Nanotubes branch out

By Chhavi Sachdev, 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 devices.

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 University.

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
Funding:  Government
TRN Categories:   Nanotechnology; Materials Science and Engineering
Story Type:   News
Related Elements:  Technical paper, "Multijunction Carbon Nanotube Network," Applied Physics Letters, January 14, 2002.


March 6, 2002

Page One

Interactive robot has character

Atomic cascade broadens laser

Biology harbors hidden complexity

Heat engines gain quantum afterburner

Nanotubes branch out


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