Graphene Nanoribbons Zip Up
When it comes to the study of nanoscale systems, controlled fabrication always poses practical challenges. For example, it is difficult to fabricate carbon nanotubes with a well-defined chirality—a measure of how the nanotubes are wrapped that determines if they are metallic or semiconducting. Since graphene has been successfully made by chemically assisted scissoring of carbon nanotubes, it seems reasonable to ask if an inverse process, rolling up graphene membranes, could form carbon nanotubes. More importantly, elastic graphene membranes might even offer better control over nanotube chirality compared to current methods of nanotube synthesis.
Using quantum molecular dynamic simulations, Oleg Kit of the University of Jyväskylä, Finland, and colleagues have tried to answer this timely question. As they report in Physical Review B, carbon nanotubes might be fabricated using graphene ribbons; not by simply rolling them up, but by mechanically twisting them. According to their calculations, a sufficiently twisted graphene ribbon starts to develop chemical bonding between the carbon atoms at opposite edges. The bonding provides the necessary force to zip up the graphene membrane.
An important result of their study is that the chirality of the nanotubes could be tuned by the strain applied to create a twist. One practical extension of Kit et al.’s work, which should be applicable to other nanoscale planar objects, is the encapsulation of molecules in carbon nanotubes. – Hari Dahal