Flux Directed Branched Nanowire Growth via VLS-GLAD

• Author / Creator

  Beaudry, Allan L

• In this thesis, a new technique named vapour-liquid-solid glancing angle deposition (VLS-GLAD) will be used to enhance structural control over branched nanowire (NW) arrays. NWs are 1D crystals that have been extensively applied in sensors, photovoltaic devices, and transistors. The functional properties of NWs have been thoroughly investigated over the past two decades, however, producing 3D architectures using NW building blocks via bottom-up fabrication remains challenging.
  VLS-GLAD uses glancing angle deposition (GLAD) to deposit a collimated vapour flux to direct the vapour-liquid-solid (VLS) growth of NWs. Branched NWs, also known as “nanotrees”, are formed by growing secondary NWs (branches) epitaxially on the sidewall of another NW (trunk). In this thesis, control over morphology, branching and alignment in indium tin oxide (ITO) NW arrays will be demonstrated.
  VLS-GLAD will be used to fabricate structures with unique morphological anisotropy by exploiting vapour flux shadowing. For instance, branches will be shown to grow preferentially on the side of trunks facing the collimated flux, enabling anisotropic branch growth that can be controlled along the height of NWs. Flux shadowing will also be used to enable the fabrication of azimuthally aligned nanotrees without requiring epitaxy at the substrate. Aperiodic signals will be encoded into diameter oscillations along the length of branches by engineering their local shadowing environment using dynamic substrate motion during growth. Such signals enable morphological time-stamps to be controllably inserted in the structures, providing insight into the VLS-GLAD process. Further, facet selective branch growth on epitaxially aligned nanotrees will be shown to enable the fabrication of precisely aligned arrays of self-similar L-, T-, or X-branched nanotrees. Using this control, VLS-GLAD may unlock access to previously unachievable 3D architectures using bottom-up fabrication.
  Extensive characterization of the branched NW arrays using a wide variety of nanomaterial characterization techniques will be presented, including: X-ray diffraction, transmission electron microscopy, and scanning helium ion microscopy. In addition, VLS-GLAD will be used to fabricate transparent branched ITO NW electrodes for organic solar cell applications. Sheet resistance and optical transmission will be optimized by tuning the deposition parameters and post-growth annealing procedures.

• Subjects / Keywords

  • Indium tin oxide
  • Nanostructured transparent electrode
  • Crystal growth
  • Epitaxy
  • Glancing angle deposition
  • Vapour liquid solid
  • Nanowires

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3SQ3C

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.