液相基底表面金属纳米结构形成机理的计算机模拟

发布时间：2018-07-17 06:32

【摘要】：本文采用Monte Carlo模拟方法,建立了三个计算机模型对液相基底表面诸多金属纳米结构的形成过程进行模拟,并将模拟结果与实验数据进行对比分析,从而解释其形成机理。通过对模拟结果的深入分析与研究,得出不同模拟参数对此类纳米结构的形貌、尺寸分布和生长机理等因素的影响,并提出改进和指导实验的建议。为了研究团簇(包括分枝状凝聚体和纳米颗粒)的形成机理,根据实验结果,我们提出假设：团簇中粒子总数大于临界尺寸时,其边缘粒子有一定几率上迁至上一层。由此建立了改进的CCA模型(RCCA模型)。模拟结果显示,随着扩散步长和沉积粒子数增加,上迁的粒子数不断增加,团簇从二维转变至三维凝聚。统计数据表明：在覆盖率从0.02 ML至0.22 ML的变化范围内,低覆盖率时(0.06ML),覆盖率随沉积粒子数呈线性增加；随着沉积粒子数的进一步增加,覆盖率和沉积粒子数之间逐渐偏离线性关系。该结果与实验数据相符合。随着沉积粒子数和扩散步长的增加,团簇的平均高度也随之增加,然后逐渐趋于饱和值。根据实验中观测到的团簇数密度、名义沉积厚度、覆盖率之间的关系,我们建立团簇凝聚塌缩模型(CAC模型),其中假设：大于某临界尺寸的团簇在凝聚过程中具有一定的塌缩概率。模拟结果显示：随着沉积粒子数的增加,覆盖率出现了与实验相符合的振荡现象。当沉积粒子数较少时,团簇尺寸多数未超过临界尺寸,覆盖率随沉积粒子数线性增加；当沉积粒子数进一步增加时,团簇尺寸超过临近尺寸,团簇的体积塌缩可随机发生,覆盖率的大小出现了一定幅度的振荡。伴随着塌缩的延续,平均团簇密度逐步增加,最后所有团簇的密度逐渐趋向稳定值。利用晶体生长过程中存在最优生长方向的实验事实,建立了一个全新的模拟模型(OCG模型),用于研究液相基底表面一维锌晶体的形成机理,模拟结果与实验事实相符。对模拟结果进行统计分析,我们发现此类一维晶体的长度和宽度分布符合对数正态分布,与实验中观察到的结果相符。随着成核数目N的增加,长度和宽度分布峰逐渐变窄,相对集中；同时平均长度和宽度逐渐减小,且分别与(1/N)0.60和(1/N)0.28成正比。对这些不同尺寸一维晶体的概率分布进行统计,结果显示：在一般情况下,相对较长或较宽的一维晶体形成概率较小；但随着N不断减小,细长一维晶体的形成几率增加。本论文各章节内容编排如下：第一章：首先简单介绍了传统的薄膜制备、表征方法以及基本物理特性,阐述了有关原子团簇、凝聚体以及薄膜生长机理的基本理论,介绍了在各种基底表面薄膜生长机理研究的最新进展；然后,系统介绍了在不同基底表面薄膜生长机理的计算机模拟研究的进展情况；最后,阐述了本文的主要研究内容和意义。第二章：在CCA模型基础上,假设团簇中的粒子数超过临界尺寸后,其边缘粒子有一定概率上迁至上一层,从而建立了改进的CCA模型。解释了液相基底表面金属原子团簇从二维到三维凝聚转变的凝聚机理,同时研究了表面覆盖率和平均高度随各参数的变化规律。第三章：假设团簇超过临界尺寸后具有一定的塌缩概率,建立了一个无格点的凝聚塌缩模型,较为系统地研究了因塌缩而导致的覆盖率变化规律及团簇密度的演化规律。第四章：基于一些晶体存在优先生长方向的实验事实,在具有周期性边界条件的正方格点上建立了一维晶体生长模型。解释了在各向同性的液相基底表面沉积原子的一维凝聚机理,并系统分析了此类晶体的长度和宽度分布及其随成核数目的变化规律。最后,我们对此种新型生长机理在未来的应用前景进行了展望。第五章：对本文的研究结果进行总结,展望下一步工作和未来研究方向。
[Abstract]:In this paper, using the Monte Carlo simulation method, three computer models are established to simulate the formation process of many metal nanostructures on the surface of the liquid base, and the simulation results are compared with the experimental data to explain the formation mechanism. The simulation results are deeply analyzed and studied, and the different simulation parameters are obtained. The influence of the morphology, size distribution and growth mechanism of nanostructures, and suggestions for improving and guiding the experiment are proposed. In order to study the formation mechanism of clusters (including branched condensate and nanoparticle), according to the experimental results, we hypothesized that when the total number of particles in the cluster is larger than the critical size, the edge particles have a certain probability. The improved CCA model (RCCA model) is established. The simulation results show that with the increase of the diffusion step and the number of deposited particles, the number of up particles is increasing and the clusters change from two-dimensional to three-dimensional condensation. Statistics show that the coverage rate is from 0.02 ML to 0.22 ML, and the coverage rate is low (0.06ML), and the coverage rate is low (0.06ML). With the increase of the number of deposited particles, the number of deposited particles gradually deviates from the linear relationship between the coverage and the number of the deposited particles. This result is in line with the experimental data. With the increase of the number of particles and the diffusion step, the average height of the cluster increases and then gradually tends to saturation. The relationship between the number density of the cluster, the nominal deposition thickness and the coverage rate, we set up the cluster condensation and collapse model (CAC model). It is assumed that the cluster with a certain size has a certain collapse probability in the process of condensation. The simulation results show that the coverage rate is consistent with the experimental phase as the number of sedimentary particles increases. When the number