A typical monolayer and single crystal is grown. Credit: Toshiaki Kato.
Typically only atom thick, 2D materials exhibit highly desirable properties for advanced technologies. The mechanisms by which such materials become imbued with such characteristics are still shrouded in mystery.
Researchers at Tohoku University have discovered a critical mechanism in the development of 2D monolayer transition metal dichalcogenide through a novel monitoring and analysis method. They published their findings in Scientific Reports.
The author of the paper said that large single layers of the material are enabled by the addition of salts. Future flexible and transparent electrical devices, such as sensor, solar cells and light emitters, need improved quality of the TMD to be realized.
A metal oxide powder is added to a liquid. The metal oxide-salt vapor rearranges directly into a solid when high temperatures are maintained. nucleation is a rearrangement of molecule that grows into the monolayer. Lowering the melting and boiling points of the metal oxide enhances the transition by allowing the vaporized molecule to supersaturate their environment and produce a liquid phase before arranging into a solid.
The growth rate of vapor-liquid-solid TMD is at least as high as the growth rate of metal oxide in the vapor phase. The nucleation phase has not yet been understood for salt-assisted growth, which is crucial for both fundamental and industrial applications.
To better understand the nucleation of vapor-liquid-solid TMD, the researchers established an image monitoring system.
The study showed the phase transition from liquid to solid by monitoring the chemical vapor deposition and automated image analysis. We found a novel nucleation mechanism through this approach.
In growth of a solid, the molecule of the vapor rearranges into it. The researchers found that in a two-step nucleation process, the molecule goes through a phase of vapor-liquid-solid growth. The molecule clusters form when the temperature changes.
"Precise understanding of the nucleation dynamics can be useful for achieving prefect structure control of the TMDs, which would be useful for future industrial applications," he said. Our method of monitoring chemical vapor deposition and automated image analysis could be applied to other nanomaterials to understand their nucleation and growth mechanisms.
The nucleation mechanism will be used to synthesise high quality TMD.
The non-classical nucleation in vapor–liquid–solid growth of monolayer WS2 was revealed by in-situ monitoring. There is a DOI titled " 10.1038/s41598-021-01666-9".
Scientific reports are in the journal.
A novel two-step mechanism was revealed in two-dimensional material formation.
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