Charge Transition Research Articles

Electron configurations at 3d orbital of metal ion determining charge transition process in memory devices

Functional polymeric materials with electrical bi-stable states possess significant potential for high-density data storage due to their nanoscale memory site, three-dimensional-stacking ability and intrinsic flexibility. Aromatic polyimides bearing donor-acceptor (D-A) skeleton could form charge transfer complex (CTC) under electrical field, leading to their feasibility as memory materials. Three novel porphyrinated polyimides DATPP-DSDA, Zn-DATPP-DSDA and Mn-DATPP-DSDA were designed and synthesized for information memory applications. Metal ions with different electron configurations at 3d orbital have a determining influence on memory behaviors of polyimides: nonvolatile write-once-read-many-times memory (WORM) for DATPP-DSDA, volatile static random access memory (SRAM) for Zn-DATPP-DSDA, but no memory performance for Mn-DATPP-DSDA. By comparing the contribution of orbital transition and hole-electron distribution of charge-transfer excited states, roles of metal ions in regulating memory types were discussed. Molecular simulation results indicate that the Zn ion could play a bridge role in paving the route for excited electrons from a D to an A, while a trap role for the Mn ion in hindering this process. This study proves the feasibility of the strategy for modulating the memory behaviors of porphyrinated polyimides by varying the central metal ion and provides the exact effects of various metal ions on regulating charge transfer processes.

Synthesis, crystal structure and properties of a yttrium complex based on mixed functional ligands

A new yttrium complex, [Y 2 (H 2 Dhbds) 3 (phen) 2 ]·[Y 2 (H 2 Dhbds) 2 (H 2 Thbs)(phen) 2 ] ( 1 ) (Na 2 H 2 Dhbds = 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt; NaH 3 Thbs = 2,3,5-trihydroxy-1-benzenesulfonic acid sodium salt), has been synthesized and structurally characterized. Complex 1 consists of two dinuclear structural units bridged by H 2 Dhbds 2- and H 2 Thbs 2- ligands, where phen molecules act as N, N-bidentate ligands, chelating Y atoms. The dinuclear structural units are connected by π-π stacking interactions between phen molecules, generating a one-dimensional chain structure. In addition, complex 1 exhibits the broad fluorescent emission band at 365 nm, which originates from intraligand charge transitions.

New organosulfur metallic compounds as potent drugs: synthesis, molecular modeling, spectral, antimicrobial, drug likeness and DFT analysis

During the present investigation, two new sulfonamide-based Schiff base ligands, 4-{[(2-hydroxy-3-methoxyphenyl)methylidene]amino}-N-(1,3-thiazol-2-yl)benzene-1-sulfonamide (L1) and 4-{[1-(2-hydroxyphenyl)ethylidene]amino}-N-(1,3-thiazol-2-yl)benzene-1-sulfonamide (L2), have been synthesized and coordinated with the transition metals (V, Fe, Co, Ni, Cu and Zn). The ligands were characterized by their physical (color, melting point, yield and solubility), spectral (UV-Vis, FT-IR, LC-MS, 1H NMR and 13C NMR) and elemental data. The structures of the metal complexes (1)-(12) were evaluated through their physical (magnetic and conductance), spectral (UV-Vis, FT-IR and LC-MS) and elemental data. The molecular geometries of ligands and their selected metal complexes were optimized at their ground state energies by B3LYP level of density functional theory (DFT) utilizing 6-311+G (d, p) and LanL2DZ basis set. The first principle study has been discussed for the electronic properties, the molecular electrostatic possibilities as well as the quantum chemical identifiers. An obvious transition of intramolecular charge had been ascertained from the occupied to the unoccupied molecular orbitals. The UV-Vis analysis was performed through time-dependent density functional theory (TD-DFT) by CAM-B3LYP/6-311+G (d, p) function. The in vitro antimicrobial activity was studied against two fungal (Aspergillus niger and Aspergillus flavus) and four bacterial (Staphylococcus aureus, Klebsiela pneumoniae, Escherichia coli and Bacillus subtilis) species. The antioxidant activity was executed as antiradical DPPH scavenging activity (%), total iron reducing power (%) and total phenolic contents (mg GAEg-1). Additionally, enzyme inhibition activity was done against four enzymes (Protease, α-Amylase, Acetylcholinesterase and Butyrylcholinesterase). All the synthetic products exhibited significant bioactivity which were found to enhance upon chelation due to phenomenon of charge transfer from metal to ligand.

