Positive Electric Field Research Articles

Supramolecularly Built Local Electric Field Microenvironment around Cobalt Phthalocyanine in Covalent Organic Frameworks for Enhanced Photocatalysis.

The local electric field (LEF) plays an important role in the catalytic process; however, the precise construction and manipulation of the electric field microenvironment around the active site remains a significant challenge. Here, we have developed a supramolecular strategy for the implementation of a LEF by introducing the host macrocycle 18-crown-6 (18C6) into a cobalt phthalocyanine (CoPc)-containing covalent organic framework (COF). Utilizing the supramolecular interaction between 18C6 and potassium ion (K+), a locally enhanced K+ concentration around CoPc can be built to generate a LEF microenvironment around the catalytically active Co site. The COF with this supramolecularly built LEF realizes an activity of up to 7.79 mmol mmolCo-1 h-1 in the photocatalytic CO2 reduction reaction (CO2RR), which is a 180% improvement compared to its counterpart without 18C6 units. The effect of LEF can be subtly controlled by fully harnessing the K+@18C6 interaction by changing the potassium salts with different counterions. In situ spectroscopy and density functional theory calculations show that the complexation of K+ by 18C6 creates a positive electric field that stabilizes the critical intermediate *COOH involved in CO2RR, which can be tuned by the halide ion-mediated K+@18C6 interaction and hydrogen-bonding interaction, consequently leading to improved catalytic performance to varying degrees.

Investigating the Current-Carrying Friction Mechanism of n-Type and p-Type Two-Dimensional TMD under a Positive Electric Field.

Nanofriction plays an important role in the performance and lifetime of n-type or p-type TMD-based semiconductor nanodevices. However, the mechanism of nanofriction in n-type and p-type TMD semiconductors under an electric field is still blurry. In this paper, monolayers of n-MoSe2 and p-WSe2 materials were prepared by chemical vapor deposition (CVD), and their nanofriction behavior under positive electric field was investigated. Atomic force microscopy (AFM) was used to analyze the nanofriction by the positive voltage applied through the needle tip: both the friction and the friction coefficient of MoSe2 increased with the increase of the applied voltage, while the friction and the friction coefficient of WSe2 decreased with the increase of the applied voltage. As the applied voltage increases, the friction force and energy dissipation exhibit corresponding trends in relation to the surface potential. The accumulation and dissipation of carriers represent significant factors influencing friction change. The diverse types of carriers give rise to variations in the friction laws. Our experiments have revealed the differences and mechanisms of friction in TMD materials dominated by different carrier types at positive voltages. It provides guidance for the application and modulation of n- and p-type two-dimensional semiconductor materials in the field of friction.

Highly selective copper recovery from industrial wastewater via electric field-enhanced ultrafiltration assisted with a picolyl-modified polyelectrolyte.

Copper-containing industrial wastewater, characterized by strong acidity, high ionic strength, and various competing metals, presents significant challenges for Cu(II) recovery. To address these issues, an electric field-enhanced ultrafiltration process was developed, assisted with a functional polyelectrolyte with high selectivity for Cu(II). The polyelectrolyte, termed PPEI, was synthesized by grafting picolyl groups onto polyethyleneimine (PEI), enhancing its affinity for Cu(II). The captured Cu(II) was subsequently recovered through electrolysis, demonstrating a sustainable approach for both Cu recovery and PPEI recycling. The synthesis and stability of PPEI were confirmed through infrared spectroscopy, particle size analysis, and dialysis validation, ensuring its reliability in practical applications. The incorporation of picolyl groups onto PPEI enhances its selectivity for Cu(II) via coordination with two amines and four pyridyl groups per copper ion. Under acidic conditions, the maximum loading ratio of copper to PPEI is 1:4 with loading capacity of 119.4 mg/g, which increases to 1.5:4 (i.e., 179.1 mg/g) under neutral to alkaline conditions due to the deprotonation of excess amines. PPEI effectively removes Cu(II) from solutions under various harsh conditions at the loading ratio of 4, maintaining 92-98 % removal efficiency in the presence of high salt concentrations (up to 1 M NaCl) and pH as low as 1, and approximately 85 % removal in solutions with competing metal ions at concentrations up to 50 times higher than Cu(II). Scanning electron microscopy and membrane flux changes indicated that the application of a positive electric field significantly reduces membrane fouling and enhances Cu(II) selectivity. The application of a +0.2 V voltage to the membrane side reduced the flux decline rate by 58 %, significantly improving membrane performance while maintaining a Cu(II) removal efficiency of over 95 %. Electrolysis optimized at a current density of ≤0.004 A/cm2 achieved an 80 % copper recovery while allowing PPEI to be released for recycling. Tests conducted using two types of real industrial wastewater demonstrated a copper removal rate of ∼95 %, with a recovery rate of ∼80 %. This study provides a novel and highly selective approach for the efficient recovery of valuable metals from industrial wastewaters.

