Charge distribution of nitrogen ions reflected from copper and graphite surfaces

A method for the theoretical estimation of the equilibrium charge distribution of ions passed through a media is proposed. It is based on the correction of charge-exchange cross sections for gases using a factor taking the density effect into account. The calculated charge distribution of N ions in graphite agrees well with the existing experimental data. This method makes it possible to estimate the charge distribution of fast N ions reflected from a Cu surface.     

Empirical estimation of the equilibrium charge distribution of heavy ions in solid and gaseous media

Based on the analysis of experimental data on equilibrium charge distributions of ions in gases and solid media, the analytical parameterization of the charge distribution width as a function of the average ion charge and nuclear charges of the ion and the target atom and that of the asymmetry as a function of the average ion charge are obtained. The proposed relations are applicable in a broad energy interval and describe the existing experimental data satisfactorily.     

低速离子在固体中的电子阻止本领

本文介绍了低速离子在固体材料中电子阻止本领的理论发展情况。着重介绍了有效电荷理论和根据有效电荷理论,由氢离子在材料中的电子阻止截面标度各种重离子在同种材料中电子阻止截面的方法。 用电导理论导出了低速离子贯穿价电子气的阻止截面公式,并给出了一套有效电荷比的经验公式。利用这套公式求得的电子阻止截面Se的值,既符合实验上发现的Se随z_1或z_2振荡的规律,又符合Se随入射离子能量的变化关系。     

正负离子碰撞过程中电荷转移的理论研究

文中用渐近方法，采用未微扰的原子波函数，导出了正负离子碰撞过程中，当离子间的距离很大时，入射离子道与出射共价道之间的交换相互作用的解析表达式。利用该相互作用的解析表达式，并考虑在入射通道里Ｈ－离子核外有两个同科电子的情况，由多通道Ｌａｎｄａｕ－Ｚｅｎｅｒ模型分别计算了低能Ｈ＋＋Ｈ－和Ｄ＋＋Ｈ－碰撞过程中的电荷转移总截面。计算结果与已有的实验数据进行了比较。     

Width of the equilibrium charge distribution of heavy ions in solid and gaseous media

Based on an analysis of the experimental data on the charge distributions of ions in gases and solids, the analytical parameterization of the width of the charge distribution as a function of the energy, the average equilibrium ion charge, ion nuclear charge, and nuclear charge of target atom has been obtained. The proposed relations are applicable in a broad energy range and describe the existing experimental data satisfactorily.     

Analytical expressions for electrostatics of graphene structures

This study focuses on electrostatics of various graphene structures as graphene monolayer, graphene nanoribbons, as well as multi-layer graphene or graphene flakes. An atomistic moment method based on classical electrostatics is utilized in order to evaluate the charge distribution in each nanostructure. Assuming a freestanding graphene structure in an infinite or in a semi-infinite space limited by a grounded infinite plane, the effect of the length, width, number of layers and position of the nanostructure on its electrostatic charge distributions and total charge and capacitance is examined through a parametric analysis. The results of the present show good agreement with corresponding available data in the literature, obtained from different theoretical approaches. Performing nonlinear regression analysis on the numerical results, where it is possible, simple analytical expressions are proposed for the total charge and charge distribution prediction based on structure geometry.     

Effect of density on the equilibrium charge distribution of carbon and oxygen ions

Theoretical estimation of the equilibrium charge distribution of carbon and oxygen ions passed through a matter is obtained. The coefficient considering the effect of density on the charge distribution of these ions is calculated for an amorphous medium consisting of atoms with the nuclear charge Z _t (Z _t ≤ 54). An oscillating dependence of the average ion charge on the nuclear charge of the target atom is obtained which cannot be described by empirical relations.     

A theoretical relation between viscosity and thermal conductivity of gases based on macroscopic balance equations

Classical theoretical methods for estimation of viscosity and thermal conductivity of gases are based on the kinetic theory and on the corresponding-state methods. By means of these methods, approximate relations between viscosity and thermal conductivity can be formulated. In this paper, a theoretical relation between viscosity and thermal conductivity based on the macroscopic balance equations is derived using the van der Waals equation of state for calculating density. The new developed relation, which is an analogy to the Eucken formula, is tested on computing viscosity of eight arbitrarily chosen non-polar gases in wide temperature and pressure ranges. Comparison with experimental data shows an agreement better than 5% which is within the margin of experimental errors. This agreement with the measured values for all the studied gases is either better than or equal to that of the three most often used theoretical methods.     

