Dissertation
Structural defects and properties of multicomponent materials
Washington State University
Doctor of Philosophy (PhD), Washington State University
12/2009
DOI:
https://doi.org/10.7273/000005905
Abstract
The relationship between the structure and properties of materials determine the behavior and performance of devices ranging from microelectromechanical systems (MEMS) to solid state lasers. This thesis focuses on two classes of materials used in high performance applications; metallic multilayer films and materials for optical applications. In the first case Mo/Pt multilayers are investigated as an alternative to Pt thin film electrodes for piezoelectric MEMS, whose strength is a limiting factor in improving the performance of the device. In the second case ceramic YAG, a common lasing medium for solid state lasers whose optical properties determine the beam quality, is investigated. In both cases material properties, mechanical in the first case and optical in the second, depend on microstructure hence improving device performance involves a better understanding of this relationship. Mo/Pt multilayers with layer thicknesses ranging from 20 to 100 nm were sputtered. The mechanical properties of the nanocomposites were evaluated using both nanoindentation and bulge testing. It was shown that the hardness of the multilayers increased as the layer thickness decreased with the behavior of the films deviating from a Hall Petch type of dependency for the smaller layer thicknesses used in this study. Aging of the films in air further improved their hardness indicating an additional strengthening mechanism. X-ray photoelectron spectroscopy revealed the presence of oxides in the aged samples pointing to precipitate hardening as the reason for the additional strengthening of the films. MEMS processing involves high temperatures in oxidizing environments hence the thermal stability of the nanolayers was also investigated. It was shown that structures with thicker layers maintained a substantial fraction of their strength and integrity. Ceramic YAG is produced with the use of silica as a sintering aid. Improving the optical properties of ceramic YAG involves elimination of the scattering sources in the final products. Investigation of precipitate formation as a function of stoichiometry and processing conditions, using primarily Scanning Electron Microscopy and X-ray Dispersive Spectroscopy, showed that staying on stoichiometry and reducing the amount of silica in the sintering process will effectively decrease or even eliminate the presence of precipitates.
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Details
- Title
- Structural defects and properties of multicomponent materials
- Creators
- Aikaterini Bellou
- Contributors
- David F. Bahr (Chair)David P Field (Committee Member) - Washington State University, School of Mechanical and Materials EngineeringM Grant Norton (Committee Member) - Washington State University, Honors College
- Awarding Institution
- Washington State University
- Academic Unit
- Voiland College of Engineering and Architecture
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 149
- Identifiers
- 99901055131901842
- Language
- English
- Resource Type
- Dissertation