Nonlithographic hierarchical patterning of semiconducting nanoparticles via polymer/polymer phase separation

We demonstrate a new and versatile nonlithographic strategy for the lateral patterning of semiconducting quantum dots (QDs) in thin polymer films via phase separation between two immiscible polymer components, one of which is attached as a stabilizing layer to the QD surface. Simple spin-casting of blend solutions containing block copolymer-stabilized cadmium sulfide (CdS) QDs with an external polystyrene (PS) brush layer (PS-CdS) and poly(methyl methacrylate) (PMMA) homopolymer results in solvent evaporation-induced organization of QDs on two disparate length scales: polymer/polymer spinodal decomposition gives rise to tunable microscopic lateral patterning of PS-CdS features (with mesoscopic feature heights), while simultaneous steric interactions between the polymer brush layers on neighboring nanoparticles give rise to a nanoscale liquidlike distribution of QDs within the PS-CdS domains. The correlation length and morphology of the lateral patterns are easily controlled via the spincasting rotation speed and blend composition, respectively. Subsequent selective removal of the PMMA component allows the production of various photoluminescent PS-CdS features with structural hierarchy on glass substrates, including cellular and wirelike networks and arrays of spatially correlated islands.