Researchers Publish Cookbook for Carbon Nanotubes

USC researchers develop method for producing carbon nanotubes with predicatable atomic structures

2 min read
Researchers Publish Cookbook for Carbon Nanotubes

Back before graphene became the favored child of the nanomaterial family, carbon nanotubes held the mantle of the “wonder material” that would replace silicon. But a succession of problems with applying carbon nanotubes to electronics led to it losing favor.

Putting them where you wanted them and connecting them was exceedingly difficult. But a perhaps more stubborn obstacle has been the difficulty of controlling their purity and quality. While all sorts of ingenious methods have been developed over the years for working around these problems, just accepting that we could never produce a set of pure carbon nanotubes and proceeding from there didn’t seem to be a satisfactory solution.

Now researchers at the University of Southern California (USC) claim to have developed a method for producing carbon nanotubes with specific and predictable atomic structures.

“We are solving a fundamental problem of the carbon nanotube,” Chongwu Zhou, a USC professor and corresponding author of the paper, said in a press release. “To be able to control the atomic structure, or chirality, of nanotubes has basically been our dream.”

The researchers, who published their work in the journal Nano Letters (“Chirality-Dependent Vapor-Phase Epitaxial Growth and Termination of Single-Wall Carbon Nanotubes”), found that if they used chirality-pure, short carbon nanotubes as “seeds,” they could essentially clone duplicates using vapor-phase epitaxial growth.

The group actually developed this growth technique last year; the latest wrinkle reported in the paper is a set of recipes for building carbon nanotubes with specific atomic structures. And having a recipe means at least one thing: the process can be repeated if you follow the instructions.

“We identify the mechanisms required for mass amplification of nanotubes,” said co-lead author Jia Liu in a press release.

Bilu Liu, another of the authors, added: “Previously it was very difficult to control the chirality, or atomic structure, of nanotubes, particularly when using metal nanoparticles. 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.”

Zhou says that the next step will be to scale up the process.  He adds in the release: “Our method can revolutionize the field and significantly push forward the real applications of nanotube in many fields.”

Whether this new development can bring carbon nanotube research back into favor for electronic applications, after years of focus and attention being lavished on graphene, remains to be seen. Working in carbon nanotubes' favor—that is, if this work can be scaled up—is the fact that researchers looking to endow electronics with graphene's amazing characteristics are not having such an easy time of it .

Image: Chongwu Zhou and Jia Liu

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3D-Stacked CMOS Takes Moore’s Law to New Heights

When transistors can’t get any smaller, the only direction is up

10 min read
An image of stacked squares with yellow flat bars through them.
Emily Cooper

Perhaps the most far-reaching technological achievement over the last 50 years has been the steady march toward ever smaller transistors, fitting them more tightly together, and reducing their power consumption. And yet, ever since the two of us started our careers at Intel more than 20 years ago, we’ve been hearing the alarms that the descent into the infinitesimal was about to end. Yet year after year, brilliant new innovations continue to propel the semiconductor industry further.

Along this journey, we engineers had to change the transistor’s architecture as we continued to scale down area and power consumption while boosting performance. The “planar” transistor designs that took us through the last half of the 20th century gave way to 3D fin-shaped devices by the first half of the 2010s. Now, these too have an end date in sight, with a new gate-all-around (GAA) structure rolling into production soon. But we have to look even further ahead because our ability to scale down even this new transistor architecture, which we call RibbonFET, has its limits.

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