Change In Electronic Energy Research Articles

Phonon-Mediated Ultrafast Electron Relaxation Dynamics in Monolayer Black Phosphorus: Instantaneous Coherent Delocalization.

Understanding carrier relaxation processes in semiconductors is crucial for designing high-performance optoelectronic and photocatalytic devices. Recent transient spectroscopic experiments on two-dimensional materials have revealed ultrafast optical responses within several tens of femtoseconds, which are usually ascribed to electron-electron scattering. Here, by conducting quantum dynamics simulations for monolayer black phosphorus, we show that electron-phonon scattering also profoundly influences the early stage of carrier dynamics. The photogenerated electron generally undergoes phonon-mediated instantaneous coherent delocalization in reciprocal space, accompanied by an entropy-driven sharp change in electronic energy. The distribution of the density of states controls the energy exchange between the electron and lattice vibrations. The phonon-induced quantum coherence significantly suspends the energy relaxation time, which is very beneficial for harvesting electron excess energy. These findings offer novel insights into the ultrafast carrier dynamics and energy flow in two-dimensional materials and may prompt new opportunities for regulation of carrier dynamic behaviors.

Dominant changes in centre Fe atom of decamethyl-ferrocene from ferrocene in methylation

Staggered decamethyl-ferrocene (*Fc) becomes the lower energy conformer at low temperature, whereas the eclipsed conformer of ferrocene (Fc) is more stable. The powerful infrared (IR) spectroscopy which has remarkably provided signatures of ferrocene (Fc) in eclipsed and staggered conformers recently is employed to investigate methylation of Fc. The most significant consequences of the full methylation of Fc in the IR spectra are the blue shift of the band at ~ 800 cm−1 in Fc to ~ 1500 cm−1 in *Fc, and the enhancement of the C–H stretch band at ~ 3200 cm−1 region in *Fc. Further analysis reveals large impact of Fc methylation on core electron energies of the centre Fe atom (1s22s22p63s23p6). The Fe core electron energy changes can be as large as ~ 10 kcal mol−1 and are directional—the Fe 2pz and 3pz orbitals along the *Cp–Fe–*Cp axis (Cp centroids, vertical) change more strongly than other Fe core electrons in px and py orbitals. The directional inner shell energy changes are evidenced by larger inner shell reorganization energy. Energy decomposition analysis (EDA) indicates that methyl groups in *Fc apparently change the physical energy components with respect to Fc. The large steric energy of *Fc evidences that the closest hydrogens on adjacent methyl groups of the same *Cp ring in crystal structure are 0.2–0.4 Å closer than the hydrogens on nearest-neighbour methyl groups on opposing rings in *Fc. A significant increase in Pauli repulsive energy contributes to the large repulsive steric energy in *Fc.

Nonreciprocal charge current in a bulk Rashba semiconductor above the band crossing point

We calculate the nonreciprocal charge current in a bulk semiconductor with Rashba spin-orbit coupling subjected to crossed electric and magnetic fields. By using a second-order distribution function derived in a perturbative approach that considers the change in the local electron energy induced by the electric field, we find that, in contrast with previous theoretical estimates, a charge current proportional to the applied magnetic field exists for all values of the chemical potential, above or below the band crossing point (BCP), the energy where the two chiral conduction bands intersect. The persistence of the quadratic electric current across the BCP is a consequence of the chiral dependence of the relaxation times, an effect neglected before.

An in-depth understanding of the solvation effect of methanol on the anisotropy of electrochemical corrosion of Ta

Although tantalum (Ta) has been studied experimentally for many years as an important anti-corrosion material, it remains a challenge to accurately predict its corrosion anisotropy theoretically. In this work, we proposed an ab initio model considering the solvation effect to investigate crystal orientation-dependent corrosion behavior of Ta. The changes in electron transfer number and energy of a tantalum atom during its dissolution from the surface in vacuum and explicit methanol molecules were studied, respectively. Based on the anodic dissolution activation energy considering solvation effect, the corrosion current densities of (200), (110) and (211) surfaces were calculated to be 3.39 × 10−8 A/cm2, 2.24 × 10−11 A/cm2 and 2.95 × 10−11 A/cm2, respectively. The results are consistent with the variation trend of peak intensity in the XRD pattern. More importantly, the corrosion current density we predicted based on the percentage of these crystalline surfaces in the polycrystalline tantalum foil is 10−7.25 A/cm2, which is very close to the experimental value (8.70 × 10−8 A/cm2). Therefore, this result is capable of providing a theoretical basis for the electrochemical machining of Ta and a new idea for studying the anodic dissolution behavior of other metals or alloys in solution.

