在許多奈米元件當中，金屬奈米線常扮演重要的角色，因為其有良好的機械性質與導電性之故，而奈米線的高比表面積也使得許多性質與塊材相比差異很大；另一方面，對於FCC結構的材料來說，雙晶界是一種相當普遍的缺陷，而其中又以Σ3契合性雙晶界更為常見，因為此雙晶界擁有較低的生成能與生成體積。基於上述，雙晶奈米線不管在實驗或模擬上都廣泛被討論著。
　　本研究透過分子動力學模擬法，探討不同尺寸及外形的銅奈米線，在不同雙晶界間距下強度的變化。對軸向為[111]且Σ3契合性雙晶界垂直於軸向的圓形截面銅奈米線來說，雙晶界的介入會使得奈米線原子應力(或位能)的分布受到改變，導致奈米線的強化或軟化，而此現象與雙晶界間距有直接的關係。對於各個尺寸的雙晶奈米線，都存在一個臨界強化-弱化的雙晶界間距，若是雙晶界間距大於此，則雙晶界無法有效地分散表面易成核位置上原子的位能，則強度與單晶奈米線相比較為弱；反之，雙晶界間距小於此時，則奈米線可以透過雙晶界而增加強度，至於此臨界強化-弱化的雙晶界間距則和尺寸有關。
　　若是比較不同外形影響奈米線強度的差異，則需考慮奈米線是否因為雙晶界而改變表面原子結構的穩定性。在圓形截面與六角形截面的奈米線中，雙晶界不會使得表面原子的組態發生太大變化，因此能夠透過雙晶界間距的調整而增加強度；但在四邊形截面與以{112}面構成的三角形截面的奈米線中，不同雙晶界原子層的排列，有可能會使得表面上原子結構的不穩定，而這將使得差排成核容易而造成強度大幅的下降；至於以{110}面構成的三角形截面奈米線，則因為奈米線表面邊上的原子結構極度不穩定，在奈米線平衡後，此位置上的原子已經過重組，因此雙晶界的介入對於此奈米線的影響小過於這個重組的因素。

In many nanomaterials, metallic nanowires play an important role in many device components because of their excellent mechanical and electronic properties, which strongly depends on their nanoscale structures and high specific surface area that is very different from macroscale materials. On the other hand, twins are common defects in FCC materials, especially for Σ3 coherent twin boundary (CTB). Therefore, the twinned nanowires are widely discussed.
In this study, molecular dynamics simulation (MD simulation) was used to investigate the strength of twinned copper nanowires with various sizes and cross-sections. For cylindrical nanowires with [111]-orientation, the distribution of atomic stress (or potential energy) would be changed due to the introduction of Σ3 coherent twin boundaries perpendicular to the axial direction, which depended on the spacing of twins, and it could also change the strength of twinned nanowires with respect to the single crystal nanowires. Critical softening-hardening twin boundary spacing with respect to single crystal nanowires existed in twinned nanowires, which depended on the size of nanowires. Whether the stress (or potential energy) of atoms at surface could be redistributed effectively by twin boundaries or not determined the strength of twinned nanowires.
If considering the effect of cross-sections on twinned nanowires, the change of atomic configuration at surface due to introduction of twins was an important factor that could influence the strength of nanowires.

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