载能原子沉积Au/Au(100)外延薄膜生长的计算机模拟

在分子动力学研究的基础上建立了载能原子的沉积动力学物理模型,并根据在局域环境下的表面原子扩散模型,通过运动学Monte Carlo方法研究了载能粒子沉积Au/Au(100)薄膜的初期生长过程,探讨了载能粒子沉积对薄膜生长的影响及其随基体温度的变化.通过计算机模拟发现：载能粒子沉积的Au/Au(100)薄膜生长仍然呈现层状生长-三维岛状生长-准二维层状.在薄膜生长初期,载能粒子的作用是促进表面原子的成核,增加基体表面的缺陷;在薄膜的生长阶段,载能粒子通过抑制三维岛的生长速率起着平滑薄膜表面形貌的作用.载能粒 关键词：     

低能CU6团簇在CU(001)表面和AU(001)表面沉积的分子动力学模拟研究

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低能Cu13团簇沉积薄膜的分子动力学模拟研究

利用分子动力学模拟方法对Cu₁₃团簇在Fe（001）表面上沉积薄膜进行了研究,分析了不同沉积条件对薄膜生长模式的影响,对比分析了不同沉积条件下表面粗糙度、缺陷分布和外延度等薄膜性质的差异。Cu₁₃团簇的初始沉积能量范围为0.1~10.0 eV/atom,沉积率为1.0 clusters/ps,衬底温度分别为300,700和1 000 K。模拟结果表明:团簇初始沉积能量主要影响薄膜生长模式,当初始沉积能量为7.5 eV/atom的Cu₁₃团簇沉积到温度为300 K的Fe（001）表面时,可形成表面光滑、内部缺陷少和较好外延度的高质量Cu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.     

沉积粒子能量对薄膜早期生长过程的影响

利用Monte Carlo(MC)模型研究了能量粒子对薄膜生长的初始阶段岛膜的形貌和岛的尺寸的影响,沉积粒子的能量范围为:0—0.7eV.在模型中考虑了原子沉积、吸附原子扩散和蒸发等过程,并详细考虑了临近和次临近原子的影响.结果表明,在所采用的参量范围内不同的基底温度情况下,能量粒子的影响有很大的区别.低基底温度情况下,沉积粒子强烈地影响着薄膜的生长过程中,岛膜的形貌、数量和尺寸随能量粒子的能量增加而有很大的变化.分析表明,这些变化都是由于能量粒子的介入使得表面吸附粒子的扩散能力增强所致 关键词： 薄膜生长 Monte Carlo方法 扩散     

Study on low-energy bombardment of Au (1 1 1) by noble metal atoms with molecular dynamics simulations

The low-energy bombardment of Au (1 1 1) surface by noble metal atoms is studied with molecular dynamics (MD) simulations. With the incident-energy dependence of adatom yields, sputtering yields, and vacancy yields for different projectiles, we find that the implantation of projectiles in shallow layers below surface can be distinguished by subplantation (in the first and second layers) and implantation (deeper than the third layer). The transition from subplantation to implantation occurs at the incident energy of about 45 eV for the low-energy bombardment of noble metal atoms on Au (1 1 1). The incident-energy dependence of defect yields is obviously different for the subplantation and implantation of projectiles. Based on our MD simulations, we discuss the influence of low-energy bombardment on film growth and the guide to the search for optimum deposition parameters.     

Be原子在Be基底上的沉积过程研究

利用分子动力学方法模拟了Be原子在Be基底上的沉积过程. 模拟了沉积粒子不同入射动能条件下, 沉积薄膜表面形态的差异. 在一定能量范围内, 增加粒子入射动能可以减小薄膜的表面粗糙度. 但是, 过高的入射动能, 不利于减小薄膜表面粗糙度. 通过沉积薄膜中原子配位数以及单个原子势能沿薄膜厚度的分布, 分析沉积原子入射动能对于薄膜及表面结构的影响. 沉积动能较大时, 薄膜的密度较大; 单个原子势能沿薄膜厚度分布较为连续; 同时薄膜中原子应力沿薄膜厚度分布较为连续. 最后, 分析了沉积粒子能量转化的过程、粒子初始动能对基底表面附近粒子局部动能增加的影响.     

Atomistic study of deposition process of Al thin film on Cu substrate

In this paper we report molecular dynamics based atomistic simulations of deposition process of Al atoms onto Cu substrate and following nanoindentation process on that nanostructured material. Effects of incident energy on the morphology of deposited thin film and mechanical property of this nanostructured material are emphasized. The results reveal that the morphology of growing film is layer-by-layer-like at incident energy of 0.1-10 eV. The epitaxy mode of film growth is observed at incident energy below 1 eV, but film-mixing mode commences when incident energy increase to 10 eV accompanying with increased disorder of film structure, which improves quality of deposited thin film. Following indentation studies indicate deposited thin films pose lower stiffness than single crystal Al due to considerable amount of defects existed in them, but Cu substrate is strengthened by the interface generated from lattice mismatch between deposited Al thin film and Cu substrate.     

