Journal
NANO LETTERS
Volume 20, Issue 7, Pages 5267-5274Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.0c01579
Keywords
Nanocrystals; self-assembly; oriented attachment; superlattice; 4D-STEM; EMPAD
Categories
Funding
- U.S. Department of Energy, Office of Basic Energy Sciences [DE-SC0018026]
- NSF MRSEC program [DMR-1719875]
- Cornell University
- Kavli Institute at Cornell
- CAPES, Brazil [13159/13-5]
- NSF [1803878]
- NSF GRFP [DGE-1650441]
- Weill Institute
- [NSF-MRI-1429155]
- Directorate For Engineering
- Div Of Chem, Bioeng, Env, & Transp Sys [1803878] Funding Source: National Science Foundation
- U.S. Department of Energy (DOE) [DE-SC0018026] Funding Source: U.S. Department of Energy (DOE)
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Understanding the mechanism and ultimately directing nanocrystal (NC) superlattice assembly and attachment have important implications on future advances in this emerging field. Here, we use 4D-STEM to investigate a monolayer of PbS NCs at various stages of the transformation from a hexatic assembly to a nonconnected square-like superlattice over large fields of view. Maps of nanobeam electron diffraction patterns acquired with an electron microscope pixel array detector (EMPAD) offer unprecedented detail into the 3D crystallographic alignment of the polyhedral NCs. Our analysis reveals that superlattice transformation is dominated by translation of prealigned NCs strongly coupled along the < 11n >(AL) direction and occurs stochastically and gradually throughout single grains. We validate the generality of the proposed mechanism by examining the structure of analogous PbSe NC assemblies using conventional transmission electron microscopy and selected area electron diffraction. The experimental results presented here provide new mechanistic insights into NC self-assembly and oriented attachment.
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