Global Tech Giants and Local Network Service Charge

We study a network usage charge in a local digital service market in response to local users' enormous demands for global online digital services such as Youtube, Facebook, Google, and so on. Local network service providers suffer from transit charges incurred by network traffic to/from the global online services, and request for mandating the global companies to make contracts with them on local network services. We investigate a situation where the local network service providers establish local cache servers for the global services to reduce the network transits, and another situation where the global online service companies are mandated to operate local subsidiaries responsible for making contracts with the local network service providers. Based on a stylized mathematical model, we find that the network service charge could increase for both cases, but with steep increases in case of a local subsidiary. Also, it is found that user surplus deteriorates for a local subsidiary case.

Control of vertical phase separation in high performance non-fullerene organic solar cell by introducing oscillating stratification preprocessing

Non-fullerene organic solar cell (NFOSC) has attracted tremendous attention due to their great potential for commercial applications. To improve its power conversion efficiency (PCE), generally, sequential solution deposition (SSD) methods have been employed to construct the graded vertical phase separation (VPS) of the bulk-heterojunction (BHJ) active layer for efficient exciton separation and charge transition. However, a variety of orthogonal solvents used in the SSD may lead to the unpredicted change in the BHJ morphology and introduce additional defects inside the BHJ bulk thus complicate the fabrication process. Here, a simple oscillating stratification preprocessing (OSP) is developed to facilitate the formation of graded VPS among the BHJ layer. As a result, a significant improvement is obtained in PCE from 10.96% to 12.03%, which is the highest value reported among PBDB-T: ITIC based NFOSC.

Electron cascade for distant spin readout

The spin of a single electron in a semiconductor quantum dot provides a well-controlled and long-lived qubit implementation. The electron charge in turn allows control of the position of individual electrons in a quantum dot array, and enables charge sensors to probe the charge configuration. Here we show that the Coulomb repulsion allows an initial charge transition to induce subsequent charge transitions, inducing a cascade of electron hops, like toppling dominoes. A cascade can transmit information along a quantum dot array over a distance that extends by far the effect of the direct Coulomb repulsion. We demonstrate that a cascade of electrons can be combined with Pauli spin blockade to read out distant spins and show results with potential for high fidelity using a remote charge sensor in a quadruple quantum dot device. We implement and analyse several operating modes for cascades and analyse their scaling behaviour. We also discuss the application of cascade-based spin readout to densely-packed two-dimensional quantum dot arrays with charge sensors placed at the periphery. The high connectivity of such arrays greatly improves the capabilities of quantum dot systems for quantum computation and simulation.

Layered Hexagonal Perovskite Oxides 21R Ba7Fe5Ge2O20 and 12H Ba6Fe3Ge3O17.

Two hexagonal-perovskite-structure oxides, 21R Ba7Fe5Ge2O20 and 12H Ba6Fe3Ge3O17, were obtained by synthesis with a high-pressure and high-temperature technique. The Fe-containing hexagonal-perovskite-structure units are sandwiched by nonmagnetic GeO4 tetrahedral layers in the structures, and thus both compounds show two-dimensional ferrimagnetic behaviors due to intra- and interunit magnetic interactions. 21R Ba7Fe5Ge2O20 has the ionic formula Ba7Fe123+Fe24+Fe324+Ge424+O20 at room temperature, and unusually high valence Fe4+ in the trimers undergoes charge disproportionation, Fe24+ + 2Fe34+ → Fe2(4+2δ)+ + 2Fe3(4-δ)+, at low temperatures. In contrast, 12H Ba6Fe3Ge3O17 with ionic formula Ba6Fe123+(Fe20.54+Ge20.54+)2Ge324+O17 does not show a charge transition.

