 in glass, to 1021 eV−1 cm−3 in glass ceramics. Structural studies show that the main crystallizing phase is Te2V2O9 which occurs with the V2O5 shell in glasses with compositions 50–50%mol and 45–55%mol. It is concluded that crystallization results in the reduction of vanadium ions in the remaining glass matrix which leads to an increase in the V4+/V5+ ratio and therefore, an increase in electrical conductivity.

Modeling High-Power Density Ceria-Based Direct Ammonia Fueled SOFC Stacks for Mobile Applications

SOFCs can be directly run with ammonia (NH3), which is anticipated to play a major role in future renewable energy systems due to its superior conditioning and storage characteristics. Here, we numerically investigate the performance of NH3-fueled SOFC stacks based on a high-power density ceria-based cell design by means of detailed multi-scale simulations on 1D-button cell and 3D-stack level. The model is validated based on electrochemical performance data collected on a Ni-GDC/GDC/SSC-GDC button cell at 500-650 °C. While the decomposition of NH3 at the surface of the Ni-particles is modeled by employing an elementary kinetic framework, a physically-based distributed charge-transfer model is consulted to account for the leakage current across the GDC electrolyte as a function of operation conditions. In this way, the intricate coupling between the mass, heat and charge transport phenomena, as well as the electrochemistry and thermo-catalytic chemistry can be studied on the industrially relevant scale to assist integration into a hybridized power generation system. Model predictions indicate the 120-cell stack running on NH3 to reach a very promising performance in the intermediate-temperature range.

Simultaneous photocatalytic tetracycline oxidation and Cr(VI) reduction by a 0D/3D hierarchical Bi2WO6@CoO Z-scheme heterostructure: In situ interfacial engineering and charge regulation mechanism

Constructing visible-light driven semiconductor heterojunction with high redox bifunctional characteristics is a promising approach to deal with the increasingly serious environmental pollution problems, especially the coexistence of organic/heavy metal pollutants. Herein, a simple in-situ interfacial engineering strategy for the fabrication of 0D/3D hierarchical Bi2WO6@CoO (BWO) heterojunction with an intimate contact interface was successfully developed. The superior photocatalytic property was reflected not only in individual tetracycline hydrochloride (TCH) oxidation or Cr(VI) reduction, but also in their simultaneous redox reaction, which could be predominantly attributed to the outstanding light-harvesting, high carrier separation efficiency and enough redox potentials. In the simultaneous redox system, TCH acted as a hole-scavenger for Cr(VI) reduction, replacing the additional reagent. Interestingly, superoxide radical (·O2−) played the role as oxidants in TCH oxidation but as electron transfer media in Cr(VI) reduction. On account of the interlaced energy band and tight interfacial contact, a direct Z-scheme charge transfer model was established, which was verified by the active species trapping experiments, spectroscopy, and electrochemical tests. This work provided a promising strategy for the design/fabrication of highly efficient direct Z-scheme photocatalysts in environmental remediation.

The effect of energy level degeneracy on symmetry-breaking charge transfer: Excited octupolar dyes.

A three-level model of symmetry-breaking charge transfer (SBCT) in excited octupolar molecules is developed. The model describes the joint dynamics of the solvent and the dye in the excited state. For this, a distribution function in the space of two reaction coordinates is introduced. An evolution equation of this function is derived. A strict definition of the reaction coordinates is given, and its dynamic characteristics are determined. The free energy surface in the space of these coordinates is calculated. To quantify the symmetry-breaking degree, a two-dimensional dissymmetry vector is introduced. The model predicts the absence of SBCT in apolar solvents and an abrupt increase in its degree to half the maximum value in weakly polar solvents. The dye dipole moment is revealed to be directed along a molecular arm independently of the direction and the strength of the electric field of the solvent created by its orientational polarization. The conditions for the occurrence and nature of this effect are discussed. The effect of the degeneracy of excited states, which is inherent in octupolar dyes in the excited state, on SBCT is revealed. Degeneracy of energy levels is shown to lead to a significant increase in the symmetry-breaking degree. The effect of SBCT on the dependence of the Stokes on the solvent polarity is calculated and compared with the available experimental data.

