硅晶体中点缺陷结合过程的分子动力学研究

采用分子动力学方法模拟研究了硅晶体中的空位和间隙原子的结合过程. 研究中采用了Stilliger-Weber三体经验势描述原子间的相互作用, 系统分别在低温300K和高温1400K进行弛豫. 计算中发现空位和间隙原子倾向于通过<111>方向结合，而<110>方向上存在着势垒. 通过势垒值的计算, 对Tang和Zawadzki势垒计算值的差异进行了解释. 关键词： 分子动力学 空位与间隙原子 扩散     

低能中子在锆中产生的辐照损伤的计算机模拟研究

以GEANT4为基础采用蒙特卡罗方法对能量为1 MeV的中子在锆 材料中的输运过程进行了模拟分析. 首先计算得出: 反冲核的能量主要分布在1 keV和15 keV之间, 中子和靶核发生两次弹性碰撞的平均空间距离为29.47 mm. 由于中子和靶核在发生连续两次弹性碰撞过程中产生的两个反冲核能量较低, 它们的空间距离又比较大, 由此可以推测出: 由初级离位原子产生的后续级联碰撞可以看做是一系列独立的子级联碰撞过程, 同时也计算了中子在靶材的不同深度区域内产生的反冲核数目和平均能量. 其次, 利用蒙卡方法计算得到的结果, 采用分子动力学方法, 分别计算了五种不同能量下的初级离位原子产生的级联碰撞情况, 给出了初级离位原子的能量与其产生的次级离位原子数目之间的关系以 及不同能量下的初级离位原子产生的损伤区域范围等情况, 通过蒙特卡罗方法和分子动力学方法的结合, 给出了能量为1 MeV的中子在锆材料中产生的初级辐照损伤分布图像. 关键词： 辐照损伤 级联碰撞 蒙特卡洛模拟 分子动力学     

替位杂质对低能Pt原子与Pt(111)表面相互作用影响的分子动力学模拟

采用嵌入原子方法的原子间相互作用势，通过分子动力学方法模拟了低能Pt原子与Cu，Ag，Au，Ni，Pd替位掺杂Pt(111)表面的相互作用过程，系统研究了替位原子对表面吸附原子产额、溅射产额和空位缺陷产额的影响规律，分析了低能沉积过程中沉积原子与基体表面的相互作用机理以及替位原子的作用及其影响规律.研究结果显示：替位原子的存在不仅影响着沉积能量较低时的表面吸附原子的产额与空间分布，而且对沉积能量较高时的低能表面溅射过程和基体表面空位的形成产生重要影响.替位原子导致的表面吸附原子产额、表面原子溅射以及空位形 关键词： 分子动力学 低能粒子 替位掺杂 表面原子产额 溅射 空位     

低能Pt原子与Pt(111)表面相互作用的分子动力学模拟

利用分子动力学模拟方法详细研究了低能Pt原子与Pt(111)表面的相互作用所导致的表面吸附原子、溅射原子、表面空位的产生及分布规律,给出了表面吸附原子产额、溅射原子产额和表面空位产额随入射Pt原子能量的变化关系.模拟结果显示:溅射产额、表面吸附原子产额和表面空位产额随入射原子的能量的增加而增加,溅射原子、表面吸附原子的分布花样呈3度旋转对称性质;当入射粒子能量高于溅射阈值时,表面吸附原子主要是基体最表面原子的贡献,入射粒子直接成为表面吸附原子的概率很小.其主要原因是:当入射粒子能量高于溅射能量阈值时,入射 关键词： 分子动力学 低能粒子 表面原子产额 空位缺陷 溅射     

