Spontaneous formation of ordered 2D and 3D superlattices of ZnO nanocrystals

The synthesis of the ZnO nanoparticles stabilized by a combination of amine and acid ligands and their spontaneous organization into 2D and 3D ordered superlattices from colloidal solutions was analyzed. The synthesis of the ZnO nanoparticles was carried out by slow hydrolysis in air of a THF solution containing the precursor ZnCy 2 as well as one equivalent of a long-alkyl-chain amine and half an equivalent of a long-alkyl-chain acid. Thus, when the reaction mixture was exposed to air and left standing at room temperature, the solvent slowly evaporated and left a white and luminescent product, which was characterized by X-ray diffraction (XRD) and transmission electron microscopy as (TEM) as crystalline, isotropic ZnO nanoparticles and very low size dispersity. 3D superlattices were obtained through slow evaporation of colloidal THF solutions. Results show that the superlattices are not monodisperse in size but display uniform hexagonal shapes.