Investigation on properties of CuI/InSe heterojunction with Z–alignment for photocatalytic water splitting

The energetic, thermodynamic and mechanically stability as well as the electronic and optical properties of the monolayers CuI, InSe and the constructed CuI/InSe heterojunction have been investigated by first–principles calculations. The solar–to–hydrogen production efficiency of CuI/InSe heterojunction with or without applied electric field or biaxial strain has been predicted and elucidated in view of electronic structure systematically. The exciton binding energy and carrier mobility in CuI, InSe and CuI/InSe as well as the hydrogen and the oxygen evolution reaction have been analyzed. The predicted results show that the constructed 2D–CuI/InSe van der Waals heterojunction with Z–alignment is energetic, thermodynamic and mechanically stable. It enables the hydrogen production to take place on the CuI layer meanwhile oxygen is generated on the InSe layer during photocatalytic water splitting. The solar–to–hydrogen production efficiency of the constructed CuI/InSe1×1×1, CuI/InSe2×2×1 and CuI/InSe3×3×1 is predicted as 31.16%, 25.61% and 24.84% respectively. The exciton binding energy of CuI/InSe is lower than that of monolayers. A moderate negative applied electric field can promote the solar–to–hydrogen production efficiency of CuI/InSe while the positive electric field makes it decrease. Similarly, a moderate positive applied strain can also promote solar–to–hydrogen production efficiency of CuI/InSe significantly while the negative applied strain decreases the solar–to–hydrogen production efficiency.

Interfacial polarization charge engineering with co-designed LQB and EBL for enhanced EQE of AlGaN DUV LEDs

Abstract In this paper, we propose to modulate the polarization charges at the interface between the last quantum barrier (LQB) and the electron blocking layer (EBL) via strategically adjusting the Al composition in the LQB and EBL simultaneously. With appropriate design of the linear gradient profile in Al composition, the original positive polarization charges at the LQB/EBL interface can be diminished or converted into negative charges, which helps to reduce the positive electric field in EBL, thus adjusting the energy band near the LQB/EBL interface. Enhanced effective barrier height for electrons, decreased effective barrier height for holes, and accumulation of a large number of holes at the LQB/EBL interface are obtained, resulting in improved electron leakage and hole injection. In comparison with the reference deep ultraviolet light-emitting diode (DUV LED), an enhanced external quantum efficiency by 37.5% at an injection current density of 100 A cm−2 is achieved for the device with negative polarization charges. The modulation strategy of polarization charges at the LQB/EBL interface via co-designing the linear gradient of Al composition in LQB and EBL can be a feasible approach for obtaining high-performance DUV LEDs.

Regulating the Positive Localized Electric Field in Mixed Matrix Membranes by Charge Reversal of ILs‐COF for Boosting CO2 Separation

AbstractCovalent organic frameworks (COFs), characterized by their high porosity and stability, hold great potential for applications in gas separations. However, achieving precise size sieving without hindering the gas diffusion rate is challenging. This study presents a novel approach to establishing tunable localized electric fields in COF channels to achieve efficient CO2 separation in Pebax‐based mixed matrix membranes (MMMs). Different charge densities of the localized electric field are achieved by the host–guest interaction between COF and varying charged ionic liquids (ILs). Remarkably, the MMM with a positive localized electric field attains the optimal CO2/CH4 separation performance with a significantly enhanced permeability (≈38%) and selectivity (≈99%), surpassing the Robeson upper bound. Through density functional theory (DFT) calculations, the enhanced CO2/CH4 selectivity of MMM is due to the “sieving effect” of a positive localized electric field on CO2 over CH4. Specifically, the negatively charged O atom in CO2 exhibits stronger electrostatic interaction than the positively charged H atom of CH4. Therefore, the strategy of regulating the localized electric field can be employed as an efficient design for CO2 separation in MMMs.

