Constant Electric Field Research Articles

Modeling of electrochemical oxide film growth – impact of band-to-band tunneling

The Point Defect Model (PDM) describes the corrosion resistance properties of oxide films based on interfacial reactions and defect transport, which are affected by the electric field inside the oxide film. The PDM assumes a constant electric field strength due to band-to-band tunneling (BTBT) of electrons and the separation of electrons and holes by high electric fields. In this manuscript we present a more complex expansion of the common models to simulate steady state oxide films to test this assumption. The R-PDM was extended by including the transport of electrons and holes and BTBT. It could be shown that BTBT only occurs in very rare cases of narrow band gaps and high electric fields and the impact of electrons and holes does indeed lead to a buffering effect on the electric field, but does not lead to a constant electric field strength. Modeling the transport of electrons and holes on the oxide film allows to specifically estimate their potential impact on the film growth. Especially during modeling of oxide films with narrow band gap and/or electrochemical reactions at the film/solution interface the electrons and holes needs to be included to the model.

Low-density components of a Holstein polaron during its uniform motion in a constant electric field in the initial period of time

In this paper, we consider the formation of low-density components of a polaron during its uniform motion in a polynucleotide chain subjected to a constant electric field. The calculations performed show that Bloch oscillations, usually observed during the oscillatory regime of polaron motion along the chain, do not completely disappear when the polaron motion along the chain becomes uniform. It is shown that after the electric field is turned on, the low-density components of the polaron, which have their own internal dynamics, are formed. And despite the fact that the macro-part of the polaron moves at a constant velocity, retaining its shape, the low-density components of the polaron demonstrate such characteristics of Bloch oscillations as the period of Bloch oscillations and the maximum Bloch amplitude.

Dependence of the nature of the Holstein polaron motion in a polynucleotide chain subjected to a constant electric field on the initial polaron state and the parameters of the chain

In this work, we consider the motion of a polaron in a polynucleotide Holstein molecular chain in a constant electric field. It is shown that the character of the polaron motion in the chain depends not only on the chosen parameters of the chain, but also on the initial distribution of the charge along the chain. It is shown that for a small set value of the electric field intensity and for fixed values of the chain parameters, changing only the initial distribution of the charge in the chain, it is possible to observe either a uniform movement of the charge along the chain, or an oscillatory mode of charge movement.

Generation of unipolar pulses of terahertz radiation with a large electric area

A physical situation is proposed and theoretically analyzed, in which, in our opinion, it is possible to generate unipolar terahertz pulses with a large electric area. In this case, the gas in the tube is excited by a femtosecond IR laser pulse. In this case, the tube with gas is placed in a constant external electric field. The generation of a unipolar pulse is based on "three-step scheme" --- ionization of gas atoms by a femtosecond pulse, subsequent acceleration of a free electron in a dc external field and subsequent annihilation of an electron upon collision with a tube wall or another atom (ion). Keywords: unipolar pulses, ultrafast optics, electric pulse area, terahertz radiation, three-step model.

Electrokinetic repeater of acoustic vibrations

It is shown that in an electrokinetic acoustoelectric transducer, when a constant DC electric field (pump voltage) is applied during reception of an acoustic signal, it becomes possible to retransmit the initial external acoustic field. This is due to the presence of simultaneously reverse electrokinetic phenomena in the transducer: electroosmosis and flow potential. The necessary theoretical substantiation of this phenomenon is presented. The data of a full-scale experiment confirming the theory are presented. Keywords: acoustoelectric conversion, electrokinetic phenomena, current potential, energy pumping, electrokinetic repeater.

Генерация униполярных импульсов терагерцового излучения с большой электрической площадью

A physical situation is proposed and theoretically analyzed, in which, in our opinion, it is possible to generate unipolar terahertz pulses with a large electric area. In this case, the gas in the tube is excited by a femtosecond IR laser pulse. In this case, the tube with gas is placed in a constant external electric field. The generation of a unipolar pulse is based on ”three-step scheme" - ionization of gas atoms by a femtosecond pulse, subsequent acceleration of a free electron in a dc external field and subsequent annihilation of an electron upon collision with a tube wall or another atom (ion).

Acoustoelectric transducer based on electrokinetic phenomenon flow potential

A mathematical model of an acoustoelectric transducer based on the use of the electrokinetic phenomenon of the flow potential is proposed. It is shown theoretically that the flow potential increases in proportion to the strength of the constant electric pumping field, which is confirmed experimentally. The described converter has variable sensitivity. Rather large values of the sensitivity of an electrokinetic microphone have been obtained experimentally. The results of the work can be used in the design of acoustoelectric transducers. Keywords: Acoustoelectric conversion, Electrokinetic phenomena, Current potential, Flow potential hydrodynamics, Energy pumping. Electrokinetic microphone sensitivity.

