Entropy driven stability of chiral single-walled carbon nanotubes

Single-walled carbon nanotubes are hollow cylinders, that can grow centimeters long by carbon incorporation at the interface with a catalyst. They display semi-conducting or metallic characteristics, depending on their helicity, that is determined during their growth. To support the quest for a selective synthesis, we develop a thermodynamic model, that relates the tube-catalyst interfacial energies, temperature, and the resulting tube chirality. We show that nanotubes can grow chiral because of the configurational entropy of their nanometer-sized edge, thus explaining experimentally observed temperature evolutions of chiral distributions. Taking the chemical nature of the catalyst into account through interfacial energies, structural maps and phase diagrams are derived, that will guide a rational choice of a catalyst and growth parameters towards a better selectivity.