Statistic Properties of Electron Energy Enhancement During the Inner Electron Diffusion Region Crossing

AbstractMagnetic reconnection can efficiently heat and accelerate the electrons through various approaches and mechanisms. The electron diffusion region (EDR), especially the inner EDR, is one of the energization areas for the electrons during the reconnection. How the electrons' energy changes when passing the inner EDR is not well understood. In this study, we investigate the electron energy change from the individual perspective using the full kinetic particle‐in‐cell simulation. It is revealed that the electron energy gain rate is related to both traveling time and path in the inner EDR. The energy from the magnetic field tends to be allocated to the electron perpendicular part and the random thermal part. Our results promote the understanding of the function of the inner EDR during magnetic reconnection.

Quantum-chemical modeling of reactions initiating sulfuric vulcanization of isoprene rubber

The quantum-chemical method of the density functional DFT B3LYP / 6-311G ** have been used for calculation of thermodynamic functions and changes in the total electronic energy during the initiation of sulfur vulcanization of isoprene rubber using the N - cyclohexyl - 2 benzthiazolyl sulfenamide accelerator in the presence of atmospheric oxygen. Since sulfur, in the process of vulcanization of rubber compounds, is in a larger amount in a dissolved state, unlike oxygen, it is concluded that in the presence of sulfur, the formation of a valid vulcanization agent (DAV) will occur, and oxidation will occur to a lesser extent. When comparing the values of the reaction energy with the addition of the S8 molecule, it was found that sulfur in the accelerator radical acceptance reactions is a more active acceptor than oxygen in similar reactions. The effect of the number of sulfur atoms on the activity of the radicals of the sulfidating complex arising upon the acceptance of sulfur by the radicals formed during the decay of the accelerator is analyzed. It was found that the cyclohexyl radicals of the accelerator are the most active, however, in subsequent reactions of DAV with rubber, the radicals of DAV obtained with the participation of benzthiazolyl fragments are more active. The study of the effect of the number of atoms on the energies of the reactions of the formation of persulfhydryl suspensions shows that the primary suspensions are most likely to contain 8 sulfur atoms formed in reactions involving biradicals formed during the decay of the eight-membered ring of a sulfur molecule

The shift of the constant energy level after the interaction of particles with the polarizing phonons

The shift of the electron energy level due to its interaction with the polarizing phonons is investigated here for the particles whose energy does not depend on the wave vector. We also analyze the influence of the value of the constant of electron - phonon interaction and other parameters of the problem on the electron energy change. The methods of Green's functions, presented by the the Feynman diagrams and using the double permutations, are present here. The paper contains the analysis of the columns of the corresponding double permutations, the analytical expressions of which form the mass operator presented by the chain fractions. We received the expressions for admissibles and inadmissibles columns for phonon components of double permutations. The numerical calculations allow to conclude about the energy shift and how it depends on the parameters.

Slow Phase Transition-Induced Scan Rate Dependence of Spin Crossover in a Two-Dimensional Supramolecular Fe(III) Complex

Slow Phase Transition-Induced Scan Rate Dependence of Spin Crossover in a Two-Dimensional Supramolecular Fe(III) Complex

Electronic bandstructure modulation of MoX2/ZnO(X:S,Se) heterostructure by applying external electric field

