Phase equilibria and emergent electromechanical coupling in two-dimensional materials
Abstract/Contents
- Abstract
- Two-dimensional monolayer crystals are a family of materials that exist in atomically thin form, lacking the chemical energy penalty associated with conventional surfaces. The first experimental isolation of two-dimensional crystals in 2005 triggered a wave of research, motivated by these ultra-thin materials' promising transport properties and their attractiveness as building blocks for atomic-scale heterostructure devices. Equally intriguing but hitherto largely unexplored device applications arise when the electronic state of a two-dimensional material interacts with non-electronic degrees of freedom. This dissertation elucidates several different instances of such coupling, along with their potential applications. First, this work discovers that that many commonly studied two-dimensional materials exhibit highly useful electromechanical coupling in the form of piezoelectricity, in contrast to their non-piezoelectric parent bulk crystals. Our density functional theory (DFT) calculations of the piezoelectric coefficients of monolayer BN, MoS2, MoSe2, MoTe2, WS2 and WSe2 reveal that some of these two-dimensional materials are more strongly piezoelectric than bulk wurtzites. Bilayers composed of two piezoelectric monolayers are then shown to possess leveraged coupling between mechanical curvature and electric fields - an emergent nanoscale property that occurs only in bilayers. The next part of this dissertation focuses on an anomalous form of electromechanical switching specific to Mo- and W-dichalcogenide monolayers. DFT calculations on these systems show that tensile strains can drive phase transitions between competing semiconducting and metallic two-dimensional crystal structures. Such strain-induced structural phase transitions occur at especially modest strains in MoTe2 (0.3-3.0% under uniaxial conditions). Finally, this work considers alloying between MoTe2 and WTe2 as a means of bringing monolayer phase transitions close to ambient conditions, for example to enable temperature-driven phase transitions near room temperature. Phase diagrams computed via DFT show that one can use the composition of alloyed monolayers to tune the relative stability of competing monolayer phases in such alloys.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2015 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Duerloo, Karel-Alexander N |
|---|---|
| Associated with | Stanford University, Department of Materials Science and Engineering. |
| Primary advisor | Reed, Evan J |
| Thesis advisor | Reed, Evan J |
| Thesis advisor | Cai, Wei, 1977- |
| Thesis advisor | Salleo, Alberto |
| Advisor | Cai, Wei, 1977- |
| Advisor | Salleo, Alberto |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Karel-Alexander N. Duerloo. |
|---|---|
| Note | Submitted to the Department of Materials Science and Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2015. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2015 by Karel Alexander Niklaas Duerloo
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