Citation
Jennings, Andrew Tynes (2012) Deformation Mechanisms in Nanoscale Single Crystalline Electroplated Copper Pillars. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/6128-HG61. https://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): |
| ||||||
Thesis Committee: |
| ||||||
Defense Date: | 23 May 2012 | ||||||
Funders: |
| ||||||
Record Number: | CaltechTHESIS:05312012-162830014 | ||||||
Persistent URL: | https://resolver.caltech.edu/CaltechTHESIS:05312012-162830014 | ||||||
DOI: | 10.7907/6128-HG61 | ||||||
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: | 08 Nov 2023 00:27 |
Thesis Files
|
PDF
- Final Version
See Usage Policy. 32MB |
Repository Staff Only: item control page