界面结构对Cu/Ni多层膜纳米压痕特性影响的分子动力学模拟

金属多层膜调制周期下降到纳米级时,其力学性质会发生显著改变. Cu-Ni晶格失配度约为2.7%,可以形成共格界面和半共格界面,实验中实现沿[111]方向生长的调制周期为几纳米且具有异孪晶界面结构的Cu/Ni多层膜,其力学性质发生显著改变.本文采用分子动力学方法对共格界面、共格孪晶界面、半共格界面、半共格孪晶界面等四种不同界面结构的Cu/Ni多层膜进行纳米压痕模拟,研究压痕过程中不同界面结构类型的形变演化规律以及位错与界面的相互作用,获取Cu/Ni多层膜不同界面结构对其力学性能的影响特征.计算结果表明,不同界面结构的样品在不同压痕深度时表现出的强化或软化作用机理不同,软化机制主要是由于形成了平行于界面的分位错以及孪晶界面的迁移,强化机制主要是由于界面对位错的限定作用以及失配位错网状结构与孪晶界面迁移时所形成的弓形位错之间的相互作用.     

Molecular dynamics study of the mechanical characteristics of Ni/Cu bilayer using nanoindentation

<正>In the present work,a three-dimensional molecular dynamics simulation is carried out to perform the nanoindentation experiment on Ni single crystal.The substrate indenter system is modeled using hybrid interatomic potentials including the many-body potential embedded atom method(EAM),and two-body morse potential.To simulate the indentation process,a spherical indenter(diameter = 80 A,1 A=0.1 nm) is chosen.The results show that the mechanical behaviour of a monolithic Ni is not affected by crystalline orientation.To elucidate the effect of a heterogeneous interface, three bilayer interface systems are constructed,namely Ni(100)/Cu(111),Ni(110)/Cu(111),and Ni(111)/Cu(111).The simulations along these systems clearly describe that mechanical behaviour directly depends on the lattice mismatch. The interface with the smaller mismatch between the specified crystal planes is proved to be harder and vice versa.To describe the relationship between film thickness and interface effect,we choose various values of film thickness ranging from 20 A to 50 A to perform the nanoindentation experiment.It is observed that the interface is significant only for the relatively small thickness of film and the separation between interface and the indenter tip.It is shown that with the increase in film thickness,the mechanical behaviour of the film shifts more toward that of monolithic material.     

纳米尺度下Si/Ge界面应力释放机制的分子动力学研究

采用分子动力学方法研究了纳米尺度下硅(Si)基锗(Ge)结构的Si/Ge界面应力分布特征,以及点缺陷层在应力释放过程中的作用机制.结果表明:在纳米尺度下, Si/Ge界面应力分布曲线与Ge尺寸密切相关,界面应力下降速度与Ge尺寸存在近似的线性递减关系;同时,在Si/Ge界面处增加一个富含空位缺陷的缓冲层,可显著改变Si/Ge界面应力分布,在此基础上对比分析了点缺陷在纯Ge结构内部引起应力变化与缺陷密度的关系,缺陷层的引入和缺陷密度的增加可加速界面应力的释放.参考对Si/Ge界面结构的研究结果,可在Si基纯Ge薄膜生长过程中引入缺陷层,并对其结构进行设计,降低界面应力水平,进而降低界面处产生位错缺陷的概率,提高Si基Ge薄膜质量,这一思想在研究报道的Si基Ge膜低温缓冲层生长方法中初步得到了证实.     

纳米Cu颗粒等温晶化过程的分子动力学模拟研究

采用分子动力学方法和镶嵌原子势,模拟了500个Cu原子(简称Cu₅₀₀) 组成的纳米颗粒的等温晶化过程.利用修正的均方位移、键对分析技术和内在结构(IS) 等方法对该过程中的结构和动力学行为进行分析研究.结果显示:与块体金属不同的是, Cu₅₀₀纳米颗粒在某一温度保温时,其晶化时间并不是一个定值, 而是存在一个统计分布,并且保温温度越低其晶化时间的分布范围越广, 最长晶化时间越长.在低温晶化时, Cu₅₀₀经历了一系列中间构型的转变才达到晶态, 表现出多步晶化的特征.文章作者研究了颗粒的初始构型对晶化进程的影响, 发现颗粒的初始结构特征和能量状态对其随后的晶化过程有着重要的影响, 同一温度下,颗粒初始构型的IS能量越低其晶化时间越长,这一点在低温时尤其明显.     

