Understanding the deformation behavior of lithiated silicon and related advances in nanoindentation
Abstract/Contents
- Abstract
- In the first part of this dissertation, silicon micropillar lithiation/delithiation studies were employed to assess the robustness of amorphous silicon, relative to crystalline silicon, to lithiation- and delithiation-induced fracture. Even the largest pillars showed no lithiation-induced interior or exterior cohesive fracture. Delithiation of fully lithiated pillars produced internal cohesive fracture initiated by delamination of the pillar/substrate interface at the base of the pillar sidewall. Finite element modeling, indicating concentrated triaxial tensile stresses that move inward and upward with progression of delithiation, provided explanation for the observed fracture evolution. The research findings demonstrate that amorphous silicon is quite robust to fracture during lithiation; the critical size for fracture of amorphous silicon particles upon lithiation is determined to exceed ~2.3 [mu] m. The second part of this dissertation is focused on nanoindentation-based lithiated silicon deformation behavior studies. Prior to indenting lithiated silicon films, advances to general nanoindentation techniques were proposed. A new physically based function for nanoindentation indenter tip shape calibration was developed. The function, which accounts for the rounded shape at the indenter tip as well as the pyramidal shape away from the tip, fits calibration data well and returns physically meaningful calibration constants. Next, modifications to the Agilent Technologies Nanoindenter XP stage were implemented to make possible nanoindentation studies of blistered lithiated silicon films immersed in paraffin oil. Lithium-silicon alloy films of various compositions were probed. Young's modulus and the hardness were found to decrease as lithium content increased. Indentation creep testing was executed on unlithiated, amorphous silicon and heavily lithiated silicon, and the results indicate that lithiated silicon creeps readily compared to unlithiated silicon. In all cases, the viscoplastic flow behavior of lithiated silicon is consistent with power law creep with a large stress exponent (> 20). Interpreting the measured large stress exponents with a model for thermally activated, shear-driven local atomic rearrangement, the activation volume for the transformation is found to be comparable to the volume of a molecular unit of Li15Si4.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2014 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Berla, Lucas Alexander |
|---|---|
| Associated with | Stanford University, Department of Materials Science and Engineering. |
| Primary advisor | Cui, Yi, 1976- |
| Primary advisor | Nix, William D |
| Thesis advisor | Cui, Yi, 1976- |
| Thesis advisor | Nix, William D |
| Thesis advisor | Dauskardt, R. H. (Reinhold H.) |
| Advisor | Dauskardt, R. H. (Reinhold H.) |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Lucas Alexander Berla. |
|---|---|
| Note | Submitted to the Department of Materials Science and Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2014. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2014 by Lucas Alexander Berla
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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