Gaseous lon mobility in electric fields of arbitrary strength

The first rigorous kinetic theory of ion mobility in neutral gases, valid for electric fields of arbitrary strength without restriction on the ion-neutral mass ratio or interaction potential, is presented. The theory is based on the use of a set of basis functions in which the ions are allowed to have a temperature different from that of the neutral gas. The convergence of a series of approximations for the mobility is good, and the resulting expressions are not expansions in powers of the field strength. In lowerst approximation, the equation for the mobility is nearly the same as that obtained from an approximate free-flight theory, except for the appearance of an effective temperature in the diffusion, or momentum-transfer, collision integral. This difference is the crucial point that allows experimental measurements of ion mobility as a function of field strength to be used to obtain information on ion-neutral potentials. Data on K⁺ ions in He, Ne, and Ar are analyzed as an example; the range of effective temperatures is approximately 100 to 20,000°K. At high effective temperatures the results agree with similar information obtained from the scattering of ion beams in gas targets.     

Coefficient of ion mobility versus electric field strength dependence in gases: Experimental determination

A technique for finding the electric field dependence of the coefficient of ion mobility in gases is suggested. For ions of 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, 1,3,5-trinitrobenzene, 1,3-dinitrobenzene, and dimethylmethylphosphonate, these dependences are taken in air by applying a variable periodic polarity-asymmetric specially shaped electric field. The accuracy of the technique suggested is estimated and compared with that of the conventional drift tube method.     

Negative differential mobility in PbTe and PbSnTe at high electric fields

Monte Carlo calculations of hot-electron drift velocity in PbTe and Pb_0.8Sn_0.2Te at 77 K are reported. The relevant scattering mechanisms together with band-structure nonparabolicity and anisotropy are included in the calculations. A negative differential mobility (NDM) does not appear when the electrons are assumed to remain confined within the L valleys of the conduction band. On the contrary, allowing for electron transfer into the W valleys and taking suitable values of the parameters related to these valleys, an NDM appears and the threshold field for the same agrees well with the experimental data. Alloy scattering in PbSnTe is found to reduce the NDM.     

Image charge approximations of reaction fields in solvents with arbitrary ionic strength

In this paper, we report a new development of image charge approximations of reaction fields for a charge inside a dielectric spherical cavity immersed in an ionic solvent with arbitrary ionic strength. This new development removes the requirement of low ionic strength of the solvent in a previous result [S. Deng, W. Cai, Extending the fast multipole method for charges inside a dielectric sphere in an ionic solvent: high-order image approximations for reaction fields, J. Comput. Phys. 227 (2007) 1246–1266], thus extending the applicability of the image charge approximations of reaction fields in the modeling of biomolecular solvation.     

Non-steady-state diffusion currents in large electric fields for discrete lattices

The transient response is derived for a model non-metallic solid based on microscopic hopping of charged carriers over discrete energy barriers in the presence of a concentration gradient and a homogeneous electric field of arbitrary magnitude.     

Oscillator strength of a two-dimensional D ion in magnetic fields

In the present paper we determine the oscillator strength of two-dimensional (2D) D⁻ ions under the influence of a static magnetic field. The results are important for the analysis of the optical transitions observed in semiconductor quantum wells. We have applied the ab initio procedure Hyperspherical Adiabatic Approach, based on the use of hyperspherical coordinates. This approach uses an adiabatic separation of the total wave function that allows accurate energies determination from molecular-like potential curves. The convergence is obtained in a systematic way by the inclusion of non-adiabatic couplings without the need of adjustable parameters.     

Drift mobility and diffusion with an electric field of Ba2+ ions in NaCl crystals

Using a carrier-free tracer¹³³Ba the temperature dependences of the diffusion coefficientD and mobility of Ba²⁺ ions in an electric field have been measured on NaCl crystals in the temperature range from 500 to 750 °C. It is shown that the obtained values ofD are not affected by an electric field (30 V/cm) and that the temperature dependence of the mobility of Ba²⁺ ions is given by(T)=(12·3±1·9) exp [-(1·51±0·09) eV/kT]. Vacancy jump frequencies near a Ba²⁺ ion and the Gibbs free energy of association of this ion with a vacancy have been calculated in terms of a simple 5-frequency model for impurity diffusion by a vacancy mechanism.     

On approximations involved in the theory of charged particletransport in gases in electric and magnetic fields at arbitrary angles

Various approximations and computer codes for the calculation of charged particle transport in gases in electric and magnetic fields have found their may into mainstream applications of various types. Some of these codes/approximations avoid the mathematical complexity associated with an accurate solution of Boltzmann's equation, but because of assumptions of symmetry and/or near isotropy in velocity space they may be incorrect. Using an accurate multiterm solution of Boltzmann's equation for electric and magnetic fields oriented at arbitrary angles with respect to each other, we highlight the inadequacies of such assumptions. In addition we explore the validity of Tonks' theorem and the effective field approximation as applied to the more general case of arbitrary orientation angles     

Mathematical modelling of the ion motion in the isochronous magnetic and radio frequency electric fields

The results of mathematical modelling of the ion motion show the possibility of the phase focusation of the ions with utilization of the radial force. This force is realized with a radial component of electric field. The beam monochromatization is analyzed simultaneously.     

