Growth of ZnSe and CdSe nanostructures in self-assembled block copolymer-stabilized templates

The rich polymorphism of amphiphilic poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO-b-PPO-b-PEO) block copolymers in selective solvents was employed to form a variety of self-assembled nanostructures and subsequently use them as templates to grow and control the size, morphology, and composition of compound semiconductor nanocrystals. II–VI nano-dots, -wires, -tubes, -plates, and hollow spheres were synthesized by a reaction between a group-II precursor that was pre-dissolved in one of the solvents and hydrogen selenide. Shape control was accomplished by tuning the composition of the template to the phase region of interest thus forming spherical, cylindrical, or planar nanodomains, while size control was achieved by manipulating the group-II concentration in the domains or by changing the domain size within a given phase region. Control over nanocrystal composition was demonstrated by synthesizing ZnSe and CdSe nanocrystals using diethylzinc and dimethylcadmium as the group-II precursor, respectively. The as-grown nanocrystals are optically active and exhibit quantum confinement due to their reduced dimensions. The stability of the templating system was also investigated and the microemulsion breakage temperature profile as a function of the dispersed phase composition was constructed. This is useful for recovery of the nanocrystals from the templating medium and post-processing for integration into functional devices. The technique is scalable and operates at room temperature without requiring mechanical mixing of the reactants to achieve uniform particle growth and monodispersity.