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Strength, Deformation and Fracture in Metallic Nanostructures

Citation

Gu, Xun Wendy (2015) Strength, Deformation and Fracture in Metallic Nanostructures. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z91J97NV. http://resolver.caltech.edu/CaltechTHESIS:02242015-173330087

Abstract

An understanding of the mechanics of nanoscale metals and semiconductors is necessary for the safe and prolonged operation of nanostructured devices from transistors to nanowire- based solar cells to miniaturized electrodes. This is a fascinating but challenging pursuit because mechanical properties that are size-invariant in conventional materials, such as strength, ductility and fracture behavior, can depend critically on sample size when materials are reduced to sub- micron dimensions. In this thesis, the effect of nanoscale sample size, microstructure and structural geometry on mechanical strength, deformation and fracture are explored for several classes of solid materials. Nanocrystalline platinum nano-cylinders with diameters of 60 nm to 1 μm and 12 nm sized grains are fabricated and tested in compression. We find that nano-sized metals containing few grains weaken as sample diameter is reduced relative to grain size due to a change from deformation governed by internal grains to surface grain governed deformation. Fracture at the nanoscale is explored by performing in-situ SEM tension tests on nanocrystalline platinum and amorphous, metallic glass nano-cylinders containing purposely introduced structural flaws. It is found that failure location, mechanism and strength are determined by the stress concentration with the highest local stress whether this is at the structural flaw or a microstructural feature. Principles of nano-mechanics are used to design and test mechanically robust hierarchical nanostructures with structural and electrochemical applications. 2-photon lithography and electroplating are used to fabricate 3D solid Cu octet meso-lattices with micron- scale features that exhibit strength higher than that of bulk Cu. An in-situ SEM lithiation stage is developed and used to simultaneously examine morphological and electrochemical changes in Si-coated Cu meso-lattices that are of interest as high energy capacity electrodes for Li-ion batteries.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Mechanics, size effect, fracture, metals, metallic glass, octet, lattice, batteries
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemical Engineering
Minor Option:Materials Science
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Greer, Julia R.
Group:Kavli Nanoscience Institute
Thesis Committee:
  • Greer, Julia R. (chair)
  • Haile, Sossina M.
  • Wang, Zhen-Gang
  • Kochmann, Dennis M.
Defense Date:14 August 2014
Funders:
Funding AgencyGrant Number
National Defense Science and Engineering Graduate FellowshipUNSPECIFIED
National Science FoundationDMR-1204864
National Science FoundationCMMI-1234364
Record Number:CaltechTHESIS:02242015-173330087
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:02242015-173330087
DOI:10.7907/Z91J97NV
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8774
Collection:CaltechTHESIS
Deposited By: Xun Gu
Deposited On:26 Feb 2015 16:58
Last Modified:27 Jul 2018 02:14

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