Kinetic modeling of charge transfer following photon bleaching post-irradiation of spatially correlated trapping and luminescent centers in LiF:Mg,Ti

Illumination of LiF:Mg,Ti by photons of energy 3.65 eV and levels of fluence from 1.2 1018 ph cm−2 to 3.6 1018 ph cm−2 results in a decrease of the thermoluminescence (TL) dose response supralinearity of peak 5 in the glow curve of LiF:Mg,Ti. No further effect on the dose response is observed at higher photon fluences up to 1.4 × 1019 ph cm−2. The threshold of dose response non-linearity usually reported at a dose of 1 Gy, is increased to 30 Gy. A kinetic model is described herein in the framework of conduction band/valence band solid state theory incorporating spatially correlated trapping centers (TCs) and luminescent centers (LCs). The model successfully simulates the bleaching action of the 3.65 eV photons on the increased region of TL dose response linearity as resulting from the depletion of the occupied trapping centers and to a lesser degree by charge transfer via the conduction band between the various configurations of the TC/LC system associated with composite peak 5.

Relationship of structure and enhanced photocatalytic activity of S-scheme BiOCl/g-C3N4 heterojunction for xanthate removal under visible light

Constructing heterojunctions is an excellent way to enhance the photocatalytic property of semiconductors. Herein, a range of S-scheme BiOCl/g-C3N4 heterojunctions with varying mass ratios were designed using a facile hydrothermal route, and their photocatalytic ability was assessed by degrading the ethyl xanthate (EX) under visible light (λ > 400 nm). The results showed that the degradation efficiency of BiOCl/g-C3N4-0.1 heterojunction for EX was up to 91.2 % within 180 min, and its apparent rate constants (Kapp) were 4.3 and 11 times greater than those of BiOCl and g-C3N4, respectively. The experimental and characterization results revealed that the excellent photocatalytic property was ascribed to the construction of S-scheme heterojunctions. Such structure not only enhanced the visible light response but also facilitated the efficient separation of photoinduced carriers with the S-scheme transfer route, retaining strong redox-capable holes and electrons to participate in surface reactions. Furthermore, the cycling experiments indicated that the fabricated photocatalysts have great recyclability and stability. Based on the results of active substance capture, the S-scheme charge transfer model was proposed and the photodegradation mechanism of EX was reasonably elucidated. Overall, this work offers some theoretical direction for the design and construction of S-scheme heterojunctions with superior visible-light-driven photocatalytic performance.

Autonomous atomic Hamiltonian construction and active sampling of X-ray absorption spectroscopy by adversarial Bayesian optimization

X-ray absorption spectroscopy (XAS) is a well-established method for in-depth characterization of electronic structure. In practice hundreds of energy-points should be sampled during the measurements, and most of them are redundant. Additionally, it is also tedious to estimate reasonable parameters in the atomic Hamiltonians for mechanistic understanding. We implement an Adversarial Bayesian optimization (ABO) algorithm comprising two coupled BOs to automatically fit the many-body model Hamiltonians and to sample effectively based on active learning (AL). Taking NiO as an example, we find that less than 30 sampling points are sufficient to recover the complete XAS with the corresponding crystal field and charge transfer models, which can be selected based on intuitive hypothesis learning. Further applications on the experimental XAS spectra reveal that less than 80 sampling points give reasonable XAS and reliable atomic model parameters. Our ABO algorithm has a great potential for future applications on automated physics-driven XAS analysis and AL sampling.

Mechanism of Transverse Charge Transfer in Thin Films of Hexagonal Boron Nitride

A mechanism of transverse charge transfer through hexagonal boron nitride (h-BN) in a MIS structure has been studied. Experimental data for charge transfer have been analyzed in terms of different models of charge transfer in insulators. It has been shown that charge transfer in h-BN is described by the model of phonon-assisted tunneling between neutral traps. The thermal and optical energies of phonon-coupled traps in h-BN have been determined. Based on charge transfer measurements, XPS spectra, and the ab initio electronic structure of intrinsic defects in h-BN it has been found that boron–nitrogen divacancies are most probably responsible for charge transfer in h-BN and transfer is provided by electrons.

Counter charge cluster formation in molecular doping of molybdenum disulfide

Studies of molybdenum disulfide (MoS2) gas sensor prototypes report orders of magnitude higher sensitivity toward nitrogen dioxide (NO2) over ammonia (NH3). Based on the cluster formation model and density functional theory calculations of charge transfer, NO2 was found to form a tightly bound cluster of counter charges upon carrier donation. In contrast, NH3 forms only a semi-localized cluster of counter charges over a wide area of MoS2, creating a larger collision cross section of coulomb interaction between the charge carrier and the counter charges. We discuss the potential effect of counter charge cluster localization on the efficiency of molecular doping.

