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Posted: Aug 01, 2011
Nanotechnology: Entering the matrix
(Nanowerk News) One of the advantages of the bottom-up fabrication of nanostructures is that self-assembly can offer a convenient way of fabricating structures that are too complex to be made in a top-down process. Shengyang Yang, Cai-Feng Wang and Su Chen from the Nanjing University of Technology in China have now demonstrated how such bottom-up composites could be used to achieve enhanced functionality via an interfacial assembly strategy ("Interface-Directed Assembly of One-Dimensional Ordered Architecture from Quantum Dots Guest and Polymer Host"). They have successfully synthesized semiconductor nanocrystal–polymer composites that assemble into light-emitting nanowires with potential use in optoelectronic applications.
Nanoparticles made from semiconductors such as cadmium telluride (CdTe) are widely investigated for their light-emitting properties, as their emission wavelength can be easily tuned by adjusting the diameter of the nanoparticles. However, integrating such quantum dots into actual devices requires them to be incorporated into larger structures such as nanowires, which has been difficult to achieve with conventional top-down fabrication processes.
The technique developed by Yang, Wang and Chen embeds CdTe quantum dots into narrow polymer nanowires during synthesis, which involves mixing a water suspension of quantum dots with a chloroform solution containing the dissolved polymer. As water and chloroform are immiscible, the quantum dots and polymer molecules meet only at the interface between the two liquids when they are mixed. There, they react to form narrow wires of quantum dot–polymer nanocomposites.
Importantly, the quantum dots retain their fluorescent properties upon integration into the nanowires, and the synthesis is flexible with respect to the starting materials. "These nanoparticle–polymer hybrids are promising in material science and technology because of their unique optical, electrical and magnetic properties," says Chen. Replacing the CdTe quantum dots with magnetic dots, for example, could give magnetic nanowires.
Another feature of the synthesis is that thicker composite fibers of up to several micrometers in diameter could be formed by keeping the polymer molecules and nanoparticles at the water–chloroform interface for longer, demonstrating the level of control available by this approach. "These nanocrystal–polymer hybrids show great potential for device applications," says Chen, "but the versatility of the approach is also crucial to understanding the structure–property relationship of these multifunctional organic–inorganic hybrid materials."