create nano toolkit
Technology Research News
The word 'chemistry' often conjures images
of test tubes filled with strangely colored liquids. But those liquids
are just the outward manifestation of what chemistry is really about --
creating and manipulating molecules.
Traditionally, chemists work with molecules to make substances with useful
properties, from new drugs to better laundry detergent. In the brave new
world of nanotechnology,
chemists use molecules as building blocks for microscopic structures and
Chemists have found an ally in some molecules that assemble themselves
into specific shapes. So rather than having to build tiny objects molecule
by molecule, researchers can harness this self-assembly skill to make
the molecules do the work.
A team of researchers at the National Institute for Materials Science
in Japan and the Communications Research Laboratory in Japan has come
up with a kind of toolkit for building structures out of ring-shaped porphyrin
molecules. Naturally occurring porphyrins include hemoglobin, which gives
blood its red color, and chlorophyll, which makes plants green.
The researchers' synthetic porphyrin has four attachment points and the
researchers can control which of the attachment points connect to a gold
surface. With three points attached, the molecules assemble into rings
of three connected at the center by the remaining attachment points. When
two adjacent attachment points on each molecule are free, four-molecule
rings form. When two opposite attachment points are free, the molecules
form long chains across the surface.
The structures could be used to make molecular electronic and optoelectronic
devices, said Shiyoshi Yokoyama, a senior researcher at the Communications
Research Laboratory. For example, the chains could be used as extremely
The smallest wires used in today's integrated circuits are etched by narrowly
focused lasers, but the finest lines they can make are about 150 nanometers
wide. Experimental etching techniques have produced lines about 10 nanometers
wide. The researchers' self-assembly approach produces chains of molecules
that are about 3 nanometers wide, or about thirty times the diameter of
a carbon atom. A nanometer is one millionth of a millimeter.
The researchers have made porphyrin chains as long as 100 nanometers and
they have made the wires branch at selected points, said Yokoyama.
Creating tiny structures is only half the game, however. The researchers
also need to make the structures do something, like conduct electricity
or convert light signals to electric signals. But even if the porphyrin
molecules were not useful by themselves they could be augmented by other
atoms or molecules.
The molecules show some initial promise on their own: "Porphyrin molecules...
show fluorescence behavior and perform interesting energetic transfers
when they are bonded or arranged closely," said Yokoyama. The researchers
have not yet determined how well the wires conduct electricity, however,
he said. "In order to do this, we are making nanometer-scale electrodes."
One of the fundamental challenges in nanotechnology research in general
is linking molecule-scale structures to the outside world. The key is
getting the structures to form where researchers want them.
Yokoyama's team is also working on this problem. "One of the most important
issues is placing the assemblies at the desired position, such as between
nano-scale electrodes," he said.
The research is an advance in structural nanotechnology, said Yuji Okawa,
a research scientist at Institute of Physical and Chemical Research (RIKEN)
in Japan. "Many molecules have been proposed which will act as functional
electronic devices," but the problem is no one has been able to build
actual electronic devices out of them, he said.
The main challenge is efficiently positioning nano-sized molecules and
connecting them into micro-sized patterns, said Okawa. "This work demonstrates
that individual... molecules can be designed to control the size and the
aggregation pattern of supramolecular structures," he said.
It's difficult to say when the technique could be used to make practical
devices, said Yokoyama. "If we need only one or two functions, we can
demonstrate them within five to ten years," he said.
Yokoyama's research colleagues were Takashi Yokoyama of the National Institute
for Materials Science in Japan, and Toshiya Kamikado, Yoshishige Okuno
and Shinro Mashiko of the Communications Research Laboratory in Japan.
They published the research in the October 11, 2001 issue of the journal
Nature. The research was funded by the Japanese government.
Timeline: 5-10 years
TRN Categories: Nanotechnology; Materials Science and Engineering
Story Type: News
Related Elements: Technical paper, "Selective Assembly On
a Surface of Supramolecular Aggregates With Controlled Size and Shape,"
Nature, October 11, 2001
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