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Nanotubes With Two Walls Have Singular Qualities

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Researchers at Rice University are working to determine the electronic properties of double-walled carbon nanotubes. In this example, the team analyzed a nanotube with two zigzag components. The individual nanotubes have band gaps and are semiconductors, but when combined, the band gaps overlap and make the double-walled a semimetal. (Illustration by Matías Soto/Rice University)

Rice University researchers have determined that two walls are better than one when turning carbon nanotubes into materials like strong, conductive fibers or transistors. Rice materials scientist Enrique Barrera and his colleagues used atomic-level models of double-walled nanotubes to see how they might be tuned for applications that require particular properties. They knew from others’ work that double-walled nanotubes are stronger and stiffer than their single-walled cousins. But they found it may someday be possible to tune double-walled tubes for specific electronic properties by controlling their configuration, chiral angles and the distance between the walls.

The Rice team found there’s even more to carbon nanotubes when they started looking at how the inner and outer walls match up using tubes with zigzag chirality. Because the electrical properties of single-walled tubes depend on their chirality – the angles of their hexagonal arrangement of atoms – the researchers thought it would be interesting to learn more about those properties in double-walled tubes. It turned out that both the distance between the walls — as small as a fraction of a nanometer — and the individual chirality of the tubes impact the double-walls’ electrical properties. In addition, the researchers found the diameter of the tube — especially the inner one, with its more pronounced curvature — has a small but significant impact on the structure’s semiconducting properties.