External Static Electric Field Research Articles

Impact of strain induced by polymer curing in benzocyclobutene embedded semiconductor nanostructures

Polymers such as benzocyclobutene are commonly used as embedding materials for semiconductor nanostructures. During the curing process of the polymer up to 250 °C, a significant impact of strain can be induced on the embedded semiconductor material due to different thermal expansion coefficients. This strain has been revealed by X‐ray diffraction in free‐standing GaAs nanowires grown on a silicon substrate, embedded in a polymer matrix. It will be shown that this strain is released during the X‐ray irradiation if additionally an external static electric field is applied. magnified image(© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Effect of Low-Voltage Static Electric Field on Growth of <i>Bacillus</i> <i>sp.</i>

Bacillus sp. was stimulated by external low-voltage static electric field of different intensity at the same time. To make comparisons of the biomass, pH, the metabolism of Bacillus sp.and the surface morphologies of Bacillus sp.treated and untreated. The results showed that when the electric field strength was between 0.5V/cm and 3V/cm, the pH was bigger in test group than control group. The growth of Bacillus sp. was inhibited at 3V/cm, and promoted at 0.5V/cm to 2.5V/cm. The growth of Bacillus sp. was promoted maximumly at 0.5V/cm. Finally, we find that low-voltage static electric field didn’t damage the morphology. The appropriate electric field strength can enhance the metabolism of Bacillus sp.

Spontaneous reorientations of meta-atoms and electromagnetic spatial solitons in a liquid metacrystal.

We show that transverse electromagnetic waves propagating along an external static electric field in liquid metacrystal (LMC) can provoke spontaneous rearrangement of elongated meta-atoms that changes the direction of the anisotropy axis of the LMC. This kind of instability may reorient the meta-atoms from the equilibrium state parallel to a static field to the state along a high-frequency field and back at the different threshold intensities of electromagnetic waves in such a way that bistability in the system takes place. Reorientation of meta-atoms causes a change in the effective refraction index of LMC that creates, in turn, the conditions for the formation of bright spatial solitons. Such spatial solitons are the self-consistent domains of redirected meta-atoms with trapped photons. We find that the instability thresholds as well as energy flux captured by the spatial soliton can be easily managed by variation of the static electric field applied to the LMC. We study the effects of soliton excitation and collisions via numerical simulations.

Ab initio simulation of the sum-frequency generation response of optically active liquids in the presence of a dc electric field—determination of the absolute molecular configuration

Quantum chemical computations have been performed to evaluate the first and second hyperpolarizability quantities of the interference term, linear in the external static electric field, that appear in the electric field-induced sum-frequency generation signal of chiral liquids. These are performed at the time-dependent Hartree-Fock level on the prototypical 1,1′-bi-2-naphtol chiral species.

Dipole polarizability of alkali-metal (Na, K, Rb)-alkaline-earth-metal (Ca, Sr) polar molecules: prospects for alignment.

Electronic open-shell ground-state properties of selected alkali-metal-alkaline-earth-metal polar molecules are investigated. We determine potential energy curves of the (2)Σ(+) ground state at the coupled-cluster singles and doubles with partial triples (CCSD(T)) level of electron correlation. Calculated spectroscopic constants for the isotopes ((23)Na, (39)K, (85)Rb)-((40)Ca, (88)Sr) are compared with available theoretical and experimental results. The variation of the permanent dipole moment (PDM), average dipole polarizability, and polarizability anisotropy with internuclear distance is determined using finite-field perturbation theory at the CCSD(T) level. Owing to moderate PDM (KCa: 1.67 D, RbCa: 1.75 D, KSr: 1.27 D, RbSr: 1.41 D) and large polarizability anisotropy (KCa: 566 a.u., RbCa: 604 a.u., KSr: 574 a.u., RbSr: 615 a.u.), KCa, RbCa, KSr, and RbSr are potential candidates for alignment and orientation in combined intense laser and external static electric fields.

Theoretical investigations of structures and properties ofAuandSsubstituted poly (2,3-di-(4′-hydroxyphenyl)-1,4-phenylene ethynyl) at different electric field intensities

Theoretical investigations on Au and S substituted poly (2,3-di-(4′-hydroxyphenyl)-1,4-phenylene ethynyl) as a molecular wire have been carried out by incorporating the external electric field (EF). The results demonstrate that both geometric and electronic structures of conjugated molecular wire are sensitive to EF. The Z component of the dipole moment and total dipole moment increases continuously since EF polarizes the molecule. Static EF modifies the frontline molecular orbitals and HLG. The I-V curve indicates the symmetrical trend respect to the original point.

