Rice University researchers have determined that an odd, two-faced ’Janus” edge is more common than previously thought for carbon nanotubes growing on a rigid catalyst. The conventional nanotube at left has facets that form a circle, allowing the nanotube to grow straight up from the catalyst. But they discovered the nanotube at right, with a tilted Janus edge that has segregated sections of zigzag and armchair configurations, is far more energetically favored when growing carbon nanotubes via chemical vapor deposition. Illustration by Evgeni Penev
Rice theory shows peculiar 'Janus' interface a common mechanism in carbon nanotube growth. When is a circle less stable than a jagged loop? Apparently when you're talking about carbon nanotubes. Rice University theoretical researchers have discovered that nanotubes with segregated sections of "zigzag” and "armchair” facets growing from a solid catalyst are far more energetically stable than a circular arrangement would be. Under the right circumstances, they reported, the interface between a growing nanotube and its catalyst can reach its lowest-known energy state via the two-faced " Janus ” configuration, with a half-circle of zigzags opposite six armchairs. The terms refer to the shape of the nanotube's edge: A zigzag nanotube's end looks like a saw tooth, while an armchair is like a row of seats with armrests. They are the basic edge configurations of the two-dimensional honeycomb of carbon atoms known as graphene (as well as other 2D materials) and determine many of the materials' properties, especially electrical conductivity. The Brown School of Engineering team of materials theorist Boris Yakobson , researcher and lead author Ksenia Bets and assistant research professor Evgeni Penev reported their results in the American Chemical Society journal ACS Nano.
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