From: Eugene.Leitl@lrz.uni-muenchen.de
Date: Sat Nov 25 2000 - 06:10:35 MST
http://www.sciencemag.org/cgi/content/full/290/5496/1530
NanoManipulator Lets Chemists Go Mano a Mano
With Molecules
Mark Sincell*
Interacting with the nanoworld is like shadowboxing in the
dark. Because objects only a few molecules across are too small to be
seen or touched directly, scientists approach them essentially blind
and numb. Now a team of physicists, chemists, biologists, and computer
scientists at the University of North Carolina (UNC), Chapel Hill, has
developed a tool that restores their eyes and fingers. It's called the
nanoManipulator.
"It is like the movie Honey, I Shrunk the Kids, except you don't
really get smaller," says UNC computer scientist Warren Robinett. "We
reconstruct your perception so that you see and feel exactly what you
would if you were the size of a virus." Robinett created the
nanoManipulator with chemist Stan Williams, who is now the director of
basic research in the physical sciences at Hewlett-Packard. The device
"puts humans in the loop in a very nice way," says Ari Requicha, an
electrical engineer who works on virtual reality interfaces at the
University of Southern California in Los Angeles.
Robinett and Williams, who have been friends since their undergraduate
days in the early 1970s, came up with the idea for the nanoManipulator
during a 1991 phone call. At the time, Williams was trying to string
single silicon atoms into a nanoscale wire, but he was frustrated by
his inability to touch the atoms. "Chemists want to get their hands
on stuff," he says. For his part, Robinett was looking for a safer
application of his expertise in programming people-sized robots that
mimic the motions of their human operator. When working with big
machines, Robinett explains, "a bug in your program can turn a robot
into an eggbeater, and it can punch a hole in your skull."
To Robinett, the scanning probe microscope (SPM) that Williams used to
view his surfaces looked like a small and safe robot. Instead of the
robot's TV camera eyes, the SPM has a computer-controlled probe that
"looks like an upside-down pyramid at the end of a flexible diving
board," says UNC computer scientist Russell Taylor. The probe skates
across the silicon surface, and a computer interface converts the
probe's wiggles into an electric signal, a bit like the way a
phonograph needle creates sounds from the bumps in a vinyl record.
The probe can also be programmed to push against the surface like a
robotic finger. In the push mode, scanning tunneling microscopes
(STMs) are commonly used to photograph products of chemical reactions,
measure the mechanical properties of various materials, and rearrange
atoms and bend carbon nanotubes. But there's a problem. To point the
tip in the correct direction, researchers first scan the surface and
find the target in the resulting three-dimensional (3D) image. Then,
they must switch from visualization mode to manipulation mode, program
the STM tip to move to the right spot, and finally press it against
the surface. In the meantime, thermal vibrations of the surface might
have bounced the atom away from the tip's preprogrammed target. It is
like trying to play blindfolded billiards during an earthquake.
But even in the push mode, the changing separation between the flexing
tip and its fixed mount creates an electric current that is
proportional to the pressure exerted on the tip. By transmitting that
current to the proper computer interface, Robinett and Williams
realized that a human could locate the target object by touch at the
same time they were pushing gently against it. All Robinett had to do
was revamp his human-sized robot control programs to link the
microscopic "robot" to a human. And the nanoManipulator was born.
In its current form, the nanoManipulator is a computer program that
fuses an STM with a real-time 3D graphics rendering program and a
haptic interface that fits over one finger like a high-tech
thimble. The scientist's fingertip gets a little push each time the
probe hits a bump. And when the scientist pushes back with his finger,
a nanoscale finger presses against the surface.
"The key to the manipulator is that it immerses users in the
environment so they develop a good feel for what they are doing," says
electrical engineer Joe Lyding, an expert in molecular computing and
visualization at the University of Illinois, Urbana-Champaign. For
example, a user can tell the difference between signal noise and real
texture by simply running a "finger" over the surface, says Williams,
who has also used the nanoManipulator to "nanoweld" atoms into a wire
strand.
Garrett Matthews, a graduate student in physics at UNC, is using the
nanoManipulator to figure out if a virus feels more like a cue ball, a
tennis ball, or a rotten tomato. The results are inconclusive. "Right
now it feels like a cue ball, but we have other measurements that
indicate it should be soft and sticky," says Matthews. Versions of
the nanoManipulator are also being used by chemists and materials
scientists at Catholic University of Leuven in Belgium, the University
of Toronto, the National Institute of Standards and Technology, and
Arizona State University in Tempe.
Williams is not surprised at the device's increasing popularity. "We
used to have to stare for hours at a black-and-white picture of a
surface just to tell what was up and what was down," he says. "The
nanoManipulator has untied our hands and opened our senses."
Mark Sincell is a science writer in Houston.
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