本研究重點在於探討矽-核/碳化矽-殼奈米線在微奈米尺度下的機械以及材料性質。在模擬理論方法上，使用分子動力學法與Tersoff勢能函數作為理論基礎，並配合開放式軟體LAMMPS做為工具，分析在不同方向、溫度、半徑、缺陷等條件下之矽-核/碳化矽-殼奈米線受單軸拉伸情形，並且分析材料的滑移系統、強度、應力分佈以及奈米線在拉伸的斷裂過程。此外，為了讓模擬的結果更貼近製程及實驗，對奈米線隨機抽取一定比例的原子數，使其產生缺陷，進而探討缺陷對機械性質的影響。其結果顯示不同方向的單晶矽、碳化矽、矽-核/碳化矽-殼奈米線中，楊氏模數及極限強度的大小為(111)＞(100)。在殼核奈米線形狀的影響相較於方向性影響的程度來的相對小，但還可以觀察出在(001)方向八邊形的極限強度及延性都較方形來的佳，在(111)方向則是圓形>六邊形大於方形。在溫度的效應下，極限強度會隨溫度降低。不論任何形狀或是方向，在核殼奈米線受到拉伸破壞時，差排及錯位皆由最外層開始發生，且慢慢往內部移動。而核殼奈米線缺陷的影響中，當孔洞都集中在外殼時，其極限強度下降的比例會比孔洞隨機散布還要來的多。

This study investigates the nanoscale mechanical behavior of Si/SiC core-shell nanowires. Molecular dynamics simulations were carried out using the program package LAMMPS with Tersoff potential. A simulation is performed on the behavior of slip system, strength, stress distribution and fracture process with different structure, geometry, orientation, and temperature under uniaxial tension. The results show the magnitude of Young's modulus and ultimate strength of single-crystal silicon, silicon carbide, Si-core/SiC-shell nanowire is in the order of (111)＞(001). The circular nanowires show better elongation and ultimate stress than the hexagonal and rectangular nanowires. When core-shell nanowires were damaged under uniaxial tension, the portion of the shell makes the larger tensile stress than the core. In addition, the dislocation and slip initiate near the shell surface and then gradually propagate toward core region during tensile process of Si-core/SiC-shell nanowire.Besides, the ultimate strength increases with decreasing temperature and increasing strain rate. The more point defects on the nanowires, the smaller ultimate stress it results.

[1] 李思毅、李佳穎、曾俊元, "奈米材料的製程及其潛在的應用," 物理雙月刊, vol. 二六卷三期 2004.
[2] J. H. Irving and J. G. Kirkwood, "The statistical mechanical theory of transport processes .4. The equations of hydrodynamics," Journal of Chemical Physics, vol. 18, pp. 817-829, 1950.
[3] B. J. Alder and T. E. Wainwright, "Studies in molecular dynamics .1. General method," Journal of Chemical Physics, vol. 31, pp. 459-466, 1959.
[4] L. Verlet, "Computer experiments on classical fluids .I. Thermodynamical properties of Lennard-Jones molecules," Physical Review, vol. 159, pp. 98-108, 1967.
[5] B. Quentrec and C. Brot, "New method for searching for neighbors in molecular dynamics computations," Journal of Computational Physics, vol. 13, pp. 430-432, 1973.
[6] D. C. Rapaport, "Molecular-dynamics study of Rayleigh-Benard convection," Physical Review Letters, vol. 60, pp. 2480-2483, 1988.
[7] G. S. Grest, B. Dunweg, and K. Kremer, "Vectorized link cell fortran code for molecular-dynamics simulations for a large number of particles," Computer Physics Communications, vol. 55, pp. 269-285, 1989.
[8] D. Roundy and M. L. Cohen, "Ideal strength of diamond, Si, and Ge " Physical Review B, vol. 64, 2001.
[9] T. Y. Kim, "Nanomechnical behavior of beta-SiC," Materials Transcations,, vol. 45, (2004) pp. 1442 to 1449, 2004.
