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Permanent link (DOI): https://doi.org/10.7939/R3SQ3C

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Flux Directed Branched Nanowire Growth via VLS-GLAD Open Access

Descriptions

Other title
Subject/Keyword
crystal growth
nanowire
glancing angle deposition
nanostructured transparent electrode
epitaxy
vapour liquid solid
indium tin oxide
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Beaudry, Allan L
Supervisor and department
Brett, Michael (Electrical and Computer Engineering)
Examining committee member and department
Cadien, Ken (Chemical and Materials Engineering)
Shankar, Karthik (Electrical and Computer Engineering)
LaPierre, Ray (Engineering Physics, McMaster University)
DeCorby, Ray (Electrical and Computer Engineering)
Department
Department of Electrical and Computer Engineering
Specialization
Microsystems and Nanodevices
Date accepted
2014-06-11T09:06:49Z
Graduation date
2014-11
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
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.
Language
English
DOI
doi:10.7939/R3SQ3C
Rights
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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