Condensed Matter Seminar Series

Carbon Solubility in Fe Nano-Clusters and the
Growth of Single-Walled Carbon Nanotubes

Stefano Curtarolo

Duke (MEMS Department)

Thursday January 17,  11:30 am,  Room 298,  Physics Building

Abstract:  Alumina-supported Fe catalysts have become a standard way to grow single-walled carbon nanotubes (SWCNTs) via chemical vapor decomposition. Contrary to the Gibbs-Thomson phenomenon, one finds that reducing the size of the catalyst requires increasing the (minimum) growth temperature. We address this apparent paradox in terms of the solubility of C in Fe nanoclusters and, by using first principles calculations, we devise a thermodynamic model to predict the behavior of the phases competing for stability in Fe-C nano-clusters at low temperature. We show that, as a function particle size, there are three scenarios: steady state-, limited-, or no-growth of SWCNTs, corresponding respectively to unaffected, reduced, and zero solubility of C in the particles. This result raises new concerns about the feasibility of growing small and very-long SWCNTs using the current Fe CVD technology, and suggests new strategies in the search for better catalysts (such as alloys).