中国物理B ›› 2023, Vol. 32 ›› Issue (3): 36804-036804.doi: 10.1088/1674-1056/ac76b5

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Coexisting lattice contractions and expansions with decreasing thicknesses of Cu (100) nano-films

Simin An(安思敏)1, Xingyu Gao(高兴誉)1, Xian Zhang(张弦)2, Xin Chen(陈欣)1, Jiawei Xian(咸家伟)1, Yu Liu(刘瑜)1, Bo Sun(孙博)1, Haifeng Liu(刘海风)1, and Haifeng Song(宋海峰)1,†   

  1. 1 Laboratory of Computational Physics, Institute of Applied Physics and Computational Mathematics, Beijing 100088, China;
    2 Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China
  • 收稿日期:2022-02-11 修回日期:2022-05-27 接受日期:2022-06-08 出版日期:2023-02-14 发布日期:2023-03-03
  • 通讯作者: Haifeng Song E-mail:song_haifeng@iapcm.ac.cn
  • 基金资助:
    Project supported by the fellowship of China Postdoctoral Science Foundation (Grant No. 2021T140073), the National Natural Science Foundation of China (Grant No. 5210011290), the Science Challenge Project of China (Grant No. TZ2018002), and the National Key Research and Development Program of China (Grant No. 2016YFB0201204).

Coexisting lattice contractions and expansions with decreasing thicknesses of Cu (100) nano-films

Simin An(安思敏)1, Xingyu Gao(高兴誉)1, Xian Zhang(张弦)2, Xin Chen(陈欣)1, Jiawei Xian(咸家伟)1, Yu Liu(刘瑜)1, Bo Sun(孙博)1, Haifeng Liu(刘海风)1, and Haifeng Song(宋海峰)1,†   

  1. 1 Laboratory of Computational Physics, Institute of Applied Physics and Computational Mathematics, Beijing 100088, China;
    2 Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China
  • Received:2022-02-11 Revised:2022-05-27 Accepted:2022-06-08 Online:2023-02-14 Published:2023-03-03
  • Contact: Haifeng Song E-mail:song_haifeng@iapcm.ac.cn
  • Supported by:
    Project supported by the fellowship of China Postdoctoral Science Foundation (Grant No. 2021T140073), the National Natural Science Foundation of China (Grant No. 5210011290), the Science Challenge Project of China (Grant No. TZ2018002), and the National Key Research and Development Program of China (Grant No. 2016YFB0201204).

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摘要： Lattice parameters are a basic quantity in material characterization, and a slight alteration in lattice parameters directly affects the properties of materials. However, there are still considerable controversies as to whether lattice expansion or contraction occurs in metallic nanomaterials with size reduction. Here, the size dependences of the lattice parameter and surface free energy of clean Cu (100) films are investigated via simulations. Lattice parameters of the exposed surfaces contract, whereas lattice expansion occurs along the direction perpendicular to the surfaces with decreasing film thicknesses. This is striking since the metallic bonds usually lack strong directionality, and it is always regarded that the lattice variations in all directions are consistent. The contraction parallel to the surface is more severe than the expansion perpendicular to the surface in films. The lattices change from cubic to tetragonal with decreasing film thickness. Consequently, common contractions and occasional expansions of the lattice parameters of Cu nanoparticles have been observed in previous experiments. Increasing free energy and surface free energy with decreasing thicknesses is the thermodynamic origin of the lattice variations. Our study therefore provides a comprehensive physical basis for the surface effects on the lattice variations.

关键词: nanostructure, lattice variations, surface free energy, simulation

Abstract: Lattice parameters are a basic quantity in material characterization, and a slight alteration in lattice parameters directly affects the properties of materials. However, there are still considerable controversies as to whether lattice expansion or contraction occurs in metallic nanomaterials with size reduction. Here, the size dependences of the lattice parameter and surface free energy of clean Cu (100) films are investigated via simulations. Lattice parameters of the exposed surfaces contract, whereas lattice expansion occurs along the direction perpendicular to the surfaces with decreasing film thicknesses. This is striking since the metallic bonds usually lack strong directionality, and it is always regarded that the lattice variations in all directions are consistent. The contraction parallel to the surface is more severe than the expansion perpendicular to the surface in films. The lattices change from cubic to tetragonal with decreasing film thickness. Consequently, common contractions and occasional expansions of the lattice parameters of Cu nanoparticles have been observed in previous experiments. Increasing free energy and surface free energy with decreasing thicknesses is the thermodynamic origin of the lattice variations. Our study therefore provides a comprehensive physical basis for the surface effects on the lattice variations.

Key words: nanostructure, lattice variations, surface free energy, simulation

中图分类号:  (Thin film structure and morphology)

  • 68.55.-a
64.60.an (Finite-size systems) 65.40.gp (Surface energy) 87.10.Tf (Molecular dynamics simulation)