SiC/C界面辐照性能的分子动力学研究

本文通过分子动力学模拟的方法,研究了5种含不同空间结构的SiC/C界面的材料受辐照后的缺陷分布随时间以及PKA位置的变化关系,并与单质SiC中缺陷分布情况进行对比.利用径向分布函数分析了辐照对界面原子排列情况的影响.研究结果表明,SiC/C界面的抗辐照能力明显低于SiC内部,不同的空间结构对界面缺陷数量存在一定影响.由径向分布函数推得界面区域石墨原子密度高则界面原子排列情况受辐照影响越大.     

铜、银和铂原子纳米团簇负热容现象的分子动力学模拟研究

本文采用微正则分子动力学方法模拟研究了铂、铜和银原子纳米团族从固态到液态的熔化过程,得到热容量随温度变化关系,结果表明这三种金属纳米团簇在熔化过程中均出现了负热容现象,并通过对团簇热能随温度的变化关系以及团簇原子数径向分布的分析,探讨了产生负热容现象的微观机制.     

银纳米团簇负热容现象的分子动力学模拟

采用分子动力学方法和嵌入原子法(EAM)多体势函数,模拟研究了银纳米团簇在不同温度直到熔化过程中的结构变化,得到了体系能量和热容量随温度的变化关系.结果显示:银纳米团簇在临近熔点附近出现了负热容现象.研究了弛豫后银纳米团簇的稳态结构变化及其在不同时刻结构的演变过程.结果表明:产生负热容现象的主要原因是纳米团簇在熔点附近,结构发生了巨大的变化,形成由{111}和{100}面围成的结构十分稳定和能量更低的多面体.     

分子动力学模拟尺寸对纳米Cu颗粒等温晶化过程的影响

采用分子动力学方法和镶嵌原子势, 模拟了4000个Cu原子和13500个Cu原子(简称Cu₄₀₀₀和Cu₁₃₅₀₀)组成的纳米颗粒以及块体Cu的等温晶化过程. 通过对这些颗粒在晶化过程中结构和动力学行为的分析研究, 发现低温时, 不同尺寸的纳米Cu颗粒均出现多步晶化, 且晶化时间的分布曲线远比高温时范围大; 除了温度, 颗粒尺寸对晶化行为也有重要的影响, 尺寸越大, 晶化时间越长, 最终的晶化程度越高; 但是晶化时间随尺寸增大而增加的趋势不会一直持续, 发现存在一个临界尺寸r_c, 小于r_c时, 晶化时间随颗粒尺寸增大而增加, 大于r_c时,晶化时间随尺寸增大而减小.     

Superior tolerance of Ag/Ni multilayers against Kr ion irradiation: an in situ study

Monolithic Ag and Ni films and Ag/Ni multilayers with individual layer thickness of 5 and 50?nm were subjected to in situ Kr ion irradiation at room temperature to 1 displacement-per-atom (a fluence of 2?×?10¹⁴?ions/cm²). Monolithic Ag has high density of small loops (4?nm in diameter), whereas Ni has fewer but much greater loops (exceeding 20?nm). In comparison, dislocation loops, ～4?nm in diameter, were the major defects in the irradiated Ag/Ni 50?nm film, while the loops were barely observed in the Ag/Ni 5?nm film. At 0.2?dpa (0.4?×?10¹⁴?ions/cm), defect density in both monolithic Ag and Ni saturated at 1.6 and 0.2?×?10²³/m³, compared with 0.8?×?10²³/m³ in Ag/Ni 50?nm multilayer at a saturation fluence of ～1?dpa (2?×?10¹⁴?ions/cm²). Direct observations of frequent loop absorption by layer interfaces suggest that these interfaces are efficient defect sinks. Ag/Ni 5?nm multilayer showed a superior morphological stability against radiation compared to Ag/Ni 50?nm film.     

Strengthening and softening in gradient nanotwinned FCC metallic multilayers

Plastic-deformation behaviors of gradient nanotwinned (GNT) metallic multilayers are investigated in nanoscale via molecular dynamics simulation. The evolution law of deformation behaviors of GNT metallic multilayers with different stacking fault energies (SFEs) during nanoindentation is revealed. The deformation behavior transforms from the dislocation dynamics to the twinning/detwinning in the GNT Ag, Cu, to Al with SFE increasing. In addition, it is found that the GNT Ag and GNT Cu strengthen in the case of a larger twin gradient based on more significant twin boundary (TB) strengthening and dislocation strengthening, while the GNT Al softens due to more TB migration and dislocation nucleation from TB at a larger twin gradient. The softening mechanism is further analyzed theoretically. These results not only provide an atomic insight into the plastic-deformation behaviors of certain GNT metallic multilayers with different SFEs, but also give a guideline to design the GNT metallic multilayers with required mechanical properties.     

