类金刚石薄膜在硅基底上的沉积及其热导率

采用分子动力学方法模拟了碳在晶体硅基底上的沉积过程, 并分析计算了所沉积的类金刚石薄膜的面向及法向热导率. 对沉积过程的模拟表明, 薄膜密度及sp³杂化类型的碳原子所占比例均随沉积高度的增加而减小, 在碳原子以1 eV能量垂直入射的情况下, 在硅基底上沉积的薄膜密度约为2.8 g/cm³, sp³杂化类型的碳原子所占比例约为22%, 均低于碳在金刚石基底上沉积的情况. 采用Green-Kubo方法, 计算了所沉积类金刚石薄膜的热导率, 其面向热导率可以达到相同尺寸规则金刚石晶体的50%左右, 并且随着薄膜密度与sp³杂化类型碳原子所占比例的升高而升高.     

金刚石表面无定形碳氢薄膜生长的分子动力学模拟

利用分子动力学模拟方法研究了CH₂基团轰击金刚石(111)面所形成的无定形碳氢薄膜(a-C:H)的生长过程. 结构分析表明, 得到的无定形碳氢薄膜中碳原子的局域结构(如C–C第一近邻数)与其中氢原子的含量密切相关. CH₂ 基团入射能量的增加会导致得到的薄膜的氢含量降低, 从而改变薄膜中类sp³成键碳原子的比例.     

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     

分子动力学模拟H原子与Si的表面相互作用

通过分子动力学模拟了入射能量对H原子与晶Si表面相互作用的影响. 通过模拟数据与实验数据的比较, 得到H原子吸附率随入射量的增加 呈先增加后趋于平衡的趋势. 沉积的H原子在Si表面形成一层氢化非晶硅薄膜, 刻蚀产物(H₂, SiH₂, SiH₃和SiH₄)对H原子吸附率趋于平衡有重要影响, 并且也决定了样品的表面粗糙度. 当入射能量为1 eV时, 样品表面粗糙度最小. 随着入射能量的增加, 氢化非晶硅薄膜中各成分(SiH, SiH₂, SiH₃)的量以及分布均有所变化. 关键词： 分子动力学 吸附率 表面粗糙度 氢化非晶硅薄膜     

CH基团与金刚石(111)面的碰撞反应及其对碳膜生长的影响

等离子体增强化学气相沉积技术中的碳膜选择性自组装机理是高性能碳膜制备过程中的挑战性基础课题.采用经典分子动力学方法,模拟了不同能量(1.625-65 eV)的CH基团在清洁金刚石和吸氢金刚石(111)面上的轰击行为,获得了吸附、反弹、反应等各类事件的发生概率,并据此探讨了含氢碳膜制备过程中CH基团的贡献.结果表明,随着入射能量的增加,CH基团对薄膜生长的贡献由单纯的吸附、反弹机理向反应、吸附混合机理转变,其中最主要的反应过程是释放一个或两个氢原子的反应,而释放氢分子的反应则很少发生.这些反应不仅使薄膜生长过程更均匀、薄膜表面更平整,还降低了薄膜的氢含量.生长机理的转变导致低能量条件下所成薄膜中的多数碳原子都包含一个氢原子作为配位原子,而高能量条件下的薄膜中的碳原子则很少有氢原子作为配位原子.另外,通过分析sp~3-C和sp~2-C数目的变化,研究了CH基团对金刚石基底的破坏作用.     

非晶氧化钛薄膜形成过程中钛离子能量对表面结构影响的机理

研究了非晶氧化钛薄膜沉积过程中入射钛离子能量对表面结构形成机理以及薄膜特性的影响.模拟结果表明,通过提高入射钛离子能量,可以有效降低成膜表面粗糙度,从而减小薄膜表面的光学散射损耗.研究发现,当入射离子能量提高后,薄膜生长模式从"岛"状生长过渡到了"层"状生长,且离子入射点附近的平均扩散系数也有显著增加,这有利于形成更加平整的高质量薄膜表面.     

Al(001)表面上沉积Ti薄膜的分子动力学模拟

采用分子动力学模拟方法,研究了Ti原子连续沉积于Al(001)表面上的薄膜生长过程,分析了入射能量为0.1、5 eV和衬底温度为300、700 K时的界面结合及微观结构.模拟结果表明,增加入射能量和衬底温度,使Ti薄膜的表面越光滑;通过径向分布函数和键对分析技术对薄膜微观结构进行分析,发现衬底温度时薄膜微观结构影响较大,温度300 K及以下时,Ti薄膜主要是FCC结构,随着温度升高,FCC结构成分减少,无序结构成分增加,而入射能量则对薄膜微观结构没有明显影响.     

