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May 16, 2006

16 atoms of Gold have a hollow center

AU16, AU17, AU18 are the metallic equivalent of carbon 60 in that they are a metallic cage thank could hold other atoms. Scientists have uncovered a class of gold atom clusters that are the first known metallic hollow equivalents of the famous hollow carbon fullerenes known as buckyballs. The fullerene is made up of a sphere of 60 carbon (C) atoms; gold (Au) requires many fewer--16, 17 and 18 atoms, in triangular configurations more gem-like than soccer ball. At more than 6 angstroms across, or roughly a ten-millionth the size of this comma, they are nonetheless roomy enough to cage a smaller atom. Lai-Sheng Wang, the paper's lead corresponding author, is an affiliate senior chief scientist at the Department of Energy's Pacific Northwest National Laboratory and professor of physics at Washington State University. The experiments were buttressed and the clusters' geometry deciphered from theoretical calculations led by Professor Xiao Cheng Zeng of the University of Nebraska and co-corresponding author. "Au-16 is beautiful and can be viewed as the smallest golden cage," Wang said. He pictures it as having "removed the four corner atoms from our Au20 pyramid and then letting the remaining atoms relax a little," and thus opening up space in its center.

It and its larger neighbors are stable at room temperature and are known as "free-standing" cages--unattached to a surface or any other body, in a vacuum. "When deposited on a surface, the cluster may interact with the surface and the structure may change."

Wang and his co-workers suspect "that many different kinds of atoms can be trapped inside" these hollow clusters, a process called "doping." "These doped cages may very well survive on surfaces," suggesting a method for influencing physical and chemical properties at smaller-than-nano scales, "depending on the dopants."

Wang's group has not yet attempted to imprison a foreign atom in the hollow Au cages, but they plan to try.

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