Ultrafast dynamics in two-dimensional layered transition metal dichalcogenides
Abstract/Contents
- Abstract
- Prototypical transition metal dichalcogenide (TMDC) materials such as molybdenum disulfide exhibit a host of novel optoelectronic functionalities in the monolayer limit, including the emergence of a direct band gap, piezoelectric responses, nonlinear optical properties, and valley selection rules. In the few-to-multilayer limit, the weak interlayer van der Waals coupling between layers is associated with a number of unique functional properties, enabling new means of modulating and controlling the electronic band structure, optoelectronic properties, and atomic-scale structure through intercalation, doping, pressure and temperature. This study utilizes ultrafast pump-probe techniques to investigate the electronic and structural dynamics of monolayer and multi-layer TMDCs on femto- and picosecond timescales. Optical pump/second harmonic probe measurements on monolayer molybdenum disulfide reveal that the material is stable under excitation conditions corresponding to one electron-hole pair per unit cell with no observed melting or sample degradation. Sub-picosecond resolution, mega-electron volt electron diffraction measurements represent the first direct measurements of optically-induced structural dynamics in monolayer molybdenum disulfide and show that the monolayer dynamically wrinkles on picosecond timescales. These large-amplitude deformations are associated with peak tensile strains of several percent and are fully reversible over tens of millions of cycles. These measurements provide the first direct probe of electron-phonon coupling time-scales in monolayer TMDCs. New possibilities for all-optical dynamic control of their coupled electronic and optical properties follow from this work. Under lower excitation conditions, femtosecond-resolution x-ray diffraction measurements show that the interlayer van der Waals/Casimir bonding in multilayer TMDC systems is strongly modulated following photoexcitation, leading to a large-amplitude, light-induced compression of the material that can be approximated by a simple analytical model. More-detailed first-principles calculations support this model. This study demonstrates a new method for probing the fundamental processes underlying dynamic tuning of van der Waals/Casimir interactions.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2017 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Mannebach, Ehren Michael |
|---|---|
| Associated with | Stanford University, Department of Materials Science and Engineering. |
| Primary advisor | Lindenberg, Aaron Michael |
| Thesis advisor | Lindenberg, Aaron Michael |
| Thesis advisor | Heinz, Tony F |
| Thesis advisor | Reed, Evan J |
| Advisor | Heinz, Tony F |
| Advisor | Reed, Evan J |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Ehren Michael Mannebach. |
|---|---|
| Note | Submitted to the Department of Materials Science and Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2017. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2017 by Ehren Michael Mannebach
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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