Title page for etd-0719116-155530


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URN etd-0719116-155530
Author Zhu-Min Lai
Author's Email Address No Public.
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Department Mechanical and Electro-Mechanical Engineering
Year 2015
Semester 2
Degree Master
Type of Document
Language zh-TW.Big5 Chinese
Title Mechanical, Thermal and Electronic Properties of Ultrathin Germanium Nanowires
Date of Defense 2016-07-22
Page Count 117
Keyword
  • molecular dynamics
  • Li ion
  • nudged elastic band method
  • germanium nanowire
  • density functional theory
  • Stillinger-Weber potential
  • basin-hopping method
  • Abstract In this study, the structure of four ultrathin germanium nanowires (GeNWs) were predicted by big-bang method combined with basin-hopping method and Stillinger-Weber potential. The thermal, mechanical and electronic properties of the GeNWs were further examined by density functional theory (DFT) and molecular mechanics. Not only the physical properties of GeNWs but also the absorption and diffusion behaviors of Li ion on GeNWs were investigated. For thermal properties, the phonon densities of states (PDOS) of four GeNWs were calculated, and the melting points of GeNWs were also predicted by molecular dynamics (MD) simulation. There are three types of GeNWs (helix, pentagon, hexagon) can remain about 400 K, but the 7-1 GeNW is melted about 230 K, which indicates that 7-1 GeNW is unstable at room temperature. Therefore, the 7-1 GeNW was excluded from post simulations and disccustions. In mechanical properties of GeNWs, the yielding stress and Young’s modules of GeNWs are greater than that of bulk Ge. The thermal effect on mechanical properties of GeNWs are also investigated, and the pentagon GeNW exhibits the best mechanical properties among these three GeNWs. In the electronic properties, the electron density of state (DOS) of GeNWs was calculated by DFT to understand orbital hybridization. The result shows that the energy bands of GeNWs shift up to cross the Fermi-level and resulting in conducting nanowires due to the less Coulomb screening effect and quantum confinement from nanowire structure. In addition, the energy band of GeNWs will exhibit significant splitting if which orbital electrons suffer from large Coulomb interactions. For the adsorption and diffustion behavior of Li ion on GeNWs, the various of adsorption sites and which corresponding adsorption energy have been calculated. The absorption energy of Li ion absorption on GeNWs are more stable than that on graphit or graphene. The barrier and transition states of Li ion diffusion on GeNWs were studied by the nudged elastic band (NEB) method, and the results show that the diffusion barrier of Li ion on GeNWsare similar with other material of Li ion battery electrode. The Li ion diffusion on the surface of pentagon GeNW between H3 and H3 adsorption sites with the lowest barrier, which only around 0.526 eV.
    Advisory Committee
  • Jin-Yuan Hsieh - chair
  • Shih-Jye Sun - co-chair
  • Jenn-Sen Lin - co-chair
  • Jian-Ming Lu - co-chair
  • Shin-Pon Ju - advisor
  • Files
  • etd-0719116-155530.pdf
  • indicate access worldwide
    Date of Submission 2016-08-19

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