Self-Assembling silver nanocubes

Silver nanocubes
Silver is one of the most impotant material for nanostructures because of its superior performance. Silver nanostructures have been synthesized with a range of different shapes, including spheres, discs, rods, wires, stars, prisms, right bipyramids, and cubes. Of these, single-crystal nanocubes are the most useful structure particularly for the production of gold nanocages as silver nanocubes serve as a sacrificial template.
Synthesis
Researchers of University of Washington have developed a polyol synthesis method which is a simple, robust and versatile one for producing silver nanocubes as monodispersed samples. Here silver atoms are formed by reducing AgNO3 precursor with ethylene glycol. Once the concentration of silver atoms has reached the supersaturation level, they will begin to nucleate and grow into silver nanostructures in the solution phase. the production rate of silver nanocubes can be improved  by adding a trace amount of sodium sulfide (Na2S) or sodium hydrosulfide. The presence of sulfide anions greatly accelerated the polyol synthesis of silver nanocubes due to a dramatic increase in the reduction rate of silver ion.
Self-assembly and synthesis
UC San Diego nanoengineers have developed a technique that enables silver nanocubes to self-assemble into larger-scale structures for use in new optical, chemical and biological sensors, optical circuitry and next-generation antennas and lenses. The metal nanocrystals are cube-shaped like bricks and spontaneously organize themselves into larger-scale structures with precise orientations relative to one another.
To construct objects like antennas and lenses, researchers used chemically synthesized metal nanocrystals. The nanocrystals can be synthesized into different shapes to build these structures by creating tiny cubes composed of crystalline silver that can confine light when organized into multi-particle groupings. Confining light into ultra-small volumes could allow optical sensors that are extremely sensitive and allow researchers to monitor how a single molecule moves, reacts, and changes with time.
Control
To control how the cubes organize researchers developed a method to graft polymer chains to the silver cube surfaces that modify how the cubes interact with each other. Normally when objects like cubes stack, they pack side-by-side like Tetris blocks. Using simulations, researchers predicted that placing short polymer chains on the cube surface would cause them to stack normally, while placing long polymer chains would cause the cubes to stack edge-to-edge.
The researchers demonstrated by creating macroscopic films of nanocubes with these two different orientations and showed that the films reflected and transmitted different wavelengths of light.
Applications
The findings could have important implications in developing new optical chemical and biological sensors, where light interacts with molecules, and in optical circuitry, where light can be used to deliver information.

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