在微机上进行的离子源中离子发射和运动的Monte—Carlo模拟计算

用Monte—Carlo模拟法研究了液态金属离子源中的离子发射过程,离子有Poi-sson分布的发射噪音,有Maxwell分布的初始速度,有随机的初始位置.离子运动时不只受场力的作用,还受到其他离子的库仑作用力.文章给出考虑和不考虑库仑作用力的轨迹各十条,可见其影响.计算用了分时进行法,即把整个计算分成若干次进行,故能在IBM微机上进行运算.     

CdTe:Sm晶体红外吸收光谱的研究

本文报道了CdTe: Sm晶体红外吸收光谱的研究结果.根据立方晶体场理论和Sm离子4f能级间的跃迁特性,分析确定了 CdTe:Sm晶体中 Sm~(2+)、Sm~(3+)离子在晶格中的位置类型及其晶体场特性,用点电荷模型计算了不同位置的Sm~(3+)周围的晶体场参数.     

新型GaAs/AlGaAs量子阱红外探测器暗电流特性

对基于GaAs/AlGaAs系子带间吸收的一种新型量子阱红外探测器,采用Poisson方程和Schrodinger方程,计算了新器件结构的能带结构、电子分布特性,在此基础上采用热离子发射、热辅助遂穿模型对器件的暗电流特性进行了模拟,计算结果与器件实测的暗电流特性吻合得很好,说明热离子发射、热辅助遂穿机制是形成器件暗电流的主要构成机制,增加垒高、降低阱中掺杂浓度及降低工作温度是抑制器件暗电流的主要途径,计算结果对进一步优化器件的设计将起到重要的理论指导作用．     

新型GaAs/AlGaAs量子阱红外探测器暗电流特性

对基于 Ga As/ Al Ga As系子带间吸收的一种新型量子阱红外探测器 ,采用 Poisson方程和 Schrodinger方程 ,计算了新器件结构的能带结构、电子分布特性 ,在此基础上采用热离子发射、热辅助遂穿模型对器件的暗电流特性进行了模拟 ,计算结果与器件实测的暗电流特性吻合得很好 ,说明热离子发射、热辅助遂穿机制是形成器件暗电流的主要构成机制 ,增加垒高、降低阱中掺杂浓度及降低工作温度是抑制器件暗电流的主要途径 ,计算结果对进一步优化器件的设计将起到重要的理论指导作用 .     

一种复杂分层介质中电磁探测的正演算法研究

针对海底可控源电磁法(CSEM)正演计算中所涉及到的极低频电磁波在含有目标体的不均匀分层介质中的传播问题,提出了基于"扰动"的格林函数算法。该算法将发射源在目标体内产生的初级场直接作为接收点处次级场的激励源,结合并矢格林函数的物理意义对次级场进行计算,从而避免了矩阵方程的求解。验证结果表明:当目标体相对于背景介质为"微扰"时,计算精度可接受。最后,给出了目标体位于不同位置时次级场幅值的2-D分布图,从图中可以明显看出目标体的分布位置及大小对于目标体的作用区域及大小的影响,为反演的进行提供了依据。     

聚焦离子束(FIB)中的离子光学问题

本文简要讨论了聚焦离子束中的离子光学问题，包括液态金属离子源的发射机制和发射特性，如虚源、角电流强度，能量分散、伏安特性，束流起伏，聚焦限制，离子束中的化学成分及源的寿命，讨论了离子光学柱体的组成与特征，束流一束径关系，束中电流密度分布，以及空间电荷效应等，回顾了静电透镜的历史以及它在离子光学系统中的重要意义。     

电解槽模拟研究场发射枪尖端的电子光学特性

本文用电解槽模拟,采用逐次放大逼近阴极尖端的方法,克服场发射枪系统阴极附近电场激剧变化及尖端与阳极尺寸上的巨大差异所引起的计算电场的困难,获得实际阴极附近足够精度的电场分布。并由此计算得到沿阴极表面亮度分布。从模拟得到的阴极区域电子轨迹,获得虚源大小及位置与电子束发射角有关的结果。     

