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Left, a computer simulation of a self-assembled honeycomb of platinum nanoparticles. Right, an actual view of the structure as seen through an electron microscrope.  (Source: Wiesner Lab, Cornell University)
Metal nanoparticles can be very useful, especially when they become usable nanostructures without outside stimulus.

Self-assembly is a relatively new development in the burgeoning field of nanotechnology. Though the idea has been kicked around for many years, manipulating particles less than a nanometer in diameter is still a difficult task. As the interest in nanotech grows, research is opening up new ideas and new methods for exploring the microscopic worlds nanoparticles inhabit.

Recently, DailyTech has covered new developments for simple, self-assembling nanoparticles, like Rice University's self-aligning nanobatons, which may aid in chemical cleanups, and Northwestern University's self-assembling flexible dialetric material, which may be used to develop flexible electronics and radiation resistant transistors for space vehicles.

While the word self-assembly brings to mind images of tiny robots that build themselves, most work in self-assembly simply involves some sort of molecule being assembled into a useful, non-mechanical structure. This week's issue of Science holds another breakthrough for self-assembling nanoparticles, one that may be of great benefit to at least two particularly interesting fields.

Cornell University researchers have found a way to assemble metals, platinum in this case, into a useful structure. Their work utilizes a co-polymer, a ligand and the metal particles themselves. Scientists have been chasing self-assembling metals via co-polymers for years, but it's the addition of the ligand, which is used to facilitate a high density solution of metal particles, that makes this process work.

Once the solution is made, it is mixed with the co-polymer. Co-polymers form known and reliable structures and the scientists utilized this to create their final metallic structures. The platinum molecules combine with a single polymer in the mixture, which allows them to take on a shape controlled by the other polymer's structure. For their tests, the Cornell researchers created a hexagonal honeycomb type structure out of the platinum nanoparticles.

Once the material has taken shape, it is annealed in an airless environment, which also turns the polymers into a carbon scaffolding. High temperatures are then used to burn away the carbon and oxidize the ligand. The metal particles melt on the exterior, allowing them to fuse together into a solid structure as the carbon scaffolding and ligand chemicals disappear.

The group feels that this process may be quite useful in forming catalyst structures for modern fuel cells. Platinum is one of the best currently available catalysts, and the honeycomb structure they have created would create a high degree of available surface area while allowing adequate flow of fuel chemicals.

The process could also be used to create the fine structures needed in the new field of plasmonics. Part of this field involves the flow of electrons across a conductor's surface. The electron waves could carry information in the amounts of and at similar speeds to fiber optics. Cornell's process could be used to create the desired metallic structures needed to produce these theoretical microchip surfaces.





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