[10] J. Wang, C. Lu, Q. Wang, P. Xiao, F. Ke, Y. Bai, et al., "Influence of microstructures on mechanical behaviours of SiC nanowires: a molecular dynamics study," Nanotechnology, vol. 23, p. 025703, 2012.
[11] M. Ollivier, L. Latu-Romain, M. Martin, S. David, A. Mantoux, E. Bano, et al., "Si–SiC core–shell nanowires," Journal of Crystal Growth, vol. 363, pp. 158-163, 2013.
[12] M. Ollivier, L. Latu-Romain, B. Salem, L. Fradetal, V. Brouzet, J. H. Choi, et al., "Integration of SiC-1D nanostructures into nano-field effect transistors," Materials Science in Semiconductor Processing, vol. 29, pp. 218-222, 2015.
[13] F. C. Wang and Y. P. Zhao, "Structural evolution of the silicon nanowire via molecular dynamics simulations: the double-strand atomic chain and the monatomic chain," Archive of Applied Mechanics, vol. 85, pp. 323-329, 2015.
[14] M. Amato and R. Rurali, "Shell-thickness controlled semiconductor-metal transition in Si-SiC Core-Shell Nanowires," Nano Lett, vol. 15, pp. 3425-30, 2015.
[15] L. A. Girifalco and V. G. Weizer, "Application of the Morse potential function to cubic metals," Physical Review, vol. 114, pp. 687-690, 1959.
[16] J. E. Jones, "On the determinations of molecular fields - 1 From the variation of the viscosity of a gas with temperature," Proceedings of the Royal Society of London Series a-Containing Papers of a Mathematical and Physical Character, vol. 106, pp. 441-462, 1924.
[17] J. E. Jones, "On the determination of molecular fields - II From the equation of state of a gas," Proceedings of the Royal Society of London Series a-Containing Papers of a Mathematical and Physical Character, vol. 106, pp. 463-477, 1924.
[18] J. E. Jones, "On the determination of molecular fields III - From crystal measurements and kinetic theory data," Proceedings of the Royal Society of London Series a-Containing Papers of a Mathematical and Physical Character, vol. 106, pp. 709-718, 1924.
[19] M. S. Daw, S. M. Foiles, and M. I. Baskes, "The embedded-atom method - a review of theory and applications," Materials Science Reports, vol. 9, pp. 251-310, 1993.
[20] F. Cleri and V. Rosato, "Tight-binding potentials for transition-metals and alloys," Physical Review B, vol. 48, pp. 22-33, 1993.
[21] J. Tersoff, "New empirical-model for the structural-properties of silicon," Physical Review Letters, vol. 56, pp. 632-635, 1986.
[22] J. Tersoff, "New empirical-approach for the structure and energy of covalent systems," Physical Review B, vol. 37, pp. 6991-7000, 1988.
[23] J. Tersoff, "Empirical interatomic potential for silicon with improved elastic properties," Physical Review B, vol. 38, pp. 9902-9905, 1988.
[24] J. Tersoff, "Modeling solid-state chemistry - interatomic potentials for multicomponent systems," Physical Review B, vol. 39, pp. 5566-5568, 1989.
[25] T. Iwaki, "Molecular dynamics study on stress-strain in very thin film (Size and location of region for defining stress and strain)," JSME International Journal Series a-Mechanics and Material Engineering, vol. 39, pp. 346-353, 1996.
[26] 林郁珊, "以分子動力學分析Si/Ge 核-殼奈米線之機械性質," 國立成功大學研究所 碩士論文, 2015.
[27] J. W. Ma, W. J. Lee, J. M. Bae, K. S. Jeong, Y. S. Kang, M. H. Cho, "Effects of surface chemical structure on the mechanical properties of Si1-xGex nanowires," Nano Letters, vol. 13, pp. 1118-1125, 2013.