A New Way To Control The Architecture of Nanocrystals

By Roland Piquepaille

Until now, the fabrication of nanocrystals implied to inject various chemicals into heated solutions. As the solution concentration changed during the reaction, the process was hard to control and the results were somewhat unexpected. But now, researchers at Argonne National Laboratory (ANL) have found an easy way to control the architecture of nanocrystals. They simply use electricity to control the nanocrystals shapes in a reproducible way. This opens the door to new applications such as using ferromagnetic nanocrystals as components in ultra high-density storage media.

Researchers at Argonne have figured out the basics of using electrochemistry to control the architecture of nanocrystals -- small structures with dimensions in billionths of meters. Their findings provide a practical method of generating large quantities of architecture-controlled nanocrystals, such as superconductors, ferromagnets and noble metals.

"The architectures of the nanocrystals are mainly controlled by applied voltages," said lead scientist Zhili Xiao of Argonne's Materials Science Division and Northern Illinois University's Physics Department. "This gives us much greater control over the growth conditions of the nanocrystals. We were able to create a great variety of structures with greater convenience and predictability compared with more traditional methods."

Here is an illustration of what the researchers were able to create and reproduce coherently. With voltages lower than 1.2 volts, they produced icosahedrons (a) and decahedrons (b). With higher voltages, they were able to design tripods (c) and nanobrushes (d). The bar at the top of each image represents 500 nanometers. (Credit: ANL)

Here are more details about the process.

Xiao and his colleagues found that they could easily control the electrochemical potential by using electric voltage. The scientists used a technique called electrodeposition, which uses electricity passing through an electrode to reduce ions from solution on a given surface. By changing the applied voltage value and the type of chemicals in the solution, the Argonne researchers were able to synthesize large quantities of nearly 30 different nanostructures, including nanoparticles of various shapes, nanowires, nanobrushes and nanoscale tripods.

Below are some other shapes of nanocrystals created by the ANL team (Credit: ANL).

What exactly can we expect from these findings?

With large quantities of these nanocrystals in hand, scientists are exploring their unique physical and chemical properties. These structures can lead to discoveries of new phenomena and applications, such as the use of ferromagnetic nanocrystals as components in ultra high-density storage media and the use of certain metal nanocrystals as catalysts for hydrogen production and sensing.

For your information, the research paper has been published by the Journal of the American Chemical Society (Vol. 126, No. 8: March 3, 2004) under the name "Tuning the Architecture of Mesostructures by Electrodeposition." It is available here if you are a subscriber.

Source: Argonne National Laboratory, March 17, 2004, via EurekAlert!