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New way to know an old friend: New method reveals clean carbon nanotube transistors with superb properties

Scientists at Aalto University, Finland, and Nagoya University, Japan, have found a new way to make ultra-clean carbon nanotube transistors with superior semiconducting properties
Nanotube transistors on a chip being tested electically
A chip with 1000 nano-sized devices being tested Credit: Aalto University

Single-wall carbon nanotubes (SWCNT) have found many uses in electronics and new touch screen devices. Carbon nanotubes are sheets of one atom-thick layer of graphene rolled up seamlessly into different sizes and shapes. To be able to use them in commercial products like transparent transistors for phone screens, researchers need to be able to easily test nanotubes for their materials properties, and the new method helps with this.

Professor Esko I. Kauppinen’s group at Aalto has years of experience in making carbon nanotubes for electronic applications. The team’s unique method uses aerosols of metal catalysts and gasses containing carbon.  This aerosol-based method allows the researchers to carefully control the nanotube structure directly.

Fabricating single carbon nanotube transistors is usually tedious. It often takes days from raw carbon nanotube material to transistors, and the devices were contaminated with processing chemicals, degrading their performance. However the new method makes it possible to fabricate hundreds of individual carbon nanotube devices within 3 hours, an over ten times increase in efficiency.

electron microscope image of nanotubes in a transistor
Electron microscope image of one of the 1000 devices on the chip. The white line between the two electrodes is a single carbon nanotube, which is being tested

Most importantly, these fabricated devices do not contain degrading processing chemicals on their surface. These so-called ultra-clean devices have been previously even more difficult to manufacture than regular single carbon nanotube transistors.

‘These clean devices help us to measure the intrinsic material properties. And the large number of devices helps to get a more systematic understanding of the nanomaterials, rather than just a few data points.’ says Dr. Nan Wei, a postdoctoral researcher in the group.

This study shows the aerosol-based nanotubes are superb in terms of their electronic quality, their ability to conduct electricity is almost as good as theoretically possible for SWCNTs.

More importantly, the new method can also contribute to applied research. One example is that by studying the conducting property of SWCNT bundle transistors, scientists may find ways to improve performance of flexible conductive films. This could prove useful for designers trying to build flexible, smash-proof phones. Follow-up work by the groups in Japan and Finland is already underway.

The article was published in “Advanced Functional Materials” in November 2019. You can read about it here http://dx.doi.org/10.1002/adfm.201907150

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