Fe-Cr合金辐照空洞微结构演化的相场法模拟

Fe-Cr合金作为包壳材料在高温高辐照强度等极端环境下服役,产生空位和间隙原子等辐照缺陷,辐照缺陷簇聚诱发空洞、位错环等缺陷团簇,引起辐照肿胀、晶格畸变,导致辐照硬化或软化致使材料失效.理解辐照缺陷簇聚和长大过程的组织演化,能更有效调控组织获得稳定服役性能.本文采用相场法研究Fe-Cr合金中空洞的演化,模型考虑了温度效应对点缺陷的影响以及空位和间隙的产生和复合.选择400—800 K温度区间、0—16 dpa辐照剂量范围的Fe-Cr体系为对象,研究在不同服役温度和辐照剂量下的空位扩散、复合和簇聚形成空洞的过程.在400—800 K温度区间,随着温度的升高,Fe-Cr合金空洞团簇形核率呈现出先升高后下降的趋势.考虑空位与间隙的重新组合受温度的影响可以很好地解释空洞率随温度变化时出现先升高后降低的现象.由于温度的变化将影响Fe-Cr合金中原子离位阀能,从而影响产生空位和间隙原子.同一温度下,空洞半径和空洞的体积分数随辐照剂量的增大而增大.辐照剂量的增大,级联碰撞反应加强,空位与间隙原子大量产生,高温下空位迅速的扩散聚集在Fe-Cr合金中将形成更多数量以及更大尺寸的空洞.     

质子对BaTiO3薄膜辐照损伤的计算机模拟

本文先应用分子动力学模拟BaTiO₃体系在初级击出原子(primary knock-on atom, PKA)轰击下缺陷产生和复合的动力学过程, 模拟结果表明：PKA的方向和能量对缺陷数目有重要影响, 并计算了Ba, O和Ti原子的平均位移阈能分别为69 eV, 51 eV和123 eV, 远大于SRIM程序默认的位移阈能25 eV. 然后应用蒙特卡罗软件包SRIM, 模拟质子在BaTiO₃薄膜中的能量损失过程, 比较位移阈能对模拟结果的影响, 分析质子能量和入射角度对空位数量以及分布的影响. 结果表明空位数量随着质子能量增加而增加, 增加的速率随能量的增加是降低的;当入射角度大于60°, 空位数量随入射角增大而明显减少.     

铝中氦原子行为的密度泛函研究

用密度泛函理论计算了大量He原子存在时He在金属铝中不同位置的能量,并在理论上预测了铝中的氦原子行为.结果表明,铝晶胞内He原子择优占位区是空位,而在整个晶体范围,最有利于容纳He原子的区域是晶界,其次是空位和位错.在fcc-铝的两种间隙位中,He原子优先充填四面体间隙位.间隙He原子的迁移能很小,易于通过迁移在晶内聚集,或被空位、晶界、位错等缺陷束缚.     

单空位缺陷对载能氢原子与石墨层间碰撞的能量交换的影响的分子动力学研究

本文采用分子动力学方法研究空位缺陷对石墨层中碳氢粒子碰撞的影响.将氢原子以不同能量分别向单空位缺陷边缘的两个碳原子轰击,分析了入射氢原子的能量损失、发生吸附反应的能量范围和靶原子的能量传递过程.研究发现,单空位缺陷边缘的碳氢粒子更易发生吸附反应;在碳氢粒子正碰过程中,氢原子随入射能量变化出现了双反射区域;碳氢粒子在空位缺陷边缘吸附后,形成了高结合能的sp²结构,并出现悬挂键,其临近的碳碳键能未降低;单空位缺陷边缘的碳原子吸附氢原子能量的能力强而传递能量的能力弱.这些结果对理解聚变反应 关键词： 面向等离子体材料 分子动力学方法 单空位缺陷     

