Electron beams turn out tinier tubes
By Eric Smalley, Technology Research NewsUnder the influence of electron beam irradiation, carbon nanotubes can form as small as 0.33 nanometers, or three atoms, in diameter, according to results of experiments conducted by researchers at Peking University in China.
The versatile strands of carbon atoms are expected to play a large role in future electronics and nanotechnology. They usually range from 0.8 nanometer to 1.4 nanometers in diameter.
"Smaller nanotubes may be used as the tips of higher resolutions scanning probe microscopes,... and also for connections between nanoelectronic devices," said Lianmao Peng, an electronics professor at Peking University.
The 0.33 nanometer tube was produced during a transmission electron microscope experiment. The electron beam irradiation either induced or assisted the growth of the small tube, Peng said.
"In general, in forming a smaller tube we have to introduce larger strain energy," said Peng. Changes in strain produce corresponding changes in electrical resistance.
"Large strain may turn a metallic carbon nanotube into a semiconducting tube, or a semiconducting tube into a metallic one. Chemically, smaller tubes with larger strain tend to be more reactive," said Peng.
The researchers don't know precisely how the smaller nanotubes differ from their larger relatives. "We still lack systematic study of the physical, electrical and electromechanical properties of very small tubes because they are smaller, and therefore more difficult to handle, and difficult to produce," he said.
Separately, two teams of researchers, one from JST-ICORP, NEC Corporation and Meijo University in Japan, and one from Hong Kong University of Science and Technology, have produced single-walled carbon nanotubes with diameters of 0.4 nanometers. They published their work in the November 2, 2000 issues of the journal Nature.
"We expect that researchers will soon be able to produce a nanometer tubes, say 0. 6 to 0.8 nanometer [in diameter], routinely and I trust that there are many groups currently using the subnanometer tubes," said Peng. "As [for] the smallest 0.33 nanometer [tubes], it may take two to five years for researchers to be able to produce these tubes routinely and in a controllable fashion."
Peng's colleagues were Z. Q. Xue, Q. D. Wu and Z. N. Gu of Peking University; Z. L. Zhang of the Beijing Laboratory of Electronic Microscopy; and David G. Pettifor of Oxford University. They published their work in the October 9, 2000 issue of the journal Physical Review Letters. The research was funded by the National Science Foundation of China, Peking University, the Chinese Academy of Sciences and the Royal Society.
Timeline: 2-5 years
Funding: Government
TRN Categories: Semiconductors and Materials; Nanotechnology
Story Type: News
Related Elements: Technical paper "Stability of Carbon Nanotubes: How Small Can They Be?" In October 9, 2000 Physical Review Letters; Technical paper "Materials science: The smallest carbon nanotube" in November 2, 2000 Nature; Technical paper "Materials science: Single-walled 4 Å carbon nanotube arrays" in November 2, 2000 Nature
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November 22, 2000
Page One
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Electron beams turnout tinier tubes
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