纳米加工过程的分子动力学模拟技术研究

简要回顾了采用分子动力学方法模拟纳米加工过程的历史,介绍了分子动力学仿真方法的基本原理以及典型单晶体材料纳米切削机理的分子动力学仿真研究成果,并从模型建立、模拟尺度以及工件和刀具的影响等方面分析了纳米加工过程分子动力学模拟研究的最新进展。结果表明,建立三维大规模及多尺度的纳米加工仿真模型已经成为目前研究的主要方向;工件和刀具对纳米加工影响的研究也逐渐深入,涉及工件的晶向、缺陷以及刀具参数和磨损等方面的问题。     

生物电荷转移效应的分子动力学模拟

本文介绍了用分子动力学模拟肌红蛋白中的铁离子和周围的水阴离子发生电荷转移的动力学过程,并进一步讨论了该过程的微观机制——讨论短程势、长程库仑势和水效应对弛豫过程的影响.     

基于激光诱导碎裂光谱下的分子动力学模拟

采用分子动力学(MD)方法对激光诱导碎裂效应进行了数值模拟.通过分子动力学方法给出了样品受到激光辐照后的物理图像.其中激光能量为60 mJ,计算步长取3 fs.数值模拟结果表明分子动力学方法完全适用于激光诱导碎裂光谱(LIBS)的理论计算.     

分子动力学在研究激光蚀除机制中的应用进展

介绍了分子动力学模拟的基本原理，并对国内外采用其研究金属、半导体、有机体等材料的激光蚀除机制的现状以及所涉及的关键技术进行了详尽的综述，最后指出了分子动力学模拟激光蚀除的进一步研究方向。     

中、低能离子注入中的剂量效应及模拟方法

在CMOS工艺超浅结形成过程中,中、低能离子注入的剂量效应直接影响杂质浓度的分布和超浅结的形成.文中基于实验数据对剂量效应对注入离子浓度分布曲线的影响进行了分析,这种影响随着注入粒子种类的改变而表现在不同的方面.同时运用分子动力学方法对剂量效应进行了模拟,模拟结果很好地符合了实验数据.     

中、低能离子注入中的剂量效应及模拟方法

在CMOS工艺超浅结形成过程中,中、低能离子注入的剂量效应直接影响杂质浓度的分布和超浅结的形成.文中基于实验数据对剂量效应对注入离子浓度分布曲线的影响进行了分析,这种影响随着注入粒子种类的改变而表现在不同的方面.同时运用分子动力学方法对剂量效应进行了模拟,模拟结果很好地符合了实验数据.     

InSb晶片表面有机物沾污清洗的分子动力学研究

清洗是混成式探测器芯片器件制造过程中的一道关键工序。探测器芯片表面所吸附的有机物沾污是清洗的主要目标。使用第一性原理与分子动力学相结合的方法研究了丙酮、乙酸乙酯对InSb晶面有机物沾污(主要成分为502)的清洗机理。第一性原理计算结果表明,丙酮与乙酸乙酯的分子反应活性位点均离域在杂原子上,两者可通过杂原子对吸附在InSb表面的502解吸附以达到清洗的目的。分子动力学模拟结果表明,乙酸乙酯可以促进丙酮分子在502膜层中的扩散能力,以此加强丙酮对502的去除作用。     

Kinetic process of nitridation on the α-sapphire surface

我们结合分子动力学模拟和动态蒙特卡洛方法,建立了蓝宝石表面的氮化模拟模型,依此揭示了氮化和过度氮化的过程和原理。通过MBE生长和同位RHEED表征,我们亦观察和分析了不同条件下的α面蓝宝石的氮化情况。结合模拟和实验,我们了解了氮化机制,并且圈定了合适的氮化范围。     

C-Si模型分子动力学三维并行仿真算法

对于单晶硅磨削过程模拟的并行算法,依据C-Si系统的分子动力学模型及其特殊模型的特性,通过分析负载均衡和消息通信,利用"最小表面"原则,给出了一种空间分解并行方案。仿真实验证明算法可以缓解负载失衡并且降低通信开销,收集的对比实验数据证实了算法的高效性。     

碳纳米管的分子动力学模拟

碳纳米管的纳米级尺寸在很大程度上限制了人们对它的了解、测试与观测，严重地影响了它的发展和应用。因此，必须有简单可行的方法来合理计算、测量碳纳米管的各种特性，计算机模拟无疑是研究这种特殊材料的极佳方法。采用分子动力学模拟的方法，来模拟碳纳米管的物理特性。首先模拟了碳纳米管的热稳定性，发现单壁开口碳纳米管的热稳定性将随着管径的增大而变差，同时开口碳纳米管在真空中保持稳定的极限温度在3000K左右。接着模拟了两根开口碳纳米管的碰撞过程以及成键情况，模拟结果表明在开口端的碳原子非常活跃，极易与其它活性原子成键并且形成新的分子结构，这预示了只要使用一些简单的切割和组合就可以用碳纳米管组成纳微机械；最后对碳纳米管轴承结构的研究显示出碳纳米管之间仅仅存在很小的范德华力，这种独特的特性预示着碳纳米管构成的纳微机械会有卓越的机械特性。     

Highly Stretchable Polymers: Mechanical Properties Improvement by Balancing Intra‐ and Intermolecular Interactions

The mechanical properties of polymers are highly dependent on the mobility of the underlying chains. Changes in polymer architecture can affect inter‐ and intramolecular interactions, resulting in different chain dynamics. Herein, an enhancement in the mechanical properties of poly(butylmethacrylate) is induced by folding the polymer chains through covalent intramolecular crosslinking (CL). Intramolecular CL causes an increase in intramolecular interactions and inhibition of intermolecular interactions. In both the glassy and rubbery states, this molecular rearrangement increases material stiffness. In the glassy state, this molecular rearrangement also leads to reduced failure strain, but surprisingly, in the rubbery state, the large strain elasticity is actually increased. An intermediate intramolecular CL degree, where there is a balance between intra‐ and intermolecular interactions, shows optimal mechanical properties. Molecular dynamics simulations are used to confirm and provide molecular mechanisms to explain the experimental results.     

