Technology Research News
Scientists are finding ways to make nanotubes
more and more complex and, therefore, potentially more useful.
After discovering the microscopic rolled-up sheets of carbon atoms, which
form naturally in soot, scientists made nanotubes that forked into two-dimensional
Y's and T's so that they could form three-way junctions in minuscule electronic
Researchers at the National Cheng Kung University in Taiwan have made
more complicated nanotubes by adding three-dimensional junctions. "We
have grown carbon nanotube branching webs having two-dimensional H-junction
and multiple Y-junctions, and... three-dimensional multiple junctions,"
Jyh-Ming Ting, a professor of Materials Science and Engineering at the
The researchers used a common chemical vapor deposition method to make
the nanotube networks, he said. In chemical vapor deposition, a vapor
of metal or semiconductor atoms condenses to form solid shapes.
These webs of connecting nanotubes could eventually make more efficient
computer circuits and sensors, and fine filtration devices. Individual
nanotubes within the three-dimensional network were less than 50 nanometers
in diameter and several hundred nanometers long -- considerably smaller
than a bacterium, which is about 1,000 nanometers across.
The three-dimensional junctions assemble automatically; the branching
is spontaneous and uncontrolled. "It starts with a single carbon nanotube
stem which then splits into two or more carbon nanotube branches under
the influence of currently unknown mechanisms," Ting said. "One or more
of the branches then serve as stems, which further split into one or more
branches. The process repeats to form a two dimensional or three dimensional
web of carbon nanotubes."
Several researchers have been experimenting with replacing semiconductor
chips with nanotubes. "If carbon nanotubes were used to replace metallization
on silicon, junctions [will] have to be made," said Ting. The joints in
the nanotube network can function as junctions, where two semiconductors
meet, he said.
The work is an important step in making nanotube networks, said Deepak
Srivastava, a senior scientist at NASA's Ames Research center. "Multiple
three-dimensional junctions at a single connection point is new," he said.
These branching tubes provide new materials that could spawn many applications
in computing, sensing, filtration, and electronic devices, he said.
The nanotubes could be used to make "multiple self-connected transistors
or logic gates at a single multiple-branching point," said Srivastava.
These devices would be considerably different from the traditional computing
or electronic architecture where each transistor is "a stand-alone device
but connected to other transistors or devices through interconnect wirings,"
Srivastava said. "With multiple transistors or... logic devices at a single
point, we could be getting rid of bulky interconnects from the circuitry."
The researchers are working towards better understanding the growth mechanism
and kinetics of carbon nanotubes, said Ting. Three dimensional nanotube
clusters could find practical applications within 2 to 3 years, he said.
Ting's research colleague was Chi-Chih Chang. They published their article
in the January 14 issue of the journal Applied Physics Letters. The research
was funded by the National Science Council (NSC) in Taiwan.
Timeline: 2-3 years
TRN Categories: Nanotechnology; Materials Science and Engineering
Story Type: News
Related Elements: Technical paper, "Multijunction Carbon
Nanotube Network," Applied Physics Letters, January 14, 2002.
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