The electronic properties of 2-Dimensional Van der Waals heterostructure of MX2(M:Mo, X:S, Se) and graphene-like ZnO by applying an external electric field(EF) in the range -0.50V/Å to 1.0V/Å is studied using first-principles calculations. The effect of the transverse electric field is measured in terms of modulation of the electronic energy bandgap and change in the band alignment properties. The bandstructure of MoS2/ZnO heterostructure(HS) shows an indirect bandgap of 1.61eV with a type-II band alignment and a large built-in electric field of 7.42eV with a valence band offset of 1.22eV across the interface. The bandstructure of MoSe2/ZnO shows a direct bandgap of 1.81eV with type-I alignment and a built-in electric field of 3.64eV with a band offset of 0.31eV. The charge density is localized on MoS2 and ZnO in VBM and CBM respectively in MoS2/ZnO HS, whereas in MoSe2/ZnO, both VBM and CBM are localized on MoSe2. With a perpendicular electric field applied across the HS, re-alignment of bandstructure and modulation of bandgap in both the HSs occurs. The energy bandgap increases linearly with the applied electric field for MoS2/ZnO(1.1–2.2eV) and remains almost constant(1.81eV) in the range -0.50V/Å to 0.50V/Å followed by a small decrease with an increase in electric field (1.60 for EF=±1.0V/Å). A cross-over in the bandgap type from indirect(type-II)→direct(type-I) in MoS2-ZnO and direct(type-I) to indirect(type-II) in MoSe2/ZnO has been observed at a critical value of electric field EF=0.75V/Å. The cross-over in band structure is consistent with the charge transfer pattern observed on the application of electric field. Tuning the electronic bandgap and changing the band-alignment with an external electric field opens a way to design futuristic electronic and optical devices.

Quantum chemistry study on the promoted reactivity of substituted cyclooctynes in bioorthogonal cycloaddition reactions

AbstractIn the present research, we focus on the energetics and electronic aspects of enhanced reactivity in the regioselective bioorthogonal 1,3-dipolar cycloaddition reaction of various substituted cyclooctynes with methyl azide, applying quantum chemistry approaches. In this respect, we assessed the structural and energetic properties of regioisomeric products and their corresponded transition states and calculated the reaction electronic energy changes and energy barriers through the cycloaddition pathways. The obtained results revealed that the trifluoromethyl substitution and fluorination of cyclooctynes lead to improved reactivity, in conjunction with increased exothermicity and decreased activation energy values. On the other hand, quantum theory of atoms in molecules computations were performed on some key bond and ring critical points that demonstrated the stabilizing topological properties of electron density and its derivatives upon trifluoromethyl substitution and fluorination of propargylic carbon of cyclooctynes which can be regarded as the essential origin of enhanced reactivity.

Radical Mechanism of Ir III /Ni II -Metallaphotoredox-Catalyzed C(sp 3 )–H Functionalization Triggered by Proton-Coupled Electron Transfer: Theoretical Insight

Photoredox catalysis can be induced to activate organic substrates or to modulate the oxidation state of transition-metal catalysts via unique single-electron transfer processes, so as to achieve c...

Chemical Energetics and Atomic Charges Distribution of Variably Sized Hydrated Sulfate Clusters in the light of Density Functional Theory

Among the ions classified in the Hofmeister series, the firstly ranked divalent sulfate anion has the strongest hydrating and water-structure making propensity. This unique characteristic actually makes it kosmotropic which causes water molecules to interact each other and contributes to gain structural stability of its hydrated clusters [SO42−(H2O)n]n = 1−40. In this study, few variably sized microhydrated sulfate clusters [SO42−(H2O)n]n = 1−4, 16 are considered separately, and inquired their chemical energetics and atomic charge distributions through ab initio based theoretical model. The main objective of this insight is to specify and interpret their thermodynamic stabilities, binding energies, and specific bonding and electronic interactions quantum mechanically. An in-depth analysis of their change in relative ground state electronic energy with respect to hydration number indicates stronger affinity of the sulfate ion towards water molecules while attaining structural stability in any aqueous type solutions. The mathematically determined values of their binding energy (DE) almost holds up the same with this structural stability order: [SO42−(H2O)16] > [SO42−(H2O)4] > [SO42−(H2O)3] > [SO42−(H2O)2] > [SO42−(H2O)], as reliable as experimentally and molecular dynamics simulation predicted trend. Moreover, the Mulliken derived partial atomic charges feature qualitative charge distribution in them which not only depicts electronic interactions between the specific atoms but also exemplifies the involvement of central sulfate units in hydrogen bond formation with surrounding water molecules.

Absorption of Powerful Light by Free Electrons in Crystals: Intraband Electron–Phonon Rabi Oscillations

The absorption of high-power visible or near-IR laser radiation by free electrons is calculated using the modified resonance approximation. The probabilities Wexc of intraband transitions at which the electron energy changes by ℏ(ω ± ωl), where ω is the frequency of light and ωl is the frequency of longitudinal optical phonons involved in the process, are determined. It is shown that specific electron–phonon Rabi oscillations at a frequency of ΩR may take place, and that the light is absorbed only up to the moment of time at which the first maximum τ1 on the dependence Wexc(t) is reached, where t is the time elapsed from the beginning of the laser pulse. It is shown that, in the case of prebreakdown light intensities, processes of high orders in the field of the light wave affect substantially Wexc, τ1, and ΩR.

