Surfactant-free self-assembly of nanocrystals into ellipsoidal architectures

A simple approach to control the self-assembly of ZnS nanocrystals into well-defined, uniform, three-dimensional, micrometer-scale, solid ellipsoidal structures with rattle-type, multishelled, and hollow architectures is presented. There is no surfactant or small molecule to assist the self-assembly of the nanocrystals. A possible mechanism of the controlled self-assembly is proposed. The growth process can be divided into two stages: 1) the formation of ellipsoidal architectures via oriented aggregation, the growth kinetics of which is primarily attributed to the charge-charge, charge-dipole, and dipole-dipole interactions of preformed ZnS nanocrystals; and 2) Ostwald ripening, which results in multishelled, rattle-type, and hollow structures. This self-assembly concept is also applicable to other metal sulfides.