无线电暗室的理论分析与计算

本文导出了无线电暗室中各点场反射系数和交叉极化率的表达式,讨论了接收、发射天线方向性图对它们的影响,求出了与发射、接收点范围有关的室内各墙上反射区位置,计算出了暗室各参量的精细特性。     

待定系数法计算场致发射体阴极表面场强和发射电流密度

在计算场致发射体阴极发射电流时 ,影响发射电流的主要因素是阴极表面的电场强度。由于发射电流密度的大小和阴极表面场强呈指数关系 ,阴极表面场强很小的变化将引起发射电流的剧烈变化 ,所以提高阴极表面场强的计算精度是至关重要的。本文提出了一种计算阴极表面场强的新方法——待定系数法 ,并用该方法计算了一个二极管场致发射体的阴极表面电场强度和电流密度。     

源搅拌混响室的仿真分析与实验研究

根据谐振腔理论,分析了理想情况下影响源搅拌混响室性能的主要因素,通过数值计算对其进行仿真验证,确定了影响混响室场均匀性的主要因素有激励天线的极化方向,摆放位置以及激励源的位置数等;在此基础上提出了一种可行的源搅拌方案,通过实验的方法,在满足一定采样数情况下,实现了混响室较好的场均匀性;同时借助K-S拟合对源搅拌混响室测量场值的统计特性进行了分析,结果表明:源搅拌混响室的一维场分布服从瑞利分布。     

多孔钨铯离子源

在光电阴极的制备及对光电阴极作表面分析中,铯离子源较中性铯源具有一定的优点。根据表面电离的原理,铯离子源使用了多孔钨、铯盐及其还原剂。本文介绍了铯离子源的制备,报告了实际测量结果。     

强流离子光学计算方法

强流离子光学与传统离子成像光学相比，最主要的区别是强流离子光学必须考虑空间电荷效应。本文讨论利用计算机辅助设计建立强流离子光学的差分计算方法，可直接绘出空间电位分布及离子运动轨迹。设计验证了几个实例，获得较好的结果。     

LY—3A型冷阴极离子源

本文介绍了LY—3A型冷阴极离子源的工作原理、结构特征和实验结果。用BF_3、PH_3、Ar、N_2等作放电物质,在离子源放电功率小于100W的情况下,~(31)P~+、~(40)Ar~+、N_2~+的束流强度均大于2mA、~(11)B~+的束流强度大于1mA,同时具有较高成份的多电荷态离子。采用溅射的方法离化固体元素,已离化引出~9Be~+、~(27)Al~+、~(24)Mg~+、~(48)Ti~+、~(52)Cr~+、~(96)Mo~+、~(101)Ru~+、~(106)Pd~+、~(157)Gd~+、~(167)Er~+等难熔金属元素离子。     

用于材料改性的宽束离子源现状及其发展

本文叙述了对材料表面改性的宽束离子源的要求，重点介绍了考夫曼型气体离子源及电子束蒸发强流金属离子源，也介绍了ＲＦ、ＥＣＲ离子源及ＭＥＶＶＡ源。     

纳米石墨片的制备及场发射特性

将可膨胀石墨粉放入家用微波炉中进行微波辐照,使石墨粉发生燃烧膨胀,将燃烧的产物用无水乙醇超声后旋涂于硅片上,用扫描电子显微镜(SEM)观察其形貌,得到仅几纳米厚的准二维结构的纳米石墨片。对其进行场发射特性测试,结果显示其具有优异的场发射性能,其开启场强为5.9V/μm,对应的电流密度为0.01mA/cm2。在场强为10.25V/μm时,得到最大发射电流密度为5.9mA/cm2。该纳米石墨片制作方法简单、快捷,可成为一种优异的准二维场发射电子源。     

Current Variability in Si Nanowire MOSFETs Due to Random Dopants in the Source/Drain Regions: A Fully 3-D NEGF Simulation Study

