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Gold in the realm of dwarves
October 25, 2004"Man has been fascinated by gold since ancient times," says a bland introduction to related scientific studies. The fact that there is still room for surprises was shown by a recent publication: Nanoparticles of the precious metal behave differently from those of its close relatives.
One of the arguments in the currently raging "nanodebate" is that particles with diameters of significantly less than one micron behave differently from larger particles - and, indeed, may even be toxic. This comes as no surprise to folk like millers and bakers. Cereal grains are harmless; and yet years of exposure to flour can cause an occupational disease commonly known as baker's asthma. Gold is another example: In the human mesocosmos it appears a shiny yellow, while members of the dwarf realm (Greek nanos = dwarf) would see red.
These findings, which were published in the Physical Review Letters periodical (Volume 93, No. 9) at the end of August, will surely also be of interest to catalysis researchers. After all, one of their crucial questions is: How are the course and speed of chemical reactions affected by the crystallinity and magnitude of the precious metal particles that are so often employed?
Researchers today are increasingly using computer simulation to produce results like those mentioned. In this particular case, though, the experts have started a kind of upscaling nanodebate. A single atom and its behavior can be computed pretty well using quantum mechanics. The larger an aggregate or a molecule becomes, however, the further the predictions deviate from the actual experimental findings.
"We examined clusters of 55 atoms and were able to confirm the amorphous structure with a photo-electron spectroscope," stresses co-author Michael Moseler of the Fraunhofer Institute for Mechanics of Materials IWM. "Our group is currently the only one that can reliably compute clusters containing up to a thousand atoms of gold."
The idiosyncratic behavior displayed by gold may have consequences in the field of microelectronics. The smaller circuits become, the thinner are the wires that join them. However, material parameters like stability or conductivity cannot be extrapolated to endlessly small sizes.
Other fields affected are genetics and protein research, where gold clusters are often used for marking biomolecules. The nature and strength of the molecular bond depend on how well the atoms of the precious metal "get along" with one another.
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