Iridium-catalyzed growth of single-walled carbon nanotubes with a bicentric diameter distribution

Iridium (Ir) nanoparticles with diameters smaller than 5 nm are synthesized by microwave chemical reduction and applied for the chemical vapor deposition growth of SWNTs with CO as the carbon source. Compared with iron-family catalysts, the optimal growth temperature of 1000 degrees C is a bit higher, which is coherently related to the intrinsic catalytic properties of the Ir nanoparticles. As revealed by molecular dynamics calculations, the Ir nanoparticles preserve the solid state at the reaction temperatures. More interestingly, the diameters of the grown SWNTs show a bicentric distribution and are very close to the average diameter of the SWNT-catalyst interface, which matches the six-fold symmetry of the Ir(111) surface. This work extends the design and development of a novel solid catalyst for synthesizing SWNTs with controlled diameters.