Nanocrystal superlattices are attracting significant interest due to novel and peculiar collective properties arising from the interactions of the nanocrystals forming the superlattice. A large variety of superlattice structures can be obtained, involving one or more types of nanocrystals, with different size and concentrations. Engineering of the superlattice properties relies on accurate structural and morphological characterization, able to provide not only a fundamental feedback for synthesis procedures, but also relevant insight on their structural properties for possible applications. Electron microscopy and X-ray based techniques are complementary approaches for nanoscale structural imaging, which however becomes challenging in presence of building blocks only a few nm in size. Here, a structure solution for a 3D self-assembly of PbS nanocrystals with bi-modal size distribution is obtained, by exploiting small angle X-ray diffraction, transmission electron microscopy, crystallographic procedures, and geometric constraints. In particular, analysis of small angle X-ray diffraction data, based on the Patterson function and on single crystal model, is shown to provide relevant information on the 3D superlattice structure as well as on particle size, the scattering signal being sensitive to particles as small as 1.5 nm. The combined approach here proposed is thus demonstrated to effectively overcome important resolution limitations in the imaging of superlattices including small nanocrystals.
A Meso-Crystallographic study of a 3D Self-assembled bi-modal Nanocrystal Superlattice
FALQUI, ANDREA;
2012-01-01
Abstract
Nanocrystal superlattices are attracting significant interest due to novel and peculiar collective properties arising from the interactions of the nanocrystals forming the superlattice. A large variety of superlattice structures can be obtained, involving one or more types of nanocrystals, with different size and concentrations. Engineering of the superlattice properties relies on accurate structural and morphological characterization, able to provide not only a fundamental feedback for synthesis procedures, but also relevant insight on their structural properties for possible applications. Electron microscopy and X-ray based techniques are complementary approaches for nanoscale structural imaging, which however becomes challenging in presence of building blocks only a few nm in size. Here, a structure solution for a 3D self-assembly of PbS nanocrystals with bi-modal size distribution is obtained, by exploiting small angle X-ray diffraction, transmission electron microscopy, crystallographic procedures, and geometric constraints. In particular, analysis of small angle X-ray diffraction data, based on the Patterson function and on single crystal model, is shown to provide relevant information on the 3D superlattice structure as well as on particle size, the scattering signal being sensitive to particles as small as 1.5 nm. The combined approach here proposed is thus demonstrated to effectively overcome important resolution limitations in the imaging of superlattices including small nanocrystals.
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