Simulation of island aggregation influenced by substrate temperature, incidence kinetic energy and intensity in pulsed laser deposition

Using kinetic Monte Carlo method, we have simulated a pulsed energetic growth process in pulsed laser deposition. During the growth of film, substrate temperature mainly influences upon film morphology by directly enhancing the adatom mobility through the temperature-dependent thermal vibration. By contrast, the effect of incidence kinetic energy on film growth is complex resulting from the collisions between the incident particles and the adatoms. The results show that improving incident kinetic energy cannot significantly accelerate the migration rate of adatom but change surface microstructure and promote single adatom formation resulting in more island aggregation density. Moreover, since pulse-influx characterizes pulsed laser deposition, the intensity per pulse contributes to the evolvement of nucleation density and the results illustrate that a general scaling law different from ordinary power law still exists in energetic growth of pulsed laser deposition.     

Effects of substrate shape, curvature and roughness on thin heteroepitaxial films of Pt on Au(1 1 1)

The growth of thin (1–10 nm) films of Pt on Au(1 1 1) was studied in order to understand and clarify differences in growth mode observed in ultra-high vacuum (UHV) studies and in electrochemical deposition studies. It was found that on flat Au(1 1 1), Pt grows in a layer-by-layer growth mode, but if the gold substrate is exposed to an acidic environment prior to Pt deposition, then the substrate becomes nanoscopically rough (islanded) and Pt growth follows a pseudo-Stranski–Krastanov (SK) growth mode in which an initially thin wetting layer becomes rougher with increasing film thickness. An analysis of curvature effects on epitaxial growth mode shows that thermodynamic curvature effects involving surface stress are negligible for the Pt/Au(1 1 1) system. Rather, the apparent SK growth is linked to kinetic effects associated with inhomogeneous in-plane elastic relaxation of Pt films on rough surfaces that drive Pt atoms from pits to the tops of islands in the early stages of growth. Implications for the control of epitaxial film roughness are discussed.     

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     

First-principles studies on the Au surfactant on polar ZnO surfaces

The surfactant effect of Au in ZnO nanostructures growth is studied using first-principles slab calculations based on density functional theory. The atomic structure and electronic properties of one monolayer of Au atoms on polar ZnO surfaces are examined. It is found that (1) one monolayer (ML) of Au capping layer on the ZnO polar surfaces may modify the growing properties of ZnO nanostructures by enhancing the binding energy by 0.41 eV/atom for Zn adsorption on the polar surfaces; (2) the Au adlayer on the polar ZnO surfaces seems more active for the adsorption of Zn atoms, which may be at the very heart of the effect that Au acts as catalyst for the growth of the ZnO nanostructures; and (3) total energy calculations show that the gold on-top geometry is energetically favorable than the gold diffused geometry, which may be useful to understand the phenomenon that Au particles are only found at the end of ZnO nanostructures during the growth process.     

载能Ni原子斜入射Pt(111)表面的分子动力学模拟

采用嵌入原子方法的原子间相互作用势,利用分子动力学模拟,详细研究不同角度入射的载能Ni原子在Pt(111)基体表面的沉积过程.结果表明,随着入射角度θ从0°增加到80°,溅射产额、表面吸附原子产额、空位产额的变化情况均可按入射角度近似地分为θ≤20°,20° < θ < 60°和θ≥60°三个区域.当θ≤20°时,载能沉积对基体表面的影响与垂直入射时的情况类似,表面吸附原子的分布较为集中,入射原子容易达到基体表面第二层及以下,对基体内部晶格产生-定的影响;在20° < θ < 60°的范围内,入射原子的注入深度有所下降,对基体内部晶格的影响减小,表面吸附原子的分布较为均匀,有利于薄膜的均匀成核与层状生长;当θ≥60°时,所有入射原子均直接被基体表面反射,表面吸附原子产额、溅射产额、表面空位产额均接近0,载能沉积作用没有体现.     

不同离子激发Au靶的多电离效应

重离子与固体表面相互作用时,会引起靶原子内壳层的电离,相应空穴退激过程中发射的X射线对研究重离子与固体表面的相互作用有着重要意义,可为相关研究提供基础数据.目前,在K和L壳层电离方面做了一些工作,而M壳层的研究较少,本文依托兰州重离子加速器国家实验室320 kV高电荷态离子综合研究平台,测量了不同能量的H~+, Ar~(8+), Ar~(12+), Kr~(13+)和Eu~(20+)离子与Au表面作用产生的特征X射线谱及其能移,计算了X射线的产额比值.结果表明:重离子引起了靶原子内壳层的多电离,多电离效应使Au的MX射线有不同程度的能移;多电离程度取决于入射离子能量、离子的原子序数和其外壳层的空穴数量.     

Spin resonance transport properties of a single Au atom in S–Au–S junction and Au–Au–Au junction

The spin transport properties of S–Au–S junction and Au–Au–Au junction between Au nanowires are investigated with density functional theory and the non-equilibrium Green's function. We mainly focus on the spin resonance transport properties of the center Au atom. The breaking of chemical bonds between anchor atoms and center Au atom significantly influences their spin transmission characteristics. We find the 0.8 eV orbital energy shift between anchor S atoms and the center Au atom can well protect the spin state stored in the S–Au–S junction and efficiently extract its spin state to the current by spin resonance mechanism, while the spin interaction of itinerant electrons and the valence electron of the center Au atom in the Au–Au–Au junction can extract the current spin information into the center Au atom. Fermi energy drift and bias-dependent spin filtering properties of the Au–Au–Au junction may transform information between distance, bias,and electron spin. Those unique properties make them potential candidates for a logical nanocircuit.     