Stacking-dependent and electric field-driven electronic properties and band alignment transitions in γ-GeSe/Ga2SSe heterostructures: a first-principles study.

In this work, we present a comprehensive investigation into the electronic properties and contact behavior of γ-GeSe/Ga2SSe heterostructures using first-principles calculations. Two stacking configurations, γ-GeSe/SGa2Se and γ-GeSe/SeGa2S, are explored, both exhibiting semiconducting behavior with type-II and type-I band alignments, respectively. Notably, our results show that the band alignment transition in these heterostructures can occur spontaneously by simply altering the stacking configuration, eliminating the need for external factors. Additionally, the electronic properties of these heterostructures are highly tunable with an applied electric field, further enabling transitions between type-I and type-II alignments. Specifically, a positive electric field induces a transition from type-II to type-I alignment in the γ-GeSe/SGa2Se heterostructure, while a negative field drives the reverse transition in the γ-GeSe/SeGa2S heterostructure. Our findings underscore the potential of γ-GeSe/Ga2SSe heterostructures for diverse applications, where the tunability of electronic properties is crucial for optimizing device performance.

First-principles study of nonlinear magnetoelectric effects in improper LuFeO3 multiferroics

Hexagonal LuFeO3 is known as an improper multiferroic material because of its ferroelectric structural distortion, measured by the Γ2− polar mode, and is driven by a trimerization structural distortion represented by the K3 non-polar mode [Fennie and Rabe, Phys. Rev. B 72, 100103(R) (2005)]. The K3 mode is also the primary structural origin of net weak ferromagnetism, associated with the ferromagnetic coupling between the in-plane geometrically frustrated spins. Here, we study the magnetoelectric coupling in LuFeO3 using first-principles calculations and applied external electric fields. We find that the weak ferromagnetism responds to the electric field polarization through the K3–Γ2− coupling, which is an intrinsic characteristic of improper multiferroics. Interestingly, the magnetoelectric coupling exhibits strong asymmetry under positive and negative electric fields. This nonlinearity is due to the competition between the K3 and the Γ2− modes according to Landau's theory and is related to asymmetrical interatomic interactions at the atomic level.

Enhancing optical absorbance and accelerating rotational speed in molecular motors through oriented external electric fields

Accelerating the rotational speed of light-driven molecular motors is among the foremost concerns in molecular machine research, as this speed directly influences the performance of a motor. Controlling the motor’s rotation is crucial for practical applications, and using an oriented external electric field (OEEF) represents a feasible method to achieve this objective. We have investigated the impact of an OEEF on the optical and kinetic properties of a novel π-donor/acceptor di-substituted molecular motor, R2,3-(NH2, CHO). We employed density functional theory (DFT) and time-dependent DFT methods to analyze the electronic excitation and thermal isomerization behavior. Our results demonstrate that the absorption wavelength, absorption efficiency of the motor, and rate constant of the thermal isomerization reaction can be adjusted by applying OEEFs, which are predictable based on the dipole moment and polarizability of the molecules under consideration. In particular, we observed a shift in the absorption wavelength toward longer ranges, an enhancement in light absorption intensity, and an acceleration in the rotation rate when applying a weak positive directional external electric field to the R2,3-(NH2, CHO) motor. In summary, this theoretical study highlights the potential of OEEFs for improving the performance of molecular motors.

Optimised stellarators with a positive radial electric field

Optimised stellarators with a positive radial electric field

First Principle Study on the Z-Type Characteristic Modulation of GaN/g-C3N4 Heterojunction.