Effects of vacancy structural defects on the thermal conductivity of silicon thin films

Vacancy structural defect effects on the lattice thermal conductivity of silicon thin films have been investigated with non-equilibrium molecular dynamics simulation.The lattice thermal conductivities decrease with increasing vacancy concentration at all temperatures from 300 to 700 K.Vacancy defects decrease the sample thermal conductivity,and the temperature dependence of thermal conductivity becomes less significant as the temperature increases.The molecular dynamics result is in good agreement with the theoretical analysis values obtained based on the Boltzmann equation.In addition,theoretical analysis indicates that the reduction in the lattice thermal conductivity with vacancy defects can be explained by the enhanced point-defect scattering due to lattice strain.     

空位缺陷对Si薄膜热导率的影响

利用非平衡分子动力学方法研究了空位结构缺陷对Si薄膜热导率的影响。当温度在300K-700K之间变化时,热导率随着空位浓度的增加而降低,并且随着温度的升高空位浓度对热导率的影响以及同一空位浓度下温度对热导率的影响都在逐渐减弱。本文还利用Boltzmann输运理论对MD模拟进行验证,结果基本与其一致。同时理论方法还表明,空位缺陷对薄膜热导率的巨大影响归因于晶格应力的存在使点缺陷也发生散射作用的结果。     

Structure and Disorder in Squaraine–C60 Organic Solar Cells: A Theoretical Description of Molecular Packing and Electronic Coupling at the Donor–Acceptor Interface

Organic solar cells based on the combination of squaraine dyes (as electron donors) and fullerenes (as electron acceptors) have recently garnered much attention. Here, molecular dynamics simulations are carried out to investigate the evolution of a squaraine–C₆₀ bilayer interface as a function of the orientation and order of the underlying squaraine layer. Electronic couplings between the main electronic states involved in exciton dissociation and charge (polaron pair) recombination are derived for donor–acceptor complexes extracted from the simulations. The results of the combined molecular‐dynamics?quantum‐mechanics approach provide insight into how the degree of molecular order and the dynamics at the interface impact the key processes involved in the photovoltaic effect.     

A Special Purpose Array Processor Architecture for the Molecular Dynamics Simulation of Point-Mutated Proteins

Point mutation of amino acids is a means used by biotechnologists to improve the performance of proteins. To study a point-mutated polypeptide, one requires its global minimum energy conformation. This conformation can be determined by molecular dynamics via Langevin's equations of motion. Molecular dynamics simulations belong to the most difficult problems to parallelize in a scalable manner. We provide a method for defining a special purpose 3D array processor architecture for the molecular dynamics simulation of point-mutated polypeptides. The architecture is derived from a spatial decomposition of a known conformation of the point-mutated polypeptide or the native conformation of the given protein. By using an approximation scheme for the deterministic forces, the interprocessor communication can be kept local. The architecture affords a simple distributed load balancer and is scalable. The computational workload of the array processor architecture to perform molecular dynamics simulations under realistic conditions is addressed. An example architecture is given by point-mutated penicillin amidase.     

碳纳米管高温热稳定性与结构的关系

使用分子动力学方法对单壁碳纳米管高温下的结构进行了计算机模拟。对扶手椅结构（10，10）和（20，20）的单壁碳纳米管进行了模拟，结果表明，碳纳米管开关端由于能量弛豫过程，直径比内部略大，在温度逐渐升高之后，构成纳米管的碳原子逐渐偏离晶格位置，小直径的碳纳米管在3000K温度之下结构是稳定的；直径小的碳纳米管的高温热稳定性比直径大的碳纳米管要好。     

电磁环境生物效应的分子动力学基础

随着电磁环境越来越复杂,电磁辐射生物效应愈加受到人们的关注,尤其是非热效应的作用至今仍然没有完全搞清楚。文章采用分子动力学模拟方法,研究微波对肌肽(生物活性分子)活性位点碰撞的空间方位和动能的影响,提出了微波后极化效应,以此阐述电磁环境生物效应的分子动力学机理。计算结果表明:随着电场强度的增大,线极化下碰撞总数增加了2.9%~13.3%,而圆极化的碰撞总数增加了2.4% ~11.2%;特定空间角度范围内,线极化微波下碰撞的概率最大增加了131.3%,圆极化微波下碰撞的概率最大增加了47.1%。该研究有助于揭示电磁环境生物效应的分子机理。     

Nanoscratching of Metallic Thin Films on Silicon Substrate: a Molecular Dynamics Study

By using a molecular dynamics method, a computer simulation of a scratch test on a nanometer scale has been performed. The specimen is composed of four atomic layers of metallic atoms deposited on a substrate of 864 silicon atoms. The thin-film materials chosen were Al, Cu, Ti, and W. The critical load had a similar tendency to the interface energy of a heterogeneous junction, and the maximum friction constant coincided fairly well with adhesion strength. On the basis of our simulation results we propose methods for detecting the critical load of scratching and for estimating the bonding of the film–substrate interface.