Direct visualization of out-of-equilibrium structural transformations in atomically thin chalcogenides

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been the subject of sustained research interest due to their extraordinary electronic and optical properties. They also exhibit a wide range of structural phases because of the different orientations that the atoms can have within a...

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Bibliographic Details
Published in:NPJ 2D materials and applications 2020-06, Vol.4 (1), Article 16
Main Authors: Kumar, Pawan, Horwath, James P., Foucher, Alexandre C., Price, Christopher C., Acero, Natalia, Shenoy, Vivek B., Stach, Eric A., Jariwala, Deep
Format: Article
Language:English
Subjects:
639/301/357/1018
639/925/357/1017
Chalcogenides
Chemistry and Materials Science
Crystal structure
Crystallinity
Equilibrium
Evaporation rate
Heating rate
Materials Science
Nanotechnology
Nonequilibrium thermodynamics
Optical properties
Phases
Scanning transmission electron microscopy
Surfaces and Interfaces
Thermodynamic equilibrium
Thin Films
Transformations
Transition metal compounds
Visualization
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Summary:Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been the subject of sustained research interest due to their extraordinary electronic and optical properties. They also exhibit a wide range of structural phases because of the different orientations that the atoms can have within a single layer, or due to the ways that different layers can stack. Here we report a unique study involving direct visualization of structural transformations in atomically thin layers under highly non-equilibrium thermodynamic conditions. We probe these transformations at the atomic scale using real-time, aberration-corrected scanning transmission electron microscopy and observe strong dependence of the resulting structures and phases on both heating rate and temperature. A fast heating rate (25 °C/sec) yields highly ordered crystalline hexagonal islands of sizes of less than 20 nm which are composed of a mixture of 2H and 3R phases. However, a slow heating rate (25 °C/min) yields nanocrystalline and sub-stoichiometric amorphous regions. These differences are explained by different rates of sulfur evaporation and redeposition. The use of non-equilibrium heating rates to achieve highly crystalline and quantum-confined features from 2D atomic layers present a new route to synthesize atomically thin, laterally confined nanostructures and opens new avenues for investigating fundamental electronic phenomena in confined dimensions.
ISSN:2397-7132
2397-7132
DOI:10.1038/s41699-020-0150-2