Multiscale Simulation of Cluster Growth and Deposition Processes by Direct Simulation Monte Carlo Method

在飞行过程中，团簇沉积膜的特征受到团簇生产方式的影响，所研究的相关物理尺度为厘米级。此外，由于基板上的偏析过程的行为是不可忽略的，最小的物理尺度是10纳米量级。尽管对这一多尺度问题进行完整的分析是非常困难的，但它为由不同尺度的相互作用的子系统组成的复杂系统的动力学提供了一个典型的研究课题。本文介绍了一种基于直接模拟蒙特卡罗（DSMC）和蒙特卡罗（MC）方法相结合的新的簇生长和沉积过程模型，以研究实验条件对簇生长和沉积过程的影响。从宏观角度出发，模拟了不同实验条件下飞行路径中团簇和惰性气体的行为。利用该模型得到了不同条件下生成的簇的几种类型的大小分布。此外，通过一个简单的模型计算了这些团簇的沉积过程，以估计团簇沉积所获得的纳米结构的形貌。在该模型中，我们假设沉积团簇由两种元素组成，沉积团簇的分离是由两种不混相元素之间的能量间隙引起的。模拟结果表明，膜的尺寸分布与实验条件密切相关，并对膜的性能有重要影响。

Cluster deposited film's features are influenced by the production method of cluster during the flight path, the relevant physical scale to be studied is as large as centimeters. Moreover, since the behavior of segregation processes on the substrate is not negligible, the smallest physical scale is of the order of 10 nm. Although a complete analysis of this multiscale problem is extremely difficult, it provides a typical research subject in the dynamics of a complex system consisting of interacting subsystems with very different scales. In this paper a new model of cluster growth and deposition processes based on a combination of Direct Simulation Monte Carlo (DSMC) and Monte Carlo (MC) methods is introduced to examine the effects of experimental conditions on cluster growth and deposition processes. From the macroscopic viewpoint, we simulate the behavior of clusters and inert gas in the flight path under different experimental conditions. Several types of size distributions of generated clusters under various conditions are obtained by the present model. Moreover, the deposition process of these clusters is calculated by a simple model to estimate a morphologies of this nanostructures obtained by cluster deposition. In this model we assume that the deposited clusters are composed of two elements and segregation of deposited clusters occurred from energy gaps between two immiscible elements. The results of the simulations reveal that the size distribution is strongly related to the experimental conditions and in turn has a major effect on the film properties.