of sedimentary particles is less, the size of the cluster is mostly not more than the critical size, and the coverage rate increases linearly with the number of deposited particles. When the number of sedimentary particles is further increased, the size of clusters is more than adjacent size, the volume collapse of clusters can occur randomly, and the size of the coverage rate oscillates a certain extent. In addition, the density of the average cluster increases gradually, and the density of all clusters gradually tends to the stable value. A new model (OCG model) is established by using the experimental facts that have the optimal growth direction in the process of crystal growth, which is used to study the formation mechanism of one dimensional zinc crystal on the surface of the liquid phase, and the simulation results are in agreement with the experimental facts. It is found that the length and width distribution of the one-dimensional crystal conform to the logarithmic normal distribution, which is in accordance with the results observed in the experiment. With the increase of the number of nucleation N, the length and width distribution peak gradually narrowed and relatively concentrated, and the average length and width are gradually reduced, and (1/N) 0.60 and (1/N) 0. respectively. The probability distribution of these one-dimensional crystals with different sizes is statistically analyzed. The results show that in general, the relatively longer or wider one-dimensional crystals have smaller probability of formation; but with the decrease of N, the formation probability of slender one-dimensional crystals increases. The chapters in this paper are arranged as follows: Chapter 1: first of all, a brief introduction is made. Traditional film preparation, characterization method and basic physical properties are introduced. The basic theories about atomic clusters, condensate and film growth mechanism are expounded. The latest progress in the research on the growth mechanism of thin film on various substrate surfaces is introduced. Then, the computer simulation research on the growth mechanism of thin films on different substrate surfaces is introduced. Finally, the main contents and significance of this paper are expounded. In the second chapter, on the basis of the CCA model, if the number of particles in the cluster is more than the critical size, its marginal particles move to the first layer in a certain probability, thus the improved CCA model is established. The cohesive mechanism of the polytransformation and the variation of the surface coverage rate and the average height with each parameter are studied. Third chapter: assuming that the cluster has a certain collapse probability after the critical size of the cluster, a non lattice condensation collapse model is established, and the variation of the coverage rate and the cluster density caused by the collapse are systematically studied. The fourth chapter: Based on the experimental fact that some crystals have preferential growth direction, a one-dimensional crystal growth model is established on the square lattice with periodic boundary conditions. The one-dimensional condensation mechanism of the atoms on the surface of the isotropic liquid base is explained and the length and width of such crystals are systematically analyzed. In the end, the prospect of the new growth mechanism in the future is prospected. In the fifth chapter, the results of this paper are summarized, and the future work and future research direction are prospected.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TB383.1;TP391.9

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