Proceedings of MATSUS23 & Sustainable Technology Forum València (STECH23) (MATSUS23)
DOI: https://doi.org/10.29363/nanoge.matsus.2023.057
Publication date: 22nd December 2022
AECs are composed of a IIa metal (Mg, Ca, Sr) and S or Se (X), feature large bandgaps positioned in the UV and are commonly used as hosts for emissive ions. AEC nanocrystals could therefore be used as UV emitters, or scatter-free emitters based on lanthanide ions. Moreover, while most AEC crystallize in the rocksalt structure, MgX can also be grown as zinc blende crystals with lattice parameters that come close to those of commonly examined and used IIb-VI chalcogenides or III-V pnictides, such as CdSe and InP. Hence, AECs could extend the range of materials to form core/shell heterostructures out of these compounds. However, such implementations of AECs are hampered by the limited knowledge of the colloidal synthesis and the surface chemistry of these compounds. Here, we report on possible routes to synthesize these materials and the resulting surface termination of AECs by organic ligands, for which we take the formation of CaS as a starting point. We show that ~12 nm large CaS nanocubes can be formed by reacting calciumacetate and diphenylthiourea in a mixture of oleylamine (OLA), trioctylamine and oleic acid (OA)[1]. Using Nuclear Magnetic Resonance (NMR) and infrared (IR) spectroscopy, we demonstrate that such as-synthesized CaS nanocubes are terminated by a dense shell of oleate ligands, which are unequally packed at the surface, and small traces of OLA. Addition of a carboxylic acid shows the dynamic behavior of this dense shell and induces a slow reorganization of the ligands by breaking up the dense packing and replacing hydroxides at the surface by oleates. Apart from providing detailed insight in the surface chemistry of CaS NCs, this work shows that known approaches and concepts to analyze and rationalize the interaction between colloidal nanocrystals and surface-active ligands can be extended to AEC nanocrystals.
This project has received funding via the BOF GOA project (funding agreement n° 01G02019). I would also like to thank all members of PCN and ATP personnel of the Department of Chemistry of Ghent University.
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