包裹在碳纳米管内Cu-Fe合金纳米线偏聚结构及稳定性研究

Segregation and Stability of Cu-Fe Alloy Nanowires Encapsulated in Carbon Nanotubes

采用分子动力学方法系统研究了包裹在刚性碳纳米管内的Cu-Fe二元合金纳米线经高温退火后的稳定结构.研究结果表明,所形成的合金纳米线具有圆柱形壳层结构且有明显的偏聚现象.其中Cu原子富集于靠近管壁的外层,而Fe原子则富集于靠近轴心的核层.偏聚程度与碳纳米管管径和合金组分显著相关,而与被包裹的金属原子数无明显相关性.管径越大,组分中Cu原子含量越高,则偏聚程度越显著.表明可通过调节合金中Cu原子含量获得最外壳层为纯Cu而内部为纯Fe或合金的'同心异质'结构纳米线.用平均原子势能对体系稳定性进行了描述,结果显示,碳纳米管管径越大,包裹在内的金属原子数目越多,Fe原子含量越高,体系稳定性越好.这种偏聚行为和稳定性随碳纳米管管径、合金组分及金属原子数的变化而变化,几乎不受碳纳米管长度和手性的影响.

Molecular dynamics simulations were performed to investigate the structures of Cu-Fe alloy nanowires encapsulated in carbon nanotubes （CNTs）. Simulated annealing method was employed to find the stable structure at 300 K. We found that all Cu-Fe atoms in CNTs were arranged in a series of concentric cylindrical layers even they had different contents, and a significant segregation was found. In these stable structures, Cu atoms are apt to stay at the surface shells, while Fe atom prefer to stay at the core shells. The degree of segregation is associated obviously with the CNTs diameter and the alloy fractions, but less depend- ents on the metal atom numbers. Both the larger diameter of CNTs and bigger content of Cu atoms result in more significant segregation. The results suggest that Cu-Fe alloy nanowires with pure Cu shell and pure Fe core or alloy core inside CNTs could produce by tuning alloy fractions. In addition, we also analyze the system stability by comparing average potential energy of each atom. The studies show that the larger diameter of CNTs, greater numbers of metal atoms and bigger content of Fe atoms result in much better stability. We also found that changing the length and chirality of the CNTs modifies the results only slightly.