rainbow nanotubes

Nanotube growth gets less ‘random’

Scientists have identified the “growth recipes” for building carbon nanotubes with specific atomic structures.

“We are solving a fundamental problem of the carbon nanotube,” says Chongwu Zhou, professor in the electrical engineering department at the University of Southern California’s Viterbi School of Engineering.

If this is an age built on silicon, then the next one may be built on carbon nanotubes, which have shown promise in everything from optics to energy storage to touch screens.

Nanotubes are transparent, and this research discovery on how to control their atomic structure could pave the way for computers that are smaller, faster, and more energy efficient than those reliant on silicon transistors.

Zhou says they are now working to scale up the process.

Until now, scientists were unable to “grow” carbon nanotubes with specific attributes—say metallic rather than semiconducting—instead getting mixed, random batches and then sorting them. The sorting process also shortened the nanotubes significantly, making the material less practical for many applications.

For more than three years, the team has been working on the idea of using these short sorted nanotubes as “seeds” to grow longer nanotubes, extending them at high temperatures to get the desired atomic structure.

“We identify the mechanisms required for mass amplification of nanotubes,” says co-lead author Jia Liu, a doctoral student in chemistry, recalling the moment when, alone in a dark room, she finally saw the spectral data supporting their method. “It was my Eureka moment.”

“To understand nanotube growth behaviors allows us to produce larger amounts of nanotubes and better control that growth,” she continues. The findings are published in Nano Letters.

Each defined type of carbon nanotube has a frequency at which it expands and contracts. The researchers showed that the newly grown nanotubes had the same atomic structure by matching the Raman frequency.

In addition, the study finds that nanotubes with different structures also behave very differently during their growth, with some nanotube structures growing faster and others growing longer under certain conditions.

“Previously it was very difficult to control the chirality, or atomic structure, of nanotubes, particularly when using metal nanoparticles,” says co-lead author Bilu Liu, a postdoctoral research associate.

“The structures may look quite similar, but the properties are very different. In this paper we decode the atomic structure of nanotubes and show how to control precisely that atomic structure.”

Additional authors of the study contributed from USC and the National Institute of Standards and Technology.

The Office of Naval Research and the Defense Threat Reduction Agency of the US Department of Defense funded the study.

Source: USC

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