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

doi:10.7503/cjcu20150313

摘要/Abstract

摘要：

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.

关键词: 合金纳米线, 碳纳米管, 分子动力学模拟, 偏聚结构

Abstract:

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 dependents 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.

Key words: Alloy nanowire, Carbon nanotube, Molecular dynamics simulation, Segregation

中图分类号:

O641

TrendMD:

田明丽, 宋月丽, 万明理, 李勇, 姬鹏飞, 周丰群. 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. 高等学校化学学报, 2015, 36(12): 2523.

TIAN Mingli, SONG Yueli, WAN Mingli, LI Yong, JI Pengfei, ZHOU Fengqun. Segregation and Stability of Cu-Fe Alloy Nanowires Encapsulated in Carbon Nanotubes^†. Chem. J. Chinese Universities, 2015, 36(12): 2523.

图/表 7

Fig.1 Top and side view of CNTs at 300 K (A) 518-metal atoms in (20,0) CNT; (B) 1358-metal atoms in (30,0) CNT; (C) 259-metal atoms in (20,0)-s CNT; (D) 518-metal atoms in (12,12) CNT. red: Cu, blue: Fe, cyan: C.

Fig.2 Radial atom numbers(NA) distributed curves of Cu and Fe atoms with different Cu contents (A) 518-metal atoms encapsulated in (20,0) CNT; (B) 1358-metal atoms encapsulated in (30,0) CNT. (A1, B1) 100%Cu; (A2, B2) Alloy, 80%Cu, 20%Fe; (A3, B3) Alloy, 60%Cu, 40%Fe; (A4, B4) Alloy, 40%Cu, 60%Fe; (A5, B5) Alloy, 20%Cu, 80%Fe; (A6, B6) 100%Fe.

Fig.3 Axial atom numbers(NA) distributed curves of Cu and Fe atoms with diferent Cu contents

Fig.4 Pair correlation functions of Cu-Fe alloy nanowires of 518-metal atoms encapsulated in (20,0) CNT Initial content of Cu: (A) 80%; (B) 60%; (C) 40%; (D) 20%.

Fig.5 Pair correlation functions of Cu-Fe alloy nanowires and pure metal nanowires for 1358-metal atoms encapsulated in (30,0) CNT (A) Cu-Cu with different Cu contents: a. 100%, b. 90%, c. 80%, d. 70%, e. 60%, f. 50%, g. 40%, h. 30%, i. 20%, j. 10%; (B) Fe-Fe with different Fe contents: a. 100%, b. 90%, c. 80%, d. 70%, e. 60%, f. 50%, g. 40%, h. 30, i. 20%, j. 10%.

Fig.6 Cu content in the outmost shell as a function vs. Cu content in the initial state

Fig.7 Average potential energy(Ep) of each atom as a function of Fe content

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