Computer simulation of proton channelling in silicon

The channelling of 3 MeV protons in the 〈110〉 direction of silicon has been simulated using Vineyard model taking into account thermally vibrating nuclei and energy loss due to ion-electron interactions. A beam made up of constant energy particles but with spatial divergence has been simulated for the purpose. The values of the minimum scattering yield and half width of the channelling dip are shown to be depth sensitive and agree well with the measured values. The dependence of yield on the angle of incidence has been found to give information of all three types of channelling. The critical angles for the three types of channelling and wavelength of planar oscillations are consistent with the previous calculations.     

Electron channelling contrast imaging of dislocations in a conventional SEM

Abstract

Dislocations in shock loaded tantalum single crystals were imaged using both transmission electron microscope (TEM) and electron channelling contrast image (ECCI) in a scanning electron microscope with a conventional backscattered electron detector. The results were compared with backscattered electron intensity profiles across dislocations calculated via the dynamic theory of electron diffraction. A one-to-one correspondence between ECCI and TEM is established. High voltage and low index reflections should be used to obtain the highest dislocation contrast and greatest imaging depth.     

多缝衍射的计算机模拟与演示

利用一个多缝衍射模型模拟光和微观粒子的干涉衍射现象。该模型可演示光的双干涉、ｎ缝衍射及色散现象;也可演示微观粒子的单、双缝衍射,物质波的概率特性及粒子从量行为到经典行为的过渡。     

夫琅禾费衍射的计算机仿真

提出了利用MATLAB软件并通过计算机仿真夫琅禾费衍射实验的两种方法：直接计算法和傅里叶变换法,前者适用于形状简单、能精确得到相应衍射强度公式的孔径的仿真;后者适用于获取复杂形状衍射屏的夫琅禾费衍射图样的仿真文中给出各种孔缝的衍射屏的仿真衍射实验结果事实表明,采用这种仿真方法可以得到任意形状衍射屏的夫琅禾费衍射图样和强度分布曲线。     

空间静电场的计算机模拟--轴测投影法

采用轴测投影法,通过三维坐标的二维投影变换,实现空间静电场的计算机模拟。     

磁控溅射辉光放电特性的模拟研究

采用二维、自洽的PIC/MCC (particle-in-cell with Monte Carlo collision) 方法,模拟了磁控溅射辉光放电过程, 重点讨论了工作参数对放电模式和放电电流的影响. 模拟结果表明, 当工作气压由小到大或空间磁场从强到弱变化时, 放电模式会从阴极空间电荷主导的放电模式过渡到阳极空间电荷主导 的放电模式.在过渡状态,对应的工作气压与磁通密度分别为0.67 Pa和0.05 T; 随着工作气压的增大,放电电流先增大后趋向平衡,当工作气压超过2.5 Pa时,电流开始随工作气压的增大而减小; 而阴极电压增大时,放电电流近似线性增加.     

LCD投影系统光学引擎的计算机仿真分析

光学引擎是决定LCD投影系统色度、光度品质的核心部件之一。根据投影系统光学引擎的结构特点，结合色度学原理，利用光路追踪法编制了光学引擎的色度、光度仿真分析软件。仿真分析软件具有双向功能：对引擎的光学系统可进行色度光度计算，并可根据色度、光度指标优化光学引擎结构。将仿真与实际的光学引擎进行了对比实验，得到多组投影视场的色坐标对比数据，最后用软件优化了一个光学引擎，得到该引擎结构的优化数据。实验结果表明：该软件可提高光学引擎的设计效率。     

基于MATLAB的傅里叶光学实验的计算机模拟

计算机模拟技术广泛应用在教学和科研当中，在傅里叶光学实验中引入计算机模拟技术能更生动和深入地揭示光学现象的物理内涵，文章提出利用MATLAB模拟傅里叶光学实验的方法，该方法的优点是操作简单灵活，能完成一般光学实验中较难实现的操作，并给出了光学滤波实验的结果。     

照明光学系统照度分布的计算机模拟分析

本文阐述了照明光学系统与传统成像光学系统的区别，提出了几种计算照明光学系统照度分布的原理和方法，并给出了一个具体的利用计算机对投影照明光学系统照度分布的模拟分析方法和运算结果。     

多晶材料晶粒生长的计算机模拟研究

多晶固体材料显微结构的演化与诸多因素密切相关 ,是一复杂的过程。运用适当的计算机模拟方法进行模拟 ,实现对晶粒生长的预测 ,可为材料研究提供新的方法和重要依据。此文以晶粒生长动力学为基础 ,建立晶粒生长模型 ;分析了晶粒生长过程的计算机模拟理论和方法 ;以MonteCarlo方法为基础 ,提出快速Q statepotts算法 ,简化计算量 ,在PC机上编程实现了正常晶粒生长过程的计算机模拟。得到的显微结构图逼真度较好。通过对结果进行分析处理 ,得到的生长因子为 0 .4 7。     

Modeling of ion-assisted deposition using BCA computer simulation

Abstract

TRIM type binary collision approximation event store codes have employed to simulate collisional effects which occur during ion-beam or plasma assisted deposition of thin films.