In this paper, we study the impact of random discrete dopants in the source/drain (S/D) leads on the current variability of a gate-all-around Si nanowire transistor. Due to the strong inhomogeneities of the self-consistent electrostatic potential, a fully 3D real-space nonequilibrium Green's function (NEGF) formalism is used. N-channel transistors with random discrete donors in the S/D regions varying in both numbers and locations have been simulated. We have studied the impact of quasi-bound (QB) states and transmission resonances associated with the attractive potential of the donors on the screening of the impurities and on the current transport. The convergence of the coupled 3D Poisson-NEGF equations for narrow wires with discrete dopants is cumbersome due to the quasi-discrete nature of QB states and resonances of the attractive impurity potential. We present a robust solution strategy dealing with the convergence challenges. Large variations in the on-current and modest variations in the subthreshold slope are observed in the I _D-V _G characteristics when comparing devices with microscopically different discrete dopant configurations. We have also estimated the access resistance associated with the random dopant regions in the source and the drain leads and find very good agreement with the resistance estimated from the bulk silicon mobility at the same doping concentration.     

应用等离子体化学反应的高频离子源中气压对引出金属离子和卤素离子含量的影响

高频离子源中等离子体化学反应引出金属和卤素离子的实验中,存在一个规律性的东西。那就是,放电室内的气压在工作范围内变化时,离子束中金属离子和卤素离子的含量也都随之改变。当气压升高时,金属离子的百分比增大,卤素离子的百分比减小;反之,金属离子的比率下降,而卤素离子的比率上升。本文对这样一个事实进行了一些讨论。     

A new injection method for AC harmonic elimination by active powerfilter

An injection method for an active filter which eliminates the harmonics present in AC lines by injecting PWM harmonic compensating current is proposed. In the proposed method, the active filter produces a pulsewidth modulation (PWM) current that cancels the existing harmonics up to any order completely. To generate such PWM current, both inverter and DC current source is needed. The current source can be replaced by a large inductor without any external power source. This can be achieved by providing the inverter with rectifying capability because the inverter has the same circuit structure as the rectifier. Therefore, the proposed model of PWM injection current includes not only the harmonic components to suppress the existing harmonics up to any order, but also the fundamental one, to raise the inductor current to any desired value. The characteristics of the injection method are investigated through a digital computer simulation. Feasibility is proved by the experimental results     

GEOSTATIONARY STATION-KEEPING BY ION THRUSTERS: GENETIC ALGORITHMS OPTIMIZATION

The orbital control of geostationary satellites requires the periodic execution of manoeuvres for gravitational and solar radiation perturbation compensation. To maintain a fine control of the satellite position, it is usually sufficient to perform orbit corrections every two weeks, firing chemical thrusters. The operational load for the manoeuvre's planning and execution is usually quite low. Innovative technologies for station-keeping are available now, based on high efficiency ion thrusters, which allow a significant propellant saving. They are included in Artemis, a telecommunications satellite developed by the European Space Agency. When low acceleration ion thrusters are adopted, a near continuous orbit control is required; the resulting long firing arcs can be in conflict with some operational or technical constraints. The station-keeping planning is a critical process, since it is not based on periodic impulsive manoeuvres, but rather on quasi-continuous firings. Furthermore the orbit control should be planned more on a seasonal or a yearly cycle rather than on short weekly cycles. Since each manoeuvre is defined by its start time and duration, the total number of parameters involved in a station-keeping optimization process amounts to several tens. The presence of many variables and logical constraints makes the use of classical optimization methods quite complex. The model proposed here is based on genetic algorithms, which allows the convergence to an optimum solution through successive iterations, in which a random set of solutions is progressively selected on the basis of a factor of merit tailored to the target. This paper presents some innovative concepts for station-keeping optimization when ion propulsion is adopted for orbital control; furthermore, the general properties of genetic algorithms are discussed, together with the results obtained in the specific station-keeping application.