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0901-Ra09-06.1

Self-Assembly of Magnetic and Semiconducting Nanoparticles on Modified Diblock Copolymer Templates N.A. Yufa, 1 A.L. Cisse, 1 S. B. Darling, 2 S.D. Bader, 2 P. Guyot-Sionnest,1 S.J. Sibener1 1 James Franck Institute, University of Chicago, Chicago, IL 60637, U.S.A. 2 Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, U.S.A. ABSTRACT Combining inorganic and organic components to create functional materials has been an active area of research in recent years. Inorganic components possess useful electric, photonic, or magnetic properties while organic components can self-assemble into a variety of morphologies on the nanoscale. We describe a novel approach for arraying nanoparticles using a modified diblock copolymer scaffold. Thin (30 nm) films of poly(styrene-block-methylmethacrylate) (PS-b-PMMA) copolymer were used as a substrate. Upon annealing, PS-b-PMMA forms lying-down cylinders of PMMA in a matrix of PS. These thin films were modified by exposure to ultraviolet light in vacuum which photochemically thinned the PMMA, creating a more highly corrugated surface. We find that colloidal superparamagnetic FePt nanodots and semiconducting CdSe nanodots deposited on this surface show a strong preference for the photochemically modified phase. This hierarchical self-assembly method may prove useful for many nanomaterials-based applications.

INTRODUCTION There has been a great deal of interest recently in creating functional structures on the nanoscale using diblock copolymers.1-3 Diblock copolymers are a natural choice since they offer a wide variety of morphologies with features on the nanoscale—spherical, cylindrical, lamellar, and gyroid. For many applications, such as ultra-high density magnetic memory, nanoparticles arrayed on the surface are appropriate systems for exploration due to their potential for forming future media with densities greater than 1 terabit/in2. We therefore concentrated our efforts on thin films with both blocks having a sizable presentation at the air interface, the goal being to guide nanoparticles selectively onto one of the polymer domains. In this study we used cylindrical polystyrene-blockpolymethylmethacrylate (PS-b-PMMA) thin films. Since only PMMA is scissioned by deep-UV radiation, it is possible to modify the film selectively, leaving behind a highly corrugated interface, as shown in the schematic in Figure 1. Magnetic nanoparticles offer the potential for significantly greater storage density compared to conventional magnetic memory. It has been shown4,5 that high magnetocrystalline anisotropy (Ku) FePt nanoparticles can be produced either by direct synthesis or by annealing superparamagnetic species. This high-Ku species would allow isolated 4 nm diameter particles to be used as bits. Herein we used superparamagnetic particles to demonstrate a proof of concept, as we do not believe that the magnetic properties of the core affect the selectivity of decoration.

0901-Ra09-06.2

(a)

30 nm

PS PMMA

Silicon Nitride (b)

Figure 1. Ultra-thin