金红石TiO_2本征缺陷磁性的第一性原理计算

基于密度泛函理论的平面波超软赝势方法模拟计算了金红石相TiO_2的四种本征缺陷(氧空位、钛空位、钛间隙缺陷、氧间隙缺陷)和两种复合缺陷(氧空位与氧间隙复合缺陷、钛空位与钛间隙复合缺陷)的铁磁特性.结合态密度、电子分布及晶体结构变化分析可知,四种本征缺陷均会在系统内引入缺陷态.氧空位、钛间隙缺陷使费米面升高,引起自旋极化,引入磁矩分别为1.62μB与3.91μB;钛空位的缺陷态处于价带顶,使费米面进入价带,表现出明显的p型半导体特性,引入磁矩约为2.47μB;氧间隙缺陷引入缺陷态但仍然处于自旋对称状态,费米面略微下降;氧空位与氧间隙复合缺陷使费米面上升的程度比单个氧空位时大,模拟的超晶胞保持了氧空位的铁磁特性,大小为1.63μB;钛空位与钛间隙复合缺陷以反铁磁方式耦合,但超晶胞仍具有一定的铁磁特性.     

基于蒙特卡罗模拟研究锆钛酸铅镧材料的中子辐照损伤

锆钛酸铅镧(Pb_0.94La_0.06Zr_0.96Ti_0.04O₃,PLZT)具有良好的介电和储能性质,是高效、高能量密度电容元件和存储器件的基体材料.为研究该材料的中子辐照损伤,首先基于Geant4程序包模拟了能量为1—14 MeV中子辐照浩钛酸铅镧(PLZT)材料产生的反冲原子能谱,然后根据产生的反冲原子种类和最大能量,利用二元碰撞方法模拟了不同能量的离子在PLZT中产生的位移损伤(包括空位和间隙原子),最后根据反冲原子能谱和对应能量离子在材料中产生的缺陷数目计算了不同能量的中子在PLZT材料中产生缺陷浓度以及分布.结果发现,对于1—14 MeV能区的快中子而言,其在厚度为3 cm的PLZT材料中产生的缺陷数目近似与中子能量无关,约为460±120空位/中子.辐照损伤在3cm厚度内随深度的增加而略有减小,总体变化小于50%,该减小主要是由于中子的反散射导致.本工作为计算中子在材料中的位移损伤提供了一种方法,同时模拟结果可为研究PLZT基电子器件的中子辐照效应提供指导.     

直拉硅单晶原生漩涡缺陷的研究

本文用化学腐蚀方法, 从含有漩涡缺陷的原生CZ硅单晶中分离出尺寸在1000--6000埃间的氧沉淀, 制成萃取复型样品,用T E M 对氧沉淀作微区电子衍射分析. 同时, 观察硅薄膜中漩涡缺陷的TEM 象, 确定了二者的对应关系. 结果表明, 构成漩涡缺陷的氧沉淀主要是呈方形片的热液石英(keatite, siliea k) 及少量呈六角片的。方英石(a-cristobalite ), 沉淀片周边沿<1 1 0> 方向, 惯习面前者的为{ 100} , 后者的为{ 1 1 1}. 样品的红外吸收光谱表明, 方片状热液石英沉淀可能与1 2 2 4 (1/cm ), 吸收峰相对应. 关键词：     

Molecular dynamics study of anisotropic growth of silicon

Based on the Tersoff potential, molecular dynamics simulations have been performed to investigate the kinetic coefficients and growth velocities of Si(100),(110),(111), and(112) planes. The sequences of the kinetic coefficients and growth velocities are μ_((100)) μ_((110)) μ_((112)) μ_((111))and v_((100)) v_((110)) v_((112)) v_((111)), respectively, which are not consistent with the sequences of the interface energies, interplanar spacings, and melting points of the four planes. However,they agree well with the sequences of the distributions and diffusion coefficients of the melting atoms near the solid–liquid interfaces. It indicates that the atomic distributions and diffusion coefficients affected by the crystal orientations determine the anisotropic growth of silicon. The formation of stacking fault structure will further decrease the growth velocity of the Si(111) plane.     