This study investigates the stability, electronic structure, and optical properties of the GaN/g-C3N4 heterojunction using the plane wave super-soft pseudopotential method based on first principles. Additionally, an external electric field is employed to modulate the band structure and optical properties of GaN/g-C3N4. The computational results demonstrate that this heterojunction possesses a direct band gap and is classified as type II heterojunction, where the intrinsic electric field formed at the interface effectively suppresses carrier recombination. When the external electric field intensity (E) falls below -0.1 V/Å and includes -0.1 V/Å, or exceeds 0.2 V/Å, the heterojunction undergoes a transition from a type II structure to the superior Z-scheme, leading to a significant enhancement in the rate of separation of photogenerated carriers and an augmentation in its redox capability. Furthermore, the introduction of a positive electric field induces a redshift in the absorption spectrum, effectively broadening the light absorption range of the heterojunction. The aforementioned findings demonstrate that the optical properties of GaN/g-C3N4 can be precisely tuned by applying an external electric field, thereby facilitating its highly efficient utilization in the field of photocatalysis.

Geometrical stability, electrical contact and optical properties for ZrX2(X = Cl, Br, I) /Zr2Cl2 semiconductor-metal heterojunctions

Exploring metal–semiconductor electrical contact behaviors is highly desirable for developing high-performance new devices. Here, transition metal halide ZrX2 (X = Cl, Br, I)/Zr2Cl2 vdW heterojunctions are constructed by semiconducting ZrX2 and metallic Zr2Cl2 monolayers. Our calculations reveal that such metal–semiconductor heterojunctions possess very high energetic, thermal, dynamic and mechanical stability, with p-type Schottky contacts in the intrinsic state, and their Schottky barrier height (SBH) decreases with the atom number of haloid elements increased. Particularly, ZrI2/Zr2Cl2 heterojunction exhibits a very low p-type SBH, 0.18 eV, favorably to design high-performance Schottky devices. Their electronic and electrical contact properties can also be modulated by physical field coupling effects. For example, p-type SBH decreases continuously to obtain quasi-Ohmic contact under applied compressive strain, and the p-type Schottky contact can be transformed to p-type Ohmic contacts under suitable positive external electric field for all heterojunctions. Particularly, ZrI2/Zr2Cl2 heterojunction achieves Ohmic contact by a relatively low positive electric field, 0.15 V/Å. It is also shown that all heterojunctions possess high intrinsic light absorption capability. The light absorption performance of ZrBr2/Zr2Cl2 heterojunction would undergo a significant enhancement under electric field. Therefore, these suggested heterojunctions hold promising application potentials for developing electronic and optoelectronic devices.

Strengthened ozone adsorption through positive electric field-induced charge migration on various TiO2 crystal surfaces: A mechanistic and theoretical study

This study investigates the enhancement of ozone adsorption on diverse TiO2 crystal interfaces through an innovative electrochemical modulation approach. The research focuses on the effects of applied electric field strength and reaction sites on ozone interfacial adsorption energies for Ti/Anatase TiO2 (0 0 1) and Ti/Rutile TiO2 (1 1 0) interfaces. The findings reveal that positive electric fields significantly enhance ozone adsorption on both interfaces, with adsorption energies increasing by up to 18% for Ti/Anatase TiO2 (0 0 1) and 15% for Ti/Rutile TiO2 (1 1 0). Notably, double water molecule sites (≡(H2O)2) play a crucial role in this enhancement process. The study demonstrates that the applied electric field alters the charge distribution at the TiO2 catalytic interface, thereby increasing interfacial charge density and promoting charge migration to ozone. Furthermore, this process leads to enhanced overlap and hybridization between ≡(H2O)2 sites and the s and p orbitals of ozone molecules, resulting in the formation of chemical bonds with lower Fermi levels. These comprehensive results demonstrate the broad applicability of the electrochemical interfacial ozone adsorption enhancement method across different crystal types and surfaces. Consequently, this study provides essential data to support the advancement of greener and more energy-efficient heterogeneous catalytic ozonation processes, potentially contributing to significant improvements in ozone-based water treatment technologies.