Terahertz spectra of electrolyte solutions under applied electric and magnetic fields

Most biomolecules require an aqueous environment to fully exert their biological activity. However, the rotation mode, vibration mode, and energy associated with the hydrogen bonding network of water are in the terahertz band, resulting in strong absorption. Therefore, it is difficult to detect liquid biological samples using the terahertz technology. Here, a high-transmittance double-layer microfluidic chip was prepared using a cycloolefin copolymer material with high transmittance of terahertz waves. Combined with terahertz time-domain spectroscopy, the terahertz spectral characteristics of deionized water, NaCl, NaCO3, and CH3COONa solutions were studied. The changes in the terahertz transmission intensity of these electrolyte solutions under constant electric and magnetic fields were measured. The results show that the terahertz spectra of different sodium salt solutions with the same concentration of 0.9 mol/L are different. Furthermore, the terahertz absorption coefficients of the different electrolyte solutions gradually decrease with the increase of their residence time under the electric field, which is contrary to the results obtained under the external magnetic field. This study provides a new idea for the detection of sodium salt solution and lays a foundation for the development of THz technology.

Dependence of the energy of emission molecular orbitals in short open carbon nanotubes on the electric field

On the examples of short open carbon nanotubes of armchair type (n,n), for n=3, 4, and zigzag (n,0), for n=5, 6, 7, the influence of the magnitude and direction of the external constant electric field vector on their field emission properties was studied. It is shown that the deviation of the field vector from the nanotube axis leads to an increase in the field strength to generate electron field emission. Emission orbitals in carbon nanotubes (n,n) found as a result of a new type of conjugation of p-electrons in cylindrical conjugated systems are more sensitive to a change in the direction of the electric field vector compared to emission orbitals in nanotubes (n,0). When the electric field vector deviates from the nanotube axis, the emission orbitals of carbon nanotubes change the less, the larger the nanotube diameter. Keywords: short open carbon nanotubes, field emission, conjugation of p-electrons, emission molecular orbital.

Упрощенные представления вероятностей излучения фотона в постоянном внешнем электрическом поле

In the case of an intense external electric field, there exist many transition channels corresponding to the violation of the vacuum stability. It was shown that depending on the setting of a problem there is a number of integral representations for the probabilities of one photon emission due to a constant electric field. These representations are the Fourier transformations of the product of two Weber parabolic cylinder functions that are solutions of the same differential equation. To simplify the study of the probabilities, we expressed such a Fourier transformation via the confluent hypergeometric function.

Accumulation and diffusion of charges in kinetics of polymer electric breakdown

In this paper, the distribution in electric durability [Formula: see text] of polymers in constant electric field at low temperatures has been measured. The results of continuous experiments and experiments of field discontinuous effect on polymer samples being remained not disruptive after exposure for time equal to mean value [Formula: see text] have been compared. During the interval, we have varied the time interval, temperature [Formula: see text] and electric intensity of opposite sign [Formula: see text] according to which various degree of regeneration of polymer electric strength properties has been observed. By the degree of regeneration, relaxation time [Formula: see text] of the accumulated charges in polymers causing breakdown has been found. It is established that the process of charge diffusion, which accumulation leads to breakdown has a thermofluctuation behavior and the activation energy of given process depends on the counter field intensity magnitude.

Charge Motion along a Polynucleotide Chains in a Constant Electric Field Depends on the Charge Coupling Constant with Chain Displacements

Various regimes of a charge motion along a chain in a constant electric field are investigated. This motion is simulated on the basis of the Holstein model. Earlier studies demonstrate a possibility of a uniform motion of a charge in a constant electric field over very long distances. For small values of the electric field intensity a Holstein polaron can move at a constant velocity. As the electric field intensity increases, a charge motion acquires oscillatorily character, performing Bloch oscillations. Since the charge motion depends on the whole set of the system parameters the character of the motion depends not only on the value of the electric field intensity. Therefore, the electric field intensity for which the uniform motion takes place differs for chains with different parameters. The character of the charge motion and distribution is considered in chains with different values of the constant of coupling between the charge and the displacements of the chain. We showed that the values of the electric field intensity for which the regime of a charge motion changes are different in chains with different values of the coupling constant. We also demonstrated that for one and the same value of the electric field intensity, in chains with different values of the coupling constant either a uniform motion or an oscillatory motion, or a stationary polaron can be observed.