Algorithm for maintaining the energy balance of the power supply system of the earth remote sensing spacecraft under critical operating conditions

In this paper, we consider the problem of maintaining the energy balance of the power supply system of the Earth remote sensing spacecraft in critical operating conditions with the most intense cyclogram of the spacecraft operation, the maximum state of degradation of energy sources and storage devices, as well as with the minimum time to replenish useful energy.The problem of maintaining balance is formulated as a problem of nonlinear mathematical programming with functional constraints. Goal of the work is improving the efficiency and survivability of the remote sensing spacecraft and maintaining the energy balance of the power system in critical operating conditions by transferring the storage devices of the accumulating subsystem of the spacecraft to a given level of charge in the minimum charge time. An algorithm for controlling the accelerated charge of the rechargeable battery with the analysis of the Nickel-hydrogen battery temperature and its time derivative is developed.in some cases, the rechargeable battery replenishment time was reduced by 12−20%. The proposed algorithm for maintaining the energy balance can be used to select the stages of the accumulating subsystem charge current and transition from the current stage to the next one in a minimum time, providing flexibility in managing the modes of electricity storage with the adaptation of the charging current profiles to changing critical operating conditions.

Evaluating first-order molecular properties of delocalized ionic or excited states in molecular aggregates by renormalized excitonic method

In the past few years, the renormalized excitonic model (REM) approach was developed as an efficient low-scaling ab initio excited state method, which assumes the low-lying excited states of the whole system are a linear combination of various single monomer excitations and utilizes the effective Hamiltonian theory to derive their couplings. In this work, we further extend the REM calculations for the evaluations of first-order molecular properties (e.g. charge population and transition dipole moment) of delocalized ionic or excited states in molecular aggregates, through generalizing the effective Hamiltonian theory to effective operator representation. Results from the test calculations for four different kinds of one dimensional (1D) molecular aggregates (ammonia, formaldehyde, ethylene and pyrrole) indicate that our new scheme can efficiently describe not only the energies but also wavefunction properties of the low-lying delocalized electronic states in large systems.

Strategic molecular design of closo-ortho-carboranyl luminophores to manifest thermally activated delayed fluorescence.

In this paper, we propose a strategic molecular design of closo-o-carborane-based donor–acceptor dyad system that exhibits thermally activated delayed fluorescence (TADF) in the solution state at ambient temperature. Planar 9,9-dimethyl-9H-fluorene-based compounds with closo- and nido-o-carborane cages appended at the C2-, C3-, and C4-positions of each fluorene moiety (closo-type: 2FC, 3FC, 4FC, and 4FCH, and nido-type: nido-4FC = [nido-form of 4FC]·[NBu4]) were prepared and characterized. The solid-state molecular structure of 4FC exhibited a significantly distorted fluorene plane, which suggests the existence of severe intramolecular steric hindrance. In photoluminescence measurements, 4FC exhibits a noticeable intramolecular charge transition (ICT)-based emission in all states (solution at 298 K and 77 K, and solid states); however, emissions by other closo-compounds were observed in only the rigid state (solution at 77 K and film). Furthermore, nido-4FC did not exhibit emissive traces in any state. These observations verify that all radiative decay processes correspond to ICT transitions triggered by closo-o-carborane, which acts as an electron acceptor. Relative energy barriers calculated by TD-DFT as dihedral angles around o-carborane cages change in closo-compounds, which indicates that the structural formation of 4FC is nearly fixed around its S0-optimized structure. This differs from that for other closo-compounds, wherein the free rotation of their o-carborane cages occurs easily at ambient temperature. Such rigidity in the structural geometry of 4FC results in ICT-based emission in solution at 298 K and enhancement of quantum efficiency and radiative decay constants compared to those for other closo-compounds. Furthermore, 4FC displays short-lived (∼0.5 ns) and long-lived (∼30 ns) PL decay components in solution at 298 K and in the film state, respectively, which can be attributed to prompt fluorescence and TADF, respectively. The calculated energy difference (ΔEST) between the first excited singlet and triplet states of the closo-compounds demonstrate that the TADF characteristic of 4FC originates from a significantly small ΔEST maintained by the rigid structural fixation around its S0-optimized structure. Furthermore, the strategic molecular design of the o-carborane-appended π-conjugated (D–A) system, which forms a rigid geometry due to severe intramolecular steric hindrance, can enhance the radiative efficiency for ICT-based emission and trigger the TADF nature.