离子推力器推力密度特性

离子推力器推力密度分布对航天器轨道维持和修正具有重要影响.采用粒子模拟-蒙特卡罗碰撞方法模拟束流等离子体输运过程,分析束流多组分粒子喷出数量和速度等微观参数,并计算得到单孔束流推力,结合放电室出口等离子体密度分布,进一步对推力密度分布特性分析,最后开展实验验证.研究结果显示:束流中单价离子、双荷离子以及交换电荷离子的推力贡献比分别为84.63%,15.35%和1.82%,可见推力主要来源于束流中的单价离子和双荷离子,交换电荷离子对推力贡献很小;推力密度分布具有较好的中心轴对称性,从推力器中心沿着径向先快速下降后趋于缓慢;与实验结果对比,经验模型相对误差约为4.1%,数值模型相对误差约为2.8%,相比经验模型,数值模型具有更好的准确性.研究结果可为离子推力器推力密度分布均匀性等优化提供参考.     

Energy and charge distribution of helium atoms reflected from a Cu surface under grazing incidence

The energy and charge distributions of helium ions and atoms reflected from a Cu surface at grazing incidence have been measured at the energies 250 and 300 keV. The dependence of the relative number of helium atoms in the scattered beam on the scattering angle at incidence angles less than 2° and scattered particle energies below 150 keV has been discovered. It is shown that, for a theoretical estimation of the charge fractions of particles reflected from the target surface, charge-exchange cross sections used in calculations must be corrected when solids are considered instead of gases.     

Defect charge states for classical modeling of diffusion processes in insulators

Some point defect properties can be accurately modeled by describing the ions classically, in terms of the shell model. This is particularly the case for point-defect diffusion in strongly ionic crystals. First, we discuss the issue of what ionic charge should be attributed to shell-model ions, including the possibility of partly covalent materials. We then discuss the issue of what defect charge states are likely to be of experimental interest and at the same time amenable to classical modeling. Finally, we discuss the rather common case where the defect charge is not well localized at a single ionic site, and where the electronic charge distribution of the defect and its neighbors will not remain fixed throughout a diffusion step.     

Effect of charge transfer efficiency on image quality in CCD line scan-based web inspection

Charge transfer efficiency limits the performance of a CCD line scan-based imaging system. Even though the degradation of the image quality due to the inefficiency in the charge transfer is often neglected in practical work it may have considerable effect on the system performance in applications where high resolution and uniform image quality are needed. In this paper the relationship between the charge transfer efficiency and the image quality in paper web inspection and, especially, in streak detection is discussed. A simple method for the estimation of the charge transfer efficiency is proposed. The method is based on the imaging of a square wave test pattern. The degradation of the image quality due to the charge transfer is analysed both theoretically and with practical imaging experiments. The results show clearly the variation in the system performance along the CCD scan. This is emphasised in the case of small and low-contrast surface defects on the web.     

Z1- AND Z2-OSCILLATIONS OF ELECTRONIC STOPPING CROSS SECTIONS OBTAINED BY SHELL-WISE CALCULATION AND HARMONIC-OSCILLATOR MODEL

A shell-wise calculation method and a quantal harmonic-oscillator model have been used to calculate the electronic stopping cross sections for heavy ions colliding with atoms or penetrating matter. The electronic energy loss is given in an impact parameter formalism. In order to generalize the theoretical models, which pertain to the cese of point charge interacting with matter, to the case for heavy ions, an effective stopping charge hased on the modified BK theory is used by way of simple scaling in the calculations. The comparisons between the calculated results and the experimental data demonstrate a favourable evidence to justify the theoretical models.     

Z1- AND Z2-OSCILLATIONS OF ELECTRONIC STOPPING CROSS SECTIONS OBTAINED BY SHELL-WISE CALCULATION AND HARMONIC-OSCILLATOR MODEL

A shell-wise calculation method and a quantal harmonic-oscillator model have been used to calculate the electronic stopping cross sections for heavy ions colliding with atoms or penetrating matter. The electronic energy loss is given in an impact parameter formalism. In order to generalize the theoretical models, which pertain to the cese of point charge interacting with matter, to the case for heavy ions, an effective stopping charge hased on the modified BK theory is used by way of simple scaling in the calculations. The comparisons between the calculated results and the experimental data demonstrate a favourable evidence to justify the theoretical models.     

