【作者】 刘洪海；

【导师】 姜恩永；

【作者基本信息】 天津大学 ， 材料物理与化学， 2005， 博士

【摘要】 纳米材料由于其所表现出来的奇异的物理、化学性质以及潜在的应用前景而引起了广泛的关注。纳米材料中两个突出的代表,原子(或分子)团簇和金属纳米线,作为连接宏观和微观材料的桥梁,各自具有不同的物理和化学性质,因而吸引着众多的研究者。在本论文中,我们主要做了以下研究工作:1以分子动力学的计算机模拟方法为基础,提出了一种虚拟探针的方法,并用它来研究团簇的生长过程。在研究中,我们发现了团簇在生长过程中出现的生长路径的分裂与合并的现象,揭示了为何包含某种特定原子数目的团簇在质谱分析实验中具有较高的丰度。2对团簇表面原子给出了一个明确的定义。提出了准确划分团簇表面原子和内部原子的理论模型数学依据,为在计算机模拟过程中识别团簇的表面原子及其壳层结构提供了一个可行的数学物理方法。利用此定义,我们发现原子层对于团簇的内部结构存在压缩作用,原子层数越多,对内部原子结构的压缩效果越明显。这种压缩效应解释了为何小团簇更趋向于呈现出具有近似的球形对称的正二十面体型结构。3我们研究了由于团簇表面顶点处原子的迁移所引起的表面熔化现象,扩展了对于小团簇表面熔化机理的认识。发现了在受到初始扰动的LJ147团簇中存在的集体振荡现象。在结构弛豫过程中,集体振荡模式会逐渐转变为团簇内原子的无规热运动,并且,随着初始扰动强度的增大,由集体振荡模式向无规热运动方式转变的速度加快。4利用经典分子动力学方法,对<110>取向Au纳米线分别在恒定作用力和不同温度下,以及恒定温度和不同拉力作用下的断裂微观过程进行了研究。发现在恒定拉力作用下,Au纳米线发生断裂的时间随着温度的降低而逐渐增加;在恒定温度下,随着拉力的增加,纳米线的断裂时间逐渐变短。研究中发现了由拉力引起的Au纳米线的晶格取向由<110>方向到<100>方向的转变现象。更多还原

【Abstract】 Nanomaterials have been widely attended because of their novel physical and chemical properties, and the potential application. As a bridge between an isolated atom and bulk material, atomic cluster and nanowire attract increasingly interest.1. Basing on the classic molecular dynamic method, we proposed a kind of virtual prober method, using which, we have explored the growing process of Lennard-Jones clusters. The splitting and merging of the growth path are found. Results explained why some clusters containing atoms of specified numbers are prominent in mass spectrum.2. A definition of the surface atom of cluster is presented in the work, basing on which, we have found the compressing effect of the atomic shells on the internal structure of the cluster, more atomic shells will provide stronger compression on the cluster structure. Results reveal that compression from the outermost surface atomic shells is responsible for the dominance of icosahedra in small clusters.3. The study reveals that the surface melting of 147-atom Lennard-Jones (LJ147) cluster starts from the migrating and floating of the vertex atoms on the surface, which generally extends the understanding on surface melting of clusters. The collective vibration mode in LJ147 cluster was found and the attenuation of which was studied.4. Using classic molecular dynamics method, we have studied the fracture of <110> Au nanowire. Results reveal that lower temperature will prolong the fracture of Au nanowire, while stronger tensile stress will shorten the time needed by the nanowire to fracture. We found that a specified tensile stress will drive the nanowire transform from initial <110> orientation to <100> orientation.更多还原