Nanotubes get as small as they can

Advanced electronics and other microscopic devices might someday depend on carbon nanotubes—minuscule rolls each made of a cylindrical layer of carbon atoms.

Now, two research teams have created stable carbon nanotubes with the smallest diameter that scientists believe is physically possible. At merely 0.4 nanometer across, they don’t even span the width of four hydrogen atoms lined up next to one another.

“Nanotubes are at the forefront in potential nanotechnology applications,” says Lu-Chang Qin with Japan Science and Technology Corporation in Tsukuba, Japan. “A natural question is, therefore, how small they can be and how to make them to test the limit of technology.”

In separate reports in the Nov 2. Nature, Qin’s group and another, from the Hong Kong University of Science and Technology, describe how each made their ultimately tiny nanotubes.

Qin’s team, including coworkers from NEC Corporation in Tsukuba and Meijo University in Nagoya, Japan, produced each of their 0.4-nanometer structures as the innermost cylinder of 18 carbon tubes bundled within one another like nesting Russian dolls. The researchers started with standard multiwalled carbon nanotubes and used a special technique to form each small tube inside, says Qin.

The Hong Kong group grew individual, single-walled nanotubes by introducing a type of hydrocarbon molecule called tripropylamine into the channels of labyrinthine crystals known as zeolites, says team member Zikang Tang. Heating the crystals then decomposed the tripropylamine, leaving behind carbon to form nanotubes in the crystals’ channels.