Structural, Dynamic, and Transport Properties of Concentrated Aqueous Sodium Chloride Solutions under an External Static Electric Field

In the absence of an external electric field, it has already been known that ion clusters are formed instantaneously in moderately concentrated ionic solutions. In this work, we use molecular dynamics (MD) simulations to investigate the changes of structural, dynamic, and transport properties in a sodium chloride solution under an external electric field from the ion cluster perspective. Our MD simulation results indicate that, with a strong external electric field E (≥0.1 V/nm) applied, ion clusters become smaller and less net charged, and the structures and dynamics as well as transport properties of the ion solution become anisotropic. The influence of the cluster structure and shell structure to transport properties was analyzed and the Einstein relation was found invalid in this system.

Asymmetric effects on the optical properties of double-quantum well systems

Linear, nonlinear, and total absorption coefficient and refractive index changes of double-quantum well (DQW) systems are studied theoretically in the presence of external static electric field applied along the growth direction. The analytical expression for the linear and nonlinear optical properties is obtained using density matrix method. Emphasis is laid on the effect of asymmetry in the shapes of DQW system on optical properties. Some interesting results are obtained and explained.

Weak-field asymptotic theory of tunneling ionization in many-electron atomic and molecular systems

The weak-field asymptotic theory of tunneling ionization in an external static uniform electric field [Tolstikhin et al., Phys. Rev. A 84, 053423 (2011)] is extended to many-electron atomic and molecular systems treated in the frozen-nuclei approximation. The leading-order term in the asymptotic expansion of the ionization rate $\ensuremath{\Gamma}$ in the value of the field $F$ for $F\ensuremath{\rightarrow}0$ is obtained. The resulting formulas express $\ensuremath{\Gamma}$ in terms of properties of the unperturbed system. The most essential difference from the one-electron case, through which the many-electron character of the present theory reveals itself, is that the structure factor for a given ionization channel, defining the dependence of the ionization rate into this channel on the orientation of the system with respect to the field, is determined by the corresponding Dyson orbital. The theory is illustrated by calculations for several few-electron systems. The asymptotic results are compared with accurate fully correlated calculations of tunneling ionization rates available in the literature.

DFT study on the influence of electric field on surface‐enhanced Raman scattering from pyridine–metal complex

The influence of a static external electric field on surface‐enhanced Raman scattering is investigated by calculating the Raman spectra and excited state properties of pyridine–Au20 complex with the density functional theory and time‐dependent density functional theory method. The external electric field with orientation parallel (positive) or antiparallel (negative) to the permanent dipole moment is respectively applied on the complex. This field slightly changes the equilibrium geometry and polarizabilities, which results in shifted vibration frequencies and selectively enhanced Raman intensities. The changes of charge transfer (CT) excited states in response to the electric field are visualized by employing the charge difference densities. Further, the energy of charge transfer transition is tuned by electric field to be resonant or not with the incident light, leading to the Raman intensities are enhanced or not enhanced. At the same time, the intensities of vibration modes are sensitive to the orientation of the field. The positive electric field enhances the totally symmetric ring breathing mode (~1009 cm−1) but suppresses the trigonal ring breathing mode (~1051 cm−1). On the contrary, the mode at 1051 cm−1 is more enhanced than the mode at 1009 cm−1 when the negative electric field is applied on the complex. The Raman spectra could be modulated by tuning the strength and direction of the electric field. Copyright © 2013 John Wiley & Sons, Ltd.

Insights on cholinium- and piperazinium-based ionic liquids under external electric fields: A molecular dynamics study

The rotational and translational response of cholinium benzoate, cholinium salicylate, piperazinium benzoate, and piperazinium salicylate to static and dynamic external electric fields was studied using non-equilibrium molecular dynamics simulations. The existence of strong intrinsic electric fields in the studied fluids requires intensities larger than 0.25 V Å(-1) to obtain remarkable changes in the fluids' properties, such as rotational motion, dipolar alignment, or ion diffusivities. Very effective dipolar alignment with the applied fields is obtained showing rotational motions in the direction of the applied field, increasing with field intensity and decreasing with field frequency. Translational movement is clearly improved by the applied fields specially for strong fields and low frequencies, which lead to ionic diffusivities increasing up to two orders of magnitude for the stronger fields in comparison with zero field situations, and thus, increasing remarkably fluids' electrical conductivity. The effect of external electric fields on the studied ionic liquids is weaker than in common imidazolium-based ionic liquids.

