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Atomic-Scale in Situ Observations of Crystallization and Restructuring Processes in Two-Dimensional MoS 2 Films.
- Source :
-
ACS nano [ACS Nano] 2018 Aug 28; Vol. 12 (8), pp. 8758-8769. Date of Electronic Publication: 2018 Aug 09. - Publication Year :
- 2018
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Abstract
- We employ atomically resolved and element-specific scanning transmission electron microscopy (STEM) to visualize in situ and at the atomic scale the crystallization and restructuring processes of two-dimensional (2D) molybdenum disulfide (MoS <subscript>2</subscript> ) films. To this end, we deposit a model heterostructure of thin amorphous MoS <subscript>2</subscript> films onto freestanding graphene membranes used as high-resolution STEM supports. Notably, during STEM imaging the energy input from the scanning electron beam leads to beam-induced crystallization and restructuring of the amorphous MoS <subscript>2</subscript> into crystalline MoS <subscript>2</subscript> domains, thereby emulating widely used elevated temperature MoS <subscript>2</subscript> synthesis and processing conditions. We thereby directly observe nucleation, growth, crystallization, and restructuring events in the evolving MoS <subscript>2</subscript> films in situ and at the atomic scale. Our observations suggest that during MoS <subscript>2</subscript> processing, various MoS <subscript>2</subscript> polymorphs co-evolve in parallel and that these can dynamically transform into each other. We further highlight transitions from in-plane to out-of-plane crystallization of MoS <subscript>2</subscript> layers, give indication of Mo and S diffusion species, and suggest that, in our system and depending on conditions, MoS <subscript>2</subscript> crystallization can be influenced by a weak MoS <subscript>2</subscript> /graphene support epitaxy. Our atomic-scale in situ approach thereby visualizes multiple fundamental processes that underlie the varied MoS <subscript>2</subscript> morphologies observed in previous ex situ growth and processing work. Our work introduces a general approach to in situ visualize at the atomic scale the growth and restructuring mechanisms of 2D transition-metal dichalcogenides and other 2D materials.
Details
- Language :
- English
- ISSN :
- 1936-086X
- Volume :
- 12
- Issue :
- 8
- Database :
- MEDLINE
- Journal :
- ACS nano
- Publication Type :
- Academic Journal
- Accession number :
- 30075065
- Full Text :
- https://doi.org/10.1021/acsnano.8b04945