Morphology, chemical composition, and defect evolution during synthesis and annealing of core/shell germanium/germanium-tin nanowires
Abstract/Contents
- Abstract
- Nanowire structures provide a platform for fundamental research. Due to the inherent nano-scale diameter and large aspect ratio, nanowires demonstrate structure-property relationships that often differ from those of bulk materials, including dimensional confinement of electronic carriers and light, a large surface area to volume ratio, and size- and shape-dependent partitioning of mechanical strain and barriers to inelastic deformation. Herein Ge and core/shell Ge/GeSn nanowires were investigated with a range of techniques to investigate their synthesis and annealing properties. First, a technique using in-situ laser reflectometry was investigated for measuring the axial growth rate in chemical vapor deposition of assemblies of well-aligned vertical germanium nanowires grown epitaxially on single crystal substrates. Finite difference frequency domain optical simulations were performed to facilitate quantitative analysis and interpretation of the measured reflectivity data. The results showed an insensitivity of reflected intensity oscillation period to nanowire diameter and density within the range of experimental conditions investigated. Furthermore, we showed that the measured reflectivity decay can be used to determine the germanium nanowire nucleation time with good precision. The link between the optical emission and atomic structure of individual vertical Ge/GeSn core/shell nanowires was investigated using transmission electron microscopy (TEM) and cathodoluminescence (CL). Optical measurements of individually as-grown nanowires were performed using scanning electron microscopy (SEM) CL. Electron beam deposited fiducial markers were utilized to identify and track individual nanowires between CL measurements and focused ion beam preparation for TEM analysis. High angle annular dark field scanning TEM (HAADF STEM) was then performed as a probe into the origin of the non-homogeneous CL emission between the identified nanowires based on observable line defects. X-ray photoelectron spectroscopy was used to analyze results from in-situ and ex-situ annealing of core/shell Ge/GeSn nanowire arrays. The annealing characteristics of the germanium-tin surface and native oxide were investigated for tin contents in the range of 2 at% to 12 at% in both air-exposed and oxide-free nanowires. For air-exposed samples, we observed the presence of a tin-rich oxide that exhibits a composition dependent temperature for thermal decomposition via in-situ annealing. Utilizing nominally air-free transfer of freshly synthesized and rapid thermally annealed core/shell Ge/GeSn nanowires, we showed the protective effects of the surface oxide when comparing samples annealed under a rough vacuum environment compared to hydrogen annealing.
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource. |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2022; ©2022 |
| Publication date | 2022; 2022 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Braun, Michael |
|---|---|
| Degree supervisor | McIntyre, Paul Cameron |
| Thesis advisor | McIntyre, Paul Cameron |
| Thesis advisor | Brongersma, Mark L |
| Thesis advisor | Dionne, Jennifer Anne |
| Degree committee member | Brongersma, Mark L |
| Degree committee member | Dionne, Jennifer Anne |
| Associated with | Stanford University, Department of Materials Science and Engineering |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Michael Braun. |
|---|---|
| Note | Submitted to the Department of Materials Science and Engineering. |
| Thesis | Thesis Ph.D. Stanford University 2022. |
| Location | https://purl.stanford.edu/zj905dq2541 |
Access conditions
- Copyright
- © 2022 by Michael Braun
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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