Influence of an electric field on flexopolarization induced by acoustic action on a liquid crystal

The work experimentally investigated the influence of an electric field on the direct flexoelectric effect that occurs under the influence of an acoustic field in liquid crystals. Thin layers of nematics 10-100 μm thick were studied. In this case, the liquid crystal sample was exposed to the piston method with an acoustic wave with a frequency of 1 kHz. The dependences of the first and second harmonics for different NLCs on the bias voltage value, shear amplitude, and crystal thickness were obtained. It was revealed that the flexosignal harmonics depend on the direction of the electric field; when a positive potential is applied to the movable plate, they take on smaller values than when negative. It was found that in low fields the magnitude of the flexosignal increases due to an increase in the amplitude of the director deviation, but at a critical value of the field it is suppressed, since the layer is stabilized by a constant electric field.

Generation and characterization of air micro-bubbles in highly hydrophobic capillaries.

The generation of air microbubbles in microfluidic systems or in capillaries could be of great interest for transportation (single cell analysis, organite transportation) or for liquid compartmentation. The physicochemical characterization of air bubbles and a better understanding of the process leading to bubble generation during electrophoresis is also interesting in a theoretical point of view. In this work, the generation of microbubbles on hydrophobic Glaco™ coated capillaries has been studied in water-based electrolyte. Air bubbles were generated at the detection window and the required experimental parameters for microbubbles generation have been identified. Generated bubbles migrated against the electroosmotic flow, as would do strongly negatively charged solutes, under constant electric field. They have been characterized in terms of dimensions, electrophoretic mobility, and apparent charge.

Lorentzian worldline path integral approach to Schwinger effect

We demonstrate that the positive frequency modes for a complex scalar field in a constant electric field (Schwinger modes), in three different gauges, can be represented as exact Lorentzian worldline path integral amplitudes. Although the mathematical forms of the mode functions differ in each gauge, we show that a simple prescription for Lorentzian worldlines' boundary conditions dispenses the Schwinger modes in all three gauges (that we considered) in a unified manner. Following that, using our formalism, we derive the exact Bogoliubov coefficients and, hence, the particle number, \textit{without} appealing to the well-known connection formulas for parabolic cylinder functions. This result is especially relevant in view of the fact that in a general electromagnetic field configuration, one does not have the luxury of closed-form solutions. We argue that the real time worldline path integral approach may be a promising alternative in such non-trivial cases. We also demonstrate, using Picard-Lefschetz theory, how the so-called worldline instantons emerge naturally from relevant saddle points that are complex.

Bloch oscillations in the spin- 12 XXZ chain

Under a perfect periodic potential, the electric current density induced by a constant electric field may exhibit nontrivial oscillations, so-called Bloch oscillations, with an amplitude that remains nonzero in the large system size limit. Such oscillations have been well studied for nearly noninteracting particles and observed in experiments. In this work we revisit Bloch oscillations in strongly interacting systems. By analyzing the spin-$\frac{1}{2}$ XXZ chain, we demonstrate that the current density at special values of the anisotropy parameter $\mathrm{\ensuremath{\Delta}}=\ensuremath{-}cos(\ensuremath{\pi}/p)$ $(p=3,4,5,\ensuremath{\cdots})$ in the ferromagnetic gapless regime behaves qualitatively the same as in the noninteracting case $(\mathrm{\ensuremath{\Delta}}=0)$ even in the weak electric field limit. When $\mathrm{\ensuremath{\Delta}}$ deviates from these values, the amplitude of the oscillation under a weak electric field is suppressed by a factor of the system size. We estimate the strength of the electric field required to observe such a behavior using the Landau-Zener formula.