单束激光脉冲俘获及放大机理的理论分析与数值模拟研究

本文提出用固体靶前放置薄膜靶来实现激光场放大的新方案, 研究了针对单束激光脉冲条件的俘获及放大机理. 理论模型与数值模拟均表明入射激光能量可以部分地以驻波形式驻留在靶间区域并得到有效放大. 研究表明在入射激光光压、俘获激光光压和电荷分离场的共同作用下, 薄膜靶电子层压缩和膨胀是能量积累存在反复振荡过程的直接原因, 经过振荡后激光脉冲得到稳定俘获.     

入射能量对Au/Au(111)薄膜生长影响的分子动力学模拟

利用分子动力学模拟了Au原子在Au(111)表面低能沉积的动力学过程.采用嵌入原子方法的原子间相互作用势,通过对沉积层原子结构的分析和薄膜表面粗糙度、层覆盖率的计算,研究了沉积粒子能量对薄膜质量的影响及其机制.结果表明:当入射能量Ein25 eV时,沉积层和基体表层均呈现规则的单晶面心立方(111)表面的排列,沉积原子仅注入到基体最表面两层,随着入射能量的增加,薄膜表面粗糙度降低,薄膜越趋于层状生长,入射能量的增加有利于薄膜的成核和致密化;当Ein 25 eV时,沉积层表面原子结构出现了较为明显的晶界,沉积原子注入到基体表面第三层及以下,随着入射能量的增加,薄膜表面粗糙度增加,沉积层和基体表层原子排列越不规则,载能沉积会降低基体内部的稳定性,导致基体和薄膜内部缺陷的产生,降低薄膜质量.此外,当基体内部某层沉积原子数约等于该层总原子数的一半时,沉积原子将能穿过该层进入到基体内部更深层.     

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.     

Etching of SiC by energetic F2: Molecular dynamics simulation

Molecular dynamics (MD) simulations were performed to investigate F₂ continuously bombarding silicon carbide (SiC) surfaces with energies in the range of 50-200 eV at normal incidence and room temperature. The Tersoff-Brenner form potential was used. The simulation results show that the uptake of F atoms, the etch yields of C and Si from the initial substrate, and the surface structure profile are sensitive to the incident energy. Like occurrence in Si etching, steady-state etching is observed and an F-containing reaction layer is formed through which Si and C atoms are removed. A carbon-rich surface layer after bombarding by F₂ is observed which is in good agreement with experiments. In the reaction layer, SiF in SiF₂ species are dominant; with increasing incident energy, the total fraction of SiF and SiF₂ increases, while the amount of SiF₃ and SiF₄ decreases. Finally, etching mechanisms are discussed.     

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The molecular dynamics simulation of interaction between CH⁺ with various energy and fusion material tungsten is conducted. The simulated results show that in the incident process, the sputtering rates of C and H atoms change suddenly at the different exposure doses when the incident energy is 50, 100 and 150eV respectively, a few of W atoms are sputtered in the interaction process, but the sputtering rate is less than 0.24%. When the exposure dose is about 3.92×10¹⁶cm⁻², the incident energy is 50eV, a hydrocarbon firm without W atom is formed on the sample surface bombarded by the ions. A mixed film of W, C and H is formed at the other energy. The deposited rates of C and H atom first decrease then increase with the incident energy increament, the minimum deposited rats appear at 250 and 200eV respectively. The density profiles of C, H atoms, C−H, C−C, W−C bonds in the sample after bombardment move towards the inside of sample, and the C sp³ dominated the sample.     

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利用分子动力学方法研究了H原子与C/Be样品的相互作用过程,当H原子轰击C/Be样品时,发现有一些H原子渗入样品中并且滞留在样品中,H原子的滞留率随H原子的初始入射能量的升高呈线性增长,有些沉积在样品中H原子与C原子相互作用形成H-C键。溅射产物以H原子和H2分子为主。H和H2的产额率随初始入射能量的变化趋势相反,分析了不同机制下产物H和H2的产额率随初始入射能量的关系,且通过分析H原子的入射能量和样品的原子密度的关系来研究轰击后的样品,发现样品中原子分布变化很小,同时分析了化合物中的化学键分布变化较小,只是其化学键的分布峰向样品表面移动。     

Umwandlung von Beryllium in Be2C und BeO durch Elektronenbestrahlung in Anwesenheit von Kohlenwasserstoff-Polymerisaten

The secondary electron yield from beryllium surfaces in presence of residual hydrocarbon vapour at a vacuum of 10^?4 tor decreases with time fromδ=0.45 to 0.25 when the incident primary electrons hit the target with an energy of 28 keV and an incident angle of 60°. Since the yield from the hydrocarbon polymer contamination layer is 0.3, it is concluded that the beryllium surface reacts with the contamination layer. This is confirmed by electron diffraction and electron microscopic observation of thin beryllium layers on different supporting foils, i.e. C-, Al₂O₃, polymeride from gas discharges, and self supporting Be. When a beryllium foil about 500 A. U. in thickness is first irradiated with low intensity (total beam current in the Siemens Elmiskop II<5 μA), a polymeride layer is formed. After increasing the beam current to 30 μA, the micrographs as well as the Debye-Scherrer diagrams show the formation of Be₂C and BeO. It is supposed that the carbon originates from the polymeride layer, and that the oxygen is supplied by the residual gas.     

