State of the catalyst during carbon nanotube growth

We review our in-situ X-ray photoemission (XPS) and in-situ transmission electron microscopy studies which determined that the catalyst is in the metallic state for Fe, Co and Ni catalysts. We show that the existence of surface carbide phases in related catalytic reactions could account for the observation of carbide peaks in XPS. The observed catalytic activity of gold is discussed in terms of carbon solubility, reaction rates, and surface coordination numbers.