Modeling of ionization–recombination processes in the atmospheric surface layer

The electrical structure of non-stationary horizontally-homogenous surface layer with multi-charged aerosol particles was mathematically modeled in the approximation of turbulent electrode effect. The profiles of positive and negative small ions and nuclei, electric field, polar air conductivity, current density and space charge density were computed in different time periods and various physical conditions. The mathematical model of non-stationary horizontally homogenous surface layer with aerosol particles was made regarding turbulent mixing and convective transport. The space-time distributions of positive and negative small ions and nuclei, electric field, electrical conductivity, current density and space charge density for various physical conditions (aerosol concentrations, turbulent mixing, convective transport, air ionization rate, electric field strength near surface, aerosol particles size) were received. Experimental data of electrical and meteorological parameters were measured and analyzed. It was received that theoretical results are in a good agreement with experimental data.     

Quantum antidot as an electrometer:Observation of fractional charge

In experiments on resonant tunneling through a quantum antidot in the quantum Hall (QH) regime, we observe periodic conductance peaks both versus magnetic field and a global gate voltage, i.e., electric field. Each conductance peak can be attributed to tunneling through a quantized antidot-bound state. The fact that the variation of the uniform electric field produces conductance peaks implies that the deficiency of the electrical charge on the antidot is quantized in units of charge of quasiparticles of surrounding QH condensate. The period in magnetic field gives the effective area of the antidot state through which tunneling occurs, the period in electric field (obtained from the global gate voltage) then constitutes a direct measurement of the charge of the tunneling particles. We obtain electron charge C in the integer QH regime, and quasiparticle charge C for the QH state.     

In-Si(111)界面上的电荷转移及铟原子的表面电致迁移现象

用反射式高能电子衍射仪首次观察到在Si(111)面上的一部分铟吸附原子在直流电场下,沿电场方向发生迁移的现象——表面电致迁移。根据所观察到的表面电致迁移过程,可以把吸附在Si(111)面上的铟原子的结合状态分成两类:紧靠着硅表面的一个单原子层铟与硅表面结合牢固,几乎不受电场影响,称为紧固层;在紧固层以上的铟层易受电场影响而发生表面电致迁移,称为迁移层。从铟原子的表面电致迁移率与温度的关系,求得表面质量迁移的激活能为0.43eV。用表面电导测量研究了In-Si(111)界面形成过程中的电荷转移现象。结果表明,吸附在硅表面的铟原子形成表面深施主能级。导致表面电致迁移的力是离化了的铟原子在电场中所受到的库仑力。 关键词：     

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.     

Charge Injection and Transport in Metal/Polymer Chains/Metal Sandwich Structure

Using the tight-binding Su--Schrieffer--Heeger model and a nonadiabatic dynamic evolution method, we study the dynamic processes of the charge injection and transport in a metal/two coupled conjugated polymer chains/metal structure. It is found that the charge interchain transport is determined by the strength of the electric field and the magnitude of the voltage bias applied on the metal electrode. The stronger electric field and the larger voltage bias are both in favour of the charge interchain transport.     

纳米硅结构中分裂能级对光电输运特性的影响

基于电子在分裂能级系统中同时存在的共振隧穿和子带输运过程,结合光生载流子作用提出了纳米硅结构中的光电输运理论模型.利用该模型计算了纳米硅结构在光照条件下的电流密度、电场强度及电子浓度分布.结果表明,光生电子在具有分裂能级的纳米硅中是以共振隧穿为主要输运方式.在此基础上,详细研究了光电流与吸收系数、外加偏压以及纳米硅层层数之间的关系,发现在特定的外界条件下光电流会出现跳变增加的现象,其物理原因是纳米硅结构中电场强度的二次分布.     

Electromagnetic interaction between local surface plasmon polaritons and an atmospheric surface wave plasma jet

We analyze the electromagnetic interaction between local surface plasmon polaritons （SPPs） and an atmospheric surface wave plasma jet （ASWPJ） in combination with our designed discharge device. Before discharge, the excitation of the SPPs and the spatial distribution of the enhanced electric field are analyzed. During discharge, the critical breakdown electric field of the gases at atmospheric gas pressure and the surface wave of the SPPs converted into electron plasma waves at resonant points are studied. After discharge, the ionization development process of the ASWPJ is simulated using a two- dimensional fluid model. Our results suggest that the local enhanced electric field of SPPs is merely the precondition of gas breakdown, and the key mechanism in maintaining the discharge development of a low-power ASWPJ is the wave-mode conversion of the local enhanced electric field at the resonant point.     