γ-TiAl金属间化合物面缺陷能的分子动力学研究

运用分子动力学方法，对γ-TiAl金属间化合物的面缺陷能(层错能和孪晶能)进行了研究. 计算得到γ-TiAl不同滑移系(或孪生系)的整体堆垛层错能曲线，结果表明，γ-TiAl较一般fcc晶体结构的金属可动滑移系(孪生系)的数量减少，在外界条件下呈脆性. 研究孪生系(1/6)〈112〉{111}的弛豫的整体堆垛层错(GSF)能和整体孪晶(GTF)能曲线，对不稳定层错能γ_usf、稳定层错能γ_sf和不稳定孪晶能γ_usf值进行分析，可以预知， γ-TiAl的主要变形机理为孪生系(1/6)〈112〉{111}的孪生和普通滑移系(1/6)〈110〉{111}的滑移，以及超滑移系(1/2)〈011〉{111}的滑移. 关键词： γ-TiAl')" href="#">γ-TiAl 堆垛层错能 孪晶能 分子动力学     

TiAl/Ti3Al体系剪切变形的分子动力学研究

利用分子动力学方法研究了正化学比的TiAl/Ti3Al双相体系中剪切变形诱发位错形核以及相关结构转变的动态过程以及切变力场对最终结构的影响.研究发现,在TiAl/Ti3Al双相体系中剪切变形诱发黏滞-滑移式的滑移行为;界面在其中起到了传递能量、均衡协变的作用,界面两侧的异相结构保留了单相形变特征.六角密堆积(HCP)-Ti3Al部分各原子层较长时间内呈整体剪切协变,其后形变分化为应力集中诱发层错区和初始完整结构回复区;而面心立方(FCC)-TiAl部分因刚性较大仅存在微协变,其后局部受力区直接诱发相邻原子层间相对滑移,发生FCC向HCP结构转变.变形结构方面,HCP-Ti3Al部分在剪切力较大区域形成连续且稳定的FCC堆垛,近界面区FCC薄层与HCP相交替并存;而FCC-TiAl部分内禀层错和孪晶共存,当力场增大时形成亚稳HCP结构.     

NMR studies of interfaces,strain and anisotropy in Co/Cu multilayers

⁵⁹Co NMR studies of multilayers are able to give three direct pieces of information: (i) the crystal phase of Co, fcc (217.4 MHz), hcp (220–228 MHz) and in exotic cases bcc (198 MHz) for films measured at T= 4.2 K, (ii) the nature of the interfaces from low frequency satellite lines, and (iii) the strain state deduced from small changes in the line positions. Extensive studies of Co/Cu multilayer interfacial structures as a function of deposition technique, layer thickness, substrate/buffer layer structure and annealing temperature have been undertaken. This work has shed new light on the relationship between interfacial structure and magnetoresistance and in particular has demonstrated that flat, atomic scale, interfaces lead to greater magnetoresistance. The difference between the Co and Cu lattice constant results in an extensive, tensile in-plane strain developing in Co layers provided that some epitaxial registry is present. Information on strain effects can be obtained from the position and width of the NMR lines. The magnetic anisotropy field can be determined by measuring the field dependence of the enhancement effect due to electronic magnetisation. This provides unique insight into the distribution of magnetic anisotropy within the Co layers, as the enhancement can be investigated independently for each NMR line and, hence, provides environment specific information on magnetic anisotropy at the interfaces and in the interior of the layers. This revised version was published online in August 2006 with corrections to the Cover Date.     

TiAl/Ti3Al体系剪切变形的分子动力学研究

利用分子动力学方法研究了正化学比的TiAl/Ti₃Al双相体系中剪切变形诱发位错形核以及相关结构转变的动态过程以及切变力场对最终结构的影响.研究发现,在TiAl/Ti₃Al双相体系中剪切变形诱发黏滞-滑移式的滑移行为;界面在其中起到了传递能量、均衡协变的作用,界面两侧的异相结构保留了单相形变特征.六角密堆积（HCP）-Ti₃Al部分各原子层较长时间内呈整体剪切协变,其后形变分化为应力集中诱发层错区和初始完整结构回复区;而面心立方（FCC）-TiAl部分因刚性较大仅存在微协变,其后局部受力区直接诱发相邻原子层间相对滑移,发生FCC向HCP结构转变.变形结构方面,HCP-Ti₃Al部分在剪切力较大区域形成连续且稳定的FCC堆垛,近界面区FCC薄层与HCP相交替并存;而FCC-TiAl部分内禀层错和孪晶共存,当力场增大时形成亚稳HCP结构. 关键词： 3Al')" href="#">TiAl/Ti₃Al 分子动力学模拟 剪切变形 层错结构     