A charge sensor integration to tunable double quantum dots on two neighboring InAs nanowires.

A single quantum dot serving as a charge sensor is integrated to scalable double quantum dots using local top finger-gate techniques on two neighboring pure-phase InAs nanowires. The single dot built on one nanowire capacitively couples one of the double dots constructed on another nanowire via a metal bridge gate. The charge occupation states of double quantum dots can be accurately monitored by the sensor even in a few-electron regime in which transport tunneling current through the double dots vanishes. In the tunneling spectroscopy of double dots, electron inter dot tunneling process is absent; however, it can be illustrated by the sensor in terms of a transconductance line between the two closest triple points. Thus, tunnel coupling strength between the double dots is quantitatively extracted from the detectable charge transition. The highly tunable multiple quantum dots with integrated charge sensors on InAs nanowires could be an essential building block for quantum information processing technology.

Tuning the charge of polyelectrolyte complex membranes prepared via aqueous phase separation.

In this work, polyelectrolyte mixing ratio is studied as a tuning parameter to control the charge, and thus the separation properties of polyelectrolyte complex (PEC) membranes prepared via Aqueous Phase Separation (APS). In this approach, various ratios of poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC) are mixed at high salinity and the PEC-based membranes are then precipitated using low salinity coagulation baths. The monomeric ratio of PSS to PDADMAC is varied from 1.0 : 0.8 through to 1.0 : 1.2. Obtained membranes have an asymmetric structure and function as nanofiltration membranes with on average 1 L m−2 h−1 bar−1 pure water permeance and <400 Da molecular weight cut-off (MWCO); except for the 1.0 : 1.2 membrane, where the water permeance was much higher (>20 L m−2 h−1 bar−1) with a similarly low MWCO. For the first time, we report the formation of both negatively and positively charged PSS–PDADMAC based APS membranes, as determined by both streaming potential and salt retention measurements. We hypothesize that the salt type used in the APS process plays a key role in the observed change in membrane charge. The point where the membrane charge transitions from negative to positive is found to be between the 1.0 : 0.9 and 1.0 : 1.0 PSS : PDADMAC ratios. The polyelectrolyte ratio not only affects membrane charge, but also their mechanical properties. The 1.0 : 0.9 and 1.0 : 1.0 membranes perform the best amongst the membranes prepared in this study since they have high salt retentions (up to 90% Na2SO4 and 75% MgCl2, respectively) and better mechanical stability. The higher permeance of the more charged, and thus more swollen, 1.0 : 0.8 and 1.0 : 1.2 membranes provide a relevant new direction for the development of APS-based PEC membranes.

ZnFe2O4 Doped TiO2 Photocatalyst Synthesis and Characterization with Effect of Different Coupling Ratios on Band Gap

In this work the effect of different coupling ratios of ZnFe2O4 and TiO2 on the band gap was investigated, to convert TiO2 as a visible light driven photocatalyst ZnFe2O4. In this work, ZnFe2O4 was synthesized utilizing sol-gel technique and calcining under normal atmosphere at 900 and#176;C. Thereafter, ZnFe2O4 was coupled with TiO2 by mixing in 50 ml water in three different coupling w/w ratios (1:1, 1:2 and 2:1) followed by the calcination of coupled catalyst under nitrogen environment at 500 and#176;C. XRD, XPS, FESEM-EDS imaging, TGA, UV-Vis, and FTIR were performed to characterize the catalyst. Crystal phase identification could be confirmed through XRD analysis with homogenous distribution of metal constituents through color mapping and surface charge transitions from XPS analysis for a better electron hole generation. Thermogravimetric analysis (TGA) confirmed that the pure ZnFe2O4 obtained at 900 and#176;C, while FTIR verified the presence of desired functional group in ZnFe2O4. Moreover, Fourier Transformation Infrared Spectroscopy (FTIR) illustrated two major peaks and no extra major impurity was detected. ZnFe2O4 is visible light driven photocatalyst and TiO2 can work only under UV light. So, the effect of different coupling ratios of ZnFe2O4 with TiO2 was examined by UV-Vis characterization. The band gap is given by 1:1 was 2.8, 2:1 was 3.17 and 1:2 was 3.02. It was observed that the most optimum coupling ratio is 1:1 and the band-gap fall under visible region. The findings of this work could be supportive significantly for the selection of suitable coupling ratio to convert UV-driven photocatalyst into visible region active photocatalyst.

