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Colloidal chemistry is a versatile route for the synthesis of heterostructured nanocrystals (HNCs) with complex hetero-junction, from centro-symmetric core/shell to linear interfaces. The type, extension, atomic composition of the inorganic interface determines the properties of the overall HNC which arise from the electronic communication between the lattices. Understanding the mechanisms of hetero-interface formation is of fundamental importance in nanoscience and could pave the way to the "engineering" of HNC structures of different materials, which are suitable for specific applications. In our work we have profited from the use of different colloidal methods (hot injection, seeded-growth, cation exchange) to synthesize complex HNCs based on CdSe and PbSe semiconducting materials. Different configurations have been achieved, like CdSe nanorods (NRs) embedding one or two PbSe dots and PbSe-CdSe-PbSe dumbbell-like HNCs with controlled distance between the PbSe quantum dots. These nanomaterials are promising candidates for the study of quantum-mechanical coupling between QDs in a semiconducting NC matrix and for the study of electron transfer at the inorganic CdSe-PbSe nanojunction. A combined HAADF-STEM and discrete tomography study allowed us a 3D reconstruction of the nanocrystalline PbSe core with atomic resolution. Reliable imaging of interfaces gives insight into the formation mechanism, based on a layer-by-layer replacement of Pb2+ by Cd2+ enabled by a vacancy-assisted cation migration mechanism. |
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