Complex colloidal semiconductor quantum- dot heterostructures, such as core/shell or core/crown nanoplatelets, can now be readily synthesized [1-4]. Such heterostructures significantly enhance the optical properties of the colloidal quantum dots. The optical properties of these colloidal quantum dots depend not only on the morphology of the heterostructure – i.e. the size and shape of the core-, but, more importantly on the chemical nature and the presence of a composition gradient at the heterostructure interfaces, and on the elastic deformation inside the quantum dots that is due to a lattice mismatch between the core and shell/crown materials. The study of these heterostructures through aberration-corrected Scanning Transmission Electron Microscopy (STEM) provides access to their structure down to the atomic scale. High Angle Annular Dark Field STEM images, in particular, provide direct access to the atomic structure of the nanoparticles, and through the contrast of the atomic columns (“Z-contrast” images) to their chemical nature. Therefore, atomic resolution STEM images allow one possible to precisely map the strain fields of the heterostructure. Finally, chemical information accessed through the Z-contrast can be correlated to quantitative STEM-EDX with a spatial resolution of 1 nm. The present talk summarizes such studies conducted on CdSe/Cd(Zn)S core/shell [1,2], and core/crown CdSe/CdS [3,4] and CdSe/CdTe nanoplatelets.

References:

[1] Core/Shell Colloidal Semiconductor Nanoplatelets
B. Malher, B. Nadal, C. Bouet, G. Patriarche, B. Dubertret
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 134 (2012) 18591-18598

[2] Colloidal CdSe/CdS Dot-in-Plate Nanocrystals with 2D-Polarized Emission
E. Cassette, B. Mahler, J.-M. Guigner, G. Patriarche, B. Dubertret, T. Pons
ACS NANO 6 (2012) 6741-6750

[3] Efficient Exciton Concentrators Built from Colloidal Core/Crown CdSe/CdS Semiconductor Nanoplatelets
M. D. Tessier, P. Spinicelli, D. Dupont, G. Patriarche, S. Ithurria, B. Dubertret
NANO LETTERS  14 (2014) 207-213

 [4] Type-II CdSe/CdTe Core/Crown Semiconductor Nanoplatelets
S. Pedetti, S. Ithurria, H. Heuclin,  G. Patriarche, B. Dubertret,
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 136 (2014) 16430-16438

Figures:

HAADF-STEM images of a CdSe/ZnS nanoplatelet observed on the edge.

Stress between the core and the shell extracted from the atomic position of the elements of columns II on the HAADF image.

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EMC Abstracts - https://emc-proceedings.com/abstract/colloidal-quantum-dot-heterostructures-studied-using-aberration-corrected-scanning-transmission-electron-microscopy/