Dynamics of nanomaterials in electron beam processing

为了建立纳米材料的电子束制备技术，开展了分子动力学研究。我们基于蒙特卡罗方法，利用弹性散射截面建立了一个新的模拟模型，该模型考虑了高能入射电子与靶原子之间的相互作用。电子的散射角由卢瑟福截面决定。然后，根据弹性散射理论，得到了电子向靶原子的传递能量和原子的散射角。使用随机数均匀地选择目标材料中的碰撞原子。在电子辐照下，用分子动力学模拟计算了靶中各原子的运动，并对碳纳米材料中的电子辐照效应进行了模拟研究，得到了以下结果。在单壁碳纳米管中，随着一次电子能量的增加，辐照损伤增强，电子辐照导致结构向类非晶态结构转变。在多壁碳纳米管和石墨石中观察到相邻材料组分之间的交联是典型的辐照损伤。在较高的电子能量下，一些被打孔的碳原子有足够的能量在结构中打孔出另一个碳原子。通过聚焦电子束辐照，观察了单壁碳纳米管的断裂、焊接和弯曲等结构变化。

Molecular dynamics studies are carried out to establish an electron beam fabrication technique for nanomaterials. We have developed a new simulation model which includes the interaction between a high energy incident electron and a target atom based on Monte Carlo method using the elastic scattering cross section. The scattering angle of the electron is determined by the Rutherford cross section. Then, the transferred energy from the electron to the target atom and the scattering angle of the atom are obtained based on the elastic scattering theory. The collision atom in the target materials is uniformly selected using a random number. Under the electron irradiation, the motion of each atom in the target is calculated with molecular dynamics simulation.The electron irradiation effects in carbon nanomaterials are studied with the simulation and the following results are obtained.1. The enhancement of the irradiation damages with the increase in the primary electron energy and the structural transition to amorphous-like structure by the electron irradiation are observed in the single-walled carbon nanotubes.2. The cross-links among neighboring material components are observed as typical irradiation damages in the multi-walled carbon nanotubes and the graphite.3. At high electron energy, some of the punched-out carbon atoms have enough energy to punch out another carbon atom in the structure.4. The structural changes such as the breakage, welding and bending of the single-walled carbon nanotubes are observed by the focused electron beam irradiation.