Study on the optical properties for the F-type color center in BeO crystal with first-principles

In this paper, we calculated the defect formation energy of oxygen vacancies with different charge states (0, +1, +2) in beryllium oxide crystal by using density functional theory (DFT). Based on defect formation energy, the positions of charge transition levels are obtained. However, there is a well-known problem that DFT will underestimate the band gap, which leads to the positions of charge transition levels are arguable. To obtain more accurate charge transition levels, we employ the hybrid functionals (HSE) to relieve the band edge problem, as well as use the finite-size corrections (FNV) to correct the defect formation energy. After obtaining the location of the charge transition level, we obtain a reliable description of the optical line shape of the F/F[Formula: see text] center containing electron–phonon coupling. The absorption spectra of the F center and F[Formula: see text] center peak at 7.1 eV and 6.3 eV, respectively. The luminescence band of the F center peaks at 4.7 eV. Furthermore, we speculate that the luminescence band near 3.7 eV is assigned to the F[Formula: see text] center.

Confinement of pyrrolidinium-based ionic liquids [CnMPyrr]+[Tf2N]− with long cationic alkyl side chains (n = 10 and 16) to nanoscale pores: Dielectric and calorimetric studies

Ionic liquids (ILs) with long cationic side chains have shown potential applications in wide fields such as phase-change materials for seasonal energy storage, environmentally friendly herbicides, components of ideal electrode material for supercapacitor devices, and more. In this paper, we investigated the glass transition dynamics, charge transport and structure properties of two pyrrolidinium-based ILs, [CnMPyrr]+[Tf2N]− with n = 10 and 16. Differential scanning calorimetry studies demonstrated the poor glass forming ability (GFA) of the tested materials, especially [C16MPyrr]+[Tf2N]−. Temperature-dependent X-ray diffraction measurements suggested the layered structures in the crystalline and liquid phases of both ILs. Through the dielectric measurements of [C10MPyrr]+[Tf2N]−, we noticed its higher conductivity than the homologues with shorter cationic alkyl chains, in the supercooled liquid state. Additionally, the derivative spectra, εder′′ = (−π/2)[∂ε′/∂ ln (f)], of [C10MPyrr]+[Tf2N]− at temperatures above Tg were examined, and no evidence of the slow sub- α mode associated with the self-aggregation of alkyl chains is detected. Next, we checked how [C10MPyrr]+[Tf2N]− and [C16MPyrr]+[Tf2N]− behaved when geometrically confined in alumina nanopores with various sizes ranging from 10 nm to 120 nm. With respect to the bulk material, confined [C10MPyrr]+[Tf2N]− samples are featured by the drastically enhanced GFA but up to 300-fold decrease in ionic conductivity. In addition, for [C16MPyrr]+[Tf2N]−, vitrification is unfulfilled even when confined into 10 nm nanopore. Nonetheless, nanoscale constraints bring pronounced melting temperature depression and enhanced conductivity to the crystalline confined samples relative to the bulk counterpart. The results of this study contribute to a more comprehensive picture of various confinement effects on ILs and will benefit the rational design of ILs-containing nanodevices.

Probing Delocalized Current Densities in Selenophene by Resonant X-ray Sum-Frequency Generation

Time-resolved, resonant X-ray sum-frequency generation in aligned selenophene molecules is calculated. A wave packet of valence-excited states, prepared by an extreme-ultraviolet pump pulse, is probed by two 12-keV X-ray probe pulses resonant with the Se core-excited states for variable time delays. At these hard-X-ray frequencies, the angström wavelength of the X-ray probe is comparable to the molecular size. We thus employ a nonlocal description of the light-matter interaction based on the minimal-coupling Hamiltonian. The wavevector-resolved resonant stimulated sum-frequency-generation signal, obtained by varying the propagation direction of hard-X-ray pulses, can thus directly monitor the transition current densities between core and ground/valence states. This is in contrast to off-resonant diffraction, which detects the transition charge densities.

