Uniform ZnSe microspheres self-assembled from ZnSe polyhedron shaped nanocrystals

Abstract

Large-scale and uniform ZnSe solid and hollow microspheres have been prepared via controllable self-assembly of ZnSe faceted nanocrystals under hydrothermal conditions. During the process, using the surfactant or not plays a key role in the ZnSe faceted nanocrystals' self-assembly into the ZnSe microspheres. Using PVP as the surfactant, the ZnSe monodisperse faceted shaped (including cubes, hexagons, and pentagons) nanocrystals with a diameter of ∼50 nm have been obtained; without using PVP surfactant, the ZnSe solid microspheres with a diameter of ∼3 μm have been achieved by the self-assembly of ZnSe faceted shaped nanocrystals; while using oleyl amine as the surfactant, which combines with N₂ bubbles from the decomposition of N₂H₄·H₂O, forming a new “soft-template”, the ZnSe hollow microspheres have been synthesized through as-called “soft-template” process. Meanwhile, hydrothermal temperature, time, and reducing agent have significant effects on the surface morphology of the ZnSe microspheres, i.e., a suitable temperature (e.g., 180 °C), longer reaction time, and using a small quantity of N₂H₄·H₂O could be beneficial to the growth of the well-defined ZnSe faceted nanocrystals and their self-assembly into microspheres. A possible mechanism for the formation of ZnSe nanocrystals and their self-assembly into ZnSe microspheres has been proposed.