  Optimized growth of Single Wall Carbon Nanotubes requires a full knowledge of
the actual state of the catalyst nanoparticle and its interface with the tube.
Using Tight Binding based atomistic computer simulations, we calculate carbon
adsorption isotherms on nanoparticles of nickel, a typical catalyst, and show
that carbon solubility increases for smaller nanoparticles that are either
molten or surface molten under experimental conditions. Increasing carbon
content favors the dewetting of Ni nanoparticles with respect to sp2 carbon
walls, a necessary property to limit catalyst encapsulation and deactivation.
Grand Canonical Monte Carlo simulations of the growth of tube embryos show that
wetting properties of the nanoparticles, controlled by carbon solubility, are
of fundamental importance to enable the growth, shedding a new light on the
growth mechanisms.