Charging dynamics of a polymer due to electron irradiation： A simultaneous scattering-transport model and preliminary results

<正>We present a novel numerical model and simulate preliminarily the charging process of a polymer subjected to electron irradiation of several 10 keV.The model includes the simultaneous processes of electron scattering and ambipolar transport and the influence of a self-consistent electric field on the scattering distribution of electrons.The dynamic spatial distribution of charges is obtained and validated by existing experimental data.Our simulations show that excess negative charges are concentrated near the edge of the electron range.However,the formed region of high charge density may extend to the surface and bottom of a kapton sample,due to the effects of the electric field on electron scattering and charge transport,respectively.Charge trapping is then demonstrated to significantly influence the charge motion.The charge distribution can be extended to the bottom as the trap density decreases.Charge accumulation is therefore balanced by the appearance and increase of leakage current.Accordingly,our model and numerical simulation provide a comprehensive insight into the charging dynamics of a polymer irradiated by electrons in the complex space environment.     

On the relation between plasma rotation induced by low-frequency resonant magnetic perturbations and transport in ergodic magnetic fields

The penetration of low-frequency resonant magnetic perturbations into a tokamak plasma and their influence on the plasma rotation are analyzed in linear and quaslisinear kinetic approaches. There are two explanations of experimentally observed acceleration of plasma rotation in the direction of the plasma current. First, it is a result of the resonant absorption of the momentum of the perturbation field by the plasma. Second, it is a result of a change in the radial electric field due to the ergodization of the magnetic field and the corresponding increase in the radial electron transport. It is shown that there is no contradiction between these two explanations. These are just two different interpretations of the same phenomenon. Published in Russian in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 6, pp. 420–423. The article was translated by the authors.     

Charging dynamics of polymer due to electron irradiation: A simultaneous scattering-transport model and preliminary results

We present a novel numerical model and simulate preliminarily the charging process of polymer subjected to electron irradiation of several 10 keV. The model includes the simultaneous processes of electron scattering and ambipolar transport and the influence of a self-consistent electric field on the scattering distribution of electrons. The dynamic spatial distribution of charges is obtained and validated by existing experimental data. Our simulations show that excess negative charges are concentrated near the edge of the electron range. However, the formed region of high charge density may extend to the surface and bottom of a kapton sample, due to the effects of electric field on electron scattering and charge transport, respectively. Charge trapping is then demonstrated to significantly influence the charge motion. The charge distribution can be extended to the bottom as the trap density decreases. Charge accumulation is therefore balanced by the appearance and increase of leakage current. Accordingly, our model and numerical simulation provide a comprehensive insight into the charging dynamics of polymer irradiated by electrons in the complex space environment.     

The observation of electroluminescence in a double barrier resonant tunnelling structure

Electroluminescence (EL) and impact ionisation phenomena in an asymmetric double barrier resonant tunnelling structure are investigated. Determination of the charge density and electric field distribution throughout the structure enables a detailed analysis of impact ionisation phenomena to be made.     

Electro-optic sampling of surface space-charge fields on III–V compounds

Time-resolved reflective electro-optic sampling (REOS) of ultrafast longitudinal surface fields on III–V compounds is accomplished with 50 fs optical pulses at 2 eV. Ultrafast carrier transport and screening effects of the photoexcited carriers initiate electric field transients short enough to impulsively launch longitudinal-optical phonons, in phase. A high-sensitivity measurement system allows the time-resolved investigation of the coherent phonon modes and carrier transport. In a special example the mapping of process-induced changes in the surface space charge region is demonstrated.     

共轭高分子链中极化子间相互作用对电荷迁移率的影响

基于综合考虑了电子与声子以及电子与电子相互作用的理论模型,采用数值方法计算了在外电场作用下共轭高聚物分子中电荷的迁移率,讨论了大小极化子共存并相互作用对分子链内电荷迁移率的影响。研究发现,电荷迁移率明显受大小极化子的载荷性质的影响,当大小极化子具有相同电性时,在低电场范围内,分子内电荷迁移率由大极化子运动性质主导,而在高电场范围内,分子内电荷迁移率由小极化子主导;另一方面,当大小极化子具有相反电性时,电荷迁移率只由大极化子运动性质主导,与电场强度无关。此外,还讨论了电子与电子相互作用对电荷迁移率"的影响。     