Surface hopping modeling of charge and energy transfer in active environments.

An active environment is any atomic or molecular system changing a chromophore's nonadiabatic dynamics compared to the isolated molecule. The action of the environment on the chromophore occurs by changing the potential energy landscape and triggering new energy and charge flows unavailable in the vacuum. Surface hopping is a mixed quantum-classical approach whose extreme flexibility has made it the primary platform for implementing novel methodologies to investigate the nonadiabatic dynamics of a chromophore in active environments. This Perspective paper surveys the latest developments in the field, focusing on charge and energy transfer processes.

Hierarchical S-scheme titanium dioxide@cobalt-nickel based metal-organic framework nanotube photocatalyst for selective carbon dioxide photoreduction to methane.

Efficient photocatalysts are of great importance for the photochemical conversion of CO2 into fuels. Herein, S-scheme titanium dioxide@cobalt-nickel based metal-organic framework (TiO2@CoNi-MOF) heterojunction photocatalysts with high surface area and porosity are designed and fabricated by a multi-step controllable strategy. The photocatalytic activity of the composites can be optimized by adjusting the loading content of CoNi-MOF in TiO2@CoNi-MOF and molar ratios of Co2+ and Ni2+ in CoNi-MOF. The optimized hybrid photocatalyst showed a much higher CO2 photoreduction activity than the control single-component samples (TiO2 and CoNi-MOF) with a high CH4 yield (41.65μmolg-1h-1) and selectivity (93.2%). The accelerated charge carrier separation induced by the S-scheme heterojunction significantly promoted the photocatalytic performance of TiO2@CoNi-MOF NTs. Meanwhile, the introduction of bimetallic CoNi-MOF nanosheets significantly resulted in the increase of active sites, CO2 adsorbability, visible-light utilization, and CH4 selectivity. Moreover, the S-scheme photoinduced charge transfer model of the TiO2@CoNi-MOF NTs photocatalyst was confirmed by photoluminescence spectroscopy, free radical trapping tests, and work function calculated from Kelvin probe. The work aims to design and fabricate heterojunction photocatalysts with high efficiency for solar fuel production.

SrTiO3 nanosheets decorated with ZnFe2O4 nanoparticles as Z-scheme photocatalysts for highly efficient photocatalytic degradation and CO2 conversion

Nanocomposite has attracted widespread attention for efficiently utilizing solar energy and improving conversion efficiency during wastewater purification and solar fuels evolution. In this study, Z-scheme ZnFe2O4-SrTiO3 nanocomposite was prepared and used as photocatalysts for tetracycline hydrochloride (TCH) degradation and CO2 conversion. The as-obtained ZnFe2O4-SrTiO3 system achieved drastically enhanced TCH degradation efficiency up to 84.56 % with respect to pure ZnFe2O4(13.81 %) and SrTiO3(49.66 %) under visible light irradiation. The influences of ZnFe2O4 content and co-existing ions on the photodegradation activities were investigated. In addition, ZnFe2O4-SrTiO3 nanocomposite exhibited outstanding CO2 photoreduction activity, the CO and CH4 evolution rate were 8.24 μmol/g/h and 2.51 μmol/g/h, which was 2.5 and 6.4 times higher than that observed for SrTiO3, respectively. The reinforced photocatalytic TCH degradation and CO2 conversion activities are mainly attributed to the obviously enhanced utilization of solar energy and the dramatically boosted electron-hole pair separation efficiency through a Z-scheme charge transfer model. In addition, a possible photocatalytic enhancement mechanism of ZnFe2O4-SrTiO3 nanocomposite is proposed in the light of trapping experiments, ESR and DFT calculations. Our studies implies that ZnFe2O4-SrTiO3 nanocomposite are expected to effectively realize wastewater purification and CO2 reduction to renewable solar fuels.