Investigation on Enhancement of AP/HTPB/Al Composite Solid Propellant Combustion Characteristics via DC Electric Field

ABSTRACT To investigate the influence mechanisms of DC electric fields on the combustion of solid propellants, a numerical model for the combustion characteristics of AP/HTPB/Al composite solid propellant under the DC electric field is established. Effects of the applied electric field on combustion flame structure, combustion surface temperature distribution, and mixing fraction distribution are analyzed. The results indicate that the applied electric field enhances the mixing effect of the propellant gas phase decomposition products, thereby altering the flame structure and bringing it closer to the combustion surface. The application of the electric field leads to an increase in the combustion surface temperature by 20–70 K. The effect of the negative electric field on the combustion surface temperature and burning rate is more significant compared to that of the positive electric field. The results provide valuable theoretical guidance in the field of solid engine combustion control.

Regulating molecules/ions sieving channels of MXene-based membranes by edge-capping strategy

Regulating molecules/ions transport within two-dimensional (2D) sub-nanometer channels to achieve a higher separation efficiency is of considerable interest for MXene membranes in sustainable water treatment. Herein, sodium tripolyphosphate (STPP) was introduced into Ti3C2Tx nanosheets to construct a series of modified STPP-MXene membranes based on the edge-capping strategy. The critical role of edge-capping in modulating selective molecules/ions separation within 2D sub-nanometer channels was highlighted. The edge-capping method was demonstrated to moderately narrow the shoulder spacing between adjacent Ti3C2Tx nanosheets and impaired their positive electric field intensity. In addition, the DFT results showed that the cations exhibited a much lower relative energy with STPP-Ti3C2Tx (-0.0024 eV) compared to Ti3C2Tx nanosheets (-0.2092 eV), causing cations to permeate more readily through the STPP-MXene membrane. As a result, the appropriately designed and prepared STPP-MXene membrane demonstrated an excellent molecules/ions selectivity (CR/NaCl selectivity = 52.6, CR/Na2SO4 selectivity = 30.3), much higher than that of the pristine MXene membrane. Moreover, by protecting the Ti at the edges of Ti3C2Tx nanosheets, the STPP-MXene membrane retained its original two-dimensional structure to maintain a stable separation performance, even when exposed to a water environment for up to 60 days. In contrast, the pristine MXene membrane was completely oxidized due to its weak stability. This study provides a theoretical basis for the feasibility of edge-capping strategy as a broad modification alternative to design high-efficiency molecular/ionic sieving MXene membranes.

Superelastic electromechanical behaviors in ferroelectric PbTiO[formula omitted] ceramics under coupled mechanical-electric fields: Higher-order piezoelectric constitutive equations from first-principles

With the recent discovery of superelastic behaviors of ferroelectric (piezoelectric) ceramics, understanding their non-linear mechanical and electromechanical responses under high stress and electric field conditions is crucial for engineering and designing advanced piezoelectric devices, such as ultrasmall actuator systems. In this study, we carry out first-principles finite electric field calculations to clarify the mechanical and electromechanical properties under the electric field for typical ferroelectric ceramics of PbTiO3. Superelastic-like non-linear deformation behavior is enhanced or suppressed depending on the electric field direction, suggesting the possible design of superelasticity. We clarified that positive and negative electric fields to spontaneous polarization promote and inhibit deformation due to strain loading, thereby providing tunable superelasticity. We also investigate the mechanical loading and electric field dependence of the piezoelectric coefficient of PbTiO3. The tunable piezoelectric response can be provided with a coupling of mechanical loading and electric field. Finally, we present higher-order piezoelectric constitutive equations applicable for superelastic-like non-linear deformations under an electric field. The present results will open promising paradigms for functional piezoelectric devices, and the proposed piezoelectric constitutive equations broaden the design scope through finite element method analysis.

Inhibiting the imprint effect of the TiN/HZO/TiN ferroelectric capacitor by introducing a protective HfO2 layer

Interfacial differences between the Hf0.5Zr0.5O2 (HZO) and the top/bottom electrodes caused by the process sequence could lead to the imprint effect of the TiN/HZO/TiN ferroelectric capacitor, which leads to serious reliability problems. In this article, a method of introducing a HfO2 protective layer is proposed to inhibit the imprint effect of the TiN/HZO/TiN ferroelectric capacitor. By introducing the HfO2 protective layer, the leakage current at the positive electric field is reduced by three orders of magnitude, the asymmetry of the coercive field is reduced from 1.5 to 0.1 MV/cm, and the endurance is improved by two orders of magnitude with no degradation in retention. The proposed method provides a feasible strategy to inhibit the imprint effect of TiN/HZO/TiN ferroelectric capacitors and is more compatible with complementary metal–oxide–semiconductor processes.

