交叉放置的單壁奈米碳管於穿透式電子顯微鏡(TEM)的電子束照射(E-beam irradiation)下，將形成一奈米級分子接面(molecular junctions)，由兩根碳管所形成的接面，若一根是半導體性，另一根是金屬性，則可當成整流二極體使用，當碳管為多端異質接面，如”Y”或”T”形接面，則可作為電晶體。而該接面電性質完全依賴於接面處原子鍵結情況，如懸鍵、sp、sp2、sp3 混成等鍵結。但這些原子鍵結結構在實驗上是很難觀察到的，因此，本研究利用tight-binding(TB)勢能函數為原子間交互作用的分子動力學模擬進行接面結構的細部觀察，而在此我們選擇碳管螺旋性作為探討參數。而TB 勢能對於鍵結斷裂及生成行為有著良好的描述。在電子束照射模擬方面，我們安排一週期性增加原子動能方式來模擬電
子撞擊碳原子的行為，這種動能安排的物理方式是基於散射理論所選用。模擬結果指出不論哪一種螺旋性碳管對在電子束照射下均能相融接，而在(5,5)-(5,5)碳管接面因為有最高sp2 及最低sp 混　成原子比例，所以顯現出最佳結構穩定性；反之，(5,5)-(9,0)碳管接面在穩定性表現為最差。在本研究中，我們成功觀察出碳管接面的形成，及分析接面的鍵結性質。最後，我們提出分子動力學的瓶頸及可能改進的方向，作為今後努力的方針。

Crossing single-walled carbon nanotubes can be welded by electron beam irradiation in a transmission electron microscope to form molecular junctions. If a junction formed by two CNTs, one of which is semiconducting
and the other of which is metallic, can act as a rectifying diode, while a multiterminal heterojunction, such as a “Y” or “T” junction, works as a transistor. The properties of these junctions completely depend on the
bonding in the joint, such as dangling bond, sp-, sp2-, or sp3- hybridized. But determination of the bonding structure of CNT junctions is difficult to do experimentally. Therefore, we choose the chirality of CNT as parameter in
this study, and perform molecular dynamics(MD) simulations of CNTs welding to study detailed information on the atomic structure of the junction. In the molecular dynamics simulation, the tight-binding(TB) potential which
allows for the breaking and forming of chemical bonds was employed to describe the intermolecular forces between atoms. The electron beam irradiation is mimicked by periodically assigning a velocity to a PKA(primary knock-out atoms). The physical way of assigning of energies
and momenta is based on scattering theories. Ths simulations indicate any types of CNT pair can be welded together in the merging process. But the chirality of CNTs influences the stability of the junction structure. The
(5,5)-(5,5) pair junction shows the best stability because it has the most sp2 and the least sp hybridized atoms. By contrast, the (5,5)-(9,0) pair reveals the worst stability. So here we successfully observe the formation of CNT
junction and analysis the bonding properties in the junctions. Finally, we point out bottlenecks of molecular dynamics simulation, and the state-of-the-art ways to overcome these bottlenecks in our future works.

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