Manipulation of optical properties of Ag/Cu alloy nanowire arrays embedded in anodic alumina membranes

Arrays of Ag/Cu alloy nanowires embedded in anodic alumina membranes (AAMs) were synthesized by directly electrodepositing from a mixing electrolyte solution containing Ag⁺ and Cu²⁺ ions. Manipulations of optical properties of the resulting samples were successfully achieved by tuning the molar ratio of Ag⁺ and Cu²⁺ ions in the starting materials. When the ratio is less than 2:20, two surface plasma resonance (SPR) peaks corresponding to Ag and Cu appear, respectively. After annealing treatment, the SPR peak corresponding to Cu disappears, and that of Ag presents a red shift. Furthermore, this red shift can be up to 85 nm when the molar ratio of Ag⁺ and Cu²⁺ reduce to 1:20, which is attributed to the transferable electrons from Cu atoms.     

Molecular dynamics investigation of plastic deformation mechanism in bulk nanotwinned copper with embedded cracks

The plastic deformation of bulk nanotwinned copper with embedded cracks under tension has been explored by using molecular dynamics simulations. Simulation results show that the cracks mainly act as dislocation sources during the plastic deformation and occasionally as sinks at later stage. The dislocation pile-up, accumulation and transformation at twin boundaries (TBs) control the plastic hardening and softening deformations. The TB dislocation pile-up zone is estimated to be 5.6–8 nm, which agrees well with previous experimental and simulation results. Furthermore, it is found that the flow stress vs. dislocation density at the hardening stage follows the Taylor-type relationship.     

Fe/Si多层膜的层间耦合与界面扩散

对以本征Si及重掺杂ｐ型和ｎ型Si作为中间层的Fe/Si多层膜的层间耦合进行研究，并通过退火，增大Fe，Si之间的扩散，分析界面扩散对层间耦合的影响. 实验结果表明，层状结构良好的制备态的多层膜，Fe，Si之间也存在一定程度的扩散，它是影响层间耦合的 主要因素，远远超过了半导体意义上的重掺杂，使不同种类的Si作为中间层的层间耦合基本 一致.进一步还发现，在一定范围内增大Fe，Si之间的扩散，即使多层膜的层状结构已经有了相当的退化，Fe/Si多层膜的反铁磁耦合强度基本保持不变. 关键词： Fe/Si多层膜 层间耦合 界面扩散     

Mg-Al合金熔体中固液界面结构的分子动力学研究

本文采用分子动力学研究了Mg-3%Al合金熔体中固液界面结构及界面附近原子的扩散行为.计算结果表明,该二元合金的固液界面为粗糙界面.垂直于界面方向的数密度分布,表现出复杂波动的特征,这种波动一直延伸到液体中.在界面附近的区域,扩散系数的三个不同方向的分量表现出了明显的各向异性,并且这种各向异性一直持续到液相当中.对界面二维结构的分析表明,界面附近液相原子的二维排列呈现出从长程有序逐渐过渡到短程有序的变化.     

Molecular dynamics simulation of structural change at metal/semiconductor interface induced by nanoindenter

The structures of the Si/Cu heterogenous interface impacted by a nanoindenter with different incident angles and depths are investigated in detail using molecular dynamics simulation.The simulation results suggest that for certain incident angles,the nanoindenter with increasing depth can firstly increase the stress of each atom at the interface and it then introduces more serious structural deformation of the Si/Cu heterogenous interface.A nanoindenter with increasing incident angle(absolute value) can increase the length of the Si or Cu extended atom layer.It is worth mentioning that when the incident angle of the nanoindenter is between-45° and 45°,these Si or Cu atoms near the nanoindenter reach a stable state,which has a lower stress and a shorter length of the Si or Cu extended atom layer than those of the other incident angles.This may give a direction to the planarizing process of very large scale integration circuits manufacture.     

原料加入顺序对制备Cu/Ag纳米粒子的影响

以硫酸铜为原料制备纳米级铜粉,再用化学还原法沉积生长Ag包覆层,制备Cu/Ag复合纳米粒子,使用紫外吸收光谱法监测反应过程.结果表明.加料方式对Cu粒子的粒径会产生影响,向水合肼中滴加聚乙烯吡咯烷铜与硫酸铜的混合液能制得粒径均匀的铜纳米粒子.同时,使用向聚乙烯吡咯烷铜与硫酸铜的混合液中滴加水合肼方法制得Cu2O继而得到...