Simulating quantum magnets with symmetric top molecules

A correspondence is established between the electric dipole matrix elements of a polyatomic symmetric top molecule in a state with nonzero projection of the total angular momentum on the symmetry axis of the molecule and the magnetic dipole matrix elements of a magnetic dipole associated with an elemental spin F. It is shown that this correspondence makes it possible to perform quantum simulation of the single‐particle spectrum and the dipole‐dipole interactions of magnetic dipoles in a static external magnetic field with symmetric top molecules subject to a static external electric field . It is further shown that no such correspondence exists for 1Σ molecules in static fields, such as the alkali metal dimers. The effective spin angular momentum of the simulated magnetic dipole corresponds to the rotational angular momentum of the symmetric top molecule, and so quantum simulation of arbitrarily large integer spins is possible. Further, taking the molecule CH3F as an example, it is shown that the characteristic dipole‐dipole interaction energies of the simulated magnetic dipole are a factor of 620, 600, and 310 larger than for the highly magnetic atoms Chromium, Erbium, and Dysprosium, respectively. Several applications of the correspondence for many‐body physics are presented, including long‐range and anisotropic spin models with arbitrary integer spin S using symmetric top molecules in optical lattices, quantum simulation of molecular magnets, and spontaneous demagnetization of Bose‐Einstein condensates due to dipole‐dipole interactions. These results are expected to be relevant as cold symmetric top molecules reach quantum degeneracy through Stark deceleration and opto‐electrical cooling.

Two-photon transitions in few-electron ions in the presence of static electric fields

Two-photon transitions in H- and He-like heavy ions in the presence of an external static electric field are explored using a relativistic Greens function approach and an independent particle model. The effects of Stark mixing on angular correlations, spectral distributions and total transition rates are analyzed in detail. Special emphasis is placed on the 2p1/2 → 1s1/2 two-photon transition in H-like ions and the 1s1/22p1/2:23P0 → 1s21/2:11S0 and 1s1/22s1/2:21S0 → 1s21/2:11S0 two-photon transitions in He-like ions.

Kerr and Cotton–Mouton effects in atomic gases: a quantum-statistical study

Theory of the birefringence of the refractive index in atomic diamagnetic dilute gases in the presence of static electric (Kerr effect) and magnetic (Cotton–Mouton effect) fields is formulated. Quantum-statistical expressions for the second Kerr and Cotton–Mouton virial coefficients, valid both in the low- and in the high-temperature regimes, are derived. It is shown that both virial coefficients can rigorously be related to the difference of the fourth derivatives of the thermodynamic (pressure) virial coefficient with respect to the strength of the non-resonant optical fields with parallel and perpendicular polarisations and with respect to the external static (electric or magnetic) field. Semiclassical expansions of the Kerr and Cotton–Mouton coefficients are also considered, and quantum corrections up to and including the second order are derived. Calculations of the second Kerr and Cotton–Mouton virial coefficients of the 4He gas at various temperatures are reported. The role of the quantum-mechanical effects and the convergence properties of the semiclassical expansions are discussed. Theoretical results are compared with the available experimental data.

How Well Can Parametrized and Parameter-Free Double-Hybrid Approximations Predict Response Properties of Hydrogen-Bonded Systems? Dipole Polarizabilities of Water Nanoclusters as a Working Model

The development of double-hybrid (DH) density functional approximations has been a crucial ingredient in the success of density functional theory (DFT). To further extend the range of applicability of these approximations, their suitability for investigating the response of hydrogen-bonded systems to external static electric fields is explored here. As a case study, we focus on the performance of parametrized and parameter-free DH density functionals for calculations of isotropic and anisotropic dipole polarizabilities of water nanoclusters. The functionals considered in our study are B2GP-PLYP, B2-PLYP, mPW2-PLYP, and SD-PBEP86 as parametrized functionals, and PBE0-DH and PBE0-2 as parameter-free models. The second-order Møller-Plesset perturbation theory (MP2) as a wave function theory (WFT) based method is also included for the sake of comparison. As a reference for methods benchmarking, the results of coupled-cluster method with single and double excitations (CCSD) are used. Scrutinizing the role of exchange, correlation, and their contributions in the functionals reveals that PBE0-DH is the best method that predicts the most accurate isotropic polarizabilities by a large margin with respect to other tested functionals. Moreover, we found that the PBE0-DH has a smaller mean absolute deviation than MP2. On the other hand, our results show that PBE0-2 outperforms other methods for anisotropic polarizabilities of clusters studied. On the whole, among all the tested DH density functionals for dipole polarizabilities of water clusters, the parameter-free PBE-based models are found to offer the best overall performance.

