THE
NEXT TIME you forget to get that special someone a gift (and you know
you will), simply stretch out your hand and say you would like to
present a golden buckyball.
You'd like to, but who knows?
Because these clusters of gold atoms are only about 6 angstroms
across — 6 millionths the diameter of a human hair — nobody will be
able to tell if you have succeeded or failed with the gift-giving
obligation.
A nanogift of gold.
Scientists at the Pacific Northwest National Laboratory in
Richland and at the University of Nebraska report in Tuesday's
Proceedings of the National Academy of Sciences that they have
discovered hollow molecular structures made of pure gold — golden
buckyballs.
Carbon buckyballs, hollow spheres made of 60 carbon atoms and
named for the geodesic dome designed by Buckminster Fuller, were
discovered in the early 1980s.
Originally known as buckminsterfullerenes (today,
technically, just as fullerenes), buckyballs became the third known
natural form of pure carbon after diamond and graphite.
In Tuesday's report, Lai-Sheng Wang, a national lab scientist
and professor of physics at Washington State University, said his team
appears to have created the first metallic version of the buckyball.
Co-authors are Xiao Cheng Zeng and chemist Satya Bulusu, both
of the University of Nebraska, and Xi Li, a WSU physics graduate
student.
"We weren't specifically looking for this," Wang said. "We were just interested in gold nanoparticles."
Elemental gold has a number of useful properties. In large
quantities, such as for a ring or an earring, gold reacts with little
and retains its expensive luster. But in very tiny quantities, at the
scale of individual atoms (or "nanoscale"), gold's character changes
dramatically.
"It becomes highly reactive, a very good catalyst," Wang
said. He and his team continued to work with gold at the nanoscale.
Years ago, Wang's team created a pyramid made of 20 gold atoms.
Nobody thought anything besides carbon could form a buckyball,
he
said. But before coming to Richland, Wang had worked with Richard
Smalley, the Rice University scientist who led the team that discovered
the original buckyball. During the past few years, Wang joined others
searching for evidence of this happening in metals.
The carbon buckyball naturally forms into a nanosphere of 60 atoms.
Although they weren't discovered until recently, buckyballs are
produced naturally in common chemical reactions such as soot from a
burning candle.
Yet the discovery of buckyballs paved the way for much of
today's nanotechnology — the art and science of working at the atomic
level.
In order to look for golden buckyballs, Wang and his team
used a laser to vaporize gold. The zapped gold atoms condensed inside a
vacuum and formed clusters varying in size from two to 100 atoms, Wang
explained. That was the easy part, he said.
"The rest of it was detective work," Wang said.
It took them years of analyzing the spectroscopic signatures of
these clusters to determine if any might be hollow, he said. What they
eventually were able to discern is that only clusters of 16 to 18 atoms
form hollow cages.
Fewer atoms, Wang said, and you get flat gold. More than 18 atoms, he said, and it's just solid gold.
So what good are these golden buckyballs? How will they be put to use?
"You can put another atom in the center," Wang said. Depending
upon the kind of atom put at the center of the cage, he said, you could
create a material with novel chemical, magnetic or even optical
properties.
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