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Deformation mechanisms in nanoscale single crystalline electroplated copper pillars

Citation

Jennings, Andrew Tynes (2012) Deformation mechanisms in nanoscale single crystalline electroplated copper pillars. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:05312012-162830014

Abstract

Scientific research in nanotechnology has enabled advances in a diverse range of applications, such as: electronics, chemical sensing, and cancer treatment. In order to transition these nanotechnology-driven innovations out of the laboratory and into real-world applications, the resilience and mechanical reliability of nanoscale structures must be well understood in order to preserve functionality under real-world operating environments. Understanding the mechanical properties of nanoscale materials is especially important because several authors have shown that single crystalline metal pillars produced through focused-ion-beam milling have unique properties when the pillar diameter, D, approaches nanotechnology-relevant dimensions. The strength, σ, of these pillars is size-dependent and is well described through a power-law relation showing that smaller is stronger: σ∝D^(-n), where n is the exponent and is found to be 0.5≤n≤1.0 in face-centered-cubic metals. In this work, the fundamental deformation mechanisms governing the size-dependent mechanical properties are investigated through uniaxial compression and tension tests of electroplated single crystalline copper pillars with diameters between 75 nm and 1000 nm. At larger pillar diameters, D >125 nm, these copper pillars are shown to obey a similar size-dependent regime, demonstrating that the “smaller is stronger” phenomenon is a function of the pillar microstructure, as opposed to the fabrication route. Furthermore, the dominant dislocation mechanism in this size-dependent regime is shown to be the result of single-arm, or spiral, sources. At smaller pillar diameters, D≤125 nm, a strain-rate-dependent mechanism transition is observed through both the size-strength relation and also quantitative, experimental measures of the activation volume. This new deformation regime is characterized by a size-independent strength and is governed by surface dislocation nucleation, a thermally activated mechanism sensitive to both temperature and strain-rate. Classical, analytical models of surface source-nucleation are shown to be insufficient to describe either the quantitative strength or the nucleation site preference. As a result, a combination of atomistic chain-of-states simulations and semi-analytical continuum models are developed in order to achieve a realistic, intuitive understanding of surface nucleation processes.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Dislocation, Nano, Pillar, Compression, Tension, Size Effect, Dislocation Nucleation
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Awards:Demetriades-Tsafka-Kokkalis Prize in Nanotechnology or Related Fields, 2012
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Greer, Julia R.
Thesis Committee:
  • Johnson, William Lewis (chair)
  • Fultz, Brent T.
  • Kochmann, Dennis M.
  • Greer, Julia R.
Defense Date:23 May 2012
Funders:
Funding AgencyGrant Number
NSF Graduate Research FellowshipUNSPECIFIED
NSF CAREER awardDMR-0748267
Record Number:CaltechTHESIS:05312012-162830014
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:05312012-162830014
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7112
Collection:CaltechTHESIS
Deposited By: Andrew Jennings
Deposited On:01 Jun 2012 18:03
Last Modified:26 Dec 2012 04:44

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