Astrid Nolte
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Tue, 04.02.2003
pte20030204038 Science/Technology
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Designer crystals 'grown' in electric fields
Model system could be used to create new optical devices

Utrecht/London (pte038/04.02.2003/14:42) - In a new procedure developed at the University of Utrecht scientists have been able to create designer crystals out of microscopic spheres in electromagnetic fields.

The tiny spheres were first added to an organic fluid, then placed in a surrounding electromagnetic field. This permitted scientists to not only determine to which extent the spheres attracted or rejected each other, but also to engineer the formation of diversely structured crystals, as reported in Nature

Certain researchers believe this model system could be used to develop new optical devices

The procedure was developed by the researchers Alfons van Blaaderen and Anand Yethiraj. In a first step, they infused an organic solution with spheres made of the polymer polymethylmethacrylate (PMMA). The spheres, which are also known as colloids, are one to two micro-metres in diameter. Their core consists of fluorescently labeled material, which helps scientists to detect them under a microscope. Their outer shell consists of a non-fluorescent material like pure silica, which enables scientists to detect touching spheres and chemically modify the surface.

Depending on the conditions of their environment, the spheres may be aligned in cubic, ordered structures (cubic crystals). The scientists were not surprised that the number of spheres per millilitre of fluid and the percentage of salt in the solution helped determine the formation of crystals out of the colloids.

But in order to find out whether the colloids could be aligned to form more complex crystalline structures, scientists then subjected the fluid to an electromagnetic field. This not only polarised the spheroids, but led them to attract or reject each other depending on the charge in their outer surfaces.

Once the electromagnetic force and charged surfaces stood in balance, tetragonal (pyramid-like) and rhombic (prism-like) crystalline structures formed.

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