Identification of LiNi and VNi acceptor levels in doped nickel oxide

Nickel oxide, in particular in its doped, semiconducting form, is an important component of several optoelectronic devices. Doped NiO is commonly achieved either by incorporation of lithium, which readily occupies Ni sites substitutionally, producing the LiNi acceptor, or by supplying reactive oxygen species during NiO film deposition, which leads to the formation of Ni vacancies (VNi). However, the energetic position of these acceptors in the NiO bandgap has not been experimentally determined until today. In this work, we close this knowledge gap by studying rectifying n++p heterojunctions consisting of NiO thin films grown on top of fluorine-doped tin oxide. These structures show sufficient rectification to perform electric characterization by defect spectroscopic techniques, specifically capacitance–voltage and thermal admittance spectroscopy. Using these methods, the (0/−) charge transition levels are determined to be 190 meV and 409 meV above the valence band edge for the LiNi and the VNi acceptor, respectively.

The second-order nonlinear optical property of hydrazones-based photochromic complexes: A DFT study

A family of hydrazone-based photochromic derivatives consisting a hydrazone switching and phenyl groups with R1 and R2 (R = H, -NO2 and -NMe2) can be induced by light to form two isomers (Z-type and E-type). In this paper, we discussed detailedly the impacts of structural change on UV–Vis absorption spectra, electronic transition properties and the first hyperpolarizability (βtot) by using density functional theory (DFT) methods. The calculation results showed that second-order NLO responses of Z-type complexes are stronger than that of corresponding E-type complexes due to the red-shift of absorption spectra, the smaller electronic transition energy (ΔEge) and the narrower energy band gap (Egap) of frontier molecular orbital. Furthermore, the push-pull complexes 4 may be potential NLO materials due to the larger βtot values, for example, the βtot values of 4Z and 4E are 1.6 × 104 a.u. and 9.3 × 103 a.u., respectively. It is that the donor (D) and acceptor (A) groups are dominated by the interaction of D and A group via intramolecular charge transition (CT). We hope that this research will introduce a new relation between the structure and the photochromic nonlinear optical activity.

Colossal dielectric response in erbium iron garnet ceramics

Polycrystalline Er3Fe5O12 ceramic sample was synthesized by a solid-state reaction technique. The dielectric properties of the sample were experimentally studied. A colossal dielectric constant more than 103 was observed over a wide temperature and frequency range. The dielectric relaxation in the sample was identified by the measurement of permittivity modulus, impedance spectroscopy, and conductivity in detail. At relatively low temperatures (T < 600 K), the dielectric relaxation under high frequencies (f ≥ 50 kHz) is triggered by the dipolar effect accompanied by the Fe2+ and Fe3+ charge transitions, while that under low frequencies (f ≤ 50 kHz) is mainly be associated with the Maxwell–Wagner effect. Moreover, a low-frequency dielectric relaxation at high temperatures (T ≥ 600 K) is probably evolving from the contribution of oxygen vacancies and grain boundaries, which is also suggested to be the origin of the colossal dielectric constant.

First-principles study of persistent luminescence mechanisms in CaB2O4:Ce3+

Abstract First-principles calculations based on the density functional theory (DFT) are carried out to explore the mechanisms of the persistent luminescence (PersL) in CaB2O4:Ce3+ phosphors. Firstly, the energies and Stokes shifts of 4f → 5d transitions of Ce3+ ions in the CaB2O4 are successfully obtained and agree well with the experimental results. Thus, the experimental excitation spectra of the CaB2O4:Ce3+ are assigned successfully. The formation energies and thermodynamic transition levels of candidate intrinsic vacancies (of Ca, O, B and BO), antisite defects (BCa) and Ce3+ ions in the host are calculated in order to understand their effects on the PersL of CaB2O4:Ce3+ phosphors. By combining the presented calculation results and Dorenbos empirical model, the charge transition levels for all the trivalent and divalent lanthanides in the host are derived, which can be adopted to predict the candidate emission and trap centers for the PersL in the lanthanide-doped CaB2O4.