Predictable nanotube structures point to silicon replacement

‘We are solving a fundamental problem of the carbon nanotube,’ said Chongwu Zhou, professor in the Ming Hsieh Department of Electrical Engineering at the USC Viterbi School of Engineering and corresponding author of the study published August 23 in the journal Nano Letters. ‘To be able to control the atomic structure, or chirality, of nanotubes has basically been…a dream in the nanotube field.’

Carbon nanotubes have shown promise in applications ranging from optics, energy storage and touch screens. It is claimed that this research discovery on how to control the atomic structure of nanotubes will pave the way for computers that are smaller, faster and more energy efficient than those reliant on silicon transistors.

‘We are now working on scale up the process,’ Zhou said in a statement. ‘Our method can revolutionise the field and significantly push forward the real applications of nanotube in many fields.’

Until now, scientists were unable to ‘grow’ carbon nanotubes with specific attributes — such as 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 USC 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.

A paper last year by the same team in Nature Communications outlined the technique, and in the current Nano Letters paper, the researchers report on their success, namely identifying the so-called ‘growth recipes’ for building carbon nanotubes with specific atomic structures.

‘We identify the mechanisms required for mass amplification of nanotubes,’ said co-lead author Jia Liu, a doctoral student in chemistry at the USC Dornsife College of Letters, Arts and Sciences, recalling the moment when she saw the spectral data supporting their method. ‘To understand nanotube growth behaviours allows us to produce larger amounts of nanotubes and better control that growth.’

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 found 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.