Ionization potential of atoms and multiply charged ions versus the nuclear charge

The terms of ions and atoms are calculated with a method based on the Bohr model. The ionization potentials of helium-like, lithium-like, and beryllium-like ions are calculated as functions of the nuclear charge and electron quantum numbers. The results calculated are in satisfactory agreement with experimental data. The accuracy of the method is found to rise with the nuclear charge of ions.     

Ionization by low energy heavy ions in nitrogen,carbon dioxide,argon and hydrocarbon gases

Experimental data on the variation of W, the mean energy expended by a charge particle in producing an ion pair in a gas, with the mass, charge and energy of the particle is examined with a view to discovering how far these variations may be explained in terms of elastic nuclear scattering. In nitrogen and carbon dioxide W appears to depend not only on the elastic nuclear scattering but also on the parameter E/MZ^4/3 for ions other than piotons. In argon any relationship is obscured by apparent discrepancies in the data, although it is possible that the variation may be similar to that in nitrogen and carbon dioxide. The data for the hydrocarbon gases is not so extensive as for the other gases and it may be that the variation of W with the mass and charge of the ion is different from that in nitrogen and carbon dioxide. It is speculated that this difference, if real, is due to super-excited states in the hydrocarbon gases.

Some empirical relationships are suggested as a practical guide for use in dosimetry.     

Au激光等离子体M带5f-3d跃迁的光谱参数

用超组态碰撞辐射模型模拟非局域热动力学平衡中Au的M带谱5f-3d跃迁的离子电离态特性，激光等离子体的光谱跃迂参数是必不可少的。利用多组态Dirac-Fock广义扩展平均能级方法，用GRASP^2系统地计算了激光Au等离子体中类铁金离子-类锗金离子的M带谱5f-3d的光谱跃迁波长．跃迁几率和振子强度，计算中考虑了重要的核的有限体积效应、Breit修正和QED修正，所得结果和最近的实验数据及理论计算值进行了比较。此结果可应用于对激光等离子体的模拟和诊断。     

Dipole Polarizabilities of the Ground States for Berylliumlike Ions

Dipole polarizabilities of the ground states for berylliumlike ions with nuclear charge Z = 4 to 10 are calculated by using the Rayleigh-Ritz variational method with multiconfiguration interaction wave functions. The representative models of convergence are listed and compared with other theoretical data for nuclear charge Z = 4 to 6. The present dipole polarizabilities are in good agreement with previous accurate theoretical values available in the literature. For results with greater nuclear charge number, the present calculations may provide benchmarked data for future theoretical and experimental studies. Dynamic dipole polarizabilities of the ground state for the beryllium atom at selected frequencies are also calculated and compared with other theoretical values in the literature.     

C20离子团簇在氧化物中穿行时库仑爆炸过程的理论研究

研究了C20团簇在几种金属氧化物(Al2O3,SiO2)中穿行时发生的库仑爆炸过程.采用线性介电响应理论,并结合Mermin形式的介电函数,得到了团簇中各组成离子的空间感应势,其中组成团簇中各组成离子的电荷分布情况由Brandt-Kitagawa有效电荷理论模型来描述.通过求解运动方程得到离子团结构随时间的演化过程,并采用Monte Carlo方法模拟了爆炸过程中的多重散射现象.我们发现,尾流效应使团簇的空间结构和电荷分布呈现非对称性.     

Charge retention in quantized energy levels of nanocrystals

Understanding charging mechanisms and charge retention dynamics of nanocrystal (NC) memory devices is important in optimization of device design. Capacitance spectroscopy on PECVD grown germanium NCs embedded in a silicon oxide matrix was performed. Dynamic measurements of discharge dynamics are carried out. Charge decay is modelled by assuming storage of carriers in the ground states of NCs and that the decay is dominated by direct tunnelling. Discharge rates are calculated using the theoretical model for different NC sizes and densities and are compared with experimental data. Experimental results agree well with the proposed model and suggest that charge is indeed stored in the quantized energy levels of the NCs.