Design, spectroscopic, structural characterization, and biological studies for new complexes via charge transfer interaction of ciprofloxacin drug with π acceptors

Ciprofloxacin (CIP) is a common antibiotic drug used as a strudy electron donor that interacts with dynamic π-acceptors such as 2,3-dinitrosalsylic acid (HDNS) and Tetracyanoethylene (TCNE) for synthesizing a new model of charge transfer (CT) complexes. The synthesized complexes were identified using diverse analytical methods such as UV–vis spectra, photometric titration measurements, FT-IR, 1H NMR Spectroscopy, and thermogravimetric analysis techniques (TGA/DTA). The stoichiometries for all the formed complexes were found to be 1:1 M ratio between the reactants. The characteristic spectroscopic properties such as transition dipole moment (μ), oscillator strength (ƒ), formation constant (KCT), ionization potential (ID), standard free energy (ΔG), and energy of interaction (ECT) for the CT-complexes were collected. The developed CT-complexes were tested for their toxicity on main organs, antimicrobial activity, antioxidant activity, and biofilm formation.

Analytical model of free charge transfer in charge-coupled devices

A one-dimensional analytical model of charge transfer in charge-coupled devices, which describes the spatial–temporal behavior of the charge carrier density in a potential well, is presented. The general solution of this model considers the transfer dynamics in terms of the electric drift field, i.e., self-induced drift and fringing-field drift, and yields an analytical solution for the total number of charge carriers. A comparison of the transfer efficiency for various electric drift fields is presented. The modulation transfer function in dependence on the transfer efficiency is analyzed, aiming especially at time-delay integration (TDI) applications. Finally, the results of this model are concluded and discussed in detail.

Rashba-like spin-orbit interaction and spin texture at the KTaO3(001) surface from DFT calculations

Rashba-like spin-orbit interaction at oxide heterostructures emerges as a much sought-after feature in the context of oxide spintronics and spin-orbitronics. ${\mathrm{KTaO}}_{3}$ (KTO) is one of the best substrates available for the purpose, owing to its strong spin-orbit interaction and alternating $+1|\ensuremath{-}1$ charged layers along the (001) direction. Employing first-principles calculations within density functional theory (DFT) and proposing a possible electrostatic model for charge transfer to the surfaces of KTO slabs, we comprehensively analyze Rashba-like spin-orbit interaction with the help of three-dimensional (3D) band dispersion, isoenergetic contours, and projected spin textures -- all directly obtained from our DFT calculations -- in a thin insulating slab and a conducting thick slab of KTO. Our results reveal reasonably strong linear Rashba interaction with no signature of Dresselhaus or higher order Rashba interactions in the systems considered here. The rigorous analysis presented here may be crucial for future developments in oxide spintronics.

A Theoretical Investigation of Charge Transfer Dynamics from Sensitized Molecule D35CPDT Dye to SnO_2 and TiO_2 Semiconductor

In this research, the dynamics process of charge transfer from the sensitized D35CPDT dye to tin(iv) oxide( ) or titanium dioxide ( ) semiconductors are carried out by using a quantum model for charge transfer. Different chemical solvents Pyridine, 2-Methoxyethanol. Ethanol, Acetonitrile, and Methanol have been used with both systems as polar media surrounded the systems. The rate for charge transfer from photo-excitation D35CPDTdye and injection into the conduction band of or semiconductors vary from a to for system and from a to for the system, depending on the charge transfer parameters strength coupling, free energy, potential of donor and acceptor in the system. The charge transfer rate in D35CPDT / the system is larger than the rate in D35CPDT/ a system depending on transition energy and driving energy. However, the charge transfer for both systems to be large is associated with large transition energy, decreasing driving energy and potential, and increasing strength coupling with Methanol solvent.

Oxygen Vacancy Induced Boosted Visible-Light Driven Photocatalytic CO2 Reduction and Electrochemical Water Oxidation Over CuCo-ZIF@Fe2 O3 @CC Architecture.

Herein, the obtained Cu0.5 Co0.5 -ZIF@Fe2 O3 @CC-150 heterojunction (termed as Cu1- x Cox -ZFC-150) showed high hydrogen and oxygen evolution reaction (HER and OER) activities with low overpotential small Tafel slope. When employed to be the bifunctional anode and cathode, they only needed a cell voltage of 1.62V. The composite also exhibited excellent photocatalytic performance on CO2 evolution into CO and CH4 . The enhanced OER kinetics and Z-scheme charge transfer model for photocatalytic property have been discussed based on the experiments and density functional theory (DFT) analysis. The optimized phase interfaces, abundant active sites, optional oxygen vacancy, and adjusted Gibbs free energy were beneficial for the fast electron/ion transport enhancing the water splitting performance.