Injection and transport of electric charge in a metal/copolymer structure

The dynamical processes of the electric charge injection and transport from a metal electrode to the copolymer are investigated by using a nonadiabatic dynamic approach. The simulations are performed within the framework of an extended version of the one-dimensional Su-Schrieffer-Heeger (SSH) tight-binding model. It is found that the electric charge can be injected into the copolymer by increasing the applied voltage. For different structures of the copolymer, the critical voltage biases are different and the motion of the injected electric charge in the copolymer varies obviously. For the copolymer with a barrier-well-barrier configuration, the injected electric charge forms a wave packet due to the strong electron-lattice interaction in the barrier, then comes into the well and will be confined in it under a weak electric field. Under a medium electric field, the electric charge can go across the interface of two homopolymers and enter into the other potential barrier. For the copolymer with a well-barrier-well configuration, only under strong enough electric field can the electric charge transfer from the potential well into the barrier and ultimately reach a dynamic balance.     

Electric field and the charge distribution on the surface of an insulator in a vacuum

The free charge steady-state distribution over the insulator surface that arises in a strong electric field in a vacuum can be found by solving the boundary-value problem for the electrostatic field strength if the angle between the field vector and vacuum-insulator interface is given. A general solution to this boundary-value problem is derived for the case of an in-plane field and rectilinear interfaces. Laws of charge and field formation that follow from the solution obtained are considered. Formulas for the electric field strength and charge density in terms of elementary functions are obtained for a number of particular cases. Power-type expressions for the electric field and a critical angle between the electrode and insulator surface that describe the field behavior and charge distribution near the vacuum-insulator-electrode contact are derived.     

Particle-in-cell investigation on the resonant absorption of a plasma surface wave

The resonant absorption of a plasma surface wave is supposed to be an important and efficient mechanism of power deposition for a surface wave plasma source. In this paper, by using the particle-in-cell method and Monte Carlo simulation, the resonance absorption mechanism is investigated. Simulation results demonstrate the existence of surface wave resonance and show the high efficiency of heating electrons. The positions of resonant points, the resonance width and the spatio-temporal evolution of the resonant electric field are presented, which accord well with the theoretical results. The paper also discusses the effect of pressure on the resonance electric field and the plasma density.     

On the transistor effect in a vertical structure with a nonconjugated polymer as a transport layer

The charge carrier transport in a multilayer film structure based on a nonconjugated polymer has been studied. The conditions under which the charge carrier transport can be controlled by an electric field due to variations in the potential at the control electrode have been established. The results obtained are discussed within the model of passage of charge particles through a multibarrier system.     

利用Matlab模拟点电荷系的电场线和等势面

根据电场叠加原理,利用Matlab的绘图功能,绘出二维平面内点电荷系的等势面和电场线。以三个点电荷为例,模拟了它们的电场线和等势面,并通过改变电荷的位置和电荷量的大小对电场的分布情况进行分析比较,在教学中能起到很好的演示作用。     

聚乙烯空间电荷包行为的形成机理与仿真方法研究

聚乙烯中的空间电荷包行为是空间电荷的一种特殊的输运行为.研究表明,空间电荷包行为由于受材料本身特性、外加电场大小以及环境温度等的影响,导致其产生过程及传输特性上存在较大差异,这些因素给空间电荷包行为产生机理研究带来了较大困难.通过对电荷的电极注入过程、载流子的体内迁移规律及空间电荷与体内陷阱的相互作用机制进行分析,探讨了不同外加电场及不同深度陷阱能级对电荷包行为造成的相关影响,在此基础上建立物理模型来描述电荷包的产生和迁移过程.模型中提出了在高于阈值电场时,载流子迁移速度与电场关系存在负微分迁移率的假设.基于此模型对空间包行为的模拟结果与实验结果取得较好的一致. 关键词： 空间电荷包 数值模拟 负微分迁移率     

Ultrafast Fiske effect in semiconductor superlattices

The current flowing across a semiconductor superlattice in tilted electric and magnetic fields is known to exhibit resonant enhancement, when Landau states of neighboring wells align at certain ratios of the field strengths. We show that the ultrafast version of this effect, in which coherent electron wave packets are involved, has a profound analogy to the Fiske effect in superconductor Josephson junctions and superfluid weak links, in that the coupling of the tunneling-induced charge oscillations (magneto-Bloch versus Josephson oscillations) to another oscillator (in-plane cyclotron oscillations versus external oscillator modes) opens an elastic rectifying transport channel. We explore the superlattice effect both theoretically and experimentally, and find that the transient self-induced current can be adequately modeled if the damping of both types of coupled electron oscillations is properly taken into account.