Our previous growth model for fullerene formation is used to explain r
ecent experiments. It becomes clear how a high efficiency of C-60 form
ation is achieved. We estimate the size dependence of intermediate str
uctures along the most efficient fullerene growth route and furthermor
e the stability of Si-20, Ge-20 vs. the unstable C-20. While C-n(-) hi
nders fullerene formation a complex C-n-M (M = metalatom) may support
fullerene formation.