Pt(111)表面低能溅射现象的分子动力学模拟

利用嵌入原子方法的原子间相互作用势，通过分子动力学模拟，详细研究了贵金属原子在Pt (111)表面的低能溅射现象.模拟结果显示：对于垂直入射情况，入射原子的质量对Pt (11 1)表面的溅射阈值影响不大.当入射原子的能量小于溅射阈值时，入射原子基本以沉积为主 ；当入射原子的能量大于溅射阈值时，溅射产额随入射原子能量的增加而线性增大；当入射 原子能量达到200 eV时，各种入射原子的溅射产额都达到或接近1，此时入射原子主要起溅 射作用.溅射原子发射的角分布概率和溅射花样与高能溅射相类似.研究表明：与基于二体碰 撞近似的线性级联溅射理论不同，当入射原子能量大于溅射阈值时，低能入射原子的溅射产 额正比于入射原子的约化能量和入射原子与基体原子的质量比.通过对低能入射原子的钉扎 能力分析，提出了支配低能溅射的入射原子反射物理机理. 关键词： 分子动力学模拟、低能溅射     

Kinetic Monte Carlo simulation of thin film growth

A three-dimensional kinetic Monte Carlo technique has been developed for simulating growth of thin Cu films. The model involves incident atom attachment, diffusion of the atoms on the growing surface, and detachment of the atoms from the growing surface. The related effect by surface atom diffusion was taken into account. A great improvement was made on calculation of the activation energy for atom diffusion based on a reasonable assumtion of interaction potential between atoms. The surface roughness and the relative density of the films were simulated as the functions of growth substrate temperature and film thickness. The results showed that there exists an optimum growth temperatureT _opt at a given deposition rate. When the substrate temperature approaches toT _opt, the growing surface becomes smoothing and the relative density of the films increases. The surface roughness minimizes and the relative density saturates atT _opt. The surface roughness increases with an increment of substrate, temperature when the temperature is higher thanT _opt.T _opt is a function of the deposition rate and the influence of the deposition rate on the surface roughness depends on the substrate temperatures. The simulation results also showed that the relative density decreases with the increasing of the deposition rate and the average thickness of the film.     

Molecular dynamics simulation of low-energy bombardment of Pt (1 1 1) surface by Cu atoms with various incident angles

The low-energy bombardment of Pt (1 1 1) surface by Cu atoms with various incident angles (θ) is studied with MD simulations. In the case of near-normal incidence (θ≤20°), the result of energy deposition is similar to that of θ=0°. In contrast, in the case wherein the incident angles are higher than 60°, the incident atom cannot penetrate through the first layer and is scattered directly on the surface. The low-energy deposition has no obvious effect on the substrate. For 20°≤θ≤60°, the oblique incidence contributes to uniformity of nucleation and layer-by-layer growth of film as well as the layer-by-layer removal of atoms in the surface layers. Based on our MD simulations, the mechanism behind the deposition and thin film formation is related to the horizontal component and the vertical component of the impact momentum.     

First-principles studies: Thiolated Au2Cr and Au6Cr clusters

The structural, energetic and magnetic properties of thiol-passivating Au₂Cr and Au₆Cr clusters are investigated by performing first-principles calculation based on density functional theory. We find that the adsorption of thiolate is energetically more favorable than thiol and that the thiolates favor “top” site adsorption on Cr atom in one methanethiolate adsorbed Au₂Cr cluster while they favor “bridge” site adsorption on top of the middle point of Cr–Au bonds in three methanethiolates adsorbed Au₂Cr cluster. In thiol-passivating Au₆Cr cluster, the thiol favor “top” site adsorption on top of atom Au while the thiolate favor “bridge” site adsorption on top of the middle point of Au–Au bonds. The energetics of the reactions indicates that these thiol-passivating Au₂Cr or Au₆Cr clusters can be used as hydrogen storage materials. There are large and positive spin populations on atom Cr. The spin populations of atoms Au, S and H are attributed to both the spin delocalization and the spin polarization mechanisms.     

Plasma‐Substrate Interaction during Plasma Deposition on Polymers

The initial stage of film growth during plasma deposition on polymers determines many film properties such as morphology and structure, interphase formation and adhesion. Therefore, the plasma‐substrate interaction is investigated regarding the energy density during film growth, which is defined by the energy flux per depositing atom. The flux of film‐forming species and the flux of energetic particles were determined for metal sputtering (silver films) and plasma polymer deposition (amino‐functional hydrocarbon films). It is shown that enhanced energy densities can be obtained during the initial film growth due to reduced deposition rates and mixing with the polymer substrate (interphase formation). Thus, good adhesion on polymers such as polyethylene terephthalate (PET) has been achieved. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)