Lane dynamics in pair-ion plasmas: effect of obstacle and geometric aspect ratio

Lane formation dynamics of driven two-dimensional pair-ion plasmas is investigated in under-damped cases where the effect of particle inertia cannot be neglected. Extensive Langevin dynamics simulations using an OpenMP parallel program are carried out to analyse the effect of obstacle and geometric aspect ratio on lane formation dynamics previously reported in Sarma et al. (Phys. Plasmas, vol. 27, 2020, 012106) and Baruah et al. (J. Plasma Phys., vol. 87, 2021, 905870202). Lanes are found to form when like particles move along or opposite to the applied field direction. Lane order parameter, cumulative order parameter and distribution of the order parameter have been implemented to detect phase transition. The effect of geometric aspect ratio on the stability of lanes is systematically determined in both the presence and absence of an obstacle. Here, a specular reflective boundary condition is implemented to mimic an obstacle. We demonstrate that an obstacle promotes the merging of lanes, and the system gradually transitions to a partially mixed phase with higher value of aspect ratio. The occurrence of lane mixing phenomena at the separation boundary of two oppositely flowing lanes at higher value of aspect ratio is observed. In the presence of an oscillatory electric field, the lane merging tendency is reduced to a large extent as compared to the system where a constant electric field is applied. Furthermore, in the presence of both space- and time-varying electric fields, an appearance of a void is observed on either side of the obstacle. The study finds that the presence of an external magnetic field promotes acceleration of the phase transition process towards the lane mixing phase; it also reveals the existence of electric field drift in the system. Our findings may prove to be useful in understanding the nature of lane dynamics in naturally occurring pair-ion plasma systems as well as their relevance to technological applications that exploit or mitigate self-organization.

Numerical simulation of dynamic characteristics of droplet in oil under a CPPM electric field

The size of droplets in oil are dynamically changes during demulsification, thereby changing the optimum demulsification electric field frequency. Thus, the constant pulsed electric field cannot meet the requirement of optimum frequency. The variable frequency pulsed electric field can cater to the change in optimum demulsification frequency, and has high demulsification ability. However, the dynamic characteristics of the droplet in oil at the variable frequency pulsed electric field are unclear. Therefore, a chaotic pulse position modulation (CPPM) electric field is considered a type of variable frequency pulsed electric field, where the pulse frequency is chaotic but pulse width and field intensity are constant. The droplet deformation dynamic model under the CPPM electric field is established by applying finite element method. The dynamic and chaotic characteristics of the droplet deformation in oil in this electric field are investigated, and the influence of pulse width and electric field intensity on droplet deformation is discussed. Results show that the deformation of droplet in oil is nonstationary vibration with the action of the CPPM electric field, and its deformation is chaotic vibration. The chaos of droplet deformation decreases with the increase in pulse width, and an optimum pulse width can be found to make the droplet have large deformation ratio and high vibration times. The deformation ratio of droplet can be increased by increasing the electric field intensity, but the droplet are easy to split and the deformation is no longer chaotic at high electric field intensity, and an optimum electric field intensity can be found to make the droplet have large deformation ratio and deformation stability.

Effects of Constant Electric Field on Biodegradation of Phenol by Free and Immobilized Cells of Bradyrhizobium japonicum 273

It is shown that bacteria Bradyrhizobium japonicum 273 were capable of degrading phenol at moderate concentrations either in a free cell culture or by immobilized cells on granulated activated carbon particles. The amount of degraded phenol was greater in an immobilized cell preparation than in a free culture. The application of a constant electric field during cultivation led to enhanced phenol biodegradation in a free culture and in immobilized cells on granulated activated carbon. The highest phenol removal efficiency was observed for an anode potential of 1.0 V/S.H.E. The effect was better pronounced in a free culture. The enzyme activities of free cells for phenol oxidation and benzene ring cleavage were very sensitive to the anode potential in the first two steps of the metabolic pathway of phenol biodegradation catalyzed by phenol hydroxylase—catechol-1,2-dioxygenase and catechol-2,3-dioxygenase. It was observed that at an anode potential of 0.8 V/S.H.E., the meta-pathway of cleavage of the benzene ring catalyzed by catechol-2,3-dioxygenase became competitive with the ortho-pathway, catalyzed by catechol-1,2-dioxygenase. The obtained results showed that the positive effect of constant electric field on phenol biodegradation was rather due to electric stimulation of enzyme activity than electrochemical anode oxidation.

Multiphoton intersubband transitions in an armchair graphene nanoribbon

We present an analytical approach to the problem of the interband transitions in an armchair graphene nanoribbon (AGNR), exposed to the time-periodic electric field of strong light wave, polarized parallel to the ribbon axis. The two-dimensional Dirac equation for the massless electron subject to the ribbon confinement is employed. In the resonant approximation the probability of the transitions between the valence and conduction size-quantized subbands are calculated in an explicit form. We trace the dependencies of the Rabi frequency for these transitions on the ribbon width and electric field strength for both the multiphoton-assisted and tunneling regimes relevant to the fast oscillating and practically constant electric field, respectively. Estimates of the expected experimental values for the typically employed AGNR and laser technique facilities show that the Rabi oscillations can be observed under laboratory conditions. The data, corresponding to the intersubband tunneling, makes the AGNR a 1D condensed matter analog, in which the quantum electrodynamic vacuum decay can be detected by the employment of the attainable electric fields.