Simulation of low energy displacement processes in a dilute cu-au alloy

Abstract

Research into displacement cascade processes in alloy systems has received little attention, yet is potentially of interest because issues such as the effect of solutes on the displacement threshold and the defect distribution and movement in cascades are important. As part of a wider study, we have initially considered the minor substitutional solute Au in a Cu matrix, and have used molecular dynamics to investigate the properties of point defects, the threshold displacement energy E_d, and temporal and spatial distribution of defects in low-energy (≤500 eV) displacement cascades. The results show that the influence of the solute on the properties of defects is important and that E_d is dramatically different from its form in pure copper. In comparison with pure copper, the recoil of the Au solute gives rise to a higher peak at longer times in the number of displaced atoms in the generation of a displacement cascade. The influence of this on defect density in the cascade and the final number and arrangement of defects has been investigated.     

外延压应变对BaTiO$lt;sub$gt;3$lt;/sub$gt;铁电体抗辐射性能影响的分子动力学研究

采用基于壳模型的分子动力学模拟方法, 研究了存在外延压应变时BaTiO₃铁电体的辐射位移效应, 以O原子作为初冲原子(primary knock-on atom, PKA), 能量为1 keV, 方向为[001], 分别计算了外延压应变为0, 0.4%, 0.8%, 1.2%, 1.6%, 2.0%时体系的缺陷数量、分布, 以及辐射前后的极化强度, 比较了压应变为2%以及无应变下损伤区域、缺陷离位距离和反向外电场下PKA的迁移距离. 结果表明, 随外延压应变增加体系极化近似线性增加, 辐射后极化降低幅度降低、缺陷产生的数量有所减小, 2% 压应变存在时缺陷原子的离位距离、PKA在反向外电场作用下的迁移距离和损伤区域都小于无应变的情况, 说明外延压应变的存在对辐射造成的晶格损伤具有抑制作用, 对辐射损伤具有改善作用, 可以通过引入外延压应变来调控BaTiO₃的辐射损伤. 关键词： 应变 3')" href="#">BaTiO₃ 辐射损伤 分子动力学模拟     

Stability of concentration-related self-interstitial atoms in fusion material tungsten

Based on the density functional theory, we calculated the structures of the two main possible self-interstitial atoms(SIAs) as well as the migration energy of tungsten(W) atoms. It was found that the difference of the 110 and 111 formation energies is 0.05–0.3 e V. Further analysis indicated that the stability of SIAs is closely related to the concentration of the defect. When the concentration of the point defect is high, 110 SIAs are more likely to exist, 111 SIAs are the opposite. In addition, the vacancy migration probability and self-recovery zones for these SIAs were researched by making a detailed comparison. The calculation provided a new viewpoint about the stability of point defects for selfinterstitial configurations and would benefit the understanding of the control mechanism of defect behavior for this novel fusion material.     

Molecular dynamics simulations of displacement cascades in Fe-10%Cr systems

Molecular dynamics simulations of the displacement cascades in Fe-10%Cr systems are used to simulate the primary knocked-on atom events of the irradiation damage at temperatures 300,600,and 750 K with primary knockedon atom energies between 1 and 15 keV.The results indicate that the vacancies produced by the cascade are all in the central region of the displacement cascade.During the cascade,all recoil Fe and Cr atoms combine with each other to form Fe-Cr or Fe-Fe interstitial dumbbells as well as interstitial clusters.The number and the size of interstitial clusters increase with the energy of the primary knocked-on atom and the temperature.A few large clusters consist of a large number of Fe interstitials with a few Cr atoms,the rest are Fe-Cr clusters with small and medium sizes.The interstitial dumbbells of Fe-Fe and Fe-Cr are in the 111 and 110 series directions,respectively.     