入射能量对H2+与SiC表面相互作用影响的分子动力学模拟

用分子动力学方法研究了入射能量对 H2+与 SiC 样品表面相互作用的影响.模拟结果表明,在 H2+轰击 SiC 样品表面的初始阶段,样品中 H 原子的滞留量增加较快,其后,增加的速率减慢,并逐渐趋于饱和.入射能量越大,样品中 H 原子的滞留量也就越大.样品在 H2+的轰击下,样品 Si、C 原子会发生刻蚀.入射能量越...     

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The scattering behaviour of H atoms on Be surface by molecular dynamics simulations was reported in this paper. When the incident energy increases from 1 to 9eV, the outcome shows the H atoms scattering rate decrease with incident energy increasing, and increase with incident angle increasing. When incident energy is 1eV, all of incident H atoms scatter above the Be surface. When incident energy are 5 and 9eV, 14.7% and 35.8% of H atoms inject into the Be sample and then scatter, respectively, and incident depths increase with energy increasing. Scattering density and energy as function of scattering angle were also discussed.     

Hydrocarbon film growth by energetic CH3 molecule impact on SiC (0 0 1) surface

Classic molecular dynamics (MD) calculations were performed to investigate the deposition of thin hydrocarbon film. SiC (1 0 0) surfaces were bombarded with energetic CH₃ molecules at impact energies ranging from 50 to 150 eV. The simulated results show that the deposition yield of H atoms decreases with increasing incident energy, which is in good agreement with experiments. During the initial stages, with breaking Si-C bonds in SiC by CH₃ impacting, H atoms preferentially reacts with resulting Si to form Si-H bond. The C/H ratio in the grown films increases with increasing incident energy. In the grown films, CH species are dominant. For 50 eV, H-Csp3 bond is dominant. With increasing energy to 200 eV, the atomic density of H-Csp2 bond increases.     

Molecular dynamics simulation of deposition and etching of Si bombarding by energetic SiF

In this study, SiF interaction with amorphous Si surface at normal incidence was investigated using molecular dynamics simulation at 300 and 600 K. The incident energies of 50, 100 and 200 eV were used. The results show that the deposition rate is not sensitive to the incident energy, while with increasing the surface temperature, the deposition rate decreases. The etch yield is sensitive to the incident energy and the surface temperature. The etch yield increases with increasing incident energy and temperature. After bombarding, a Si_xF_y interfacial layer is formed. The interfacial layer thickness increases with increasing incident energy mainly through enhanced penetration of the silicon lattice. In the interfacial layer, for SiF_x (x = 1-3) species, SiF is dominant and only little SiF₃ is present. At the outmost and innermost of the interfacial layer, SiF species is dominant. Most of SiF₃ species is concentrated above the initial surface.     

Al原子在Pb基底上的沉积过程研究

利用分子动力学方法模拟了Al原子在Pb基底上的沉积过程. 对Al原子在Pb基底(001)面上沉积的形态与Pb原子在Al(001)基底上沉积的形态做了比较. 由于界面间势垒的不同, 两个体系界面间的形态有明显的差异. 分析了基底温度、基底晶面指向、沉积原子的入射动能对界面间原子混合的影响. 模拟结果显示: 随着基底温度升高, 基底原子的可移动性大大增加, 与沉积原子发生较大程度的混合; 入射能的改变对界面间原子的混合影响很小; 基底表面取不同的晶格指向时, 基底与沉积原子间的混合行为也有明显的不同. 利用径向分布函数分析了沉积原子的入射能对薄膜中原子排列有序性的影响. 较高入射能对应更有序的薄膜结构; 由径向分布函数的结构可以推测Al原子在Pb(001)基底表面沉积时界面间可能有金属间化合物生成. 关键词： Pb/Al体系 沉积过程 分子动力学 入射能     

CF interaction with Si(1 0 0)-(2 × 1): Molecular dynamics simulation

In this study, the interaction of CF with the clean Si(1 0 0)-(2 × 1) surface at normal incidence and room temperature was investigated using molecular dynamics simulation. Incident energies of 2, 12 and 50 eV were simulated. C atoms, arising from dissociation, preferentially react with Si to form Si-C bonds. A Si_xC_yF_z interfacial layer is formed, but no etching is observed. The interfacial layer thickness increases with increasing incident energy, mainly through enhanced penetration of the silicon lattice. Silicon carbide and fluorosilyl species are formed at 50 eV, which is in good agreement with available experimental data. The level of agreement between the simulated and experimental results is discussed.