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Self aggregation and organization of nanoparticulate building blocks to form mesocrystals (Quantum dot solids) with special shapes and tunable properties is promising for many applications because such 2D and 3D arrangements combine the size-dependent properties of the individual nanoparticles (NPs) with new features that are derived from the unique collective properties inherent within arrays of ordered particles. At the present time mesocrystals are of increasing interest because these structures have further promising applications as light emitting devices, photodetectors and solar cells [1].
In this work we investigate the internal ordering of PbS mesocrystals at the atomistic scale with respect to the superlattice formed through the self assembly of the NPs. The hierarchical structures were synthesized using a gentle diffusion technique employing spherical lead chalcogenide NPs as building blocks.
The PbS mesocrystals were characterized by SEM. In order to shed some light on the inner ordering of the PbS mesocrystals FIB cuts have been performed and subjected to detailed TEM investigations. The results of the HR-TEM studies show that a distinct structural relationship between the crystallographic orientation of the PbS (galena) core of the NPs and their ordering within the fcc superstructure of the mesocrystals exists. Additionally, careful examinations of the HR-TEM images along the different projections of the individual nanocrystals have revealed that the appearance of the individual NPs is closely related to that of truncated octahedra. These findings are further supported by means of atomistic simulations undertaken on the NP assemblies as well as of the constitution of the monomeric building blocks.
[1] S. M. Rupich et al., JACS, 132 (1), 2010, p. 289-296 |
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