真空条件下飞秒激光制备纳米铝颗粒的分子动力学计算

Molecular dynamics calculation of aluminum nanoparticles prepared by femtosecond laser under vacuum conditions

纳米铝颗粒作为新式储氢及储能材料,在环保方面有重要意义,其可以在真空中由激光烧蚀废铝制造。为了分析激光烧蚀制造纳米铝颗粒反应过程,更好地指导纳米铝颗粒的制备,将双温模型与分子动力学结合,利用Lammps分子动力学软件对烧蚀及溅射过程进行了模拟,获得了激光烧蚀过程中溅射团簇的种类、数目及体积的变化情况。在整个模拟过程中,团簇的主要变化依次为溅射原子结合生成大团簇、大团簇裂解为小团簇及团簇分解生成铝原子。

As a new type of hydrogen storage and energy storage material,aluminum nanoparticles can be manufactured by laser ablation of aluminum targets in a vacuum.To analyze the reaction process of laser ablation,manufacture aluminum nanoparticles,and better guide the preparation of aluminum nanoparticles,the two-temperature model and molecular dynamics model were combined for utilizing the advantages of the two models.By the two-temperature model,the energy transfer between electronic and lattice can be calculated.Besides,by the molecular dynamics model,the atom motion can be calculated and the smallest unit of computation is the atom.To simulate the ablation and sputtering process,Lammps,the molecular dynamics simulation software was applied.During the simulation process,the spatial distribution and the bonding situation of every atom were analyzed in every time step.Combining the atom position information and the bonding situation,the species,numbers and volume of every time step were obtained.To calculate the increase and decrease in the number of every type of cluster,the change of Al clusters can be collected.Then,the changing law and mechanism of laser ablation can be inferred.Using Python programming methods,the changes in the number of various clusters at each time step were analyzed,and then the changing mechanism of the clusters was obtained.It was found that during the entire simulation process,affected by the density of aluminum clusters,clusters are more likely to combine when the density is higher,and clusters are more likely to decompose when the density is lower.In the whole simulation process,the main changes of clusters are as follows:sputtering atoms combine to form large clusters,large clusters split into small clusters,and clusters decompose to form aluminum atoms.As a result,the largest proportions of newly generated clusters were large clusters,medium-sized clusters,and small clusters in order,while the largest proportions of reduced clusters were small clusters,large clusters,and medium clusters in order.And the whole change process can be summarized as three steps.Firstly,sputtering atoms and small clusters are combined to form large clusters.Secondly,large clusters are decomposed into medium clusters.Thirdly,medium clusters are decomposed into small clusters and aluminum atoms.