  Although carbon nanotubes consist of honeycomb carbon, they have never been
fabricated from graphene directly. Here, it is shown by quantum
molecular-dynamics simulations and classical continuum-elasticity modeling,
that graphene nanoribbons can, indeed, be transformed into carbon nanotubes by
means of twisting. The chiralities of the tubes thus fabricated can be not only
predicted but also externally controlled. This twisting route is an opportunity
for nanofabrication, and is easily generalizable to ribbons made of other
planar nanomaterials.