Formation of Free Electrons in Collisions of Xe Atoms with α Particles

We have measured the cross sections of elementary processes occurring during collisions of impinging 3He2+ particles with kinetic energies in the range 1–100 keV with Xe atoms, which are accompanied with the formation of free electrons and ions in different final charge states: Xen+ (n = 1–6) and He(2 – m)+ (m = 0–2). We distinguish between ionization processes, in which the impinging α particle does not change the charge state, and processes of capture of one or two electrons, which lead to the formation of a singly charged helium ion or atom with additional removal of electrons from the xenon atom to the continuum. We have determined the cross sections of formation of free electrons in each of these processes and calculated the contribution of multielectron processes to the formation of free electrons. It is shown that upon a change in the energy of collisions between 3He2+ ions from 1 to 100 keV (the velocity of an impinging ion changes from 0.12 to 1.2 a.u.), the mechanism of removal of electrons from the xenon atom changes basically. For low approach velocities of particles, the formation of an autoionization state of the quasi-molecule and its subsequent decay take place. At higher velocities (V > 0.7 a.u.), free electrons are mainly formed because of an abrupt change in the potential energy of electrons when a fast α particle approached the nucleus of the xenon atom.

Simulation of electron transfer processes in a semiconductor structure using graphene and boron nitride

This paper presents the results of simulating the electron transfer processes in a three-dimensional semiconductor structure containing graphene and layers of boron hexagonal nitride using the Monte – Carlo method. Graphene is currently considered one of the most promising materials for the creation of new semiconductor devices with good performance for high frequency ranges. The use of graphene, which has high mobility of charge carriers, high thermal conductivity and a number of other positive properties, allows the development of new semiconductor devices with good output characteristics. The simulation allowed us to obtain the main characteristics of electron transfer, namely, dependence of speed, average energy, mobility on the strength of the electric field in a semiconductor structure containing a layer of graphene and boron nitride region. Electron transfer processes were simulated considering temperature variations of graphene and boron nitride layers, which is observed with increasing strength of the electric field in the structure. The analysis of the obtained dependencies showed that at small values of electric field strength, which does not exceed approximately 2.5 kV/cm, there is a nonlinear change in electron energy and temperature. At more significant values of electric field strength a quasi-linear change in temperature is observed. The similar course of dependence is observed also for the dependences of the average energy of electrons on the intensity of the electric field for the graphene layer.. The resulting dependencies of electron transfer characteristics can serve the basis for determining output characteristics in multi-layer semiconductor devices containing layers of graphene, boron hexagonal nitride and other materials.

BeiDa Imaging Electron Spectrometer observation of multi-period electron flux modulation caused by localized ultra-low-frequency waves

Abstract. We present multi-period modulation of energetic electron flux observed by the BeiDa Imaging Electron Spectrometer (BD-IES) on board a Chinese navigation satellite on 13 October 2015. Electron flux oscillations were observed at a dominant period of ∼190 s in consecutive energy channels from ∼50 to ∼200 keV. Interestingly, flux modulations at a secondary period of ∼400 s were also unambiguously observed. The oscillating signals at different energy channels were observed in sequence, with a time delay of up to ∼900 s. This time delay far exceeds the oscillating periods, by which we speculate that the modulations were caused by localized ultra-low-frequency (ULF) waves. To verify the wave–particle interaction scenario, we revisit the classic drift-resonance theory. We adopt the calculation method therein to derive the electron energy change in a multi-period ULF wave field. Then, based on the modeled energy change, we construct the flux variations to be observed by a virtual spacecraft. The predicted particle signatures well agree with the BD-IES observations. We demonstrate that the particle energy change might be underestimated in the conventional theories, as the Betatron acceleration induced by the curl of the wave electric field was often omitted. In addition, we show that azimuthally localized waves would notably extend the energy width of the resonance peak, whereas the drift-resonance interaction is only efficient for particles at the resonant energy in the original theory.

