Synthesis of Zinc and Lead Chalcogenide Core and Core/Shell Nanoplatelets Using Sequential Cation Exchange Reactions

We present the synthesis of a novel type of chalcogenide nanoplatelets. Starting from CdS core or CdSe/CdS core/shell nanoplatelets, we use sequential cation exchange to copper and then to either zinc or lead to obtain ZnS and PbS core or ZnSe/ZnS and PbSe/PbS core/shell structures. The procedure preserves well the 2D geometry of the nanoplatelets, provided that they are more than 6 monolayers (∼1.8 nm) thick. The core/shell structure is also well conserved during the cation exchange as verified by TEM images. The nanoplatelets exchanged with Zn crystallize in a zinc blende structure, like the initial Cd-based material, whereas when Pb is used, the final nanoplatelets have a rock-salt crystal structure. We explored the copper cation exchange process using energy dispersive X-ray spectrometry with 1 nm resolution on nanoplatelets standing on their edges, and we show that copper ions diffuse uniformly from the outside of the nanoplatelet to the inside during the exchange