Computer simulations on mechanical and electrical properties of nanoscale materials

[摘要] Nanoscale materials have highly regular atomistic structures with very few defectsdue to their small sizes. The small size and near-perfect structure give such materialsunique properties compared with materials at a larger scale. This work investigatesthe structures and properties of several nanoscale materials using various computersimulation methods.The great strength of carbon nanotubes comes from the strong covalent bondingbetween carbon atoms, and has been of great interest in research, however both thetheoretical and experimental results obtained are in a wide range. In this work,different atomic mechanisms about the nucleation of structural failure are proposedand analyzed, revealing the competition of two routes of forming defects--brittlebond breaking and plastic yield. The relevance of these two routes are shown tobe dependent on nanotube symmetry, test time, and temperature. The nanotubestrength is decided by the dominant route chosen under these parameters.Helical symmetry exists in many nanoscale structures, but it's far less utilizedin computer simulations compared with translational and rotational symmetry. Inthis work a model for helical symmetry in tight-binding computational method isdeveloped, then the implemented code are used to calculate the structure of thinsilicon nanowires, as well as the properties of twisted armchair graphene nanoribbons, such as their deformation energy, band gap, and electrical conductance.Inspired by carbon nanotube, this work also investigates very thin silicon nanotubes.They are shown to have stable structures when filled with various metalatoms along the axis. They can also go through significant structural changes fromone stable atomistic configuration to another. Such thin metal-endohedral siliconnanotubes can then combine to form thicker silicide wires that are morphologicallyidentical to experimental disilicide wires synthesized from epitaxial growth.

[发布机构] Rice University

[效力级别] nanotube