Study of electronic structure, optoelectronics, linear and nonlinear optical properties and chemical descriptors of dibromodinitrofluorescein isomers in gasphase and solvent media using abinitio and DFT methods

In this work, we have studied the electronic structure, optoelectronics, linear and nonlinear optical properties of dibromodinitrofluorescein isomers in the gas phase and some solvents media using RHF and B3LYP levels of theory with a cc-pVDZ basis set. Our results suggest that solvent media have an effect on certain properties while some are unaffected. We have also determined the energy band gap and some other parameters like ionization potential, electron affinity, and molar refractivity. Finally, we have calculated the reactivity descriptors through some parameters including chemical hardness (η), chemical potential(μ), electrophilicity index(ω), softness (ϑ), electronegativity (EN), Fermi energy (EF), Electro accepting power (ω+), electron-donating power (ω−) and net electrophilicity Δω±, the reflectivity (R), optical frequencyωop, Max of Electron charge (ΔEMAX), Energy change (ΔE) and total Energy minimum(ΔEMIN) of the compounds. Due to the large ⟨α⟩, β, γ, E, P, χ, Ɛ, n, and D of these molecules, we think that these molecules have potential applications in the field of optoelectronics, such as optical communication, optical computing, optical switching, and dynamic image processing.

Performance Parameter Analysis of a Hall Effect Thruster With Modified Bohm Parameter Model

The Hall effect thruster (HET) is an electric propulsion system in which electrons confined in a certain region collide with neutral particles due to the Hall effect. The neutral particles are ionized, and the ions are accelerated by the electric field to produce thrust. Thus, a Hall thruster has a simpler structure than an ion thruster. To improve the accuracy of the HET performance analysis, the energy change of electrons is predicted by considering thermal conduction. The number of ions produced by ionization and the change in electron energy via multivalent ionization are investigated. To minimize the independent variables, the boundary condition is modified after considering the physical correlation of each variable, and a semi-experimental model equation for the Bohm parameter is proposed. The performance results have greater similarity to the experimental results than those of the previous analytical model. Based on this, the performance changes according to the thruster operating conditions are predicted and compared. It is confirmed that the thrust increases by about 10–20% according to the change of propellant mass flow rate due to the increase of ion exit velocity.

Design and application of electron energy measurement system based on silicon photodiode

The change in electron energy is the key to ionization. Studying the change law plays an important role in analyzing the gap discharge process. In this paper, an electron energy measurement system is designed based on a silicon photodiode, and the feasibility analysis is given. Combined with a photomultiplier tube, the electron energy of a slightly uneven field of a 3 cm ball-to-plate gap under dc voltage is obtained during the discharge process. This system can obtain the relationship curve between external voltage and electron energy, which provides help in analyzing the development of the discharge process and the establishment of the criteria.

Structure-property relationship of graphene coupled metal (Ni, Co, Fe) (oxy)hydroxides for efficient electrochemical evolution of oxygen

Design of high-efficiency electrocatalysts for the oxygen evolution reaction (OER) is critical to meet future energy demands. A series of heterogeneous electrocatalysts based on graphene coupled mixed-metal (oxy)hydroxides containing specific concentrations of nickel, cobalt, and iron were synthesized to investigate the influence of metal composition on the structure, properties, and activities for OER. The addition of iron led to isolated metal (oxy)hydroxide sheets from a few hundred nanometers to less than 5 nm, leading to a high surface area. The increased d-spacing between layers of hydroxide and abundant hydroxyl groups adsorbed on the surface of the electrocatalysts contribute to better catalytic performance as displayed by the remarkable improvement in Tafel slopes. In addition, the presence of cobalt and nickel can aid in lowering the onset potential of OER. Small amounts of iron in NiFe and NiCoFe systems were found to significantly decrease the overpotential. The best OER electrocatalysts of the series were obtained for the ternary metal hydroxide of composition Ni0.33Co0.34Fe0.33, which generates a low overpotential of 0.332 V in reaching 10 mA cm−1 in 0.1 M KOH and the Tafel slope is as low as 51 mV dec−1. Density functional theory calculations demonstrate the improvements of electronic structure and free energy changes of the ternary metal oxyhydroxide for more efficient OER electrocatalysis. Overall, this work provides a solid foundation for further development of high-efficiency, scalable, and cost-effective mixed-metal (oxy)hydroxide electrocatalysts.