Calculations can been performed using simplifying rate equation models, into which yields obtained from static TRIM simulations are inserted. Alternatively, the dynamic-composition code TRIDYN allows direct and complete simulations of the time-dependent processes.

Results are shown for different processes of ion-beam assisted deposition (IBAD), ion-beam mixing (IBM) post-treatment, and plasma-enhanced chemical vapour deposition (PECVD). Simulations of the formation of boron nitride films deposited from evaporated boron and energetic nitrogen show an excellent agreement with experimental results for nitrogen concentrations below the stoichiometric limit. For high N/B flux ratios, non-collisional mechanisms (ion-induced outdiffusion, surface trapping of outdiffusing nitrogen) have been included in the simulations, again producing good agreement with the experimental results. The ion-induced interface mixing of boron films on iron substrates is compared to experimental adhesion studies both for Ar⁺ post-treatment and Ar⁺ bombardment during deposition, demonstrating that the final adhesion is also influenced by other than purely collisional mechanisms. A special version of TRIDYN is used to treat the ion-induced densification of carbon films grown during simultaneous Ne⁺ bombardment, with reasonable agreement with experimental results. Finally, simple models are evaluated for the growth, composition and structure of C:H films grown in methane plasmas. The hydrogen content of the films decreases with increasing ion energy due to ion-induced release of hydrogen. Attempts to understand their bonding structure, in terms of the sp³/sp² ratio, on the basis of ion-induced preferential displacement, fail with respect to the energy dependence.     

计算机模拟光源的非单色性对迈克尔孙干涉条纹可见度的影响

通过开发的“迈克尔孙模拟实验平台”中的数值模拟和实验现象模拟，讨论分析了光源的非单色性对迈克尔孙干涉条纹可见度的影响，用直观的计算机图形将抽象的光的时间相干性理论形象化，从而弥补了光学实验教学中的理论欠缺和理论教学与实验相脱节的不足．     

刚体绕瞬心的转动方程的计算机模拟

在《大学物理》上曾对刚体绕瞬心的转动方程进行过广泛深入的讨论，这些讨论都是建立在解析分析的基础上，本则用计算机模拟的方法研究这个方程．计算机模拟的结果不仅形象直观地表现了公式的丰富内涵，也证明计算机模拟是教学研究的一种优秀工具．     

非晶/微晶两相硅薄膜电池的计算机模拟

在对不同晶相比硅薄膜的实验研究的基础上，利用有效介质理论估算了这种两相材料的光吸 收系数、迁移率寿命乘积及带隙宽度等参量，计算机模拟了不同结晶比硅薄膜电池的伏安特 性及光谱响应；结果为随着本征层微晶成分的增多，电池的开路电压逐渐减小，短路电流逐 渐增大，本征层的最佳厚度逐渐增大，填充因子有降低的趋势，电池的效率随晶相比的增大 而减小. 电池的光谱响应曲线表明，随晶相比的增大电池的长波响应明显提高. 根据这些模 拟结果，分析讨论了在考虑Lambertian背反射的情况下，非晶/微晶叠层电池的底电池采用 晶相比为40％—50％的两相硅薄膜材料做本征层是最佳选择. 关键词： 两相硅薄膜 太阳能电池 计算机模拟     

Computer simulation of high energy displacement cascades

Abstract

A methodology developed for modeling many aspects of high energy displacement cascades with molecular level computer simulations is reviewed. The initial damage state is modeled in the binary collision approximation (using the MARLOWE computer code), and the subsequent disposition of the defects within a cascade is modeled with a Monte Carlo annealing simulation (the ALSOME code). There are few adjustable parameters, and none are set to physically unreasonable values. The basic configurations of the simulated high energy cascades in copper, i.e., the number, size and shape of damage regions, compare well with observations, as do the measured numbers of residual defects and the fractions of freely migrating defects. The success of these simulations is somewhat remarkable, given the relatively simple models of defects and their interactions that are employed. The reason for this success is that the behavior of the defects is very strongly influenced by their initial spatial distributions, which the binary collision approximation adequately models. The MARLOWE/ALSOME system, with input from molecular dynamics and experiments, provides a framework for investigating the influence of high energy cascades on microstructure evolution.     