Study on the regulation of ε-CL-20 by an external electric field.

To explore the influence of the external electric field (EEF) on ε-CL-20. The molecular structure, frontier molecular orbitals (FMOs), global reactivity parameters (GRP), surface electrostatic potential, nitro charge, and UV-Vis spectra of ε-CL-20 under EEF were studied using density functional theory (DFT). The calculation results show that the electric field applied along N16-N24 has a significant effect on the structure of ε-CL-20. With an increase in the positive EEF, the bond length of the initiating bond decreases, and the bond order and bond dissociation energy increase, which increases the thermal stability of ε-CL-20 to a certain extent. In addition, with an increase in the positive EEF intensity, the LUMO migrates from both sides of the positive electric field to one side of the nitro group, and the HOMO migrates from the skeleton to the nitro group. It is worth noting that in the negative EEF, when the electric field strength changed from 0 to 0.016 a.u., the negative charge of the total nitro group gradually decreased. When the electric field strength becomes 0.02 a.u., the negative charge of the total nitro group suddenly increases, and ε-CL-20 is significantly polarized. When the electric field strength is sufficiently strong, the occupied and unoccupied orbitals of the ε-CL-20 molecule change, resulting in a change in the energy level difference between the occupied and unoccupied orbitals, which further excites the corresponding excited state, resulting in a new UV-Vis absorption peak. Based on the density functional theory (DFT), the structural optimization and energy calculation were carried out by using B3LYP/6-311 + G(d, p) and B3LYP/def2-TZVPP methods, respectively. After optimization convergence, vibration analysis was performed without imaginary frequencies to obtain stable configurations. Then the molecular structure, frontier molecular orbitals (FMOs), global reactivity parameters (GRP), surface electrostatic potential, nitro charge, and UV-Vis spectra were analyzed.

Controllable electrical contact characteristics of graphene/Ga2X3 (X = S, Se) ferroelectric heterojunctions

Reducing the interface barrier between metals and semiconductors is crucial for designing high-performance optoelectronic devices based on van der Waals heterojunctions (HJs). This study proposes four models of HJs composed of graphene (GR) and Ga2X3 (X = S, Se) and systematically investigates their interface electronic properties, along with strain engineering and electric field effects. The results indicated that exploiting the interface dipole-induced potential step allows modulation of the Schottky barrier height (SBH) and contact type of the HJs by altering the contact interfaces. In the BGR/Ga2S3 HJs (BGR means GR positioned at the bottom of Ga2X3), only a small positive (negative) electric field is required to realize the transition from n-type Schottky to p-type Schottky (Ohmic) contacts. Also, strain engineering provides additional means for flexible and controllable contact types, facilitating the design of reversible logic circuits. It indicates the physical insights and strategic interventions of GR/Ga2X3 HJs tunable SBH and offers theoretical guidance for the design of two-dimensional ferroelectric nanodevices with high-quality electrical contact interfaces.

Effects of external static electrical field on thermal and electrical conductivity in the Al-Cu, Al-Ni, and Al-Si eutectic alloys

This study aims to investigate the effects of external positive and negative static electric fields (E+ and E- respectively) on thermal conductivity (K) and electrical conductivity (σ) in Al-33 wt. % Cu, Al-6.4 wt. % Ni and Al-12 wt. % Si eutectic alloys. For this purpose, the solidifications of Al-Cu, Al-Ni, and Al-Si eutectic alloys were directionally done under E+ and E-. The directions of E were chosen to be parallel (E+) and antiparallel (E-) to the solid-liquid (S-L) growth direction and the magnitudes of E were approximately (+10) and (−10) kV cm−1 and (+16) and (-16) kV cm−1 for the Al-Cu, Al-Ni, and Al-Si eutectic alloys, respectively. The effects of E+ and E− on the K and σ were determined by the longitudinal heat flow and the four-point probe methods, respectively. While the K and σ values decreased with increasing temperature, the K and σ were increased and decreased with E+ and E−, respectively.