Fullerene-coated field emitters activated by a potassium ion flux in high electric fields

Activation of fullerenes covering tip field emitters by a potassium ion flux is studied. New data for the effect of the coating thickness, emitter temperature during coating application, time of ion processing, and ion energy on the activation efficiency are derived. These data are used for optimization of the activation process. The result is a twofold decrease in the voltage necessary to obtain fixed emission currents. The performance of activated emitters in strong electric fields is investigated, and conditions under which the emission current is high are established. It is shown that emitters with a diameter of the top of 0.3 μm can stably operate at emission currents of up to 100 μm A.     

Modification of semiconductor materials using laser-produced ion streams additionally accelerated in the electric fields

The laser-produced ion stream may be attractive for direct ultra-low-energy ion implantation in thin layer of semiconductor for modification of electrical and optical properties of semiconductor devices. Application of electrostatic fields for acceleration and formation of laser-generated ion stream enables to control the ion stream parameters in broad energy and current density ranges. It also permits to remove the useless laser-produced ions from the ion stream designed for implantation.For acceleration of ions produced with the use of a low fluence repetitive laser system (Nd:glass: 2 Hz, pulse duration: 3.5 ns, pulse energy:∼0.5 J, power density: 10¹⁰ W/cm²) in IPPLM the special electrostatic system has been prepared. The laser-produced ions passing through the diaphragm (a ring-shaped slit in the HV box) have been accelerated in the system of electrodes. The accelerating voltage up to 40 kV, the distance of the diaphragm from the target, the diaphragm diameter and the gap width were changed for choosing the desired parameters (namely the energy band of the implanted ions) of the ion stream. The characteristics of laser-produced Ge ion streams were determined with the use of precise ion diagnostic methods, namely: electrostatic ion energy analyser and various ion collectors. The laser-produced and post-accelerated Ge ions have been used for implantation into semiconductor materials for nanocrystal fabrication. The characteristics of implanted samples were measured using AES.     

平行电磁场中的Rydberg锂原子吸收谱的模型势计算

用B样条基组展开方法结合模型势计算了Rydberg锂原子在平行电磁场下的振子强度谱. 径向和角向均采用高阶Ｂ样条基组.计算结果与已有的实验结果符合得很好.利用分波分析法,对部分谱线的振子强度的强弱进行了分析. 本文方法简单有效，易于推广到交叉电磁场中Rydberg原子的精确谱的计算. 关键词： B样条 能谱 振子强度 平行电磁场 Rydberg原子     

Strain fields in arbitrary shaped quantum wires

The intent of this work is to develop a more generalized approach towards strain field calculations in embedded quantum wires (QWRs). Higher degree polynomials are used to achieve better discretization of QWR in arbitrary shapes and to avoid some of the singular points in the strain field calculations. Calculations are performed for simpler geometries such as triangular and square shaped QWRs to verify the validity of the approach. The same approach is tested for more complicated shapes such as crescent shaped QWRs with and without lateral quantum wells. The strain field distributions, are observed to be similar to those obtained from the analytical expressions. However, in the case of crescent shaped QWRs, the strain distribution is different in the region above the QWR. The difference is the result of the better discretization and of the removed singular points. The use of higher degree polynomials provides better discretization for shapes of interest.     

Effect of electric fields on the ion current signals in a constant volume combustion chamber

Ion current sensing has the potential to become a promising combustion diagnostic technique for mass productive engines. In this paper, the effect of electric fields on ion current signals measured from a series of methane/air flames in a constant volume combustion chamber (CVCC) is investigated both experimentally and numerically. Based on simultaneous flame Schlieren imaging and ion current measurement, the relation between the flame/electrodes contact area and the ion current signal waveform is explored under different electric field configurations. A CFD model, which incorporates flame plasma hydrodynamics, neutral/charged species reaction kinetics and ion-electric field interactions, is constructed. The effect of the electric field on the ion distribution and the charged species flux are analyzed, and the signal amplitude and timing are well predicted under the equivalence ratio range of Ф?=?0.7–1.1. Besides, the behavior of electrons, which is normally neglected in previous studies, is also analyzed in this work. The results show that it will affect the signal as well. The electron produced in the flame front zone can hardly diffuse into the pre-flame zone (<?350?K) even its mobility is 3-4 order higher than those of the positive ions. Therefore, the anode of the ion probe, which placed in the pre-flame zone, cannot detect the ion current signal until it contacts the flame front.     

Impurity bands in semiconductors in arbitrary magnetic fields

For a random distribution of impurities we study the shift of the centre of the impurity band and its width as a function of magnetic field. This is done by calculating the first and second moments of the density of states in a tight binding approximation.