• Fe does not possess a high mobility on the rim, leaves position very infrequently - no “scooting” around! • Pure carbon SWNTs immediately show self-capping in absence of catalyst, clusters are more robust to high temperatures, form giant fullerenes • Presence of Fe weakens SWNT bond network due to charge transfer, makes rims “softer” • Tendency to form Fe clusters observed, in case of Fe20 clusters, collapse to barbell-shaped fragments is observed • Tendency to form long-lived Fe-C2-Fe aggregates, no sign of C2 incorporation into SWNT sidewalls