Exploring electric field induced structural evolution of water clusters, (H2O)n [n = 9–20]: Density functional approach

Response of neutral water clusters (H(2)O)(n), n = 9-20, to external uniform dipolar static electric fields is studied for some lowest-energy conformers for each "n" within an energy band of about 9 kcal mol(-1) of their field-free counterparts. We perform density functional theory computations with B3LYP∕6-311++G(2d,2p) model chemistry. Increasing the electric field destabilizes and distorts a cluster by elongating, hence weakening its hydrogen bonds, culminating into a catastrophic structural breakdown beyond a specific threshold field-strength. The electric field induced conformational transitions to extended structures stretched along the field direction to lower-energy configurations that appear as local minima on their potential energy surface are presented. It is observed that a typical structural transition of this type is always accompanied by an abrupt increase in the electric dipole moment of the cluster over and above its smooth increment with increasing applied field; the increase being phenomenal during breakdown. Interestingly, the HOMO-LUMO energy gap for a given conformer is found to diminish with increasing field strength, abruptly approaching zero at structural breakdown. In essence, the structural evolution traced through hydrogen-bond networks of the clusters reveals multiple enhancements in size by "opening up" of three-dimensional morphologies to form net-like structures with less number of hydrogen bonds. These clusters exhibit greater structural complexity than that encountered in the relatively small clusters reported previously.

Static-field-induced states

Considering an electron interacting with an atomic or molecular potential and an external static electric field, one usually focuses on narrow resonances at negative energies originating from the bound states in the absence of the field; we call them tunneling states (TSs). Meanwhile, there also exist relatively broad resonances at positive energies having no counterparts in the absence of the field; we call them static-field-induced states (SFISs). In this paper, the recently developed weak-field asymptotic theory of TSs [O. I. Tolstikhin et al., Phys. Rev. A 84, 053423 (2011)] is extended to SFISs. An asymptotic quantization condition defining the energies of SFISs in an arbitrary potential in the three-dimensional case is derived. The parabolic scattering amplitudes appearing in this quantization condition are defined. The theory is illustrated by calculations for the zero-range and Coulomb potentials. The SFISs in these potentials are found and their energies are shown to be in good agreement with the asymptotic results over a wide interval of the values of the field.

Dynamics of Particle in Confined-Harmonic Potential in External Static Electric Field and Strong Laser Field

Dynamics of a particle in confined-harmonic potential, subjected to external static electric and time-dependent laser fields is studied. The energy levels and wave functions of unperturbed harmonic oscillator are evaluated using B-polynomial Galerkin method. Matrix formulation is used throughout the procedure. This procedure is very simple and efficient in comparison with other methods. Modifications of wave functions and energy levels due to static electric field are also calculated. Finally, absorption spectra of such a driven oscillator are studied and explained.

Behaviour of iron oxide (Fe3O4) Janus particles in overlapping external AC electric and static magnetic fields

The assembly behaviour of Fe3O4-capped Janus particles with magnetically and electrically anisotropic properties is investigated in overlapping external AC electric and static magnetic fields. Generally, Fe3O4 Janus particles have been shown to form double and staggered chains in external static magnetic and AC electric fields, respectively. Here, the reaction of Fe3O4 Janus particles to sequentially applied AC electric and static magnetic fields in parallel and perpendicular field geometry is studied in order to elucidate to what extend the asymmetric nature of the Janus particle can be addressed independently by each field during assembly. A parallel field geometry leads to contraction of the Janus particle chains, whereas a perpendicular field geometry leads first to the rotation of the Janus particle chains towards the more dominant field followed by rhombohedral stacking of the chains into two-dimensional, two-particle thick sheets as a result of the weaker field. The Janus particle assembly behaviour in each field geometry tested is parameterized by the characteristic angle, θ, and the inter-particle distance, d. The observed response of the Fe3O4 Janus particles is shown to be driven by the interaction of electric and magnetic dipoles generated in the caps by the external AC electric and static magnetic fields, respectively, as well as the polarization of the polystyrene particle. Reversibility of the assembly behaviour correlates strongly with the fact that the electric dipoles disappear immediately after the AC electric field is turned off, whereas the magnetic dipoles remain permanently in the Fe3O4 caps even after the static magnetic field is removed. As a result, the Fe3O4 Janus particle assembly behaviour is responsive to both the electric and the magnetic fields and their behaviour can be manipulated by the sequence and relative orientation of the external fields.

Electro-optical tunable waveguide Bragg gratings in lithium niobate induced by femtosecond laser writing

We report the fabrication of femtosecond laser-induced, first-order waveguide Bragg gratings in lithium niobate in the low repetition rate regime. Type-II waveguides are written into an x-cut lithium niobate wafer and structured periodically to achieve narrowband reflections at wavelengths around 1550 nm. Additionally, electrodes are employed to allow for electro-optic tuning of the spectral response. We demonstrate wavelength control of the central reflection peak by applying a static external electric field. A maximum shift of the reflection peak of Δλ = 625 pm is observed.