Controlled Synthesis of Zinc Selenide Nanostructures Using Oil-Water-Amphiphilic Block Copolymer Liquid Crystals
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0942-W04-08
Controlled Synthesis of Zinc Selenide Nanostructures Using Oil-Water-Amphiphilic Block Copolymer Liquid Crystals Georgios N. Karanikolos1, Paschalis Alexandridis1, and T. J. Mountziaris2 1 Chemical and Biological Engineering, SUNY-Buffalo, Buffalo, NY, 14260 2 Chemical Engineering, University of Massachusetts, Amherst, MA, 01003 ABSTRACT A technique for simultaneous size and shape control of compound semiconductor nanostructures using poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) block copolymer/water/p-xylene lyotropic liquid crystals as templates is reported. Luminescent quantum dots of ZnSe were grown in the spherical domains of reverse (water-in-oil) cubic liquid crystals, hollow nanospheres and hollow nanotubes were grown around the dispersed spherical and cylindrical oil domains of the normal (oil-in-water) cubic and hexagonal phases respectively, and free-standing quantum wells (nanoplates or nanolaminates) were grown in the lamellar liquid crystals. The ZnSe nuclei were formed at room temperature by a spontaneous and irreversible reaction between zinc acetate that was dissolved in the water phase, and hydrogen selenide that was allowed to diffuse into the liquid crystalline templates. The nanostructures were characterized by HR-TEM, XRD, and optical spectroscopy. The shape of the nanocrystals can be controlled by selecting the structure of the templating phase. The size of the nanocrystals can be controlled by the size of the nanodomains and the concentration of the zinc precursor in them.
INTRODUCTION Semiconductor nanocrystals confining excitons (i.e., electron-hole pairs) in zero, one, or two dimensions are currently attracting great attention due to their unique size- and shape-dependent properties that have the potential to revolutionize clinical diagnostics, photovoltaics, and highdensity optoelectronics [1-3]. The ability to control both the shape and size of these nanocrystals is essential for precise tuning of their optical and electronic properties, as well as their overall functionality, to enable their use in proposed applications [4]. In the present study we demonstrate that simultaneous size and shape control of ZnSe nanostructures can be achieved using liquid crystal templates formed by self-assembly of a poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) (PEO-PPO-PEO) amphiphilic block copolymer in the presence of water and p-xylene. PEO-PPO-PEO block copolymers, due to their amphiphilic character, exhibit very rich structural polymorphism when dissolved in selective solvents of different polarity, and can attain a number of microstructures such as spheres, cylinders, and lamellae [5-7]. In our previous work, luminescent ZnSe quantum dots [8, 9] and single-crystalline nanorods [10] with average diameters below 10 nm were synthesized in oil-in-water microemulsions and lyotropic liquid crystals respectively, using the PEO-PPOPEO/heptane/formamide self-assembled system and a reaction between diethylzinc dissolved in
heptane with hydrogen selen
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