利用傅立叶变换研究铜双晶纳米线的断裂行为

Breaking Behavior of a Bicrystal Copper Nanowire Studied Using a Fourier Transformation Method

利用超大规模分子动力学模拟程序研究了[111]襓[110]双晶铜纳米线的拉伸断裂行为.针对样品的周期性结构,开发了离散傅立叶变换进行晶体特征分析的技术.通过转换实空间的原子密度分布函数,得到振幅-频率图和归一化的长轴原子密度分布图.这两种处理方法提供了晶体取向和结晶状态的信息,其中振幅-频率图适合描述大范围的晶体特征,而归一化长轴的原子密度分布则反映了局部的细节.利用该方法,考察了不同拉伸时刻[111]襓[110]双晶铜材料的晶体取向和结晶状态.在拉伸过程中,从振幅-频率图可以观察到4.78nm-1处的[111]特征峰和7.81nm-1处的[110]特征峰发生了低频移动和峰形变宽的现象;同时在断裂时刻观察到了5.50nm-1处的[100]特征峰.证明[111]襓[110]铜双晶纳米线在拉伸形变过程中发生了界面融合,同时界面层原子向[100]晶向的转变,最终导致了双晶纳米线在[111]晶向一侧断裂.傅立叶变换晶体分析技术在纳米材料和器件的研究中可以发挥积极的作用.

Ultra-large scale molecular dynamics simulations were used to investigate the breaking behavior of a [111｜｜[110] bicrystal copper nanowire. From the periodicity of the copper crystal structure, we developed a discrete Fourier transformation technique to analyze the periodic structure of the crystal system. In particular, the atomic density distribution along the long axis of the nanowire was transformed into a amplitude-frequency relation or into a normalized atomic density distribution. These two treatments enable us to further study the crystal grain orientation and the crystal structure at different stretching moments of the nanowire. The amplitude-frequency analysis provided information about the large-scale crystallographic features while local characteristics were determined by the normalized atomic density distribution. From analyses of the simulation data, we found that the [111｜｜[110] bicrystal copper nanowire showed an amalgamation of the grain boundary and a rotation of the crystal grains during stretching and this led to a rupture in the [111] crystal grain. After breaking, the nanowire underwent a new recrystallization process as determined by amplitude-frequency analysis and normalized atomic density distribution. The Fourier transformation technique proposed in this work provides a powerful tool for theoretical investigations of nanomaterials.