Structural phase changes and strain engineering in two-dimensional materials
Abstract/Contents
- Abstract
- Two-dimensional (2D) materials are a family of crystals that are only a few atomic layers thick. The discovery of 2D materials has triggered increasing research efforts, motivated by their unique properties, such as ultra-low thickness, high mechanical strength and high flexibility. In the first part of this dissertation, I show that electrostatic gating can induce structural semiconductor-to-semimetal phase changes in 2D materials. Dynamic control of conductivity and optical properties via atomic structure changes is of technological importance in information storage. Energy consumption considerations provide a driving force towards employing thin materials in devices. Monolayer transition metal dichalcogenides (TMDs) are nearly atomically thin materials that can exist in multiple crystal structures, each with distinct electrical properties. By developing new density functional-based methods, I discover that electrostatic gating device configurations have the potential to drive structural semiconductor-to-semimetal phase transitions in some monolayer TMDs. I show that semiconductor-to-semimetal phase transition in monolayer MoTe2 can be driven by a gate voltage of several volts with an appropriate choice of dielectric. I find that the transition gate voltage can be reduced arbitrarily by alloying, for example, for MoxW(1-x)Te2 monolayers. My findings identify a new physical mechanism nonexistent in bulk materials to dynamically control structural phase transitions in 2D materials, enabling potential applications in phase-change electronic devices. Next, I discuss low energy consumption phase change memory that utilizes electrostatically induced structural phase changes in 2D materials. I compare electrostatically driven phase transition with thermally induced phase transition from an energy perspective. I discover that electrostatically driven phase transition is much more energy efficient and does not necessarily generate heat dissipation into its surroundings, which is unavoidable and the most significant part of energy consumption in thermally driven phase transition. In the last part of this work, I describe strain engineering in 2D materials using lithographically or otherwise patterned adatom adsorption. I discover that the monolayer strain results from a competition between the in-plane elasticity and out-of-plane relaxation deformations. I find that some adsorption patterns have the potential to produce strains of as large as 5\%, larger than the strains applied using a substrate approach.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2016 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Li, Yao |
|---|---|
| Associated with | Stanford University, Department of Applied Physics. |
| Primary advisor | Reed, Evan J |
| Primary advisor | Suzuki, Yuri, (Applied physicist) |
| Thesis advisor | Reed, Evan J |
| Thesis advisor | Suzuki, Yuri, (Applied physicist) |
| Thesis advisor | Lindenberg, Aaron Michael |
| Advisor | Lindenberg, Aaron Michael |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Yao Li. |
|---|---|
| Note | Submitted to the Department of Applied Physics. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2016. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2016 by Yao Li
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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