Molecular dynamics simulations of displacement cascades in Feben 10%Cr systems

Molecular dynamics simulations of the displacement cascades in Fe-10%Cr systems are used to simulate the primary knocked-on atom events of the irradiation damage at temperatures 300, 600, and 750 K with primary knocked-on atom energies between 1 and 15 keV. The results indicate that the vacancies produced by the cascade are all in the central region of the displacement cascade. During the cascade, all recoil Fe and Cr atoms combine with each other to form Fe-Cr or Fe-Fe interstitial dumbbells as well as interstitial clusters. The number and the size of interstitial clusters increase with the energy of the primary knocked-on atom and the temperature. A few large clusters consist of a large number of Fe interstitials with a few Cr atoms, the rest are Fe-Cr clusters with small and medium sizes. The interstitial dumbbells of Fe-Fe and Fe-Cr are in the lan111ran and lan110ran series directions, respectively.     

Radiation effects of 50-MeV protons on PNP bipolar junction transistors

The effects of radiation on 3CG110 PNP bipolar junction transistors (BJTs) are characterized using 50-MeV protons, 40-MeV Si ions, and 1-MeV electrons. In this paper, electrical characteristics and deep level transient spectroscopy (DLTS) are utilized to analyze radiation defects induced by ionization and displacement damage. The experimental results show a degradation of the current gain and an increase in the types of radiation defect with increasing fluences of 50-MeV protons. Moreover, by comparing the types of damage caused by different radiation sources, the characteristics of the radiation defects induced by irradiation show that 50-MeV proton irradiation can produce both ionization and displacement defects in the 3CG110 PNP BJTs, in contrast to 40-MeV Si ions, which mainly generate displacement defects, and 1-MeV electrons, which mainly produce ionization defects. This work provides direct evidence of a synergistic effect between the ionization and displacement defects caused in PNP BJTs by 50-MeV protons.     

Microstructure evolution of T91 steel after heavy ion irradiation at 550 ℃

Fe-Cr ferritic/martensitic (F/M) steels have been proposed as one of the candidate materials for the Generation IV nuclear technologies. In this study, a widely-used ferritic/martensitic steel, T91 steel, was irradiated by 196-MeV Kr⁺ ions at 550 ℃. To reveal the irradiation mechanism, the microstructure evolution of irradiated T91 steel was studied in details by transmission electron microscope (TEM). With increasing dose, the defects gradually changed from black dots to dislocation loops, and further to form dislocation walls near grain boundaries due to the production of a large number of dislocations. When many dislocation loops of primary a₀/2<111> type with high migration interacted with other defects or carbon atoms, it led to the production of dislocation segments and other dislocation loops of a₀<100> type. Lots of defects accumulated near grain boundaries in the irradiated area, especially in the high-dose area. The grain boundaries of martensite laths acted as important sinks of irradiation defects in T91. Elevated temperature facilitated the migration of defects, leading to the accumulation of defects near the grain boundaries of martensite laths.     

Al掺杂对HfO2俘获层可靠性影响第一性原理研究

采用基于MS(Materials Studio)软件和密度泛函理论的第一性原理方法, 研究了HfO₂ 俘获层的电荷俘获式存储器(Charge Trapping Memory, CTM)中电荷的保持特性以及耐擦写性. 在对单斜晶HfO₂中四配位氧空位(V_O4) 缺陷和V_O4 与Al替位Hf掺杂的共存缺陷体(Al+V_O4)两种超晶胞模型进行优化之后, 分别计算了其相互作用能、形成能、Bader电荷、态密度以及缺陷俘获能. 相互作用能和形成能的计算结果表明共存缺陷体中当两种缺陷之间的距离为2.216 Å时, 结构最稳定、缺陷最容易形成; 俘获能计算结果表明, 共存缺陷体为双性俘获, 且与V_O4缺陷相比, 俘获能显著增大; Bader电荷分析表明共存缺陷体更有利于电荷保持; 态密度的结果说明共存缺陷体对空穴的局域能影响较强; 计算两种模型擦写电子前后的能量变化表明共存缺陷体的耐擦写性明显得到了改善. 因此在HfO₂俘获层中可以通过加入Al杂质来改善存储器的保持特性和耐擦写性. 本文的研究可为改善CTM数据保持特性和耐擦写性提供一定的理论指导.