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Molecular dynamics simulation studies of material modification by charged particle irradiation.

机译：通过带电粒子辐照进行材料改性的分子动力学模拟研究。

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摘要

Charged particle irradiation processes, such as ion beam deposition and electron beam irradiation are often used to modify the properties of various materials. However, detailed reaction mechanisms that lead to structural changes in the substrates are difficult to determine experimentally, as primarily indirect information is obtained using experimental methods. Computer simulation methods are complementary to experimental approaches and are able to provide insight into the way in which the system reaches its final state.; In these studies, molecular dynamics simulations are used to investigate polyatomic ion beam deposition on polymer surfaces and carbon nanotube welding under electron beam irradiation. The interatomic forces in the simulations are determined using the reactive empirical bond order potential for short-ranged covalent interactions and the Lennard-Jones potential for long-range van der Waals interactions. For hydrocarbon ion deposition, some inclined angles are found to be more efficient for the deposition of the precursors necessary for polymer thin-film growth than normal incidence deposition. Also, incident energies of 50 eV/ion are predicted to be more efficient than 25 eV/ion, and polystyrene (PS) substrates facilitate the growth of hydrocarbon thin films more than does polyethylene.; In studies of fluorocarbon ion deposition, the simulations show how and why CF3+ and C3F5+ play different roles in low-energy plasma deposition processes on PS. CF3+ ions dissociate more readily on impact and the large number of F atoms that are produced form covalent bonds with the PS chains, which both efficiently fluorinates the PS and slows down thin film growth. In contrast, C3F5+ ions produce more fluorocarbon polymer film precursors that enhance thin film growth, while at the same time fluorinating the surface at a slower rate.; In the study of carbon nanotube welding, the structure of the generated junctions is characterized by a large degree of bonding disorder that leads to lower strength and higher ductility than those characterizing "ideal" junctions. The generated junctions also operate as quantum dots, in contrast to the ohmic behavior of ideal junctions.
机译：带电粒子辐照过程（例如离子束沉积和电子束辐照）通常用于修改各种材料的特性。但是，导致基质结构变化的详细反应机理很难通过实验确定，因为主要使用实验方法获得间接信息。计算机仿真方法是对实验方法的补充，能够洞悉系统达到最终状态的方式。在这些研究中，分子动力学模拟用于研究聚合物表面上的多原子离子束沉积以及电子束辐照下的碳纳米管焊接。模拟中的原子间力使用短距离共价相互作用的反应性经验键序势和长范德华相互作用的Lennard-Jones势确定。对于烃离子沉积，发现某些倾斜角比垂直入射沉积更有效地沉积聚合物薄膜生长所需的前体。同样，预计50 eV / ion的入射能量比25 eV / ion的能量更有效，并且聚苯乙烯（PS）衬底比聚乙烯更能促进烃薄膜的生长。在碳氟化合物离子沉积的研究中，模拟表明CF3 +和C3F5 +如何以及为何在PS的低能等离子体沉积过程中发挥不同的作用。 CF3 +离子在撞击时更容易解离，产生的大量F原子与PS链形成共价键，这既有效地氟化了PS，又减慢了薄膜的生长。相反，C3F5 +离子会产生更多的氟碳聚合物薄膜前体，从而增强薄膜的生长，同时以较慢的速度氟化表面。在碳纳米管焊接的研究中，所产生的结的结构的特征在于高度的键合无序，与“理想”结相比，其导致更低的强度和更高的延展性。与理想结的欧姆行为相反，生成的结也可以用作量子点。

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  • 作者

    Jang, Inkook.;

  • 作者单位

    University of Florida.;

  • 授予单位 University of Florida.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2004
  • 页码 103 p.
  • 总页数 103
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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