Computer simulation of the oxygen mobility in CaMnO3-x

The perovskite-type metal oxide CaMnO_3-x is known to accommodate substantial amounts of oxygen vacancies. High-resolution electron microscope investigations give evidence for ordering of the vacancies, i.e. well-defined structures in the compositional range of CaMnO_2.5 < CaMnO_3-x < CaMnO₃. Within this range the metal cation positions do not change, i.e. perovskitic framework is conserved while a remarkably high oxygen anion mobility is recorded. In addition, the electronic and magnetic structure, and thus the physical properties, depend directly on the oxygen stoichiometry.

This contribution focusses on the oxygen mobility in different CaMnO_3-x phases exhibiting oxygen vacancy ordered structures, i.e. CaMnO_3.0, CaMnO_2.80, CaMnO_2.75, CaMnO_2.66, CaMnO_2.55 and CaMnO_2.50. In these compounds the formal oxidation state of manganese changes from Mn⁴⁺ (x=0) to Mn³⁺ (x=0.5).

For the computer simulation of the defect structure and for the mobility of the oxygen anions within these defect structures we applied the method of interatomic potentials in a simple rigid-ion approximation. The parameters of interaction were calibrated on the basis of empirical data. i.e. equilibrium geometry and cohesive energies of the binary oxides CaO, MnO₂ and Mn₂O₃ were taken into account for the present calculations.

Stabilities, oxygen migration barriers and dielectric constants of selected representants of CaMnO_3-x are presented.     

Computer simulation of some dynamical properties of the Lorentz gas

We carried out molecular dynamics simulations of a Lorentz gas, consisting of a lone hydrogen molecule moving in a sea of stationary argon atoms. A Lennard-Jones form was assumed for the H₂-Ar potential. The calculations were performed at a reduced temperatureK ^* =kT/_{H 2–Ar} = 4.64 and at reduced densities ^*= _{Ar Ar} ³ in the range 0.074–0.414. The placement of Ar atoms was assumed to be random rather than dictated by equilibrium considerations. We followed the trajectories of many H₂ molecules, each of which is assigned in turn a velocity given by the Maxwell-Boltzmann distribution at the temperature of the simulation. Solving the equations of motion classically, we obtained the translational part of the incoherent dynamic structure factor for the H₂ molecule,S _tr(q, ). This was convoluted with the rotational structure factorS _rot(q, ) calculated assuming unhindered rotation to obtain the total structure factorS(q, ). Our results agree well with experimental data on this function obtained by Egelstaffet al. At the highest density ( ^*=0.414) we studied the dependence ofS(q, ) on system size (number of Ar atoms), number of H₂ molecules for which trajectories are generated, and the length of time over which these trajectories are followed.     

小粒子动态光散射信号的计算机模拟及分析

用计算机模拟了小粒子（０．００１μｍ～１μｍ）的动态光散射信号，并对其进行了分析，同时运用分形几何学（ＦｒａｃｔａｌＧｅｏｍｅｔｒｙ）的理论和概念，对信号的时间复杂性进行了分数维（ＦｒａｃｔａｌＤｉｍｅｎｓｉｏｎ）的计算，得出了它与粒子尺寸之间的关系。     

质子束尾波场中利用密度跃变实现电子捕获及加速的粒子模拟

用2D3V粒子模拟程序研究了高能质子束驱动的尾波场加速电子的方案,及其在此方案中应用背景等离子体密度的跃变致使等离子体电子自注入加速相区的可能性。粒子模拟结果显示:密度跃变实现了电子的自注入,并且捕获的电子束处于加速相位,等离子体尾波场纵向电场对捕获的电子束起箍缩作用;捕获的电子束随着传输,表现为窄能谱分布;同时随着密度跃变大小的增大,可以增加等离子体电子的捕获。     

质子束尾波场中利用密度跃变实现电子捕获及加速的粒子模拟

 用2D3V粒子模拟程序研究了高能质子束驱动的尾波场加速电子的方案,及其在此方案中应用背景等离子体密度的跃变致使等离子体电子自注入加速相区的可能性。粒子模拟结果显示:密度跃变实现了电子的自注入,并且捕获的电子束处于加速相位,等离子体尾波场纵向电场对捕获的电子束起箍缩作用;捕获的电子束随着传输,表现为窄能谱分布;同时随着密度跃变大小的增大,可以增加等离子体电子的捕获。