Improvement of monodispersity and shape symmetry of silica shell for PbS quantum dots by introducing surface silanization and adjusting reverse micelle size

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Semiconductor quantum dots (QDs) are one of the promising constituent materials of quantum information processing devices. The technique of silica coating of colloidal QDs using the reverse micelle method has been realized for improving position controllability, but the problem is that monodispersity and shape symmetry deteriorate when increasing the coating thickness. In this paper, we report three effective ways to achieve large silica-coated QDs with solving this problem, i.e. proper silanization on the QD surface, control of reverse micelle size by adjusting the amount of QD solvent, and two-step formation of silica shell. Proper substitution of ligands on the QD surface in the early stages of silica shell formation was important for uniform coating reaction. An amount of toluene as QD solvent determined the size of reverse micelles during the silica shell formation. There was an optimum combination of inverse micelle size and silica shell size to obtain silica-coated QDs with good monodispersity and high shape symmetry. We succeeded in growing the thick silica shell with expanding reverse micelle size by additionally supplying toluene with the raw material using the optimum silica-coated QDs as a growth nucleus.